Toxoplasmosis pathophysiology: Difference between revisions
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Members of the cat family (Felidae) are the only known definitive hosts for the sexual stages of ''T. gondii'' and thus are the main reservoirs of infection. Cats become infected with ''T. gondii'' by carnivorism . After tissue [[cyst]]s or [[oocyst]]s are ingested by the cat, viable organisms are released and invade [[epithelial cell]]s of the [[small intestine]] where they undergo an asexual followed by a sexual cycle and then form oocysts, which are excreted. The unsporulated oocyst takes 1 to 5 days after excretion to sporulate (become infective). Although cats shed oocysts for only 1 to 2 weeks, large numbers may be shed. Oocysts can survive in the environment for several months and are remarkably resistant to disinfectants, freezing, and drying, but are killed by heating to 70°C for 10 minutes.<ref>http://www.dpd.cdc.gov/dpdx/HTML/Toxoplasmosis.htmhttp://www.cdc.gov/ncidod/dpd/parasites/toxoplasmosis/factsht_toxoplasmosis.htm | Members of the cat family (Felidae) are the only known definitive hosts for the sexual stages of ''T. gondii'' and thus are the main reservoirs of infection. Cats become infected with ''T. gondii'' by carnivorism . After tissue [[cyst]]s or [[oocyst]]s are ingested by the cat, viable organisms are released and invade [[epithelial cell]]s of the [[small intestine]] where they undergo an asexual followed by a sexual cycle and then form oocysts, which are excreted. The unsporulated oocyst takes 1 to 5 days after excretion to sporulate (become infective). Although cats shed oocysts for only 1 to 2 weeks, large numbers may be shed. Oocysts can survive in the environment for several months and are remarkably resistant to disinfectants, freezing, and drying, but are killed by heating to 70°C for 10 minutes.<ref>http://www.dpd.cdc.gov/dpdx/HTML/Toxoplasmosis.htmhttp://www.cdc.gov/ncidod/dpd/parasites/toxoplasmosis/factsht_toxoplasmosis.htm | ||
</ref> | </ref> | ||
==== Transmission ==== | |||
[[Image:Toxoplasmosis LifeCycle.jpg|center|thumb|300px|Life cycle of ''Toxoplasma gondii'']] | |||
Transmission may occur through: | |||
* Ingestion of raw or partly cooked meat, especially pork, lamb, or venison containing Toxoplasma cysts. Infection prevalence in countries where undercooked meat is traditionally eaten, such as France, has been related to this transmission method. Oocysts may also be ingested during hand-to-mouth contact after handling undercooked meat, or from using knives, utensils, or cutting boards contaminated by raw meat.<ref name=CDC>{{cite web | |||
| url=http://www.dpd.cdc.gov/DPDx/HTML/Toxoplasmosis.htm | |||
| title=Toxoplasmosis | |||
| publisher=Centers of Disease Control and Prevention | |||
| date=2004-11-22 }}</ref> | |||
* Ingestion of contaminated cat faeces. This can occur through hand-to-mouth contact following gardening, cleaning a cat's litter box, contact with children's sandpits, or touching anything that has come into contact with cat faeces. | |||
* Drinking water contaminated with Toxoplasma. | |||
* Transplacental infection [[Uterus|in utero]]. | |||
* Receiving an infected [[organ transplant]] or [[blood transfusion]], although this is extremely rare.<ref name=CDC /> | |||
* Accidental inoculation of tachyzoites | |||
====[[Transplacental]] Transmission==== | |||
*infection in [[1st trimester]] - incidence of transplacental infection is low (15%) but disease in neonate is most severe. | |||
*Infection in [[3rd trimester]] - incidence of transplacental infection is high (65%) but infant is usually asymptomatic at birth. | |||
The cyst form of the parasite is extremely hardy, capable of surviving exposure to freezing down to −12 degrees Celsius, moderate temperatures and chemical disinfectants such as bleach, and can survive in the environment for over a year. It is, however, susceptible to high temperatures—above 66 degrees Celsius, and is thus killed by thorough cooking, and would be killed by 24 hours in a typical domestic freezer.<ref>[http://www.ncagr.com/vet/ToxoplasmosisTxt.htm]</ref> | |||
Cats excrete the [[pathogen]] in their faeces for a number of weeks after contracting the disease, generally by eating an infected rodent. Even then, cat faeces are not generally contagious for the first day or two after excretion, after which the cyst 'ripens' and becomes potentially pathogenic. Studies have shown that only about 2% of cats are shedding oocysts at any one time, and that oocyst shedding does not recur even after repeated exposure to the parasite. Although the pathogen has been detected on the fur of cats, it has not been found in an infectious form, and direct infection from handling cats is generally believed to be very rare. | |||
==References== | ==References== | ||
Revision as of 18:44, 12 December 2012
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]
Pathophysiology
Toxoplasma gondii is a protozoan parasite that infects most species of warm blooded animals, including humans, causing the disease toxoplasmosis.
