Public Health Concerns of Mice & Rats

Robbin Lindsay

Zoonotic Diseases and Special Pathogens,

National Microbiology Laboratories,

Public Health Agency of Canada,

Canadian Public Health Inspectors Meeting,

Winnipeg, Manitoba

September 16, 2011

Importance of Rodents

•Economic impact Damage to food and feed consumption

Structural damage

Other damage related to chewing/digging

•Impact on human health Stress/anxiety associated with infestation/disease potential

Direct injury from encounters (scratches or bites)

Allergic reactions to rodent by-products

Transmission of disease-causing pathogens

Pathogens transmitted by rodents

• Flea-borne infections Plague

Murine typhus (endemic)

• Louse-borne infections Epidemic typhus (R. prowazekii)

• Transmitted in excreta Cestode infections (Hymenolepiasis, Echnicoccus)

Nematode infections (Trichinosis)

Rat-bite fever (Streptobacillus moniliformis)

Salmonellosis

Toxoplasmosis

Tularemia **

Leptospirosis

Arenavirus (LCMV)

Hantaviruses (Sin Nombre virus)

Plague

Causative agent – Yersinia pestis

Member of family Enterobacteriaceae (11 species, 3 known human pathogens)

Gram negative bacteria, nonmotile, non-spore forming coccobacillus

Plague

Disease in USA typically occurs in May to September

Three primary forms of disease: bubonic*, septicemic* & pneumonic

Average case fatality rates about 14% (failure to seek early treatment)

Plague in Canada

1988 detection of plague in two dead bushy-tailed woodrats in BC,

only confirmed case of disease in wild animal

Human cases sporadic but last reported case in 1937 sparked large

surveys in BC, Alberta, & SK [1938, 1943 (RCMC) and 1948]:

Y. pestis in 6 of 817 ground squirrel tissues &

in 32 of 939 pools of fleas (SE AB)

in 2 of 61 pools of fleas from GS in SK

Serosurvey of rural dogs and cats conducted in 1995 in AB and SK

confirmed endemicity of plague [Over 4 sites in 2 provinces, 9.6% of

240 dogs and 5.4% of 242 cats with antibodies to Y. pestis]

Reasons for the rarity of human infections in Canada compared to

USA are unknown but may be linked to limited distribution of

Cynomys species (which have low resistance/high mortality) in

Canada

Plague “rediscovered” in Canada

Sask Disease Control Laboratory submitted samples from a dead prairie dog found in

Grasslands National Park to NML in early August, 2010

Isolates of Y. pestis obtained from prairie dog liver (Emerging Bacterial Diseases: NML)

Reconfirms endemicity of plague in Western Canada, minimal public health significance but

may be of concern for re-introduction of black-footed ferrets

Francisella tularensis

Tularemia: The Organism • Francisella tularensis

– small, pleomorphic, non-spore-forming, nonmotile

coccobacillus, Gram-negative

– obligate intracellular pathogen

• Macrophages

– 4 subspecies F. tularensis most in northern hemisphere

• F. tularensis tularensis (Type A; NA only, more virulent)

• F. tularensis holarctica (Type B; Old & New World, less virulent)

Ecology

• Host range

– Documented in 190 mammalian, 23 avian, 3 amphibian and 88 invertebrate species

– Primarily a disease of lagomorphs (rabbits & hares) and rodents

– In North America, most important species are:

cottontails (Sylvilagus spp.), blacktailed jack rabbits and snowshoe hare (Lepus spp.), beavers & muskrats

Key reservoirs varies by geographic locality & local ecological factors, transmission dynamics complex & poorly defined

Modes of Transmission: animals

• Vector-borne

– Ticks

• Transstadial transmission but not transovarial transmission

• 14 species in NA (different spp. in old world)

– Dermacentor andersoni *

– Dermacentor variabilis *

– Amblyomma americanum

– Haemaphysalis leporispalustris*, H. chordelis*, Ixodes dentatus

* Widespread in Canada

– Fleas, tabanid flies (mainly deer flies in Chrysops e.g., Chrysops discalis)

• Mosquito infrequent in NA but not old world

• Others: ingestion, infective bites or scratches, ingestion or direct inoculation with contaminated sources (soil, water, vegetation)

Transmission to people

• Humans can become infected by: • handling, skinning, eating or being scratched or bitten (rare) by an

infected vertebrate

• Drinking contaminated water, making skin contact with contaminated water or mud

• inhalation of infected aerosols (many potential sources: hay, grain, soil, water?)

