GLOBAL WATER PATHOGEN PROJECTPART THREE. SPECIFIC EXCRETED PATHOGENS: ENVIRONMENTAL ANDEPIDEMIOLOGY ASPECTS

ADENOVIRUSES

Annika AllardUmeå UniversityUmeå, Sweden

Apostolos VantarakisUniversity of PatrasPátrai, Greece

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Citation:Allard, A. and Vantarakis, A. 2017. Adenoviruses. In: J.B. Rose and B. Jiménez-Cisneros, (eds) Global WaterPathogen Project. http://www.waterpathogens.org (J.S Meschke, and R. Girones (eds) Part 3 Viruses)http://www.waterpathogens.org/book/adenovirusesMichigan State University, E. Lansing, MI, UNESCO.https://doi.org/10.14321/waterpathogens.11Acknowledgements: K.R.L. Young, Project Design editor; Website Design: Agroknow(http://www.agroknow.com)

Last published: March 7, 2017

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Summary

Adenoviruses are associated with numerous diseaseoutbreaks, particularly those involving daycares, schools,children's camps, hospitals, military settings, and otherhealth care centres. Today, fifty-two different serotypes ofadenovirus have been identified. However, several typeshave also recently been identified with moleculartechniques and designated as genotypes. All serotypes andgenotypes have been divided into seven species (A to G)that infect humans. Of all the known adenovirus types, onethird are associated with human disease as gastroenteritis,respiratory infections, eye infections, acute hemorrhagiccystitis, and meningoencephalitis, while two thirds ofinfections are asymptomatic.

Children and immunocompromised individuals are moreseverely impacted by adenovirus infections. Adenoviruseshave a worldwide distribution, where infections occurthroughout the year causing 5 to 10% of all febrile illnessesin infants and young children. Most individuals haveserologic evidence of a prior adenoviral infection by the ageof 10. Although many adenovirus types are found in stoolfrom patients with diarrhea, only enteric adenoviruses (type40, 41 and 52) have been shown to be the causative agentsof gastrointestinal disease. Enteric adenoviruses replicatein the gut to 1011 virions per gram of stool, but many othernon-enteric viral particles (i.e. types 1,2,5,3 and 7) maypersist for months and even up to years in stool after aninfection. These phenomena may explain why adenovirusesare ubiquitous in the environment where contamination ofhuman faeces or sewage occur in such areas of increasedpopulation densities.

Adenoviruses have been detected in various watersworldwide including wastewater, river water, drinkingwater, ocean, and swimming pools. Adenoviruses typicallyoutnumber the enteroviruses, when both are detected insurface waters. Evidence has shown that adenovirusessurvive longer in water than enteroviruses and the hepatitisA virus; this may be due to their double-stranded DNA. Amajority of the results are based on PCR technology andindicate only the presence of nucleic acids and do notinclude infectivity data.

Adenoviruses are frequently detected in highconcentrations in wastewater and wastewater-contaminated waters, so their use as potential indicatorsfor the presence of human faeces has been suggested as acomplement to bacterial indicators. It is well documentedthat bacteria behave differently to viruses in aquaticenvironments, particularly with regard to their survivaltimes. In this respect, adenoviruses are good candidates forindicators of virus contamination with long term survivalproperties, high resistance to ultraviolet light, and a DNAgenome which simplifies and decreases the cost ofmolecular detection procedures compared to the costlyRNA processing.

In recent years, there have been several studies analyzingground water samples showing the presence of

adenoviruses with no correlation between the presence ofviruses and bacterial indicators (i.e. Escherichia coli).These results may be useful for risk assessment studiessince ground water is a common source of drinking waterand subsequently connected to the interest of public health.Adenoviruses are more often found in ground water thanother viral types, and they have been abundant in untreatedriver water and finished water after conventional watertreatment plant processes. The different treatmentprocesses (conventional and alternative) for reducingconcentrations of adenoviruses in water, have shownvariable efficiency. In addition, environmental conditionshave been reported to present variable effect on adenovirusstability.

In summary, the knowledge of adenovirus importance hasincreased significantly during the last decades, andadenovirus is now playing an important role in both clinicalsettings and in the environmental context.

AdenovirusBoth respiratory and enteric human adenoviruses

(HAdV) are found in water, cause waterborne diseaseandare present at a higher frequency in sewage than otherenteric viruses (Pina et al., 1998). These viruses have beensuggested to be preferred candidates as index organismsfor viral pathogens because they fit most criteria for anidea l i nd i ca to r such a s r e s i s t ance t o manychemical/physical agents and to UV light (Katayama et al.,2008; Gerba et al., 2002; Girones et al., 2014).

The first adenovirus strains were isolated in 1953 fromlymph nodes and got their name from adénos, the Greekword for gland(Rowe et al., 1953).The following year itbecame clear that the virus caused acute respiratoryinfection. Thus, two basic properties of adenoviruses weredetected; their ability to cause acute respiratory infectionand the propensity to persist in lymphoid tissue. Today,fifty-two different serotypes of adenovirus have beenidentified; however, several types have also in recent yearsbeen identified with molecular techniques. All types havebeen divided into seven species (A to G) that infect humans.This species breakdown is affected by the receptor bindingstructure.Adenoviruses are a family of viruses that globallyinfects most children already before the age of five.Highfever for a week is often seen but approximately everysecond adenovirus infection is non-symptomatic.Adenoviruses rarely cause life-threatening infections,except in immunodeficient individuals. It is now knownhowever that environmental occurrence and transmission isimportant.

1.0 Epidemiology of the Disease andPathogens

1.1 Global Burden of Disease

Adenoviruses have a worldwide distribution, andinfections occur throughout the year (Fox et al., 1977).Adenoviruses cause 5 to 10% of all febrile illnesses in

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infants and young children and most individuals in NorthAmerica have serologic evidence of a prior adenoviralinfection by the age of five. (Fox et al., 1977). Bothrespiratory and enteric adenovirus infections are prevalentin daycare centers and in households with young childrenbut nosocomial transmission has also been documented(Liu et al., 2014; Tran et al., 2010).Adenovirus species Frepresenting human adenovirus type 40 and 41 has beenfound to be associated with acute gastroenteritis and isresponsible for 1 to 20% of the cases of diarrheal diseaseglobally in both outpatients and hospitalized children(Uhnoo et al., 1984; Brandt et al., 1984; Li et al., 2004).Type 40 and 41 primarily affect young children less than 2years of age and the infection occur throughout the year.The clinical characteristics include watery diarrheaaccompanied by vomiting, low-grade fever, and milddehydration.The burden of adenovirus infections isparticularly important in immunocompromised hosts (Lion,2014), where a variety of clinical syndromes can occur andreactivation of endogenous adenovirus plays a role indiseases in these patients.

1.1.1 Global distribution

Human adenovirus (HAdV) infections are common andubiquitous with a worldwide distribution.Even if most HAdVspecies appear to circulate globally, predominant typesdiffer between countries or geographic regions, and theychange over time (Lin et al., 2004; Ishiko et al., 2008;Ampuero et al., 2012). Transmission of new strains acrosscontinents may occur and lead to replacement of hithertodominant HAdV types (Kajon et al., 2010).The prevalence ofadenovirus respiratory infections in children in North andSouth America ranges from 2 to 14% and may be higherduring outbreaks (Fox et al., 1977; Videla et al., 1998).Many (30-70%) respiratory illnesses in unvaccinated newmilitary recruits in USA are adenovirus associated as well(Russell et al., 2006). About 5 to 15% of acute diarrhealinfections in all continents are due to enteric adenoviruses(Dey et al., 2011; Uhnoo et al., 1984; Kim et al., 1990;Barnes et al., 1998; Van et al. 1992; Moore et al., 2000).