Members of the cat family (Felidae) are the only known definitive hosts for the sexual stages of T. gondii and thus are the main reservoirs of infection. Cats become infected with T. gondii by carnivorism . After tissue cysts or oocysts are ingested by the cat, viable organisms are released and invade epithelial cells of the small intestine where they undergo an asexual followed by a sexual cycle and then form oocysts, which are excreted. The unsporulated oocyst takes 1 to 5 days after excretion to sporulate (become infective). Although cats shed oocysts for only 1 to 2 weeks, large numbers may be shed. Oocysts can survive in the environment for several months and are remarkably resistant to disinfectants, freezing, and drying, but are killed by heating to 70°C for 10 minutes.[1]
Transmission
Transmission may occur through:
- Ingestion of raw or partly cooked meat, especially pork, lamb, or venison containing Toxoplasma cysts. Infection prevalence in countries where undercooked meat is traditionally eaten, such as France, has been related to this transmission method. Oocysts may also be ingested during hand-to-mouth contact after handling undercooked meat, or from using knives, utensils, or cutting boards contaminated by raw meat.[2]
- Ingestion of contaminated cat faeces. This can occur through hand-to-mouth contact following gardening, cleaning a cat's litter box, contact with children's sandpits, or touching anything that has come into contact with cat faeces.
- Drinking water contaminated with Toxoplasma.
- Transplacental infection in utero.
- Receiving an infected organ transplant or blood transfusion, although this is extremely rare.[2]
- Accidental inoculation of tachyzoites
Transplacental Transmission
- infection in 1st trimester - incidence of transplacental infection is low (15%) but disease in neonate is most severe.
- Infection in 3rd trimester - incidence of transplacental infection is high (65%) but infant is usually asymptomatic at birth.
The cyst form of the parasite is extremely hardy, capable of surviving exposure to freezing down to −12 degrees Celsius, moderate temperatures and chemical disinfectants such as bleach, and can survive in the environment for over a year. It is, however, susceptible to high temperatures—above 66 degrees Celsius, and is thus killed by thorough cooking, and would be killed by 24 hours in a typical domestic freezer.[3]
Cats excrete the pathogen in their faeces for a number of weeks after contracting the disease, generally by eating an infected rodent. Even then, cat faeces are not generally contagious for the first day or two after excretion, after which the cyst 'ripens' and becomes potentially pathogenic. Studies have shown that only about 2% of cats are shedding oocysts at any one time, and that oocyst shedding does not recur even after repeated exposure to the parasite. Although the pathogen has been detected on the fur of cats, it has not been found in an infectious form, and direct infection from handling cats is generally believed to be very rare.
References
- ↑ http://www.dpd.cdc.gov/dpdx/HTML/Toxoplasmosis.htmhttp://www.cdc.gov/ncidod/dpd/parasites/toxoplasmosis/factsht_toxoplasmosis.htm
- ↑ 2.0 2.1 "Toxoplasmosis". Centers of Disease Control and Prevention. 2004-11-22.
- ↑ [1]