• handling (present in tick feces) or being bitten by infected arthropods

• working with this agent prior to the development and widespread use of biological safety cabinets/laminar flow hoods

– No person to person transmission documented

Disease in humans

• Incubation

– 3-15 days

– Varies with virulence of strain

and dose

• Typical symptoms:

– Sudden fever

– Chills

– Headache

– Myalgia

• 6 clinical syndromes

– Ulceroglandular

– Glandular

– Oculoglandular

– Oropharyngeal

– Typhoidal

– Pulmonary

• Morbidity & Mortality

– depends on strain and route of inoculation [e.g., Type A, aerosol (untreated): 30-60%]

– historically 5 –15% case-fatality rates (type A), currently reported <2% and Type B rarely fatal.

Tularemia cases in Canada

Rarely reported disease in Canada Nationwide (1940 to 1981) – 289 reported cases (12 deaths)

Sporadic cases & small number of cases more recently

e.g., MB (1994-2004) 6 cases

BC (up to 1997) 3 cases

QC (1975-2001) 26 cases

Some with obvious occupational exposure (trappers)

Unique cases of tularemia

• Martha‟s Vineyard – “Dog-borne” tularemia (shaking off water in a crowded cabin)

– “Lawnmower tularemia” (aerosolizing F. tularensis during landscaping or clearing of bush)

• Tularemia in zoological parks – Non-human primates (& handlers) in Assiniboine Park Zoo, Winnipeg, MB

– Similar outbreak in Zoological Park in Colorado

• Pet associated-tularemia – transmission of tularemia among wild-caught Prairie dogs (at pet exotic pet

distributor) to humans

– tularemia associated with the bite of a pet hamster

– recent outbreaks in hamsters/gerbils in MB pet breeder (feral rodents)

– widespread epizootic in deer mice in SK

Leptospirosis: The pathogen

Most widely distributed zoonosis in the world • Gram-negative, obligate aerobes

• Pathogenic & saprophytic strains

• Infect various animals shed in urine, persist in fresh water,

damp soil, mud and vegetation

• Taxonomically “unsettled group”, prior to 1989,

Leptospira interrogans (patho) & L. biflexa (sapro)

About 200 & 60 serovars, respectively, identified for each,

• Molecular differentiation on-going (16 genomospecies)

Leptospirosis: Modes of transmission

Maintain in nature: • Chronic infection (renal tubules) of selected hosts

• Common maintenance hosts include: rodents (rats, mice, voles)

• Select serovars associated with certain hosts (not absolute)

Rats (icterohaemorrhagiae, ballum)

Mice (ballum)

Cattle (hardjo, pomona, grippotyphosa)

Pigs (pomona, bratislava, tarassovi)

Sheep (hardjo, pomona)

Dogs (canicola)

• Incidental hosts infected by direct or indirect contact

• Human exposed via contact with hosts or contaminated water

(occupational, recreational and avocational exposures)

Leptospirosis: Disease in people

Complex manifestation: • Spectrum of symptoms extremely broad

• Two type: icteric (severe) & anicteric (less severe)

• Clinical presentation biphasic (acute & immune phase)

• Most cases sub-clinical or mild

• Recognized cases: fever of sudden onset, chills,

headache, myalgia, abdominal pain,

rash (less often) [3-10 d],

• aseptic menigitis (children), pulmonary hemorrhage

• for anicteric leptospirosis mortality near zero

• difficult differential diagnosis (tropics especially)

Leptospirosis: Disease in people 2

Icteric leptospirosis (jaundice) • 5-10% of cases, mortality 5-15%, rapid progression

• complications due to ARF, liver damage, hemorrhage,

pulmonary & cardiac involvement

• Ocular complications (uveitis in people, horses)

• Acute infestation during pregnancyabortion, fetal death

• No evidence of chronic or latent infection (Lyme?)

