Babesiosis in Dogs or Piroplasmoses

Filed Under: Dogs, Diseases, Parasites

Babesia canis is an intracellular protozoan parasite that affects red blood cells (erythrocytes) of the dog. There are 73 identified species of which two infect dogs. These parasites are all spread by ticks, usually of the Ixodid family which are also known as hard ticks. Babesia species are typically host specific, indicating that they will not infect more than one vertebrate species. Babesia gibsoni and Babesia canis are the two species that generally infect dogs. Not only does Babesia parasitize their host vertebrate, but will adversely affect the tick vector parasitizing it as well. The geographic distribution of each Babesia species generally correlates with the range of the tick vector used to transmit the parasite.

Babesia gibsoni is found primarily in northern Africa and the Far East. This parasite is a small pleomorphic organism usually found singly within an erythrocyte. The tick vectors of B. gibsoni are Haemaphysalis bispinosa and Rhipicephalus sanguineus.

Babesia canis has a greater range, covering most of southern Europe, Africa, Asia, and North, Central, and South America. Babesia canis is larger than B. gibsoni and is usually found paired within erythrocytes. There are three strains of Babesia canis based on their differences in pathogenicity (ability to cause disease) and the vectors used in transmission. Babesia canis vogeli is the strain that occurs in tropical and subtropical regions of most continents and is the least pathogenic of the three strains. B. canis vogeli is the strain found in the United States and is transmitted by the brown dog tick, also known as Rhipicephalus sanguineus. The brown dog tick almost exclusively parasitizes dogs and is probably the most widely distributed tick species in the world. Babesia canis canis is the strain found in Europe and parts of Asia and is transmitted by Dermacentor reticularis. Babesia canis rossi is the strain of the highly pathogenic Babesia found in southern Africa and is transmitted by Haemaphysalis leachi.

All Babesia are introduced into the host by the bite of an infected Ixodid tick. All infected ticks may transmit the infection but the adult female tick appears to be the most important in parasite transmission. Once inside the host, Babesia attaches only to erythrocyte membranes, where the erythrocyte engulfs it through the process of endocytosis. Babesia canis undergoes asexual reproduction within the erythrocytes by a process called binary fission. Babesia at this stage of development are called merozoites; most commonly occurring in pairs.

Ticks become infected following the ingestion of erythrocytes while taking a blood meal from an infected dog. Within the tick, the parasite undergoes both sexual and asexual reproduction. The final stage of development results in the formation of sporozoites within the tick’s salivary glands. Once the infected ticks feed on the dog, the sporozoites are passed from the saliva of the tick into the circulation of the host. A tick must feed a minimum of three days to transmit Babesia canis.

Babesia may also be transmitted by blood transfusions. A major source of B. Gibsoni transmission among Pit Bull Terriers in the United States is dog fights.

Most infections of Babesiosis found in dogs within the United States are subclinical. These animals do not show any clinical signs of disease until they are stressed or treated with corticosteroids. Inapparent carriers may also serve as a potential source of infection to susceptible puppies.

Clinical signs are usually related to a hemolytic anemia which can be seen clinically as pale mucous membranes and weakness. The dog will be depressed, often have an elevated temperature or fever, will vomit, is anorexic (doesn’t want to eat), and may have a large spleen (splenomegaly). Complicated cases include acute renal failure, bleeding problems (coagulopathies), liver dysfunction, acute respiratory distress, myocarditis (inflammation of the heart), hypotension, neurologic manifestations, and pancreatitis (inflammation of the pancreas). Animals in acute crisis may occasionally be in shock or become comatose with less than a one-day history of illness, often resulting in death. Acute cases are commonly encountered in southern Africa, Asia, and southern Europe; or seen in young puppies.

The primary changes seen in hematology include anemia, thrombocytopenia (lack of platelets) and lymphocytosis (increase in white blood cell numbers). The thrombocytopenia is rarely low enough for spontaneous bleeding to occur. Babesiosis should be included in the differential diagnosis of all cases of anemia in puppies.

Diagnosis of Babesiosis is made by demonstrating the Babesia organism within infected erythrocytes. Serology is reliable in detecting infections with low parasite numbers.

Treatment of Babesiosis may involve supportive therapy including a blood transfusion for severely anemic patients. The elimination or suppression of the parasite may be obtained with specific antibabesial drugs such as diminazene aceturate and imidocarb dipropionate. Diminazene (Berenil®) is the most commonly used drug for treating Babesia worldwide, but is not available in the United States. Diminazene has a narrow therapeutic range in the dog and is typically dosed at 3.5 mg/kg by intramuscular injection and should not exceed 6 mg/kg for toxic side effects are common. Side effects include swelling at the site of injection, behavioral changes, gastrointestinal upset, ataxia, paresis, coma and even death.

Imidocarb dipropionate is the only drug approved for Babesia treatment in the United States. Imidocarb is dosed at 5 mg/kg, given intramuscularly twice at 14-day intervals. Imidocarb has also been shown to be effective against Ehrlichia canis and its use is especially attractive in cases of duel infection. The injection is painful and side effects are common. Side effects may include tremors, elevated temperatures, facial swelling, rubbing of the eyes, and restlessness. Pretreatment with atropine will help alleviate some of the side effects.

Oxytetracycline is effective against babesia infecting cattle but is ineffective for the treatment of babesia in the dog. Metronidazole usage has only limited effectiveness. Clindamycin is used in human infections of Babesia. Although its use in the dog is considered to be extra label, Clindamycin may be of benefit at a dose rate of 25 mg/Kg given by mouth divided twice daily.

When a dog is asymptomatic, treatment for babesia may not be worth the side effects. Some Babesia species may not be cleared by any of the available drugs. Female dogs testing positive for babesia should not be bred.

Immunity to babesia depends on the innate resistance of the host and the extent to which the host is able to mount an immune response to the parasite. The greyhound and pit bull terriers may be more susceptible to infection then are other breeds of dog. Increasing the dog’s exposure to ticks will increase the possibility of infection. Young dogs, especially those two to eight months of age, are most at risk for infection. Adults appear more resistant to infection.

The key to babesia prevention is to eliminate the exposure of the pet to ticks. When tick exposure occurs, it is imperative to remove the tick before the three-day incubation period necessary to transmit the disease. Effective tick products are available that will prevent tick attachment or cause the death of ticks once access to the pet has been achieved. Whenever possible, inapparent carriers of babesia should be identified and treated so they will not serve as a reservoir of infection, capable of transmitting the disease to others through the bite of a tick.

A vaccine has been produced in France, which touts an efficacy rate of 70 to 100%, but appears to be effective only against certain strains. The vaccine usage may be advantageous with immunosuppressed dogs, especially in endemic areas.

References:

Taboada, Joseph DVM and Sandra Merchant DVM. “Babesiosis of Companion Animals and Man”. The Veterinary Clinics of North America, Small Animal Practice, Tick-Transmitted Diseases. Vol. 21. No. 1. Jan. 1991. pp 99-121.

Ettinger, Stephen DVM, and Edward C. Feldman DVM. “Canine Babesiosis”. Textbook of Veterinary Internal Medicine. 6th Edition. Vol. 1. p. 700.

Georgi, Jay and Marion Georgi. Parasitology for Veterinarians. 5th edition. W.B.
Saunders Co. pp. 97-99.

Wetzel, Linda Marie. “Vector-Transmitted Diseases in Companion Animals: Trends, Risks, Controls.” DVM News. April 2007. Pp. 10-11.

Topics: ticks

Symptoms: anemia, fever, loss of appetite, vomiting

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