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Pet Owner Version

Blood Parasites of Cats


Alicja E. Tabor

, BSc, PhD, Centre for Animal Science, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland;

Phillip D. Carter

, BVSc, MVS, Local Land Services, New South Wales, Australia;

Peter Rolls

, BVSc, MVS, Tick Fever Centre, Department of Agriculture and Fisheries, Queensland, Australia;

Jaime L. Tarigo

, DVM, PhD, DACVP, Department of Pathology, College of Veterinary Medicine, University of Georgia;

Joanne B. Messick

, VMD, PhD, DACVP, Purdue University College of Veterinary Medicine;

Kelly E. Allen

, PhD, Department of Veterinary Pathobiology, College of Veterinary Medicine, Oklahoma State University;

Jozef Vercruysse

, DVM, Ghent University;

Ivan W. Morrison

, PhD, BVMS, Roslin Institute, University of Edinburgh;

Christine Petersen

, MD, DVM, PhD, FASTMH, Center for Emerging Infectious Diseases, University of Iowa;

Tara L. Grinnage-Pulley

, DVM, PhD, Department of Epidemiology, College of Public Health, University of Iowa

Reviewed/Revised May 2018 | Modified Oct 2022

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 mostly been reported in domestic cats in southern Africa. Intermittent cases caused by other Babesia species have also been reported in other areas. 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. Supportive treatment is helpful and may include the use of anti-inflammatory drugs, antioxidants, and corticosteroids. Blood transfusions may be life-saving in very anemic animals. Preventing exposure to ticks by using appropriate tick control products and removing any ticks promptly will help keep your cat from being exposed to this parasite.

A small number of cases of human babesiosis have been reported, but it is unclear whether the species of Babesia that infect cats are the same as those that infect people. Fatal cases have been reported in people whose spleen had been removed or who had a weakened immune system. Human Babesia infections are acquired by way of bites from infected ticks or through contaminated blood transfusions.


Cytauxzoonosis is a life-threatening disease of cats caused by the parasite Cytauxzoon felis. The parasites live and breed within bobcats and 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. Cytauxzoonosis is typically diagnosed when ticks are active, usually during April through September. 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. Cats cannot transmit the disease to other cats without the presence of ticks.

After transmission, the parasite infects a cat's white blood cells. The infected cells then occlude blood vessels, blocking blood flow and causing body tissues to die. Red blood cells also become infected but are not responsible for the destructive effects of the disease.

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 has historically been ineffective when the infection is caused by a severe strain, but new, aggressive treatments are often more successful. Keeping cats out of areas where ticks are found is the best way to prevent this disease. Using tick preventives (such as tick collars) may also reduce transmission of the disease in many, but not all, cases.

Hemotropic Mycoplasmas (Hemoplasmosis, Feline Infectious Anemia, Hemobartonellosis)

Hemoplasmas (previously known as Haemobartonella and Eperythrozoon) are parasites of red blood cells that can cause hemolytic anemia Hemolytic Anemia Anemia occurs when there is a decrease in the number of red blood cells. It can develop from loss, destruction, or lack of production of red blood cells. Anemia is classified as regenerative... read more in domestic cats. The anemia can range from mild to severe. In general, infections do not show signs in healthy adults but can cause severe anemia in animals with an impaired immune system or other diseases (such as feline leukemia virus Immunodeficiencies Caused by Viruses or feline immunodeficiency virus Immunodeficiencies Caused by Viruses ). However, Mycoplasma haemofelis is an exception and can cause severe, sometimes life-threatening anemia even in healthy adults.

Hemoplasmas are seen in many parts of the world and are 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 in cats can cause a disease called feline infectious anemia. It is more common among outdoor 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. Laboratory blood tests are used to confirm the diagnosis.

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 antibiotics. 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 blood parasite of wild and domestic carnivores (meat-eating animals). In cats, the disease is caused by Hepatozoon felis. In dogs, 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 carnivore then gets the disease by eating the tick, not from being bitten by the tick.

Infected cats do not typically show any signs of infection. The condition is diagnosed by identifying the parasite within blood samples or by other laboratory tests. The condition may be difficult to treat, but several drugs have successfully been used to treat the parasite in cats. Because hepatozoonosis is transmitted by ticks in other species, using a flea and tick preventive is recommended.

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.

Infected tsetse flies inject the protozoa into the skin of animals, where they grow for a few days and cause localized swellings called chancres. They enter the lymph nodes, then the bloodstream, where they multiply quickly. The immune response is very strong; however, not all trypanosomes are killed by the immune response, which results in longterm infection.

The severity of disease varies with the species and age of the animal infected and the species of trypanosome involved. The incubation period is usually 1 to 4 weeks. The primary signs are fever, anemia, and weight loss. The eyes are often affected. Internally, the lymph nodes and spleen are usually swollen. The diagnosis is confirmed by laboratory testing to identify trypanosomes in the blood of an infected cat.

Several drugs can be used for treatment; however, most drugs only work if the correct dose is given. It is very important to follow the prescribed dosage exactly. Some trypanosomes have become resistant to certain drugs, which may be the cause in cases that do not respond to medical treatment.

The risk of infection can be reduced in areas where the disease is common by keeping cats indoors or by getting rid of tsetse flies and using preventive drugs, which are given to stop an infection from getting started. Flies can be partially controlled by using sprays or dips on the pets to be protected, spraying insecticides on fly-breeding areas, using screens coated with insecticide, and clearing brush to reduce the habitat for the flies. Animals can be given preventive drugs in areas of high risk for infections, but this is rarely undertaken in domestic cats. There is no vaccine.

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 in camels, dogs, and horses. It does not usually cause significant disease in cats, but infection in cats can lead to the transmission of the protozoa to other species. The development and effects of the disease, signs, diagnosis, and treatment are similar to those of tsetse-transmitted trypanosomiasis (see above).

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. Although cats can be infected, they do not have a major role in transmission of the disease to people. 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.

For More Information

Also see professional content regarding blood parasites Blood Parasites .

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