Children are especially susceptible but elderly are alsoagain susceptible to the enteric types 40 and 41 due towaning immunity with increasing age. Due tocontamination by human faecesor sewage into theenvironment HAdVs seem to be more common indeveloping countries with poor sanitary conditions (Dey etal., 2011; Filho et al., 2007; Moyo et al., 2014).However,the incidence of all HAdV infections is higher incrowded closed settings, such as day care centers,boarding schools, geriatric facilities, military trainingcamps, and hospitals. Intrafamiliar infections are alsocommon and HAdVs are frequent in immunocompromisedpatients. Every serotype can cause a unique infection,which means theoretically that it is possible to acquiremore than 50 adenovirus infections to get immunity. Types53-68 are genetically typed and antibody specificity has notyet been investigated or confirmed against these recenttypes.The adenoviruses most commonly reported to beassociated with human disease globally are HAdVC1,-C2, -C5, -B3, -B7, -B21, -E4, and -F41 (Guo et al., 2012;

Yliharsila et al., 2013; Tabain et al., 2012; Barrero et al.,2012).

1.1.2 Symptomatology

HAdVare most frequently associated with upperrespiratory tract syndromes, such as pharyngitis or rhinitisbut can also cause pneumonia. Less commonly,adenoviruses cause gastrointestinal, ophthalmologic,genitourinary, and neurologic diseases. Most adenoviraldiseases are self-limiting, although fatal infections canoccur in immuno-compromised hosts and occasionally inhealthy children and adults, especially children withgastrointestinal infections in the developing world. Thenumber of diarrheal deaths caused by adenovirus (HAdV-40and HAdV-41) was estimated in 2011 to be 3-4% of alldiarrheal deaths among children under 5 years of age inthe world (Lanata et al. 2013). Patients who haveundergone organ or hematopoietic cell transplantationtogether with AIDS patients and children with severecombined immunodeficiency represent a new group ofpatients showing a spectrum of adenovirus infections fromasymptomatic shedding to fatal disseminated disease.Adenovirus infections in solid organ transplant recipientsmay range from asymptomatic to severe and disseminated,with prolonged viral shedding and significant morbidity andmortality, including associated graft dysfunction andrejection (Taniguchi et al., 2012). Adenovirus morefrequently affects paediatric than adult solid organtransplant recipients. Despite the frequency with whichthey are found in stool or urine specimens, adenovirusesare an uncommon cause of morbidity or mortality in HIV-infected patients.

1.2 Taxonomic Classification of the Agents

1.2.1 Physical description of the agent

Adenoviruses (members of the family Adenoviridae) aremedium-sized (90–100nm), nonenveloped viruses with anicosahedral nucleocapsid containing a double strandedDNA genome of approximately 35,000 base pairs (Figure1).The viral capsid has the form of an icosahedron and iscomposed of 252 capsomers. Of these, 240 have a six-foldsymmetry and are therefore called hexons. Twelvecapsomers have a five-fold symmetry, pentons andproduces the particle corners. From every corner anantenna like fiber is protruding. This fiber is a glycoproteinthat varies in length of adenoviruses belonging to differentsubgroups. The fiber acts as the most important receptor-binding structure. Many of the other peptides function ascement and couple hexon and penton capsomeres to adense capsid (Figure 2). Viral histon-like proteins mediatespacking of the viral genome (Russell, 2009). In 2010, theatomic resolution structure of the complete virion appearedas a result of two structural biology techniques: X-raycrystallography and cryoEM (San Martin, 2012).

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_

Figure 2.Transmission electron micrograph of two Adenovirus particles visualizing the dense capsid

structure(https://en.wikipedia.org/wiki/Adenoviridae)structure

1.2.2 Taxonomy

Human adenoviruses (HAdVs) are classified in thegenus Mastadenovirus, which contains seven known HAdVspecies HAdV-A to HAdV-G. Traditionally, the HAdV specieswere classified by hemagglutination and serumneutralization reactions into different serotypes (Rosen,1960; Kjellen and Pereira, 1968). Today, there have beenreported 68 HAdV types (Brister et al., 2013). Thediscovery and division of the HAdV types 52–68 are basedon the genomic sequencing and bioinformatic analysis andthen differ from the pre-existing 51 HAdV serotypes that

have been identified by traditional serological methods incomposition and pathogenicity (Gao et al., 2014). Serotype52 constitutes a new HAdV species (G) and has beenreported after genomic sequencing and phylogeneticanalysis of an isolate in the U.S. (Jones et al., 2007). NewHAdV types have since been identified by several authorsbased on genomic data, including several emerging andrecombinant viruses (Matsushima et al., 2012). A primateadenovirus from New World monkeys was detected whichcrossed the species barrier to infect humans (Kohl et al.,2012). The majority of new HAdV types are homologousrecombination within the same subgenus, and as a result,

Figure 1. Schematic representation of AdenovirusSpecial:Cite&page=WUSM_Microbes_and_Pathogenesis_Wiki:_Adenovirus_Group_9&id=395020)

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certain new serotypes acquire different pathogenicities.Recombination is a common evolutionary way for HAdV;however, the mechanism of recombination and the potentialhazards to human beings remain unknown (Ghebremedhin,2014).

1.2.3 Tissue Tropism/Cellular receptors/Latency

In the past few years, not just one but multipleadenovirus receptors have been identified, describingdifferent HAdV species affinity for individual tissues.However, members of the largest species, species D, showgreat variability in their tropisms, with growth in tissuesranging from ocular to gastrointestinal and respiratorytissues (Pauly et al., 2014). The basis of tissue tropism isstill not well established. Adenoviral keratoconjunctivitis,which is a major cause of ocular morbidity, is mostcommonly caused by representatives of species D,including types 8, 19, and 37, but also by humanadenoviruses -E4, -C5, -B3, -B7, -B11, and -B14 (Lynch etal., 2011). Gastrointestinal manifestations are mainlyassociated with HAdV-F40 and -F41, but HAdV-G52 anddifferent members of species D, including some of the mostrecently identified types (types 65 and 67), have also beenobserved (Matsushima et al., 2012; 2013). Respiratory tractinvolvement has been associated mainly with humanadenoviruses -B3, -B7, -B16, -B21, and -E4 and variousmembers of species C (Metzgar et al., 2010). Theseexamples indicate that certain adenoviruses have strongtropisms for specific tissues, but the same clinicalmanifestations can be caused by other human adenovirustypes and species, thus requiring diagnostic screeningmethods with broad specificity.What is known today is thatthe fiber protein from species A, C and F interacts with acellular protein that belongs to the superfamilyimmunoglobulins. This receptor is called CAR, coxsackieadenovirus receptor because it is also binds tocoxsackievirus. Other types of adenoviruses utilizealternative cellular receptors such as CD46, desmoglein 2,sialic acid, or heparan sulfate (Arnberg et al., 2012).

