coccidians

Parasitology (dra Madrid)

Coccidians

20 February 08 November 07

Coccidians

Coccidian Parasites

▪ Members of the class Sporozores (Phylum Apicomplexa)

▪ Obligate intracellular protozoans

▪ Gliding motility

▪ Reproductiono Sexual phase: sporogony, gametogonyo Asexual phase: schizogony, merogony

(trophozoites, schizonts, merozoites)

▪ Species included:o Isosporao Sarcocystiso Cryptosporidiumo Cyclosporao Toxoplasmao Pneumocystis

Isospora belli

▪ Coccidian parasite

▪ Infects epitheial cells of the small intestine

▪ Infections usually in immunocompromised patients

▪ Geographic distributiono Worldwide, in tropical and subtropical areaso High prevalence: Haiti and other tropical areas

with poor sanitary conditions

▪ Transmission: food and water

▪ Dse common in children and male homosexuals especially those with AIDS

▪ Definitive hosts: human and animals

Pathogenesis

▪ Parasites develop and multiply in the epithelial cells of the small intestine

▪ Trophozoites develop into schizonts(contain merozoites); rupture of schizonts release the merozoites invade new epithelial cells, and continue the cycle of asexual multiplication

▪ After 1 week sexual stage begins: devt of male and female gametocytes fertilization devt of oocysts excreted in the stool

▪ Immature oocyst contains usually 1 sporoblast further maturation sporolast divides in 2 (oocyst now contains 2 sporoblasts); sporoblasts secrete a cyst wall and becomes sporocysts sporocysts divide 2x to produce 4 sporozoites each

▪ Infection occurs by ingestion of sporocyst-containing oocysts; sporocysts excyst in small intestine, release their sporozoites invade epithelial cells and initiate schozogony

Isospora belli (Life cycle)

▪ At time of excretion, immature oocyst contains usually 1 sporoblast

▪ Sporoblast divides into two, secrete a cyst wall sporocysts

▪ Sporocyst divide to produce sporozoites

▪ Infection occurs in ingestion of sporocyst containing oocyst(oocyst containing 2 sporocyst with each containing 4 sporozoites)

▪ Sporocyst excyst in small intestinerelease sporozoitesenter epithelial cells of distal duodenum and proximal ileum

o Invade new epithelial, continue asexual multiplication

▪ Trophozoites develop into schizonts which contain multiple merozoites

o Rupture of schizonts release of merozoites invade new epithelial cells and continue of asexual multiplication

▪ After 1 wk, sexual stage begins – male and female gametocytes

o Microgametocytes fertilize macrogametocytes

▪ Fertilization product: oocyst excreted in stoolo Oocyst mature in 48 hrs oocyst initially has

1 sporoblast divides into 2 sporoblast develop into sporocysts (2)

o 4 long and slender sporozoites develop within each sporocyst

▪ Oocyst of isospora contains 2 sporocysts, each with 4 sporozoites

Isospora belli: Clinical Manifestations

▪ Infections often asymptomatic even with excretion of oocysts

▪ Symptomatic infections:o Diarrhea: intermittent for monthso Fever, malaise, anorexia, abdominal pain,

flatulenceo Malabsorption along with weight loss and

rarely deatho In immunocompromised hosts, severe diarrheao Eosinophilia

▪ Intestinal biopsies show:o Mucosal lesions of shortened villio Hypertrophied cryptso Infiltration of lamina propria with pmn

leucocytes especially eosinophils

▪ Dissemination to other organs: seen in AIDS patients

▪ Prognosis is good but infection may last for months

Isospora belli: diagnosis

▪ Detection of oocysts in feces

▪ Oocysts in stools: ellipsoidal shape

YNA, joy, cams, shar – 2B1 1 of 7

Parasitology – Coccidians by Dra Madrid of 7

Isospora belli: treatment

▪ Asymptomatic infections: bed rest and a bland diet

▪ Trimethoprim-sulfamethoxazole: drug of choice

Sarcocystis

▪ Worldwide: infects humans and animals

▪ Disease: sarcosporidiosis and sarcocystosis

▪ Complex life cycle – involves intermediate hosts

▪ Definitive hosts: man and carnivores (dog)

▪ Human definitive hosts for 2 species:o Sarcocystis hominiso Sarcocystis suihominis

