Blood Parasites of Dogs

Zoonotic Information

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

Babesiosis is a disease transmitted by ticks. It is caused by protozoan parasites of the genus Babesia, which infect the 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 dogs occur at various rates throughout the world.

Signs of infection vary from a mild illness that passes quickly to a severe disease that rapidly results in death. In some cases, the parasite causes a longterm disease with severe and progressive anemia as the main symptom. Babesiosis can be confused with other conditions that cause fever, anemia, destruction of red blood cells, jaundice, or red urine. Therefore, laboratory tests should be performed to confirm the diagnosis.

Your veterinarian will be able to prescribe the appropriate medication. 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.

Hemotropic Mycoplasmas (Hemoplasmas)

Mycoplasma haemocanis is a parasite that lives on the red blood cells of affected dogs. Infections do not usually cause signs, but red blood cell destruction (hemolysis) can be seen in dogs that have had their spleens removed. The parasites are transmitted through the transfer of infected blood (for example, blood transfusions or contaminated needles) or through the bites of lice, flies, ticks, and mosquitoes. Veterinarians use blood tests to diagnose the presence of parasites. Specific types of antibiotics are used to treat hemoplasma, but even after treatment, some dogs will remain infected. Additional medications or a blood transfusion may also be necessary for dogs with anemia. Screening all donors prior to blood transfusions and controlling insects can help limit the spread of hemoplasma parasites.

Hepatozoonosis

In much of the world (India, Africa, southeast Asia, the Middle East, southern Europe, and islands in the Pacific and Indian Oceans), infected dogs have no signs of infection or only mild signs. Having a suppressed immune system due to another disease appears to play an important role in the development of significant signs. In the United States, more severe signs may occur, even in dogs that do not have a suppressed immune system. Most cases in the US have been diagnosed in Texas (primarily along the Gulf Coast), Oklahoma, and Louisiana, but cases have also been reported as far east as Tennessee, Alabama, Georgia, and Florida. This is a recent disease that has primarily spread north and east from the Gulf Coast of Texas, where it was originally detected in 1978.

Dogs older than 4 to 6 months old are usually resistant to infection with H. canis. However, H. americanum causes severe signs even in adult dogs.

American Canine Hepatozoonosis

Infection by H. americanum creates areas of inflammation within body tissues, which can cause signs of disease such as fever, depression, weight loss, poor body condition, muscle loss and weakness, discharge from the eyes, and bloody diarrhea. These signs may come and go. Fluctuating fevers of from 102.7 to 106°F (39.3 to 41.0°C) may also be seen. Surprisingly, many dogs have a normal appetite. Severe sensitivity or pain near the spine is also common, as are stiffness and a general reluctance to move. Eventually, hepatozoonosis may lead to inflammation of the kidneys or amyloidosis of the kidneys (a condition in which there is a buildup of an abnormal protein called amyloid in kidney tissues).

Muscle biopsies are considered the best way to diagnose hepatozoonosis. Specific blood tests, visualizing infected blood cells, and x-rays may also help with diagnosis. Other laboratory findings may include a significant increase in the white blood cell count and a mild to moderate anemia.

Hepatozoonosis is a life-long infection in dogs. No known treatment completely clears the body of the organism. In the past, most dogs showed only temporary improvement, with frequent relapses within 3 to 6 months and death within 2 years of diagnosis. However, remission can now usually be achieved by using new drug combinations. These new therapies have resulted in a marked improvement in the outlook for dogs with 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. Tsetse flies are restricted to Africa; however, horseflies and other biting flies can transmit the disease in other locations (such as in Central and South America). In dogs, Trypanosoma brucei is most likely to cause disease. Domestic animals may be a source of human infections.

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 vulnerable to 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 dog.

Frequently asked questions

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