Canine Anaplasmosis

By Heather Norton-Bower, DVM

 

What causes Anaplasma infections?

Like Lyme disease, canine Anaplasmosis is a bacterial disease spread by ticks. Ixodid ticks (also called black-legged ticks or deer ticks) are the primary vector for Anaplasma phagocytophilum, which was first reported in dogs from Minnesota and Wisconsin in 1996. Another type of Anaplasma bacteria spread by ticks, Anaplasma platys, is also perhaps on the rise in the Midwest, but it is less common at this point. Animals living in the Midwest are often exposed to                   A. phagocytophilum and some studies indicate that 40% or more of dogs living in endemic areas will be positive.

What are the clinical symptoms of Anaplasma?

Most pets that test positive for A. phagocytophilum will never show any symptoms of an infection. Those that do will show signs of illness in the early days of the infection, usually a week or two after the tick bite. The most common symptoms are fever, lethargy, anorexia (not wanting to eat), and reluctance to move due to joint pain (polyarthritis). Because of the similar symptoms to Lyme disease, A. phagocytophilum can’t be distinguished from Lyme disease on clinical symptoms alone.

How do we diagnose Anaplasma infections?

At Westgate Pet Clinic, we run an in-house serology test for A. phagocytophilum at the same time as the annual heartworm test (Idexx SNAP 4Dx test, this test can also be attached to senior wellness screens). The Idexx 4Dx test also tests for exposure to Borrelia burgdorferi, the bacteria that are responsible for causing Lyme disease, and Ehrlichia canis, which is rarely positive in dogs in this part of the Midwest. Tests are usually positive within 3-4 weeks of clinical exposure, and there is evidence that the test may be positive as early as 8 days post infection. We may also see evidence of the organism in the patient’s blood. Finding the organism in circulating neutrophils (neutrophils are the most plentiful white blood cell) allows a definitive diagnosis.

What does a positive Anaplasma test on the 4Dx mean?

A positive test indicates that your pet has been exposed to Anaplasma bacteria through a tick bite and has antibodies. It does not necessarily mean that your pet is ill or will become ill, as most pets that have a positive on the 4Dx test never develop any clinical symptoms or laboratory evidence of the disease. Many animals will be persistently positive for A. phagocytophilum on the 4Dx test for months or years to come. Currently it is unknown whether a patient that is persistently positive can later develop clinical symptoms or signs of chronic disease, but there are no confirmed reports at this time.

What laboratory results help to determine whether my pet is sick or at risk for clinical disease from Anaplasma?

The most common blood abnormality found in dogs that are “sick” from A. phagocytophilum is a mild to severe decrease in the platelet count (platelets are responsible for clotting). This problem is seen in more than 80% of infected dogs that are showing clinical symptoms of the disease and may be associated largely with an immune-mediated destruction of platelets. There may also be mild to moderate anemia (low red cells) and various changes in the white blood cell line. As commented above, we may see the organism in neutrophils. When we have a pet that has tested
positive to A. phagocytophilum for the first time, we always do a platelet estimate and look for evidence of the organism in the neutrophils. If these latter things are normal, then the pet is unlikely to have problems.

How is Anaplasma treated?

Similar to Lyme disease, a pet with clinical symptoms of Anaplasma will quickly respond to doxycycline therapy within 1-2 days of starting therapy. The recommended course has been to use doxycycline twice daily for a month. Because of the persistence of positive antibody
tests beyond the treatment period, it is possible that the organism may not be completely eliminated. However, clinical symptoms should go away. Currently, it is not advised to treat a patient with multiple courses of antibiotic in an attempt to attain a negative test status. Whether to treat a healthy, non-symptomatic patient with a positive test may be discussed with your veterinarian, but generally an aggressive tick-control program is the focus.

How does one prevent Anaplasma disease?

The best way to prevent Anaplasma and other tick-vector diseases is to use good protection against ticks during the tick season (beginning of spring through the end of fall here in Minnesota). At Westgate we recommend using Frontline Top Spot, which is a very safe topical product that is easily applied once monthly at home to your pet’s skin.

What about the less common Anaplasma platys?

A positive on the SNAP 4Dx may actually mean a positive for A. platys, because there is evidence of occasional cross-reactivity between the bacterial strains on this test. For patients that develop illness, A. platys will cause some of the same symptoms as A. phagocytophilum, but severe cases will show evidence of bleeding or bruising because the organism always causes a severe decrease in platelets (thrombocytopenia). Unlike A. phagocytophilum which appears to be one-time temporary problem for the occasional patient, A. platys may cause cycles of low platelets after an initial acute flare-up. If your pet shows evidence of this type of disease, the platelets will be inspected because the organism is found in circulating platelets. Treatment is similar to that for
A. phagocytophilum.