▪ Humans can also act as intermediate hosts

▪ Take several forms

▪ Simplest is called the zoiteo Banana shaped cell with a pointed end

equipped for entering host cells

▪ Sporocysts are composed of 4 zoiteso Oval; can survive on ground and infect

intermediate hosts

▪ Sporozoites are formed from sporocysts

▪ Sarcocysts are formed from sporozoiteso Composed of large numbers of zoites

surrounded by a cyst wallo Those that can be seen by the naked eye are

called macrocysto Microcysts are sarcocysts that remain about

the same width as the muscle fiber and can be seen only under the microscope

Sarcocystis (Life cycle)

Definitive hosts are infected when they eat undercooked meat w/c contains sarcocyst sarcocyst wall digested release of zoites enter intestinal cells and change into male and female forms fertilization sporocysts passed out in the feces of the host (definitive host)

Sporocysts ingested by intermediate hosts sporozoites (w/c are formed from sporocysts) penetrate intestinal epithelial tissues hematogenous spreadbrain, muscles and other tissues

** sporozoites enter muscle cells, and encyst and develop into sarcocysts

** in other tissues, sporozoites become schizonts and then encyst

Sarcocystis (Clinical Manifestations)

▪ In humans,o Gastroenteritis, myalgia, weakness, mild

increase of creatine kinase

▪ In the intermediate hosts, the brain, muscle, and kidney tissues can be damaged

o Loss of appetite, fever, weight loss, and anemia;

o Gait abnormalities, weakening of limbs, muscle wasting, and head tilt

o Infected animals have been observed to move in circles

▪ Accidental ingestion of sporocysts results in direct infection of humans without the intermediate host

o Occurs rarely and is called human intramuscular sarcocystis

Sarcocystis (diagnosis)

▪ In the definitive host, demonstration of sporocysts in the fecal material using flotation method

▪ In the intermediate host, detection of schizonts in the skeletal muscle or in brain tissue during autopsy

▪ Detection of antibodies in serum or CSF using Western blot, IFA and ELISA

Sarcocystis (treatment and prognosis)

▪ No effective treatment known

▪ Corticosteroid – to decrease muscular inflammation

▪ Trimethoprim-sulfamethoxazole – effective in treating intestinal infections

▪ In most animal infections due to this parasite do not cause serious pathologic changes

Sarcocystis (Epidemiology)

▪ Worldwide geographic distribution

▪ Few human cases, most from SE Asia

▪ Prevalence may be high due to numerous asymptomatic infections

▪ Other animals w/c may be infected: cattle, horses, dogs, cats, rabbits, mice, and chicken

▪ Infections in avian species have no known human threat

▪ Sporocysts remain infective for many months in water at 4-10C; infectivity prolonged during the cooler months of the year

▪ Infected carcasses left unburied on farmland can remain infective for cats and dogs for weeks on cool weather

▪ Freezing does not prevent spread

▪ Macrocysts from sheep have to be heated for 20 mins to kill them

Sarcocystis (prevention and control)

▪ No known control methods


▪ Uncooked dead animal should not be fed to other animals

▪ Good sanitation and hygiene

Cryptosporiosis

Cryptosporidium

▪ Causal agent:o Many species exist that infect humans and a

wide range of animalso Although Cryptosporidium parvum and

Cryptosporidium hominis (formerly known as C. parvum anthroponotic genotype or genotype 1) are the most prevalent species causing disease in humans, infections by C. felis, C. meleagridis, C. canis, and C. muris have also been reported

▪ C. parvum – now considered a parasite of bovines w/c can infect humans

▪ C. hominis – infect only humans

▪ Prevalence in the Philippines has been reported to be low at 2.6%

▪ Coocidian protozoan

▪ 1907 – discovery of the organism

▪ 1976 – first case of human cryptosporidiosis

▪ Infect several different hosts, can survive most environments for long periods of time (“hard cysts”); inhabits all climates and locales

▪ Taxonomically classified as Sporozoa – oocyst releases 4 sporozoites

▪ Monoxenous life cycle – completes entire cycle w/in a single host

▪ Sexual and asexual cycles

▪ Six distinct developmental stages

Cyptosporidium (Life cycle)