Currentlyavailable evidence indicates that HAdVs canpersist in a latent state in a variety of susceptible cellsfollowing primary infection. Latency is characterized byexpression of viral proteins by the host cell withoutreplication of a complete virus. A latent form of adenovirusinfection was shown to persist in tonsillar lymphocytes innearly 80% of children investigated, and the number ofadenoviral genomes per lymphoid cell apparently declineswith age (Garnett et al., 2009). Moreover, latent HAdVinfections were described to occur in intestinal Tlymphocytes and in lung epithelial cells, where they seemto play a role in the pathogenesis of obstructive airwaydisease (Hogg, 2001).

This related to the reactivation of endogenousadenovirus infections.

1.3 Transmission

1.3.1 Routes of transmission

Infections are typically transmitted by exposure toinfected individuals via inhalation of aerosolized droplets ordirect conjunctival inoculation, as well as by fecal-oralspread, including contact with recreational marine water,swimming pools freshwater or tap water (Wyn-Jones et al.,2011; Love et al., 2014; Bofill-Mas et al., 2010; vanHeerden et al., 2005; Artieda et al., 2009). Fomitetransmission can occur through exposure to infected tissue,airflow filters, or environmental surfaces (Russell et al.,2006; Soller et al., 2010). The stability of the virus at lowpH is a matter of debate, but human adenoviruses areresistant to gastric and biliary secretions and can thereforebe detected at high levels in feces (Matthes-Martin et al.,2013). Human adenoviruses are infrequently found in theurine of immonocompetent individuals but are present inthe urine of immunocompromised patients an especially inAIDS patients (Echavarria, 2008; De Jong et al., 1983;Horwitz et al., 1984). However, this secretion is probablynegligible in the context of disease transmission.

1.3.2 Reservoirs

Human adenoviruses are ubiquitous in the environmentwhere contamination by human faeces or sewage hasoccurred. Human adenoviruses typically are not pathogenicto animals and animal adenoviruses are only pathogenic tothe species of origin. However, asymptomatic infectionswith human adenovirus type 12 have been documented insimian species, and antibodies to canine, bovine and simianadenoviruses have been found in humans (AWWAssociation, 2006). Adenoviruses have a broad range ofvertebrate hosts and are known to cause respiratoryinfections in horses, cattle, pigs, sheep, and goats. The fowladenoviruses are associated with many disease conditionsin domestic fowl, but have also been found in wild birds,bats and reptiles (http://www.ictvonline.org/).

1.3.3 Incubation and duration periods

Following human adenovirus transmission, theincubation period ranges from 2 days to 2 weeks,depending on the viral type and mechanism of acquisition(Langley, 2005; Bhumbra and Wroblewski, 2010).Respiratory symptoms caused by adenoviruses are mostcommonly seen amongst children under the age of two andfor this selected group the incubation period before theonset of symptoms is generally 4-8 days, median 5.6 days(Lessler et al., 2009). For intestinal infections theincubation period is 3 to 10 days.Fever, coryza, cough, andsore throat, usually lasting 3-5 days, are typical symptomsof adenoviral upper respiratory disease andmost adenoviralinfections last from a few days to a week (Tabain et al.,2012). However, severe respiratory infections may lastlonger and cause lingering symptoms, such as a cough.Pneumonia can last anywhere from 2 to 4 weeks andpinkeye can persist for another several days to a week.More severe keratoconjunctivitis can last for several weeks(Pihos, 2013)and entericadenoviruses can cause diarrheathat lasts up to 2 weeks which is longer than other viraldiarrhea episodes (Uhnoo et al., 1984).

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Adenoviruses

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1.3.4 Period of communicability and shedding levels

The contagiousness of adenovirus is facilitated by veryhigh levels of viral particles (100,000-1,000,000/mL) in thesputum or oral secretions of infected adults. InAlthoughmany adenovirus types are found in stool from patients withdiarrhoea, only enteric adenoviruses (type 40/41/52) havebeen shown to be the causative agents of gastrointestinaldisease. A close comparison of stools from diarrheal andcontrol patients has shown that whereas non-enteric HAdVparticles are shed in stools from both diarrheal and controlpatients, enteric HAdV particles are found almostexclusively in diarrheal stools. As shown by several studies,up to 50% of healthy children carry non-enteric HAdVwhereas enteric HAdV is rarely present in healthychildren(Allard et al.,1992). Enteric adenoviruses replicatein the gut to 1.0x1011virions per gram of stool and entericHAdV carriage is about 8 times higher than non-entericHAdV carriage in diarrheal stool samples. Moreover, assecretions of non-enteric adenoviral particles may persistfor months, the presence of these adenoviruses in stoolsalong with other viruses is common. HAdV 1, 2, 3 and 5 isreported to be excreted intermittently for up to 906 days(Fox et al., 1977). Quantitative Microbial Risk Assessment(QMRA) studies have been applied to drinking andrecreational water (Chigor et al., 2014; Kundu et al., 2013)and a QMRA model associated with inhaling bioaerosolsthat are contaminated with HAdV at risk-prone workplaceshave been presented by Carducci et al. (2016). Riskmanagement and dose response models can be found atQMRAwiki (http://qmrawiki.canr.msu.edu/).

1.4 Population and Individual Control Measures

1.4.1 Vaccines and therapy

1.4.1.1 Vaccines

Vaccination and infection control measures have beenapplied in certain settings to prevent adenovirus infectionsand live oral enteric-coated vaccines directed againstadenovirus serotypes 4 and 7 had been used for years inmilitary recruits in United States since the 1971 (Top et al.,1971). In the 1999, the manufacturer of the vaccinesstopped production and subsequently new outbreaks ofadenovirus serotypes 4 and 7 disease in training campsoccurred, including several fatalities, underscoring thecontinued need for the vaccines (Potter et al., 2012). Inaddition adenovirus serotype 14, a subtype B2 adenovirus,emerged in military recruit training sites and became thepredominant strain (Binn et al., 2007; Metzgar et al., 2007).However, in 2011, a new l ive, oraladenovirusvaccineagainst adenovirus serotypes 4 and 7 was approvedfor use in United States military personnel aged 17 through5 0 y e a r s ( h t t p : / / w w w . f d a . g o v /downloads/BiologicsBloodVaccines/Vaccines/ApprovedProducts/UCM247515.pdf. USA TPharmaceut. 2011). During thetwo years following reintroduction of the vaccine, UnitedStates military trainees had a 100-fold decline inadenovirus disease burden. It was also a marked decline inthe incidence of disease caused by adenovirus serotypesother than 4 and 7, including adenovirus serotype 14

(Radin et al., 2014). These data suggest that the emergenceof adenovirus 14 in military recruits during the non-vaccination period was related to the discontinuation of theadenovirus serotypes 4 and 7 vaccine program, sinceheterotypic antibodies to adenovirus 14 were developedfollowing adenovirus 7 immunization. Vaccines againstadenoviruses have not been used in a large scale outsidethe United States.

Fecal shedding of adenovirus type 4 and type 7 livevaccine oral strain viruses was evaluated in a safety andimmunogenicity study of 58 subjects (30 vaccine recipientsa n d 2 8 p l a c e b o r e c i p i e n t s(http://www.fda.gov/downloads/BiologicsBloodVaccines/Vaccines/ApprovedProducts/UCM247515.pdf. USATPharmaceut. 2011). Stool or rectal swabs and throatswabs were collected on Day 0, 7, 14, 21, 28 and 56.Vaccine virus strains were shed in the stool as early as day7 following vaccination. Eight of 30 vaccine recipients(27%) tested positive at least once for adenovirus type 4fecal shedding; 18 of 30 vaccine recipients (60%) testedpositive for adenovirus type 7 fecal shedding. Noadenovirus shedding was detectable in any subject by 28days following vaccination. Vaccine strain virus was notdetected in the throat of any subject.