• Treatment: oral doxycycline, hospitalized - IV penicillin

• Immunity is primarily humoral, life-long but serovar specific

• Few vaccines for people (Chinese rice workers)

Leptospirosis: Incidence in NA

US 100-200 cases per year (50% Hawaii)

Canada many fewer (most travel-related)

More activity from veterinary side • Associated with abortions in cattle, pigs, horses

• Serological surveys: activity coast to coast

• Dominant serovars: Cattle (hardjo, pomona)

Swine & horses (bratislava, pomona, ictero.)

Dogs (canicola, autumnalis, grippotyphosa)

Wildlife: skunks & red fox (pomona), wapiti

(autumnalis, bratislava, ictero.), BTD (pomona)

Emerging serovars: grippotyphosa, bratislava?

2 Vet cases: AB (86); serosurvey 92 NS vets & abbatoir

(9-16% AB+ve; bratislava, ictero.); QC (92) 5% AB+ve

ON 97 Cluster of infections (grippotyphosa), trappers

Leptospirosis: Diagnosis

Diagnostic algorithm at NML • Screen with PanBio ELISA (IgM)

• Reactor to Micro agglutination test (MAT) with serovars:

[Autumnalis, Ballum, Canicola, Hardjo,

Icterohaemorrhagiae, Grippotyphosa, Pomona & Tarassovi]

& PanBio EIA (IgM)

• other diagnostic procedures:

• Isolation (various tissues) in EMJH media [low yield]

• PCR (various tissues)

400-500 samples per year [0-8 MAT +ve/yr]

Leptospirosis: Prevention

Avoid contact with contaminated sources • swimming or wading in water especially tropical

• vaccinate dogs & farm livestock (cattle, pigs)

• use of protective clothing (occupational high risk situations)

• implementation of rodent control

• prophylactic treatment in some high risk activities

Lymphocytic Choriomeningitis Virus (LCMV)

New World Complex

Arenaviridae Paramyxoviridae

Filoviridae Bornaviridae

Old World Complex

Machupo virus

Junin virus

Sabia virus

Guanarito virus

Lymphocytic Choriomeningitis Virus (LCMV)

Lassa Virus

Reservoirs & transmission

• Chronically infected house mice (Mus musculus) are the natural reservoir of the virus (lab & field)

• LCMV in high titres in urine, feces, saliva, nasal secretions [used animal bedding a potential fomite]

• Exposure via inhalation, broken skin or into nose, eyes, or mouth and possible by bite of an infected animal

• Humans are exposed through:

– contact with infected mice or less frequently from pet rodents (infected via contact with feral infected mice),

– congenital infections (mother to offspring) and,

– organ transplant

Spectrum of disease

• Infection with LCMV is not uncommon (5% of general population), disease is relatively rare with most infections asymptomatic or only mild febrile illness

• People with weakened immune systems more severe or fatal cases (especially dangerous for those receiving organ donations)

• Infection during pregnancy can cause spontaneous abortion, and severe birth defects (hydrocephalus, chorioretinitis, blindness or mental retardation)

• Pet rodents like hamsters: asymptomatic or loss of appetite, lethargy, rough coat, inflammation of the eyes and eventually death (weeks or months later)

• Viral hepatitis caused by LCMV in non-human primates can be fatal

Callitrichid Hepatitis (CH)