▪ 6 distinct developmental stages:o Excystation of the orally ingested oocyst in the

small bowel with the release of 4 sporozoiteso Invasion of intestinal epithelial cells; initiation

of asexual intracellular multiplication stageo Differentiation of the microgametes (males)

and macrogametes (females)o Fertilization initiating sexual replicationo Development of oocystso Formation of new, infectious sporozoite w/in

the oocyst, excreted in the stool

▪ Sporulated oocysts, containing 4 sporozoites, are excreted thru feces (and possibly respiratory secretions)

▪ Following ingestion, excystation occurs sporozoites are released and parasitize epithelial cells of GIT (or other tissues) undergo asexual (schizogony or merogony) and then sexual multiplication (gametogony)

▪ Fertilization of macrogamonts (female) by microgametes (male) oocysts develop sporulate in host, and excreted

o Because oocysts sporulate inside host, autoinfection can occur

▪ Oocysts are infective upon excretion, thus permitting direct and immediate fecal-oral transmission

Cryptosporidiosis (Clinical Manifestations)

Immunocompetent:

▪ Acute self-limiting diarrheal illness

▪ 1-2 week duration

▪ Frequent, watery diarrhea

▪ N/V, abdominal cramps, low grade fever

Immunocompromised

▪ Debilitating, cholera-like diarrhea (upto 20L/day)

▪ Severe abdominal cramps

▪ Malaise

▪ Low grade fever

▪ Weight loss

▪ Anorexia

**Pa-add ng Cryptosporidosis epidemiology at yung persons likely to be infected

Cryptosporidium: Transmission

▪ Ingestion of fecally contaminated food and watero Drinking water taken from surface water

sources such as lakes and river; swimming pools and water park wave pools, untreated water

o Cyst is resistant to various drinking water filtration treatments such as chlorination

o Food can get contaminated; oocyst do not survive cooking but can occur in foods not heated or in foods not cooked after handling

▪ Animal to person transmissiono From household pets is rareo Definite correlation between calves shed

oocysts and pathogen present in 90% of all dairy farms

▪ Person to persono Occurs at a high frequency in day-care centers;

clustered populationo Nosocomial settings

Cryptosporidium: Pathogenesis

▪ Upon excystation, sporozoites releasedo Adhere to the surface of the intestinal mucosao Sporozoite-specific lectin adherence factor:

agent of attachment to the intestinal surfaceo Release of cytokines by mucosal cells

activate phagocytes to release soluble


factors that increase intestinal secretion of water and chloride; inhibit absorption

▪ Epithelial cells damaged via:o Direct result of parasite invasiono Damage through T cell-mediated inflammation,

producing villus atrophy and crypt hyperplasia

Cryptosporidium: diagnosis

▪ Staining methods eg. Modified acid-fast stain to detect oocysts in stool specimen

▪ PCR

Cryptosporidium: treatment

▪ No safe and effective therapy

▪ Immunocompetent individuals – supportive care

▪ Pharmacologic therapies:o Immunocompromised patients, spiramycin and

dicalzuril sodium have produced partial responses

o Paromomycin, a promising drug…decreases severity of infection and improve intestinal function

▪ Immunologic therapieso Feeding of bovine colostral immunoglobulin

ameliorate symptoms; release of intestinal IgA w/c clears infection

Cryptosporidium: prevention

▪ Practice good hygieneo Wash hands thoroughlyo Protect others: don’t go swimming if have

diarrhea

▪ Avoid possibly contaminated watero Do not swallow recreational watero Do not drink untreated water (shallow wells,

lakes, rivers, ponds and streams)o Do not use untreated ice or drinking water

during travel to areas with unsafe water supply

▪ Avoid possibly contaminated foodso Wash and/or peel raw vegetables and fruits

with clean watero Avoid uncooked foods during travel to

countries with minimal water treatment and sanitation systems

Cyclospora cayetanensis

▪ Originally called a cyanobacterium-like body (CLB)

▪ Life cycle presumed to be similar to other intestinal coocidia

Cyclospora: parasite bology

▪ The oocysto Formed after asexual and sexual cycleso Passed in feces

o Are unsporulated when passed (after 5 or more days, 2 sporocysts develop, each containing 2 sporozoites w/in oocyst)

▪ Mature oocysto Sporulatedo Contains 2 sporozoiteso Considered infective stageo When ingested, sporozoites are released

enter intestinal cells undergo schizogony and gametogony

** pa insert ng picture n life cycle, first slide sa page 10 ng trans ng 2B

Cyclospora: Clinical Manifestations

** hindi ulit mabasa…ito yung secnd slide sa page 10

Cyclospora: diagnosis

▪ Direct microscopic examination of fecal specimens using concentration techniques and acid-fast staining (Kinyoun’ stain)