Antiviral therapy is general ly reserved forimmunocompromised hosts and patients with severeadenovirus disease. There have been no controlled trialsdemonstrating benefit for any antiviral agent in humanadenoviral disease. The antiviral agent most commonlyused for adenoviral infection is cidofovir, which is currentlyapproved for the treatment of cytomegalovirus (CMV)infections. This agent appears more active againstadenovirus in vitro than other antiviral drugs such asganciclovir (Doan et al., 2007). Antiviral drugs as ribavirinor vidarabine have no consistent activity against adenovirusin vitro (Sabroe et al., 1995).

1.4.1.3 Immunotherapy

Treatment with donor lymphocytes stimulated in vitrowith adenovirus can reduce the viral load and successfultreatment of adenovirus disease in immuno-compromisedpatients has been reported (Feuchtinger et al., 2006). T-cellrecovery with reconstitution of human adenovirus specificimmune responses is essential for effective clearance ofinvasive infections, and the initial treatment step shouldtherefore include reduction of immunosuppressivetreatment whenever possible (Matthes-Martin et al., 2012).

1.4.1.4 The use of adenovirus vectors for gene therapy

There has been considerable interest and effort indeveloping adenovirus vectors for gene therapy.Adenoviruses have several advantages over some otherviral vectors such as retroviruses and adeno-associatedvirus. Adenovirus vectors can infect a variety of cell types,including non-dividing as well as dividing cells, and can beprepared readily in large quantities in tissue culture(Vetrini and Ng, 2010; Chai et al., 2012)

1.4.1.2 Antiviral agents

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8

use as vaccine vectors (Gaydos and Gaydos, 1995). Asalready mentioned, live, oral, enteric-coated, adenovirusserotypes 4 and 7 vaccines were safely used for years inmilitary training camps to prevent epidemics of acuteadenoviral respiratory disease. These live, oral viralvaccines have an advantage in the ability to generate bothmucosal and systemic immunity. Thus, replication-competent as well as replication-defective adenovirusvectors are attractive candidates for immunization againstother infectious pathogens (Tatsis and Ertl, 2004).

1.4.2 Hygiene measures

Adenoviruses can stay viable for prolonged periods onenvironmental surfaces such as sinks hand towels but alsoat medical instruments and the virus isresistant to manycommon disinfectants. To prevent healthcare-associatedoutbreaks of adenovirus infections, such as epidemickeratoconjunctivitis (EKC), health care providers shouldstrictly follow infection control practices, including contactand droplet precautions, use proper disinfectants andpromptly respond to and report clusters of cases (Threlkeldet al., 1993).Because of the stability adenoviruses can alsocause significant nosocomial infections other then EKC(Swartling et al., 2015) and hand washing does not reliablyremove adenoviruses from contaminated fingers (Buehleret al., 1984; Faden et al., 2005) Decontamination ofenvironmental surfaces and instruments may be difficultsince adenoviruses are very resistant to lipid disinfectantsbut are inactivated by chlorine or formaldehyde(Flomenberg, 2009). They can be inactivated by contactwith 1:5 dilution of bleach for 1 minute or 2 minutescontact with alcohol-based hand gels (Robinson andEchavarria, 2007).Adenoviruses can be physicallyinactivatedby heat (Flomenberg, 2009) by heating to 56°Cfor 30 min or 60°C for 2 min. In laboratory environmentsautoclaving for 30 minutes at 121°C or 250°F (15 lbs persquare inch of steam pressure) is recommended (Robinsonand Echavarria, 2007). In a home environment, where high-concentrated chlorine use not is recommended based onenvironmental grounds, surface disinfection with 10%bleach (1:10 dilution household bleach, such as clorox) canbe applied allowing a contact time of 15 minutes. Forstainless steel surfaces, bleach disinfection should be

followed with 70% ethanol wipedown to avoid corrosion.Liquid waste may be treated by exposing to bleach (finalvolume 10%) for 15 minutes before disposing into sink.

2.0 Environmental Occurrence andPersistence

Waterborne viruses can be introduced and remaininfectious in source waters used for recreational anddrinking water, these pathways ultimately may result inillness in some portion of the exposed population(Kokkinoset al., 2011a; Gibson, 2014; Kotwal and Cannon, 2014).

2.1 Detection Methods

Adenoviruses (HAdV) like other viruses need to beconcentrated from environmental samples and especiallyfrom water due to typically lower concentrations and theirsmall size. Several investigators have used differentmethods to detect adenoviruses in various environmentalsamples including water (Ahmed et al., 2015; Calgua et al.,2013; Ogorzaly et al., 2013; Puig et al., 1994; Sassoubre etal., 2012; Thompson et al., 2003) and air (Ziros et al., 2011;Verani et al., 2014), based on PCR procedures. Cell culturestechniques and cell culture techniques combined with PCRhave also been used (Grabow et al., 1992; Reynolds et al.,1996; Chapron et al., 2000; Ko et al., 2003; 2005). Also,recently, new metagenomics methods have been used (Awet al., 2014).

2.2 Data on Occurrence in the Environment

2.2.1 Raw sewage, sludge and treated wastewater

Adenoviruses of several types have been detected indomestic sewage and sludge in various countries. Thirteenstudies from 11 different countries have been reviewed inTable 1. Adenoviruses have also shown to be resistant todisinfection and thus have been detected in treatedwastewater effluents as well, with sometimes highdetection rates. In several cases, more than 80% of sewagehas been found positive for adenoviruses (Prado et al.2011,Amdiouni et al. 2012, Wong et al., 2013).

Another promising application for adenoviruses is their

1.4.1.5 Adenovirus-based vaccines against infectious pathogens

Another promising application for adenoviruses is their

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2013

2011

Silverman et al.,NR

(16/20)80.0%

Untyped (Accra)Ghana

Prado et al.,2.3+04

1.7Ε+02 to64.2%SewageRaw

F (40, 41)HAdV C, D andBrazil

al., 2010Schlindwein et

4.6E+07 to 1.2E+09100%

SludgeWastewater

TreatedUntyped(Florianópolis)

Brasil

ReferenceConcentration

Average (Range) GC/LaSamples)(# of

PositivePercentAnalyzedMatrices

TypeVirusArea

Table 1. Detection of HAdv in raw sewage, treated wastewater and sludge

Adenoviruses

9

et al., 2014Grøndahl-Rosado

(59/64)92.0%

WastewateruntypedNorway

2013Hewitt et al.,5.2E+0411 sites(37/37) at

100%SewageRawΗΑdV FHAdVNew Zealand

Dong et al., 20102.59E+054.63E+03 to4.6E+06,1.87E+04 toWastewater

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(Auckland)New Zealand

2012Amdiouni et al.,NR

two sitesPCR atby ICC-(10/22)

samples45.5%Wastewater

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2007Haramoto et al.,

6.7Ε+048.5Ε+04100%SewageRawHadV F

Total(Tokyo)Japan

2005He and Jiang,11Ε+04100%SewageRawUntypedJapan

Verani, 2013Carducci and

6.02E+06(47/52)90.0%

WastewaterTreated

HAdV45HAdV31,HAdV2,

(Pisa)Italy

Verani, 2013Carducci and6.16E+08(52/52)

100% Untyped(Pisa)

Italy

2010La Rosa et al.,7.0Ε6+0876.0%Untyped(Central)

