toxoplasma

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Toxoplasma gondii

Toxoplasma gondii

coccidian protozoan parasite

Zoonotic ,opportunistic pathogen infects animals, cattle, rodents,birds, pigs, sheep and humans.

Final host: (Felidae family,eg: cat)

Intermediate host: (mammals)

Risky group:
Pregnant women
meat handlers (food preparation)

Final host (Cats)

the only animal species to shed the infectious stage (Oocysts) in their feces.
Cats (domestic & wild) get it by eating rodents, raw meat, cockroaches, flies, or by contacting infected cats, infected cat feces, or contaminated soil.
Sexual cycle


Intermediate host: Humans (Mammals)
Asexual tissue cycle.
Motile, disease producing phase = tachyzoites.
Non-motile “slow” phase in tissue cyst = bradyzoites.

Morphology

Toxoplasma gondii exists in three morphological forms, all parasite stages are infectious.

Tachyzoites.

Bradizoites (tissue cysts).
Oocysts.

Tachyzoite

Intracellular 3x6µ, crescent shaped; one end is more pointed than the other, subterminal placed nucleus.
Asexual form. acute phase
Multiplies by endodyogeny: a process of division where 2 daughter zoites are formed within the parent parasite, which is destroyed when the young zoites are released.
attack every type of nucleated cells
enclosed in a parasite membrane to form a cyst measuring 10-100 µ in size.

Bradyzoites

slow-growing stage inside the tissue cysts.
mark the chronic phase of infection.
Intact tissue cysts probably do not cause any harm and can persist for the life of the host without causing a host inflammatory response.
Protective cyst wall is finally dissolved and bradyzoites infect tissue and transform into tachyzoites.


Oocysts in the feces of cat
10-13 µ in diameter
noninfectious before sporulation.
Unsporulated oocysts are subspherical to spherical.
Sporulated oocysts are subspherical to ellipsoidal.
Each oocyst has two ellipsoidal sporocysts.
Each Sporocyst contains four sporozoites .
Shedding occurs 3-5 days after ingestion of tissue cysts

Unsporulated

Sporulated

Life Cycle

Sources of infection
Contaminated water or food by oocysts.
Undercooked meat. Ingestion of tachyzoites and bradyzoites (cysts) in flesh of infected host.
Mother to fetus: when mother develops acute infection during pregnancy.
Organ transplant (rare).
Blood transfusion (rare).


A. Acquired toxoplasmosis
1. majority are asymptomatic
2. acute toxoplasmosis:
In immunocompetent adults: flu-like symptoms, sometimes associated with fever& lymphadenopathy.
In immunocompromised individuals: (AIDS, transplant and cancer patients) :parasitemia, involvement of brain, liver lung and other organs results in Retinitis ,Chorioretinits ,Pneumonias ,severe neurological disorders, and often death.
B. congenital toxoplasmosis.

choreoretinitis(post_natal toxoplasmosis): occurs later in life in individuals who acquired toxoplasmosis congenitally; focal lesion in retina presenting as decreased visual acuity.

Toxoplasmosis

Congenital Toxoplasmosis
Intracerebral calcification: toxoplasmic encephalitis
Chorioretinitis: Ocular toxoplasmosis
Hydrocephaly.
Congenital disease

Microcephaly .
Convulsions.
Mental retardation .
Cardiomegaly .

1-5/1000 pregnancies

5-10% result in miscarriage
8-10% result in serious brain and eye damage
10-13% of the babies will have visual handicaps.
Although 58-70% of infected women will give a normal birth
Both the probability and severity of the disease depend on when the infection takes place during pregnancy.
Early: low transmission, but severe disease
Late: high transmission, more benign symptoms.

Lab Diagnosis of Toxoplasmosis:

The demonstration of the Toxoplasma gondii organism in blood, CSF, or tissue (L.N, spleen &liver). the parasite appear Crescentric or fusiform in shape with nucleus which appear red while total parasite appear blue.
Serology:

Sabin’s Feldman dye test: is a sensitive and specific serologic test. It measures IgG antibody and is the standard reference test for toxoplasmosis. High titers suggest acute disease. It is based on principle that Antibodies to Toxoplasma will render the membrane of the laboratory cultured T.gondii impermeable to Alkaline methylene blue , so the organism are unstained in the presence of serum with antibodies (positive result); if there are no antibodies, trophozoites with intact membrane are stained and appear blue under microscope (negative result).
Indirect haemagglutination test (IHA)
Indirect fluorescent Ab test
ELISA
Latex agglutination test

Toxoplasmine skin test

Polymerase Chain Reaction(PCR) Molecular technique that can detect the parasite's DNA, it has successfully been used to diagnose congenital, ocular, and cerebral and disseminated.
Animal inoculation: inoculation of suspected infected tissues into experimental animals.
Culture: inoculation of suspected infected tissues into tissue culture.


Treatment
pyrimethamine with sulfadiazine for 1 month
Intravenous clindamycin used to treat encephalitis in AIDS patients
spiramycin has been used to treat toxoplasmosis in pregnancy
Treatment of Infected Newborns
Infected babies should be treated as soon as possible after birth with pyrimethamine and sulfadiazine which can help prevent or reduce the disabilities associated with toxoplasmosis.

Prevention and control

Avoid consumption of raw or undercooked meat( cook meat thoroughly(
Wash hands after handling raw meat , soil & Wear gloves when you garden or handle soil.
There are no vaccines currently available for T. gondii
Prevention of congenital transmission
Pregnant women should avoid contact with cats
early diagnosis of acute infection in mothers and administration of a prophylactic regimen of spiramycin.

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