• Recognized in 1980‟s - an acute viral hepatitis with a high attack

rate and fatality rate of ~ 75%

• Outbreaks restricted to zoo and animal park collections of the

primate family Callitrichidae, including Marmosets and Tamarins

• Serological data implicated an arenavirus in the infection

• Stephenson et. al. (1994) identified etiologic agent as Lymphocytic

choriomeningitis virus (LCMV)

Biodôme de Montréal

• The Biodôme is the former Velodrome of the Montreal Olympics

converted into 5 different „Biospheres‟ including tropical

rainforest

• Two Tamarins and one Marmoset died

from illnesses consistent with CH

• Liver, spleen, kidney, brain and lung

samples sent to NML for testing

• Feral mice noted in some of the exhibits

Work undertaken by Special Pathogens: NML

Callitrichid Hepatitis: Case Summary

SPECIES SEX AGE ILLNESS

DURATION

CLINICAL SIGNS BLOOD WORK GROSS HISTO

Cottontop Tamarin

(Saguinus oedipus)

Female 18 yo 4 days Weakness, hind limb paresis,

terminal neurological signs

Not available Mottled liver, pulmonary

congestion, periodontal

disease

Necrotizing/lymphocy

tic hepatitis,

alveolitis/bronchiolitis,

splenic lymphoid

hyperplasia with

necrosis

Same Female 5 yo 1 day Weakness, diarrhea,

dehydration, terminal

neurological signs and bloody

diarrhea

Clinical chemistry

compatible with liver

disease, lipemic serum

Minimal gross changes Same

Goeldi‟s Marmoset

(Callimico goeldii)

Male 15 yo 2 days Weakness, appetite loss Same Hydrothorax/hydroperic

ardium, pulmonary

edema, mottled liver

with large reddish

lesions

Necrotizing/histiocytic

and neutrophilic

hepatitis, alveolitis,

ependymitis

Callitrichid Hepatitis:Gross Pathology

Biodôme de Montréal

Goeldi’s Marmoset

André Dallaire, FMV

400 x

Diagnostic Procedures

• Nucleic acid was isolated from each tissue sample using commercial extraction kits and widely reactive RT-PCR assays set up to amplify a region of LCMV S segment

• Isolation of virus attempted using Vero E6 cell lines

• LCMV RNA was found to be present in all samples – sequence analysis found all tissues to contain same unique LCMV sequence

• After second blind passage, LCMV RNA was detectable in cell culture supernatant – no cytopathic effect present on monolayer

Nucleotide Substitutions (x100)

Bootstrap Trials = 1000, seed = 111

0

30.7

51015202530

810362.seq

Armstrong 53b.seq

46.5

eu480450.seq

38.4

MX.seq

WE.seq

55.3

200504261.seq

31.4

40.3

CH-5692.seq

NA

810366.seq

MontrealCHV.seq

28.0

Y.seq

79.9

33.2

Dandenong.seq

M1.seq

65.5

LE.seq

91.7

87.4

Mopeia.seq

Phylogenetic Analysis

- 400 bp fragment of nucleoprotein used for analysis

- Sequence of this isolate most closely related to LCMV sequences from

North American sources

Biodôme de Montréal: Follow-up

• Wild mice were present in enclosure and were considered

the likely route of infection

• 7 mice were trapped, humanely killed & liver and spleens

sent for PCR-based testing

• All mice were found to be infected with the same strain

of LCMV as was found in the primates

• Rodent exclusion procedures put in place

Genus Human disease

Bunyavirus LaCrosse encephalitis, others

Phlebovirus Rift Valley fever, sandfly fever

Nairovirus Crimean-Congo hemorrhagic fever

Tospovirus Plant virus, no known human disease

Hantavirus Hemorrhagic fever with renal syndrome

Hantavirus pulmonary syndrome

5 genera, 250 species

Family Bunyaviridae

Hantaviruses - History

• Korean War, 1951-54: >3,200 cases “Korean

Hemorrhagic Fever”

• Fever, shock, ARF, pulmonary edema

• 10% case-fatality rate

• Tents “overrun with rodents”

