An example of a very damaging odd little parasite is Toxoplasma a protozoan that is spread through the faeces of cats, but can affect other species, including humans. Most cats are asymptomatic carries that become infected by ingesting prey animals such as birds or eating raw meats.
Once a cat is infected with these cysts, they are then shed from the cats faeces and can infect other hosts such as dogs, birds and humans via ingestion, usually through infected soil or water.
In other animals the parasite becomes encysted in muscles and organs such as the heart, eyes and nervous system. Clinical signs vary hugely depending on the number of parasites present. Most cats show no signs of infection and only shed the parasite for up to 20 days after the initial infection, which can make it a difficult diagnosis. Testing should be considered in cats with inflammation of their eyes, sensitive muscles and a fever. On post mortem examination of cats with suspected toxoplasmosis, over 35% had lesions with the lungs and toxoplasma could be identified on histopathology.
Toxoplasma is zoonotic, meaning people can be infected. The most common signs of infection in the early stages of the disease is flu like symptoms and abdominal pain. Some people might be asymptomatic. Pregnant woman are at a higher risk than the rest of the population. If they are infected during pregnancy, the parasite can cross the placenta and result in sight or neurological abnormalities in their unborn child. Infected animals and people can be treated with appropriate antibiotics.
Cats that hunt or are fed raw food diets are at a much higher risk of becoming infected than those fed commercial diets and kept indoors.
People can help avoid infection by cooking meats such as lamb and pork throughly, not drinking raw milk, keeping cats indoors, feeding commercial pet foods and maintain good hygiene when handling litter trays. Infection of people is rare but serious. Good hygiene measures including swift cleaning up of cat litter is the best preventative around.