Toxoplasmosis is the most common parasitic infection worldwide. It is estimated to affect several billion people. Toxoplasmosis is becoming a global health hazard as it infects 30–50% of the world human population. The disease is caused by a single-celled organism Toxoplasma gondii. Toxoplasmosis presents a serious health risk for people. Infection is especially dangerous for people with supressed immune system and pregnant women. The cat is the only animal in which sexual reproduction of the organism occurs, so cats are the only domestic animals that have the potential to shed the infected eggs. It is the most common food-borne parasitic infection requiring hospital treatment, and the third most common cause of hospitalization due to food-borne infection. Both competent and immunocompromised persons can develop the disease, especially retinochoroiditis (ocular toxoplasmosis). In non-pregnant immunocompetent adults, acute disease may also lead to impaired eye sight. For example, in the United States, one million new infections occur each year, which result in approximately 20,000 cases of retinal pathology.2
Recently, an exploratory study performed with a data mining technique on electronic records of 1.3 million patients of the University of Michigan Health System showed the existence of a strong association between dog and cat-bite injuries and the probability of being diagnosed with depression at some point in life. The association was stronger for cat bites than dog bites. While only 9 % of all patients of the data set were ever diagnosed with depression, this diagnosi was found in 41 % of those with cat bites and 28 % of those with dog bites. 4
Toxoplasmosis affects cats that ingest raw meat or prey that contains the parasite Toxoplasma gondii. Kittens can become infected in the womb and die before birth. Although infection is very common in cats, most cats do not get sick. Kittens are at the highest risk.
The signs of toxoplasmosis often include fever, lack of appetite, lethargy, diarrhea, and weight loss. Pneumonia, liver disease, and infection of the central nervous system are more devastating. Many afflicted cats do not survive.
Toxoplasmosis in dogs and cats can cause chorioretinitis (a form of bacterial uveitis which can lead to loss of vision), anterior uveitis (inflammation of the iris), or both. Eye lesions are a common manifestation of systemic toxoplasmosis. A diagnosis is made through blood tests. Infections involving only eyes can be treated successfully.
Dogs may act as a mecanical factor in transmitting toxoplasmosis to people by rolling in infected feces and by ingesting fecal material. It is estimated that 50% of stray dogs and cats carry T.gondii antibodies, which means that they have been infected and may transmit the parasite to people. Reports show that dogs in shelters, dogs living in close contact with wild birds and rodents in rural areas, and dogs fed raw meat are at mich higher risk for being infected.
T. gondii oocysts have been found on fresh fruits and vegetables from shops and gardens, suggesting environmental contamination in Poland. The risk of acquiring T. gondii infection from environmental sources versus meat was measured and the investigators detected sporozoite-specific protein (SSP) antibodies in 43% of recently infected pregnant women in Chile, implying the significant risk of the contaminated environment, which was almost equal to the hazard of meat containing the parasite cysts. In Japan, parasite antibodies were found to be 10.3% in pregnant women, while another report showed 5.4% IgG anti-T. gondii antibodies in HIV patients. Moreover, ocular toxoplasmosis was diagnosed through detection of T. gondii DNA in ocular fluid taken from patients.1
Cats that will live in households with pregnant women should be tested for the presence of toxoplasma antibodies. A positive-testing cat is probably immune to infection. A negative-testing cat is susceptible to infection, and, if exposed, might shed the organism in the feces for a week or two afterward. In either cases, be sure to reduce your cat's chance of exposure by following the list of recommendations.