• Rodent-association established in 1978

• Virus isolated in 1981from rodents collected

along Hantaan River in Korea (=Hantavirus)

Rodent-associated viruses

World-wide: Two lineages of hantaviruses

Old World - 9 species, 4 which cause disease

New World - 23 species, 11 which cause disease

Arvicolinae

Murinae

Sigmodontinae

Chronically infected

rodent

Virus is present in aerosolized

excreta, particularly urine

Horizontal transmission of infection

by intraspecific aggressive behavior

Virus also present in throat

swab and feces

Secondary aerosols, mucous membrane

contact, and skin breaches are also

sources of infection

General cycle of transmission of hantaviruses

Hantaviruses and disease in humans

• Hemorrhagic Fever with Renal Syndrome (HFRS)

o Old world hantaviruses

o Mortality rate ranges from <1 to 15%

o Restricted to Asia and Europe

o Annually 200,000 HFRS cases in Europe and Asia

• Hantavirus Pulmonary Syndrome (HPS)

o First described in 1993

o New world hantaviruses

o Mortality rate approx. 35%

o 1600 confirmed cases in the America‟s (PAHO website)

Sin Nombre Peromyscus maniculatus

Rio Segundo Reithrodontomys mexicanus

El Moro Canyon Reithrodontomys megalotis

Andes Oligoryzomys longicaudatus

Bayou Oryzomys palustris

Black Creek Canal Sigmodon hispidus

Rio Mamore Oligoryzomys microtis

Laguna Negra Calomys laucha

Muleshoe Sigmodon hispidus

New York Peromyscus leucopus

Juquitiba Unknown Host

Maciel Necromys benefactus

Hu39694 Unknown Host

Lechiguanas Oligoryzomys flavescens

Pergamino Akodon azarae

Orán Oligoryzomys longicaudatus

Caño Delgadito Sigmodon alstoni

Isla Vista Microtus californicus

Bloodland Lake Microtus ochrogaster

Prospect Hill Microtus pennsylvanicus

New World Hantaviruses

Bermejo Oligoryzomys chacoensis

Calabazo Zygodontomys brevicauda

Choclo Oligoryzomys fulvescens

Sin Nombre (530)

Black Creek Canal (1)

Bayou (3)

New York (2)

Virus Type

Location of North American HPS Cases by Virus Type

as of July, 2010

Total Cases: USA-545 in 34 States; Canada-74 in 5 provinces

10 41 19 3

1

HPS cases by year in Canada (n=74)

0

2

4

6

8

10

1989

1991

1993

1995

1997

1999

2001

2003

2005

2007

2009

British Columbia Alberta Saskatchew an Manitoba Quebec

3.7 (2)

R1

R6

R5

R4

R2 R3

R7

R9 R8

R10

R11

R12

R13

1.3 (1)

2.3 (1)

0.8 (2)

2.3 (1) 1.7 (5)

4.8 (2) 1.3 (2) 1.4 (1)

0.08 (1)

2.3 (7)

0.6 (6) 7.2 (8)

2.8 (5) 3.6 (5)

4.6 (1)

Incidence of HPS over 13 year period in AB & SK

HPS cases by month of exposure (n=74)

0

5

10

15

20

25

Janu

ary

Febru

ary

Mar

chApr

il

May

June

July

Aug

ust

Sep

tem

ber

Octobe

r

Nove

mbe

r

Dece

mbe

r

Month

Mean age – 39.7 yoa (range: 7-76)

Cases more frequent in males (49; 66%) than females (25; 34%)

Mortality higher in females (37.5%) than males (24.4%)

Overall case fatality rate of 29% (20/69)

Age distribution of HPS cases and percent

mortality within each age class (n=74)

0

5

10

15

20

25

0-10 11-20 21-30 31-40 41-50 51-60 61-70 70+

No

. o

f cases

0

20

40

60

80

100

Number of cases Percentage mortality

Why are there so few HPS cases?

