Blood parasites (protozoa or bacteria) live in the bloodstream and are often spread by ticks or biting insects. Some parasites can be transmitted through insect bites to humans and cause serious disease. Several of these are highlighted separately; see Babesiosis, Surra, and Chagas Disease.
Cytauxzoonosis
Cytauxzoonosis, caused by the protozoal parasite Cytauxzoon felis, is a life‑threatening disease. The parasite lives in bobcats and spreads to domestic cats by ticks, mainly in wooded areas of the southern and southeastern United States at times of the year when ticks are active.
After the parasite infects an animal, it invades the white blood cells, which block small blood vessels and cut off flow. It also invades red blood cells, but with less damage.
Symptoms of cytauxzoonosis usually appear about 10 days after a tick bite and get worse over several days. Affected cats often have high fever, weakness, depression, dehydration, trouble breathing, loss of appetite, and jaundice, and their body temperature might fall just before death.
Cytauxzoonosis can be confirmed via blood tests. Newer aggressive treatments have improved survival, but the disease remains very serious. Prevention focuses on avoiding tick‑infested areas and using vet‑recommended tick control.
Hemotropic Mycoplasmosis
Hemotropic mycoplasmosis is caused by hemotropic mycoplasmas (or hemoplasmas), which are tiny bacteria that are attracted to, infect, and damage red blood cells. These bacterial parasites can cause hemolytic anemia.
Healthy adult cats infected by hemoplasmas might not show any symptoms, but severe disease can occur in cats infected by feline leukemia virus (FeLV), feline immunodeficiency virus (FIV), or other disease-causing agents.
The bacterium Mycoplasma haemofelis can cause serious anemia even in healthy cats. These organisms are thought to spread via fleas and other bloodsucking insects, through bite wounds, and from mother to kittens.
Symptoms of hemotropic mycoplasmosis include fever, pale or yellow mucous membranes, poor appetite, weakness, depression, enlarged spleen, and, in chronic cases, weight loss and extreme thinness. Breathing difficulty appears with severe anemia.
Hemotropic mycoplasmosis is diagnosed via blood tests.
Prevention is based on good flea and insect control and monitoring for illness. The disease is treated with antibiotics and supportive care. Oxygen and blood transfusions might also be required. Up to one‑third of untreated cats with severe infection might die.
Hepatozoonosis
Hepatozoonosis, caused by the protozoon Hepatozoon felis, often causes no clear symptoms in cats. It is diagnosed by finding the parasite in blood or via specialized lab tests.
Treatment can be difficult, but several drugs are available. Because related parasites in other species are tickborne, flea and tick prevention is recommended.
African Tsetse-Transmitted Trypanosomiasis
African tsetse‑transmitted trypanosomiasis is spread by tsetse flies in sub‑Saharan Africa and caused by Trypanosoma protozoa. The species that most often affects cats is Trypanosoma brucei.
After an infected tsetse bites an animal, the parasites multiply in the animal's skin and then spread to its lymph nodes and blood.
Symptoms of trypanosomiasis, which usually appear within 1–4 weeks after the bite, include fever, anemia, weight loss, eye problems, and enlarged lymph nodes and spleen.
A diagnosis of trypanosomiasis is confirmed by finding parasites in blood.
Several drugs can be used to treat trypanosomiasis, but correct dosing is critical and drug resistance is more and more of a problem. In areas where trypanosomiasis is common, keeping cats indoors, controlling flies, and managing the environment help decrease risk. No vaccine is available.