Italy

2010La Rosa et al.,3.3Ε+0996.0%Untyped

(Central)Italy

Peccia, 2013Bibby and

NR100%Sludgeand -BHAdV-C

USA

Peccia, 2013Bibby and

NR100%SewageRawuntypedUSA

Hurst, 1988Williams and

FFUsb5.4E+048.5E+02 to100%untyped(Cincinnati)

USA

2014Hellmér et al.,1.9E+053.3Ε+05 toNRSewageRawuntyped(Gothenburg)

Sweden2006

Bofill Mas et al.,3.87E+070.38 toNRuntyped(Barcelona)Spain

and three serial anaerobic filters, activated sludge with extended aeration and final chlorination of the effluents.Upflow Anaerobic Sludge Blanket (UASB reactor) cFFU 1 FFU equals one virus; bGC Gene copies 1 GC equals one virus;a

NR - Not Reported

50 to 1.3E+07,

Treated Wastewater

Raw Sewage

Raw Sewage

TreatedWastewater

100%

2.15E+01Treated

Raw Sewage

Sludge

Adenoviruses

10

Since adenoviruses are frequently detected in highconcentrations in treated wastewater and wastewater-contaminated waters, their use as potential indicators forthe presence of human sewage has been affirmed. Also, acorrelation has been noticed between the presence of HAdVwith other viruses in sewage such as human polyomavirusor norovirus (La Rosa et al. 2010; Kokkinos et al. 2011b;Hewitt et al., 2013).

Quantification of adenoviruses show usually highadenovirus concentrations in raw sewage, combined seweroverflows, primary-treated effluent, secondary-treatedeffluent, and chlorinated effluent from wastewatertreatment plants (Fong et al., 2010). Average adenovirusDNA concentrations in sewage and CSOs could be morethan 106virus particles/liter. Various adenovirus types (41,12, 40, 2, 3) have been isolated from raw sewage, sludgeand primary effluents. Surface water samples impacted bywastewater show virus concentrations and may not besuitable for full-body recreational activities (Kokkinos et al.,2011a). High concentrations of adenovirus in these watersmay be due to inefficient removal during wastewatertreatment and to the high persistence of these viruses inthe environment (Fong et al., 2010; Rodriguez et al., 2012).

).2011Madoni, (sewage treatment plants such as ones artificial

including, freshwater habitats in most genus widespread, is aEuplotes genera of the Ciliates. disinfectants

artificial and natural from both protectionand in their viruses of spread in the protozoa for these important role

ansuggesting adenoviruses, human of internalizationpersistent to susceptible are Euplotes octocarinatusprotozoan ciliated of the cells the showed that (2013)

Battistini et al. . environmental conditions in viruses enterichuman for reservoirs could be protists that suggested

alsostudies). These Verani et al., 2016 (hoursNaOCl for 24 towards 5mg/l ofprotected was Acanthamoeba polyphaga

byinternalized HAdV5 showed that experimental study). AnLorenzo-Morales et al., 2007 (Canary Islands

the of waters from isolated. Acanthamoeba spp of strains 34 of 236 (14.4%)within detected) was type 2 adenovirus

mostly (adenovirus of serotypes different of 4 DNAviral) and Scheid and Schwarzenberger, 2012 (phagocytosis

via most likely, Acanthamoeba spp. into incorporated that adenoviruses could bedemonstratedbeen

. It has alsoenvironment in the same living microorganismsvarious of vehicles or reservoirs act as mayFLA

, and it has been shown thatwater reservoirs similar fromrecovered (FLA) have been Free-living amoebae. worldwide

artificial water reservoirs and natural several in prevalent to befound). Adenoviruses have been Kishida et al., 2012(

studies previous in suggested as concentration viralof independent were heterotrophic plate count and turbidity

such asdata indicator microbial general, while viruses

the presence of with correlated highly was river basin in ainfectious gastroenteritis acute with patients number of

densities. Thepopulation increased of areas from obtainedmainly are samples positive adenovirusMost 2).Table(

countries different 5 made in studies in 8 surface water oflitre per copies genome from 1 to about 100,000 ranged

Concentrations. surface waters in human pathogens viralof prevalence high a showing world the around surface waters

ofcases several in detectedAdenoviruses have been

2.2.2 Surface waters

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Table 2. Detection of Adenoviruses in surface water

Area Virus Type MatricesAnalyzed

PercentPosivite

(# ofSamples)

ConcentrationAverage (Range)

 GC/LaReference

Brazil(Florianó-polis) Untyped Lagoon

96.0%(46/48) NR Fongaro et al., 2012

Brazil(Peri Lagoon, SantaCatarina State)

Untyped Lagoon 70.8% summer62.5% winter NR Elmahdy et al., 2016

Hungary Untyped River56%

(45/80)16 sites

19.6E+03 Kern et al., 2013

Japan(Tokyo)

HAdV types 40 and41 River

44%(23/52)1 site

8E+03 Kishida et al., 2012

Japan HAdV types 40 and41 River61.1%(11/18)

3.16E+03 to1.38E+05 Haramoto et al., 2010

South Africa(Durban) Untyped River

32.0%(8/25)5 sites

NR Lin and Singh, 2015

South Africa(Eastern Cape)

HAdV C type 1,2,6,B1 type 7, and F

types 40,41River

31.0%(22/72)6 sites

1E+00 to 8.5E+04 Sibanda and Okoh,2012

South Africa(Eastern Cape)

HAdV types 21,40 and 41 River

35.0%(25/72)6 sites

1.2E+01to 4.71E+03 Chigor et al., 2012

Taiwan HadV type 41 River30.8%(4/13)

13 sites6.10E+02 to8.51E+02  Huang et al., 2015

Taiwan HAdV types2,5,31,41 River34.3%

(99/288) 2.8E+03 Tao et al., 2015

USA HAdV40 andHAdV41 Surface water48.3%(14/29) NR Chapron et al., 2000

USA(Michigan) HAdV F types Lake

24.1%(14/58)2 sites

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Table 3. Detection of Adenoviruses in groundwater and drinking water

Area Virus Type MatricesAnalyzedcPercentPosivite

(# of Samples)

ConcentrationAverage (Range)

GC/LaReferences

Brazil Untyped Tap water 23.3%(17/73) NR Kluge et al., 2014

Brazil Untyped Tap water 100%(36/36) 1.0E+7 Garcia et al., 2012

Brazil Untyped Network water 100%(6/6) NR Fongaro et al., 2013

Brazil Untyped Surface water

83.0%(10/12) virions

66.0%(8/12) infectious

viruses

NR Fongaro et al., 2012

France Untyped Ground water 11.7%(7/60) NR Ogorzaly et al., 2010

Ghana Untyped Tap water 16.6%(1/6) NR Gibson et al., 2011

Japan HAdV 40 41 Tap water 39.0%(25/64) NR Haramoto et al., 2012

Korea HAdV types1,5,6,40, 41 Tap water39.1%(9/23)

from 11 sites

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2.2.4 Drinking water

Adenoviruses have been isolated in drinking water inseveral countries such as Norway (Grøndahl-Rosado et al.,2014) Japan (Haramoto et al., 2012), Brazil (Kluge et al.,2014; Garcia et al., 2012), Ghana (Gibson et al., 2011),West Africa (Verheyen et al., 2009), and Korea (Lee andKim, 2002). Total coliforms and Escherichia coli assessed indrinking water samples showed a lack of correlationbetween bacterial indicators and the presence of humanadenoviruses indicating a lack of proper public healthmeasures in drinking water (Fongaro et al., 2013). In ayear-long survey of the occurrence of adenoviruses indrinking water in South Africa, detection peaked betweenApril and July (winter in South Africa), when up to 30% oftreated surface water samples from two different sites werepositive for adenoviruses (van Heerden, 2003) (Table 3).