Possibilities

Host resistance factors (children versus adults, genetic

susceptibility?)

Only recent infected deer mice (younger animals) shed

enough virus into the environment to cause illness?

Virus particles do not survive for extended period in

older droppings so illness occurs only after exposure to

fresh droppings?

Risk Factors for HPS

Infections are more common in males

Disease is rare in children

Certain occupational groups are more at

risk

High risk activities include cleaning

(creating dust) in confined spaces

(buildings, abandoned vehicles, etc.)

contaminated by rodent droppings

Different approaches used to understand

hantaviruses in Canada

• Passive surveillance

• Active surveillance/case investigations

• Field studies on transmission dynamics

Focused primarily towards deer mice

but other species collected & tested

Passive surveillance

Collaborators across Canada including: Public health inspectors, pest control personnel,

wildlife biologists, university facility, private

contractors, etc.,

Rodents collected using: Snap traps & various live traps

Whole carcasses, Nobuto strips (or

blood samples) shipped to NML Screen for AB with ELISA, lungs harvested

from selected positives for PCR

Serological survey for hantaviruses in

deer mice from across Canada

Sin Nombre virus

Seronegative rodents

Seropositive rodents

BC-627

(3) AB-2051

(7.9) SK-887

(4)

MB-1490

(3.6) ON-1898

(2.9)

QC-503

(6.2)

NF-62 (3.2)

NS-287

PE-122

NB-232

(5.6)

YT-107

(8.4) NT-184

380/7,891 (4.8%) deer mice with antibodies

Active surveillance

Intensive small mammal survey proceeding HPS cases Collaboration with local public health authorities & residents

Objectives: Define risk factors for hantavirus exposure

• Widespread & extensive rodent collection

• Field collection of relevant tissues

• Laboratory testing for AB and virus in various

tissues or fluids (RT-PCR)

Outcomes of active surveillance

Previous epidemiological investigations have revealed:

• Risk (“infected” mice) typically present throughout community

where human case (s) occur but can vary amongst them

• Distribution of “infected” animals can be highly focal

• Most human cases occur singly but multiple exposure to same

point source can occur

• Reasons for exposure of victims (relative to others in

community) difficult to establish in many instances

Quickly generate

humoral immune

response (IgG)

Detectable stages of

viremia, (now shown

to be sporadically)

Systemic infection

with no deleterious

effects SNV RNA detected

in urine and/or saliva

of a small proportion

of DM

SNV in deer mice

Study of SNV hampered by the lack

of a reliable infectious assay

Route of infection (?)

Aggression or Breeding

Environ. contaminant

Transmission dynamics remain poorly understood

Some evidence to suggest that:

Recently infected animals more likely to shed SNV than chronically

infected ones

Relatively few animals with detectable SNV RNA in excreta (few

infectious animals -> rare human cases)

Transmission among deer mice likely blood-borne

Still lack information on role of:

Distribution of SNV-infected deer mice at local spatial scale

Relationship between deer mouse abundance & probability of human

exposure (usually confounded by impact of human behaviour)

Disease prevention

Primarily through public education

Recognize rodents and/or evidence of rodent-infestation

Where possible, rodent-proof structures & reduce deer

mouse populations

Clean areas contaminated by rodent droppings using

appropriate PPE and disinfectants (avoid creating

aerosols in areas contaminated by mice)

Conclusions

• Contact with rodents can result in potential exposure to disease-causing agents in Canada

• Fortunately most rodent-associated pathogens are either rare or relatively focal in their distribution such that human disease is infrequent

• Simple preventative measures can be utilized to further reduce or minimize exposure to these rodent-borne pathogens

Questions?

Routes of exposure

Infected rodents excrete virus in urine, feces

or saliva and humans usually infected when

aerosolized virus is inhaled

Other routes of exposure theoretically

possible such as through bites but rarely

reported

Human to human transmission only reported

for Andes strains in South America