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Blood Parasites of Cats

By Peter H. Holmes, BVMS, PhD, Dr HC, FRCVS, FRSE, OBE, Emeritus Professor and Former Vice-Principal, Faculty of Veterinary Medicine, University of Glasgow
Michael Bernstein, DVM, DACVIM, Director, Medical Services, Angell Animal Medical Center
Karen L. Campbell, MS, DVM, DACVIM, DACVD, Professor and Section Head, Specialty Medicine, Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois
Nemi C. Jain, MVSc, PhD, Professor Emeritus of Clinical Pathology, Department of Veterinary Pathology, Microbiology, and Immunology, School of Veterinary Medicine. University of California
Wayne K. Jorgensen, BSc, PhD, Science Leader Applied Biotechnology Livestock, Agri-Science Queensland
Susan L. Payne, PhD, Associate Professor, Department of Veterinary Pathobiology, Texas A&M University
David J. Waltisbuhl, BASc, MSc, Senior Scientist DPI&F Actest, Yeerongpilly Veterinary Laboratory

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Blood parasites are organisms that live in the blood of their animal hosts. These parasites can range from single-celled protozoa to more complex bacteria and rickettsiae. The method of transmission varies depending on the parasite, but often they are transmitted through the bites of ticks or flies.


Babesiosis is a disease that is transmitted by ticks. It is caused by protozoan parasites of the genus Babesia, which infect red blood cells. Babesiosis affects a wide range of domestic and wild animals and occasionally humans. While the major economic impact of babesiosis is on the cattle industry, infections in other domestic animals, including cats, occur at various rates throughout the world.

Illness of varying severity due to Babesia felis has been reported in domestic cats in Africa and India. An unusual feature is its lack of response to the normal medicines used to destroy Babesia parasites. However, your veterinarian can provide alternative medications for this disease (Veterinary.heading on page Blood Parasites of Dogs : Babesiosis).


Cytauxzoonosis is caused by parasites of the genus Cytauxzoon. These are natural parasites of wild cats of North America, including the bobcat and the Florida panther. The parasites are transmitted to domestic cats by ticks. Most cases occur in the southern and southeastern states of the US and are usually associated with access to wooded areas. The disease progresses quickly and is usually deadly, although a strain found in northwestern Arkansas and northeastern Oklahoma may be less dangerous. The disease can also be transmitted by blood infection, which appears to have less deadly results.

Signs of infection usually begin about 10 days after a tick bite and come to a peak about 6 days later. Cats may be feverish, weak, depressed, and dehydrated, have difficulty breathing, and refuse to eat. Temperatures may be as high as 105°F (40.5°C) but usually fall below normal at the point of death. Gums and other mucous membranes are often yellow (jaundiced). Your veterinarian will perform blood tests to identify this infection. Treatment is often unsuccessful when the infection is caused by a severe strain, but new treatments have shown promise in some cases. Keeping cats out of areas where ticks are found is the best way to prevent this disease.

Hemotropic Mycoplasmas (Hemoplasmosis, Feline Infectious Anemia, Hemobartonellosis)

Red blood cell parasites called hemoplasmas and previously known as Haemobartonella and Eperythrozoon and formerly classified as rickettsial organisms are now understood to be more closely related to mycoplasmas. This infectious anemia is an acute or chronic disease of domestic cats. It is seen in many parts of the world and is caused by a specialized type of bacteria that multiplies within the bloodstream. It is thought to be transmitted by bloodsucking insects such as fleas. Transmission via bite wounds is another possibility, and transmission from mother to kitten can also occur during pregnancy.

Hemoplasma infection is more common among 1- to 3-year-old cats, particularly males. The first signs of illness usually appear 1 to 5 weeks after transmission of the parasite, and recovery does not make the animal immune to reinfection. Cats that have recovered from infection may still carry the parasite and relapse when stressed. Some cats may not appear to be sick, but are carrying the infection in a suppressed (or latent) form. Signs of illness may only appear when the cat has another disease or is stressed.

Any anemic cat should be evaluated by a veterinarian for the infection. In severe cases, fever usually reaches 103 to 106°F (39 to 41°C). The more quickly the anemia develops, the more severe the signs observed. Pale mucous membranes or jaundice, loss of appetite and energy, depression, weakness, and an enlarged spleen are common signs of this disease. In chronic cases, weight loss or emaciation may be seen, but there is less likely to be jaundice or an enlarged spleen. The degree of breathing difficulty varies with the degree of anemia.

The number of red blood cells affected depends on the severity of the infection and the stage in the life cycle of the parasite. A series of daily blood tests are normally used to confirm the diagnosis, because these red blood cell parasites are not always present in every blood sample.

To help prevent this disease in your cat, reduce the animal’s exposure to bloodsucking insects and stay alert to your cat’s overall condition. If unusual symptoms such as loss of energy, depression, or other signs of declining health appear, take your cat to your veterinarian for an examination.

Treatment involves both supportive care and specific drugs. Without treatment, up to one-third of cats may die in the early stages of infection. Cats that have difficulty breathing may require oxygen, and whole blood or red blood cell transfusions may be needed. Antibiotics are effective in many cases and may be prescribed by your veterinarian. If antibiotics are recommended, be sure to provide your pet with the prescribed dosages on the schedule given to you by your veterinarian.


Hepatozoonosis is a tick-borne disease of wild and domestic carnivores (meat-eating animals) caused by protozoa of the genus Hepatozoon. This organism is transmitted by the brown dog tick, but its method of transmission is unusual. The tick picks up the organism from an infected host while biting the animal. An uninfected cat then gets the disease by eating the tick, not from being bitten by the tick.

(For a more detailed description of hepatozoonosis, including causes, spread, transmission, signs, diagnosis, and treatment, see see Blood Parasites of Dogs : Hepatozoonosis.)

African Tsetse-transmitted Trypanosomiasis

Tsetse are small, winged biting flies that feed on the blood of humans and other animals. They only occur in sub-Saharan Africa, where they are responsible for transmitting a group of diseases caused by protozoa of the genus Trypanosoma, which affect all domestic animals. In cats, Trypanosoma brucei is probably the most important disease-causing species. This disease is not common in North America. (For a more detailed discussion of Tsetse-Transmitted Trypanosomiasis, see see Blood Parasites of Dogs : African Tsetse-transmitted Trypanosomiasis.)

Surra ( Trypanosoma evansi Infection)

Surra is separated from the tsetse-transmitted diseases because it is usually transmitted by other biting flies that are found within and outside tsetse fly areas. It occurs in North Africa, the Middle East, Asia, the Far East, and Central and South America. It is mostly a disease of horses, but cats and other domestic animals are susceptible. The disease can be deadly. The development and effects of the disease, signs, diagnosis, and treatment are similar to those of tetse-transmitted trypanosomiasis (see Blood Parasites of Cats : African Tsetse-transmitted Trypanosomiasis).

Chagas’ Disease ( Trypanosoma cruzi Infection)

Chagas’ disease is caused by infection with another trypanosome, Trypanosoma cruzi. Insects transmit the disease between susceptible species of animals, including opossums, armadillos, rodents, and wild, meat-eating animals. The trypanosome causes disease in humans and occasionally in young cats (and dogs). The disease occurs in Central and South America and localized areas of the southern US. Domestic animals may become infected and introduce the trypanosome into houses where the bugs are present. People then become infected by contamination of eye wounds or by eating food contaminated with insect droppings that contain trypanosomes. Other domestic animals act as source hosts. Your veterinarian can tell you if you live in an area where infections are likely.

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