2.2.5 Seawater

Several researchers around the world have reported onthe presence of adenoviruses in seawater Finland(Hokajärvi et al., 2013), USA, (Love et al., 2014; Jiang et al.,2001) Australia, (Ahmed et al., 2010; Kueh et al., 1989) andJapan (Haramoto et al., 2007). In a Europe-widesurveillance study that was carried out to determine thefrequency of occurrence of two human enteric viruses inrecreational waters (Wyn-Jones et al., 2011), adenoviruseswere selected as an indicator based on their near-universalshedding and environmental survival. Researchers havealso reported that the presence of adenoviruses was notstatistically connected with the presence of othermicroorganisms in seawater (McQuaig et al., 2012; Wyer etal., 2012). In most cases the counts of faecal indicatorbacteria were not able to predict the presence ofadenoviruses in bathing waters. The detection ofadenoviruses suggests that the presence of infectiousviruses in recreational waters may constitute a publichealth risk upon exposure. Recent studies support the casefor considering adenoviruses as an indicator of bathingwater quality (Wyn-Jones, 2011).

2.2.6 Fish and shellfish

There are so far no studies on the presence ofadenoviruses in fish. However, in shellfish, there are manyreports since shellfish are filter feeders and concentrate theviruses in their tissues. While shellfish complying withEuropean Regulations based on quantification of fecalbacterial indicators (FIB) are introduced into markets,several researchers confirm that current controls anddepuration treatments limiting the number of FIB do notguarantee the absence of viruses in shellfish (Rodriguez-Manzano, 2013). Presence of adenoviruses were reportedin Italian mussels and found no direct correlation betweenthe presence of human pathogenic viruses and bacterialindicators (Serracca et al., 2010). In Japan enteric humanadenoviruses were detected in 52% of the clams tested(Hansman, 2008). In Brazil, high loads of human

adenoviruses in the environment were connected with highnumbers of viruses in shellfish (1.2xe5 per gram) (Rigottoet al., 2010). In India, high prevalence of adenoviruses(17% positive in oysters and 24% in clams) was noticedbetween May to December and the presence of MS-2 phageand human enteric viruses showed and association whilefecal coliforms and enteric viruses showed no association(Umesha et al., 2008).

Studies have also linked illness in the community tovirus types found in shellfish. In Tunisia, adenovirusesdetected in shellfish were related to the types in clinicalsamples (Sdiri-Loulizi et al., 2010). Similar findings werereported in Morocco (Karamoko et al., 2005) and Italy (LaRosa et al., 2012). However, the detection of adenoviralgenomes in shellfish exceeded the persistence of theirinfectivity, in most cases with 4-6 weeks (Hernroth andAllard, 2007) and it was suggested that a warning systembased on PCR amplification of virus DNA mightoverestimate the risk for transmission of viable virusessince the presence of a PCR was not necessarily associatedto viability of the virus and thus its relevance for publichealth.

2.2.7 Air

Many enteric viruses are present in wastewater and dueto their small s ize, they may be transmitted indroplets.Εxposure to virus contaminated droplets in severallabour places mainly wastewater treatment plants (WWTP)and its consequence on workers' health have beendocumented. Very few studies have investigated thepresence and concentrations of airborne virus in WWTP.Masclaux et al. (2014) detected that adenovirus waspresent in 100% of summer WWTP AIR samples and 97% ofwinter AIR samples. Concentrations of potentiallypathogenic viral particles in WWTP air are non-negligibleand could partly explain the work-related gastrointestinalsymptoms often reported in employees in this sector.Concentrations reported were2.27×106genomeequivalent/m3. Different concentrations have been observedalso according to the plant areas: 2455 GC/m3 at thesewage entrance, 1622 GC/m3 at the biological oxidationtank, 933 GC/m3 at the sludge treatment and 589 GC/m3 atthe side-entrance manhole (Carducci et al., 2016).

Wan et al (2012) evaluated the distributions of airborneadenovirus in public areas in the pediatric department ofChildren's Hospital in northern Taiwan and high detectionrates of airborne adenovirus DNA were obtained in Marchwith average 278.9CG/m3. Tseng et al. (2010) investigatedthe possibility of aerosol transmission of viruses in childrenin the pediatrics department of a medical center in Taipei,Taiwan. HAdV were detected in the aerosol of air samples(36% of the samples). In toilets of healthcare settings andoffices HAdV were found in over 60% of samples atconcentrations respectively of 6.6 107 GC/mL and 1.2107GC/mL in water, of 5.8x106GC/ m3 and 3.9x104GC/m3inair and of 483 GC/cm2 and 91 GC/cm2 on surfaces (Verani et

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al., 2014). HAdV was detected in apartments with averagein winter 2106 GC/m3 and in summer 173 GC/m3 (Moon etal., 2014).

2.3 Persistence

Data on adenoviruses have shown that their genomewas more stable compared with genomes of other virusesor bacteria (El-Senousy et al., 2014). The presence ofadenoviral DNA in groundwater may be misleading in termof health risk, especially in the absence of information ontheir infective status (Ogorzaly et al., 2010). According to alinear regression model in a year-long study ingroundwater, infectivity reductions of HAdV2 ranged from0.0076 log10(10)/day (at 4°C) to 0.0279 log10(10)/day (20°C).No adenoviral genome degradation was observed at 4°C,and the reduction was estimated at 0.0036 log10(10)/day at20°C (Ogorzaly et al., 2010). Adenoviruses could not bedetected on produce after 24h of irrigation with watercontaminated with viruses (Ward and Irving, 1987).Adenoviruses were found to be stable in biosolids for atleast 60 days with no degradation (Wei et al., 2010). In astudy of health risks associated with land applied biosolidsno notable decline in HAdV numbers detected by PCR wasobserved during 6 months (T90 ≥ 180 days) (Schwarz et al.,2014).

Temperature is considered as the major factordetermining virus persistence in the environment. Thepersistence of infectious particles, encapsidated genomesand free nucleic acids of HAdV 41 was evaluated indrinking water and surface water at 4°C, 20°C and 37°C byPrevost et al. (2016). The infectivity of HAdV 41 persistedfor at least 25 days, whatever the water temperature, andfor more than 70 days at 4°C and 20°C, in both drinkingand surface water. Encapsidated genomes persisted beyond70 days, whatever the water temperature. Free nucleicacids (i.e. without capsid) could persist for at least 16 daysin drinking and surface water (Prevost et al., 2016).