▪ Fluorescent microscopyo Appear blue or green circles

Cyclospora: treatment

▪ Self-limiting disease

▪ Treatment not necessary if symptoms are mild

▪ The only effective drug is cotrimoxazole

▪ No alternative drug if not tolerated

▪ Oocyst disappear from the stools a few days after treatment

Cyclospora: epidemiology

▪ Epidemics reported: Haiti, Peru and Nepal

▪ Raspberries from Guatemala were incriminated in infections in the US

▪ Leafy vegetables were found to contain oocysts Peru and Nepal

▪ Lettuce and basil pesto-salad incriminated in other cases in the US

▪ Contaminated water: main source of infection

▪ No animal reservoirs found; cyclosporidiosis is considered a human disease

Cyclospora: prevention and control

▪ Follow good sanitary practices

▪ In most endemic areas: boiling water seems to be the best method since chlorination is not effective

▪ Wash fruits and vegetables with clean water


Pneumocystis carinii

▪ Causal agento P carinii is now considered a fungus based on

nucleic acid and biochemical analysiso However, it has morphologic and biologic

characteristics that, while incompletely understood, place it close to the protozoa

▪ Diffuse type of pneumonia in immunocompromised hosts

▪ New name: Pneumocystis jiroveci

▪ Exist in ______________________________ (hindi mabasa: 4th

slide, page 11)

▪ Painsert na rin ng slide 5 (picture naman to) at slide 6 sa page 11

P carinii: structure

▪ Cyst: thick walled; spherical to ovoid; o 4-6 um in diameter; contains up to 8

pleomorphic sporozoites

▪ Sprozoites: intracystic structure

▪ Trophozoite: thin walled extracystic cell; represents excysted sporozoite

▪ Organism does not enter the host cell but attaches to its surface during replicative cycle; no evidence of toxin production

P carinii: clinical features

▪ Dyspnea

▪ Nonproductive cough

▪ Fever

▪ Diffuse infiltrates on CXR

▪ Extrapulmonary lesions (< 3%): o LN, spleen liver, and bone marrow

▪ Illness may last from 4-6 weeks

▪ Pneumocystis pneumonia (PCP) occurs in immunosuppressed individuals and in premature malnourished infants

P carinii: Pathogenesis

▪ Portal of entry, not established

▪ Likely mode of transmission: inhalation

▪ In most individuals, dormant and dispersed in the lung eith no apparent host response

P carinii: diagnosis

▪ Id of organism in pulmonary tissue or lower airway fluids through lung biopsy, inducement of sputum, bronchoalveolar lavage, needle aspiration of lung

P carinii: treatment

▪ Trimethoprim-sulfamethoxazole: DOC

▪ Alternative drugs: o Pentamidineo Atovaquoneo Primaquine + clindamycino Trimthoprim + dapsone

Toxoplasmosis

Toxoplasma gondii

▪ Worldwide distribution

▪ Infects humans and many species of animals

▪ Definitive host: cato Complete cycle occurs in this hosto Cats get infected by ingestion of infective

oocyst from soil or tissue of infected animals (mice)

o In cat intestines, undergoes schizogony, gametogony and sporogony

T gondii (parasite biology)

▪ In the cato In intestinal epithelium of the cat, merozoites

multiply (schizogony), followed by differentiation into microgametocytes and macrogametocytes (gametogony)

o Fertilization of the macrogamete gives rise to an oocyst

o Oocyst passed out with cat feces in unsporulated stage

▪ Complete sporulation: 3-4 dayso In mature oocyst: 2 sporocysts, each with

sporozoites are formed

▪ Can be ingested with contaminated food or water by another host

o In humans or other hosts:

▪ Mature oocyst excysts (inside intestine of new host) release 4 sporozoites penetrate lamina propria

▪ Parasites enter lymphatics different organs, tissues and body fluids

o Following entry of sporozoite into a new cell, t transforms into a tachyzoite

▪ Tachyzoites: formed during initial and acute phase of infection

Fast multiplying tachyzoites give rise to slow multiplying bradyzoites that form cysts

o Only these 2 stages are present in humans and other animal intermediate hosts

o Asexual multiplication is by a variation of binary fission called endodyogeny

▪ Formation of plasma membrane by the 2 new daughter parasites even before the division of the nucleus

o Cells in w/c endodyogeny occur eventually burst releasing trophozoites w/c invade other cells


o Pa-add ng toxoplasma life cycle (1st 2 slides sa page 14)

