Toxoplasmosis pathophysiology
|
Toxoplasmosis Microchapters |
|
Diagnosis |
|---|
|
Treatment |
|
Case Studies |
|
Toxoplasmosis pathophysiology On the Web |
|
American Roentgen Ray Society Images of Toxoplasmosis pathophysiology |
|
Risk calculators and risk factors for Toxoplasmosis pathophysiology |
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.
Associated Conditions
The parasite itself can cause various effects on the host body, some of which are not fully understood.
Reproductive changes
- A recent study [4] has indicated Toxoplasmosis correlates strongly with an increase in boy births in humans.
- According to the researchers, depending on the antibody concentration, the probability of the birth of a boy can increase up to a value of 0.72 ... which means that for every 260 boys born, 100 girls are born.
- The study also notes a mean rate of 0.60 to 0.65 (as opposed to the normal 0.51) for Toxoplasma positive mothers.
Behavioral changes
- It has been found that the parasite has the ability to change the behavior of its host[5]
- The mechanism for this change is not completely understood, but there is evidence that toxoplasmosis infection raises dopamine levels.
- The behaviors observed, if caused by the parasite, are likely due to infection and low-grade encephalitis, which is marked by the presence of cysts in the brain, which may produce or induce production of a neurotransmitter, possibly dopamine,therefore acting similarly to dopamine reuptake inhibitor type antidepressants and stimulants.[6]
- Studies have found that toxoplasmosis is associated with an increased car accident rate, roughly doubling or tripling the chance of an accident relative to uninfected people.[8][9]
- This may be due to the slowed reaction times that are associated with infection.[9] "If our data are true then about a million people a year die just because they are infected with toxoplasma," the researcher Jaroslav Flegr told The Guardian.[10]
- The data shows that the risk decreases with time after infection, but is not due to age.[8][11]
- However there is also evidence of a delayed effect which increases reaction times.[12]
- Other studies suggest that the parasite may influence personality. There are claims of toxoplasma causing antisocial attitudes in men and promiscuity.[13]
- Even signs of higher intelligence in women, and greater susceptibility to schizophrenia and manic depression in all infected persons.[14][13][15]
IQ
- The study suggests that male carriers have lower IQs, a tendency to achieve a lower level of education and have shorter attention spans, a greater likelihood of breaking rules and taking risks, and are more independent, anti-social, suspicious, jealous and morose.
- It also suggests that these men are deemed less attractive to women.
- Women carriers are suggested to be more outgoing, friendly, more promiscuous, and are considered more attractive to men compared with non-infected controls.
Schizophrenia
- The possibility that toxoplasmosis is one cause of schizophrenia has been studied by scientists since at least 1953.[16]
- These studies had attracted little attention from U.S. researchers until they were publicized through the work of prominent psychiatrist and advocate E. Fuller Torrey.
- In 2003, Torrey published a review of this literature, reporting that almost all the studies had found that schizophrenics have elevated rates of toxoplasma infection.[16]
- A 2006 paper has even suggested that prevalence of toxoplasmosis has large-scale effects on national culture.[17]
- These types of studies are suggestive but cannot confirm a causal relationship (because of the possibility, for example, that schizophrenia increases the likelihood of toxoplasma infection rather than the other way around).[16]
- Acute Toxoplasma infection sometimes leads to psychotic symptoms not unlike schizophrenia.
- Some anti-psychotic medications that are used to treat schizophrenia, such as Haloperidol, also stop the growth of Toxoplasma in cell cultures.
- Several studies have found significantly higher levels of Toxoplasma antibodies in schizophrenia patients compared to the general population.[18]
- Toxoplasma infection causes damage to astrocytes in the brain, and such damage is also seen in schizophrenia.
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]
- ↑ Jaroslav Flegr. Women infected with parasite Toxoplasma have more sons, Naturwissenschaften, August 2006. full text
- ↑ Berdoy M, Webster J, Macdonald D (2000). Fatal Attraction in Rats Infected with Toxoplasma gondii. Proceedings of the Royal Society of London, B267:1591-1594. CiteULike
- ↑ Flegr J, Havlícek J, Kodym P, Malý M, Smahel Z (2002). "Increased risk of traffic accidents in subjects with latent toxoplasmosis: a retrospective case-control study". BMC Infect. Dis. 2: 11. PMC 117239. PMID 12095427.
- ↑ 7.0 7.1 7.2 ">Jaroslav Flegr (2007). "Effects of Toxoplasma on Human Behaviour". Schizophrenia Bulletin. 33 (3): 757–760. Unknown parameter
|month=ignored (help) - ↑ 8.0 8.1
- ↑ 9.0 9.1 Yereli K, Balcioglu IC, Ozbilgin A. (2005). "Is Toxoplasma gondii a potential risk for traffic accidents in Turkey?". Forensic Sci Int. PMID 16332418. Unknown parameter
|month=ignored (help) - ↑ "Can a parasite carried by cats change your personality?". The Guardian. September 25, 2003.
- ↑ "Dirt infection link to car crashes". BBC News. August 10, 2002.
- ↑ J. Havlícek, Z. Gašová, A. P. Smith, K. Zvára and J. Flegr, Decrease of psychomotor performance in subjects with latent ‘asymptomatic’ toxoplasmosis, Parasitology (2001), 122: 515-520
- ↑ 13.0 13.1 "Dangerrrr: cats could alter your personality". Times Online. June 23, 2005.
- ↑ "Can a parasite carried by cats change your personality?". The Guardian. September 25, 2003.
- ↑ Novotná M, Hanusova J, Klose J, Preiss M, Havlicek J, Roubalová K, Flegr J (2004). "Probable neuroimmunological link between Toxoplasma and cytomegalovirus infections and personality changes in the human host". BMC Infect Dis. 5: 54. PMID 16000166. Unknown parameter
|month=ignored (help) - ↑ 16.0 16.1 16.2 Torrey EF, Yolken RH (2003). "Toxoplasma gondii and schizophrenia". Emerging Infect. Dis. 9 (11): 1375–80. PMID 14725265.free full text
- ↑ Lafferty, Kevin D. "Can the common brain parasite, Toxoplasma gondii, influence human culture?". Proceedings of the Royal Society B: Biological Sciences (FirstCite Early Online Publishing). doi:10.1098/rspb.2006.3641. ISSN 0962-8452 (Paper) 1471-2954 (Online).
- ↑ Wang H, Wang G, Li Q, Shu C, Jiang M, Guo Y (2006). "Prevalence of Toxoplasma infection in first-episode schizophrenia and comparison between Toxoplasma-seropositive and Toxoplasma-seronegative schizophrenia". Acta Psychiatrica Scandinavica. 114 (1): 40–8. PMID 16774660.