In a review (Bertrand et al., 2012), virus persistence wasfound to be lower at temperatures ≥ 50°C than at temperatures <50°C, but there was also a significant temperature–matrix effect.Virus inactivation appeared to occur faster in complex than insimple matrices. The virus genome was shown to be moreresistant than infectious virus (Bertrand et al., 2012; Fongaro etal., 2013). Enriquez et al. (1995) studied the survival of poliovirustype 1, HAV and the enteric adenoviruses (types 40 and 41) in tapwater at various temperatures for up to 60 days. Overall, theyfound that the enteric adenoviruses were more stable than theother viral types at both 4°C and 15°C and at room temperature.However, in primary and secondary sewage the entericadenoviruses did not survive significantly longer than poliovirus 1at either 4°C or 15°C. El-Senousy et al. (2014) also showed thatHAdV40 was more persistent than both rotavirus and hepatitis Ain ground water. Inspiked experiments with HAdV40 in groundwater 0.05 log10, 0.5 log10 and 1.5 log10 reduction of copy numbersat 4°C, 20°C and 35°C were shown. Infectious units reductionafter 12 weeks were 0.5 log10, 1.5 log10 and 3.0 log10 at the sametemperatures. Charles et al. (2009) also showed in spikedexperiments with HAdV2 that these genomes were stable ≥ 2years in ground water with a retaining infectivity ≥ 1 year. Bofill-

Mas et al. (2006)studied the stability of HAdV during 300 days insewage samples at 20°C resulting in T90of 60.9 days and aT99of132.3 days. By cloning experiments the adenovirus types 40, 41,31, 34, 35, 11 and 12 were detected over 105 days showing nosignificant differences in stability between the different typespresent during the experiment (Bofill-Mas et al., 2006).

3.0 Reductions by Sanitation Management

Adenoviruses have been detected in raw sewagethroughout the world and are associated with a number ofhuman illnesses but their occurrence and pathogenicityhave not been well studied (Jiang, 2006; Mena and Gerba,2009; Jacob et al., 2015). The continued monitoring oftreated wastewater by other researchers revealed theaverage concentration of adenoviruses in treatedwastewater (see Table 1). No correlation between thepresence of viruses and Escherichia coli has been found(Maunula et al., 2012). Moreover, the possible treatedsewage reuse in agriculture or elsewhere must beconsidered with concern (Crabtree et al., 1997; Kokkinos etal., 2010).

3.1 Wastewater Treatment

3.1.1 Pit Latrines, Vault Toilets, Dry Toilets

There were no data on adenovirus reductions in vaulttoilets, dry toilets.

3.1.2 Manure-based Composting

In the composting process of dairy manure HAdV type41 was more stable than RNA viruses in composts withcenter temperatures between 65°C and 70°C. There was noreduction in DNA after one day, and about a 2.1 log10loss at5 and 7 days (Wei et al., 2009). In the same experiment,more than a 4 log10reduction of adenoviral infectivity wasnoted after one day in compost. According to NorthAmerican regulatory bodies total viral inactivation isexpected to occur if compost particles maintaintemperatures greater than 55°C for at least 3 days. Thiscould either be the result of t ime–temperaturerequirements in ensuring that the time–temperaturecriteria are met by all compost particles (Wichuk andMcCartney, 2007).

3.1.3 Septic tanks

No log reduction data on adenoviruses in septic tanksare available.

3.1.4 Waste stabilization ponds

Wastewater treatment ponds (lagoons) are one of themost common types of technologies used for wastewatermanagement worldwide, especially in small cities andtowns. They are particularly well-suited for systems wherethe effluent is reused for irrigation.Human adenoviruses inwastewater treatment plants have been used as anindicator of the effectiveness of different treatment

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processes. HAdV concentrations in wastewater were morevariable in small and medium-sized WTP than in large-sizedplants. HAdv concentrations were detected in influent ofmost WTP with a reduced median concentration in effluent.Highest culturable HAdV concentrations in effluent werefrom a medium-sized WWTP. No matter of treatment type,adenoviruses are likely to be present in non-disinfectedeffluent, with associated human health risks dependent onconcentration and receiving water usage (Sidhu and Toze,2009; Hewitt et al., 2011).Sheludchenko et al. (2016)showed a log10reduction of adenoviruses of a 1.2 log10andJurzik et al. (2015) showed no reduction.On average,inwaste stabilization ponds,one log10reduction of viruses wasachieved for every 14.5–20.9 days of retention, but the 95thpercentile value of the data analyzed was 54 days. (Verbylaand Mihelcic, 2015).

3.1.5 Wetlands

Wetlands, open-water cells can be used to promotesunlight disinfection and remove pathogenic viruses fromwastewater. Sunlight inactivation is an important mode ofdisinfection for viruses in surface waters and rates foradenovirus inactivation are reported (Silverman et al.,2015).Rachmadi et al. (2016) showed an adenovirusremoval of 1-2 log10 in wetlands during a 9-month period. Aweak negative correlation between adenoviruslog10concentration and water temperature as well as pHwas observed (Rachmadi et al., 2016). HAdV type 3 showedinactivation rates with one log10reduction times of morethan 33 days in constructed reedbeds (Sidhu et al., 2010).

3.1.6 Aerated lagoons

The removal was found to be zero for HAdVduring thewastewater treatment in aerated lagoons (O'Hara andRubin, 2005; Jurzik et al., 2015).

3.1.7 Wastewater Treatment Facilities

3.1.7.1 Combined sewer overflows

Concentrations of adenovirus DNA in the combinedsewer overflows discharges (CFOs) were not significantlydifferent from adenovirus DNA concentrations in rawsewage showing an average concentration of 5.35x105

viruses/liter.Removal of adenoviruses was lower than 2log10 at the treatment plant(Fong et al., 2010). Hata et al.(2014) reported thatrainfall events can introduce largeamount of viral contaminants including adenoviruses intosurface water by intermittent discharges from combinedsewer overflows (CSOs).

3.1.7.2 By primary /preliminary treatment

Adenoviruses showed high stability in urban sewage(Silvia Bofill-Mas et al., 2006) and they were detectedfrequently in high concentration in raw sewage influentsbut were also detected less frequently in plant effluent andat much lower concentrations with removals shown to be2-3 log10 by primary sewage treatment.In this studya t90 of

60.9 days for HAdVwas reported.In another study, theaverage log10removals were 2.2–3.5 for adenoviruses whenusing sand filters in a cold temperature climate (Kauppinenet al., 2014).

3.1.7.3 By Secondary treatment and membrane bioreactors

In a one-year quantitative survey in six differentJapanese activated sludge waste-waterplants adenovirusamong other enteric viruses were observed. Adenovirusesweredetected at the highest positive ratio among the testedviruses; almost 100% in bothsecondary-treated wastewaterand in effluent after chlorination. The reductionofadenovirus was 2 log10 and was also found to be fairlyconstant and independent ofthe concentration of viruses inthe influent (Katayama et al., 2008).No removals ofadenovirus across disinfection was seen in membranebioreactors (MBR) and low median log10removals of 0.24was detected in conventional secondary plants with a fewremovals of individual samples near or above the analyticalvariability of 1.2 log10genomic copies per liter (Francy et al.,2012).

