Classification
1. Toxoplasma gondii is placed in the phylum Apicomplexa
2. Invasive stages have typical apical complex
3. Part of life cycle in cats and other felids is similar to Eimeria and Isosopora
4. Toxon = arc; Plastos = form. One stage in the life cycle is arc- shaped.
5. The species name is derived from the host in which the parasites was first described: Ctenodactylus gundi = small African rodent.
Geographagic Distribution: worldwide
Epidemiology and Hosts
· 1. 500 million people worldwide have antibody to T. gondii
· 2. Prevalenc is the same in men and women
· 3. Prevalence of T. gondii in other animals.
o a. Sheep -20%
o b. Cattle - 25%
o c. Pigs - 30%
o d. Dogs - 30%
o e. Cats - 45%
o f. Birds - 12%
o g. Toxoplasma gondii infects many species of warm-blooded vertebrates (euryxenous)
· 4. Modes of transmission:
o a. Feline feces containing infective oocyst
o b. Eating raw of undercooked meat
o c. Congenital and acquired toxoplasmosis
Toxoplasma is transmitted to cats that ingest either sporulated oocysts or tissues infected with tachyzoites, but the most common source of infection is ingestion of tissues containing cysts. On ingestion of cysts, bracyzoites released in the gastrointestinal tract initiate an enteroepithelial cycle of asexual and sexual multiplication, followed by oocyst development and shedding of unsporulated oocysts with feces. An extraintestinal cycle, like that seen in nonfelids, also occurs in cats
Life cycle
The coccidium Toxoplasma gondii infects all warm-blooded animals, including humans. Felids (both domestic and wild) are the only definitive hosts; felids and nonfelids are intermediate hosts. Toxoplasma can betransmitted to intermediate hosts via oocysts in feline feces, via cysts in host tissues (meat), and via techyzoites transplacentally. Unsporulated oocysts in feline feces sporulate outside the body and become infectious. On ingestion, sporozoites excyst and multiply in the intestine and associated lymph nodes as tachyzoites. Tachyzoites multiply by endodyogeny (see Figure 2.30) for numerous generations, spreading through tissues and circulation, and then encyst. Cysts persist most frequently in the brain, liver, muscles, and retina. They are usually spherical or elongate, thin-walled structures containing a few to several hundred slender PAS-positive bradyzoites or slowly multiplying zoites. Cysts ingested by a nonfeline host release bradyzoites, which become tachyzoitesm, and the cycle is repeated. Infection by either oocysts or cysts during pregnancy can result in transplacental infection of the fetus with tachyzoites.
Pathology
Trachyzoite multiplication results in focal necrosis, the most characteristic lesion of toxoplasmosis. Inflammation usually follows necrosis. Pneumonitis is the predominant lesion in fatal toxoplasmosis in cats and dogs; placental necrosis with white flecks or multiple white, chalky, necrotic nodules and associated abortion predominate in sheep and goats. Histologcially, this necrosis is confined to the cotyledons where individual and small group of tachyzoites are often difficult to recognize among degenerating host cells. Encephalomyelitis is the predominant lesion in sheep.
Diagnosis
Diagnosis of Toxoplasma is performed at postmortem by identification of organisms in infected tissue. Diagnosis in live animals is aided by serologic tests and by bioassay or xenodiagnosis in mice.
Prevention and Control
The following preventative measures apply to all persons, but because toxoplasmosis is most severe in the perintatal period, they should be emphasized for pregnant women and for young children.
· 1. Avoid contamination with oocysts from cat feces by:
o a. Feeding cats dry, canned or thorougly cooked food
o b. Preventing cats from hunting birds and rodents
o c. Emptying litter boxes daily, before oocysts sporulate
o d. Wearing gloves or thoroughly washing hands after working in the garden or with soil, and before eating or touching the face
o e. Covering children’s sandboxes when not in use
o f. Preventing aerosols in the laboratory during centrifugation of potentially infected biological samples
o g. Boiling drinking water from streams, ponds, or lakes frequented by cats
· 2. Avoid ingestion of tissue cysts by cooking meat to over 660 C and washing hands after handling raw meat.
The following preventative measures apply to farms and other animal-rearing facilities. Avoid contamination of feed or water with oocysts in cat feces by:
· 1. Using rodenticides and traps to prevent cats from hunting rodents
· 2. covering, closing or locking feed-storage facilities to prevent cats from entering and defecating
· 3. Promptly removing cat feces from building stalls or cages; and flushing, burning, or burying them to destroy oocysts
· 4. Providing adequate dry, canned, or thoroughly cooked food and separate water to prevent cats from sharing facilities used by other animals.