T gondii: intermediate hosts

▪ Man, rodents, farm animals

T gondii: parasite biology

▪ Infective stages:o Oocysto Tachyzoiteso Bradyzoite

▪ The oocysto Ovoidal, thin walledo Mature cyst in intestine of the new host

excystsrelease 4 sporozoites, penetrates intestinal mucosa; can also gain entry to the lymphatics and spread to other organs

▪ The Tachyzoiteo The transformed stage when sporozoite enters

a new cello Found during initial and acute stage of

infection Rapidly multiplying Present in humans and other animal

intermediate hosts Can be transmitted to other humans

by blood transfusion, transplacental and organ transplantation

▪ The bradyzoiteo Formed after tachyzoiteo Encysted formo Found during chronic latent (asymptomatic)

infectionso Persists for years in human tissue (brain,

retina, muscles, etc)o Can also be found in other animal intermediate

hostso Can be transmitted by organ transplantation

and eating meat of infected animals

T gondii: Multiplication

▪ Sexual phase – occurs in cat

▪ Asexual replicationo Occurs in both definitive and intermediate

hostso Endodyogeny – variation of binary fission

Formation of the plasma membrane by the 2 new daughter parasites before nuclear division

Cells burst trophozoites

T gondii: parasite forms

▪ The trophozoiteo 4-8 um in length; 2-3 um in widtho Crescent-shapedo Pointed anterior end; rounded posterior end

o Rhoptries and micronemes found on the anterior end; for cell penetration

o Nucleus: spherical on the posterior end

▪ The pseudocysto Usually contains proliferating tachyzoiteso Can be taken in tissue sections of patients with

acute infectionso Does not have a well-defined wall

▪ The cysto Usually contain bradyzoiteso Seen during chronic infectionso Well-formed wallo Can be found in muscles and CNS

T gondii: clinical manifestations

▪ Asymptomatic – majority of cases

▪ Acute toxoplasmosis – fever, lymphadenopathy (infectious mononucleosis-like picture)

▪ Reactivation toxoplasmosis – in immunocompromised patients (AIDS, cancer, drug immunosuppression, organ transplant recipients); presents with specific organ involvement

o Encephalitis: most common manifestationo Myocarditis, focal pneumonia

▪ Choreoretinitiso Occurs later in life in those who acquired

toxoplasma congenitallyo Retinal focal lesions: dec visual acuity, dec

vision, retinal lesions on retinoscopy

▪ Congential toxoplasmosiso Mother to fetuso Increased transmission rate in third trimester

but increased severity of fetal disease in the 1st

trimestero Presents as hydrocephalyo Hepatomegaly, cerebral calcifications, mental

retardationo Stillbirth and abortion may result when

mothers acquire infection during the 1st trimester of pregnancy

T gondii: diagnosis

▪ Observation of parasites in patient specimens s.c. bronchoalveolar lavage for immunocompromised or lymph node biopsy

▪ Isolation of parasites from blood or other body fluids, by intraperitoneal inoculate into mice or tissue culture

▪ Detection of parasite gamete material by PCR, esp in detecting congenital infection

▪ Serologic test – routine method of diagnosis; detect presence of antibodies against T gondii

o Sabin-Feldman methylene blue dye testo IgM indirect fluorescent antibody techniqueo IgM enzyme immunoassay

T gondii: treatment

▪ Regimen: pyrimethamine+sulfadiazine x 1month


▪ Other drugs: clindamycin, azithromycin, clarithromycin, dapsone, and atovaquone

▪ Corticosteroids – prevent hypersensitivity reactions

▪ Trimethoprim-sulfamethoxazole – prophylaxis for immunocomromised

T gondii: Epidemiology

▪ Endemic worldwide both in humans and animals

▪ Dse usually not manifested except in immunodeficiency or immunosuppression

▪ Infection more common in warm climates and at lower altitudes than in cold climates and mountainous regions

▪ Only 2% of human population is seropositive for T gondii

T gondii: prevention and control

▪ Food should be protected from being contaminated with cat feces

▪ Cook eggs and meat well

▪ Avoid unpasteurized milk.

END OF TRANS

coccidians

Documents