Also, the environmental monitoring carried out at awastewater treatment plant in Italy, showed the presenceof adenovirus DNA in 100% of the raw sewage samples andin 85-100% of the effluent, an average reduction of 2 log10for adenovirus was found via activated sludge andchlorination. Moreover, this reduction was lower in rainythan i n sunny wea ther : 1 .67 Log 1 0 and 2 .34Log10respectively (Carducci et al., 2008; Carducci andVerani, 2013).The virus removal in a full-scale MBR havebeen reported between 3.9 and 5.5 –log10 for adenoviruses(Chaudhry et al., 2015). The greatest contribution to totalremoval was provided by the backwashed membrane,followed by inactivation, the cake layer, and attachment tosolids. Increases in turbidity and particle counts afterbackwashing indicated potential breakthrough of particles,but virus removal following backwash was still high. Theability of the MBR process to provide more than 4 log10 ofremoval for adenovirus was confirmed (Chaudhry et al.,2015). Another study was conducted to characterizeeffluent water qualities produced by satellite MBRs withrespect to adenoviruses. They were detected in all effluentsamples irrespective of membrane cleaning or breachingstatus (Hirani, 2013; 2014). Studies about the removalefficiencies of the viral particles in the full-scale MBRprocess showed that the average removal of humanadenoviruses was about 5.0 ± 0.6 log10. The removalefficiencies for the enteric adenovirus type F species(average log10removal 6.5±1.3 log10) were typically higher(p-value

Adenoviruses

16

clarification effluent and granular mediafiltration effluentsamples but only in 31.2% of membrane filtration effluentand 41.7% of final effluent samples, respectively. Theaverage HAdVs loads were significantly reduced along thetreatments but HAdVs were still present in final effluent(mean log10removals of HAdV from primary clarifer influentto second clarification, granular media filtration, membranefiltration and final effluent were 3.0, 3.2, 5.2, and 5.1,respectively). Comparison showed that membrane filtrationwas technically superior togranular mediafor the removalof HAdVs(Liu et al., 2013). Human adenoviruses weredetected in 82–100% of wastewater samples in a treatmentplant in Germany with median concentration of6.8x103gene copies/L. By using polishing ponds as a tertiarytreatment a 2.2log10reduction in bacteria and phages wasachieved, but no reduction for adenoviruses was seen(Jurzik et al., 2015).

3.2 Disinfection

3.2.1 Chlorine

Adenoviruses are not completely removed(100%) bytertiary treatment processes including disinfection(Lazarova et al., 1999), yet the use of chlorine disinfectionis an effective strategy to control adenoviral waterbornetransmission via some level of log10reductions (Girones etal., 2014). The kinetics of inactivation of human adenovirus2 in natural and artificial seawater was studied. A4log10reduction of adenovirus viability could be achieved at aCT value of 2.6 mg Cl2min/L (CT; disinfectant concentrationx contact time) (Page et al., 2009).In another study, after 30min exposure to free chlorine (2.5mg/L), human adenovirus2 showed 2.6and 2.7 log10reductions and a 2.3 and 2.4log10PFU reductions in natural and artificial seawater,respectively, although infectious viral particles were stillobserved (de Abreu Corrêa et al., 2012).

Inactivation of adenovirus type 2, 40 and 41 werecompared after exposure to 0.2mg/L of free chlorine or 1mg of monochloramine per liter in buffered reagent-gradewater at 5°C. Adenovirus type 2 needed 1600 mg-min/litermonochloramine for 3 log10 reduction at pH 8.0. Adenovirustype 40 and 41 showed 3 log10 inactivation with 5 seccontact time with 0.2 mg of free chlorine (Cromeans et al.,2010). Other investigations have reported similar time span

for chlorine inactivation of the different adenovirus types(Thurston-Enriquez et al., 2003a; Baxter et al., 2007). Inanother study, chlorine disinfection efficacy wasinvestigated for human adenovirus 2 (HAdV2) in untreatedgroundwater source and partially treated surface waters.Chlorine disinfection of HAdV2 proceeded very rapidly (3-4log10 inactivation within 5 to 10s) in each source water andwhen CT values could be calculated disinfection was moreeffective at pH 7 than pH 8 (Kahler et al., 2010). However,water quality could play a substantial role in theinactivation of viruses and should be considered whendeveloping chlorination plans, but more information isneeded on the disinfection efficacy of chlorine for viruses insource water (Kahler et al., 2010).3.2.2 Ozone and other oxidants

According to U.S. EPA Ground Water Rule,adenoviruses are readily inactivated by ozone with CTvalues as low as 0.07 mg-min/L for a 4 log10inactivation atpH 7 and 5°C (Thurston-Enriques et al., 2005). In light ofthis, the combined use of ozone with UV may be a viableand safe water treatment strategy that utilities couldemploy to achieve desired reductions in pathogenicmicroorganisms.

The inactivation of adenoviruses in fecal sludge at pH8.9 and 55mM of NH3 resulted in a 3log10reduction after 21days (Magri et al., 2015). In another study, the treatmentwith PIX (FeCl3) or PAX (AlCl3) coagulants and peraceticacid (PAA) was studiedandshowed that both PIX and PAXflocculation reduced numbers of HAdV 40 with about 2 log10but the virus was more resistant against PAA compared tothe other microorganisms such as bacteria and alsoNorovirus GI (Pradhan et al., 2013).

3.2.3 Ultraviolet

Adenoviruses are recognized as the most UV-resistantwaterborne pathogen of concern to public healthmicrobiologists (Meng and Gerba, 1996). Pilot experimentsfor the inactivation of human adenoviruses are shown inTable 4. The U.S. EPA has stipulated that a UV fluence(dose) of 186 mJ/cm2 is required for 4 log10inactivationcredit in water treatment (Gerba et al., 2002) even if lowerdoses have been reported with an adenovirus reduction tothe limit of detection (1 TCID50/100L) at UV doses of 40 to45 mJ/cm2 (Jacangelo et al., 2003).

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HAd 1,3,4, 5, 6,40, 41 Cell culture suspension 90 mJ/cm

2 Nwachuku et al., 2005

HAd Treated wastewater 40 to 45 mJ/cm2 Jacangelo et al., 2003HAd Spiked tertiary treated wastewater 170 mJ/cm2 Thompson et al., 2003HAd 41 Cell culture suspension 225 mJ/cm2 Ko et al., 2005HAd 2 Filtered drinking water 60 mJ/cm2 Shin et al., 2005HAd 2 Cell culture suspension 40 mJ/cm2 Lee and Shin, 2011HAd 5 Cell culture suspension UV-OH 400 mJ/cm2b Monteiro et al., 2015

a Treated water: chlorinated water; b UV-OH:UV-electro-oxidation

A dose of approximately 170 mJ/cm2was required toachieve 4 log10inactivation in wastewater (Thompson et al.,2003). These findings suggest that UV doses effective atmeeting certain wastewater regulations for total coliformbacteria may not provide suitable inactivation of the UV-resistant human adenoviruses. A comparative inactivationof different adenovirus serotypes (type 1, 3, 4, 5, and 6) byUV was done. The results of the study confirmed thatadenovirus are the most resistant enteric viruses toinactivation by UV light and that adenovirus type 40appears to be the most resistant (Nwachuku et al., 2005).Similar results have also been presented for adenovirustype 41 indicating a high resistance to UV-light (Ko et al.,2005). Median log10removal of adenoviruses duringdisinfection process was low in both MBR and conventionalsecondary plants (no removal detected and 0.24). In a fewcases removal of individual samples were near or above theanalytical variability of 1.2 log10genomic copies per liter(Francy et al., 2012).

By using polychromatic UV sources a significantenhancement in inactivation of adenoviruses can beachieved. As already described most adenovirusinactivation data have been based on UV disinfectionexperiments using UV irradiation at 253.7 nm producedfrom a conventional low-pressure UV source (Francy et al.,2012; Hijnen et al., 2006; Shin et al., 2005; Thurston-Enriquez et al., 2003b). By using a medium-pressuremercury lamp a complete spectrum of 200-300 nm can beproduced. When full-spectrum polychromatic UV lampswere used, 4 log10 inactivation of adenovirus type 40 wasachieved at a UV fluence o