1. Toxoplasma gondii is placed in the phylum Apicomplexa
2. Invasive stages have typical apical complex
3. Part of life cycle in cats and other felids is similar to Eimeria and Isosopora
4. Toxon = arc; Plastos = form. One stage in the life cycle is arc- shaped.
5. The species name is derived from the host in which the parasites was first described: Ctenodactylus gundi = small African rodent.
Geographagic Distribution: worldwide
Epidemiology and Hosts
· 1. 500 million people worldwide have antibody to T. gondii
· 2. Prevalenc is the same in men and women
· 3. Prevalence of T. gondii in other animals.
o a. Sheep -20%
o b. Cattle - 25%
o c. Pigs - 30%
o d. Dogs - 30%
o e. Cats - 45%
o f. Birds - 12%
o g. Toxoplasma gondii infects many species of warm-blooded vertebrates (euryxenous)
· 4. Modes of transmission:
o a. Feline feces containing infective oocyst
o b. Eating raw of undercooked meat
o c. Congenital and acquired toxoplasmosis
Toxoplasma is transmitted to cats that ingest either sporulated oocysts or tissues infected with tachyzoites, but the most common source of infection is ingestion of tissues containing cysts. On ingestion of cysts, bracyzoites released in the gastrointestinal tract initiate an enteroepithelial cycle of asexual and sexual multiplication, followed by oocyst development and shedding of unsporulated oocysts with feces. An extraintestinal cycle, like that seen in nonfelids, also occurs in cats
Life cycle
The coccidium Toxoplasma gondii infects all warm-blooded animals, including humans. Felids (both domestic and wild) are the only definitive hosts; felids and nonfelids are intermediate hosts. Toxoplasma can betransmitted to intermediate hosts via oocysts in feline feces, via cysts in host tissues (meat), and via techyzoites transplacentally. Unsporulated oocysts in feline feces sporulate outside the body and become infectious. On ingestion, sporozoites excyst and multiply in the intestine and associated lymph nodes as tachyzoites. Tachyzoites multiply by endodyogeny (see Figure 2.30) for numerous generations, spreading through tissues and circulation, and then encyst. Cysts persist most frequently in the brain, liver, muscles, and retina. They are usually spherical or elongate, thin-walled structures containing a few to several hundred slender PAS-positive bradyzoites or slowly multiplying zoites. Cysts ingested by a nonfeline host release bradyzoites, which become tachyzoitesm, and the cycle is repeated. Infection by either oocysts or cysts during pregnancy can result in transplacental infection of the fetus with tachyzoites.
Pathology
Trachyzoite multiplication results in focal necrosis, the most characteristic lesion of toxoplasmosis. Inflammation usually follows necrosis. Pneumonitis is the predominant lesion in fatal toxoplasmosis in cats and dogs; placental necrosis with white flecks or multiple white, chalky, necrotic nodules and associated abortion predominate in sheep and goats. Histologcially, this necrosis is confined to the cotyledons where individual and small group of tachyzoites are often difficult to recognize among degenerating host cells. Encephalomyelitis is the predominant lesion in sheep.
Diagnosis
Diagnosis of Toxoplasma is performed at postmortem by identification of organisms in infected tissue. Diagnosis in live animals is aided by serologic tests and by bioassay or xenodiagnosis in mice.
Prevention and Control
The following preventative measures apply to all persons, but because toxoplasmosis is most severe in the perintatal period, they should be emphasized for pregnant women and for young children.
· 1. Avoid contamination with oocysts from cat feces by:
o a. Feeding cats dry, canned or thorougly cooked food
o b. Preventing cats from hunting birds and rodents
o c. Emptying litter boxes daily, before oocysts sporulate
o d. Wearing gloves or thoroughly washing hands after working in the garden or with soil, and before eating or touching the face
o e. Covering children’s sandboxes when not in use
o f. Preventing aerosols in the laboratory during centrifugation of potentially infected biological samples
o g. Boiling drinking water from streams, ponds, or lakes frequented by cats
· 2. Avoid ingestion of tissue cysts by cooking meat to over 660 C and washing hands after handling raw meat.
The following preventative measures apply to farms and other animal-rearing facilities. Avoid contamination of feed or water with oocysts in cat feces by:
· 1. Using rodenticides and traps to prevent cats from hunting rodents
· 2. covering, closing or locking feed-storage facilities to prevent cats from entering and defecating
· 3. Promptly removing cat feces from building stalls or cages; and flushing, burning, or burying them to destroy oocysts
· 4. Providing adequate dry, canned, or thoroughly cooked food and separate water to prevent cats from sharing facilities used by other animals.
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