Canine Babesiosis

Background

Canine babesiosis is a disease caused by the intraerythrocytic protozoan parasites Babesiacanis and Babesiagibsoni.  Babesiosis is transmitted by ticks to susceptible canine hosts.  Rhipicephalussanguineus is the most common tick vector in the United States.  Splenectomized dogs, immunocompromised dogs and young dogs between the ages of two and eight months are most susceptible to infection.  Canine babesiosis occurs worldwide.  Within the United States it is most common in the southeast.  Although canine babesiosis is considered uncommon in the U.S., it is of clinical significance due to its morbidity and mortality.  It is an important differential when history and clinical signs are consistent with infection and other more common diseases have been ruled out. 

Pathogenesis and Clinical Signs

Animals are affected after an infected tick bites and feeds on a susceptible host for a minimum of three days.  When the babesia organism is introduced into the host, it attaches to erythrocyte membranes and is endocytosed.  Hemolytic anemia and hypotensive shock are typical clinical syndromes of infection.  Hemolytic anemia results from direct erythrocyte damage by the parasite, and both intravascular and extravascular immune-mediated destruction of red blood cells.  Infection can produce thrombocytopenia, the mechanism of which consists of immune-mediated destruction and sequestration in the spleen.  Physical examination reveals splenomegaly, lymphadenomegaly, fever and less frequently, lethargy, vomiting, hematuria, and icterus.  Hypotensive shock results from the release and production of vasoactive amines and cytokines which produce vasodilation.  It most often occurs in puppies with the peracute form of the disease.  Death may occur and is seen most often in

B. gibsoni infections and in puppies affected with B.  canis and B.gibsoni.   Chronic infections,  subclinical carrier states and atypical canine babesiosis may also occur. 

Diagnosis

Infection with B. canis or B. gibsoni is definitively diagnosed by demonstration of the parasites on red cells.  Blood smears may be stained with Diff-Quik or preferably Wright’s or Giemsa stain.  Stained smears demonstrate 2.4mm x 5.0mm, piriform-shaped, intraerythrocytic parasites which are usually paired (B. canis), or 1.0mm x 3.2mm pleomorphic, single to multiple, intraerythrocytic organisms (B. gibsoni).  Blood samples collected from the peripheral capillary beds in the tip of the ear or the nail bed are most likely to reveal parasites.  The feathered edge and monolayer of the smear should be closely examined for parasitized red blood cells.  Practitioners may read their own smears and/or submit them to a nearby veterinary diagnostic laboratory.  Babesia organisms may be a challenge to find in chronic infections or in asymptomatic carrier animals.  Submission of a blood sample for serologic testing is an important adjunct diagnostic tool to help rule in the disease particularly when titers are significantly elevated.  Serologic testing is available at Louisiana Veterinary Medicine Diagnostic Laboratory and at the University of Illinois Laboratories of Veterinary Diagnostic Medicine.  Serologic tests which are currently available include the indirect fluorescent antibody test (IFA), which is used most frequently, and a more recently developed dot ELISA test.

Treatment

The most effective drugs used in the treatment of canine babesiosis include diminazeneaceturate, phenamidineisethionate, and imidocarbdipropionate which are not available or approved for use in the United States.  Treatment of canine babesiosis in the U.S. is therefore mostly aimed at treating symptoms.  The majority of babesia cases diagnosed in dogs in the U.S. are caused by the less virulent strains of B. canis and dogs frequently recover from these infections naturally with supportive therapy.  Clindamycin has been successfully used to treat canine babesiosis and may be considered in refractory or more severe and virulent infections.  

Prevention

Prevention of canine babesiosis is mostly aimed at controlling the vector.  It is an important aspect since treatment is not always successful.  The environment should be treated to decrease tick numbers, dogs should be treated to control tick infestations, and ticks should be removed from parasitized animals as quickly as detected. 

Recently, a vaccine which minimizes the severity of infection was developed.  The vaccine is reported to be 70 to 100% effective in diminishing the pathologic effects which typically ensue upon infection.  The vaccine is currently available in Europe where canine babesiosis is more common life-threatening disease.

Blood transfusion poses a significant risk to recipient animals, therefore it is recommended that donor animals be tested for infection with babesia organisms.  Splenectomy prior to testing significantly improves the likelihood of finding organisms in a blood sample from an infected donor. 

Conclusion

It is important for practitioners to keep less common diseases such as Babesiosis in the list of differential diagnoses for acute hemolytic anemia, shock and icterus.  It is equally important that practitioners know how to diagnose diseases which are less common and that they be diligent in their efforts to find a cause for disease when the more common possibilities have been ruled out.  Animals are traveling more often today than ever before, making exotic diseases more common and more likely to spread to new areas.  Canine babesiosis is an important diagnostic consideration which practitioners should not neglect to consider. 

-by Kristen Ripberger, Class of 2000

-edited by Armando Irizzary, DVM