Tick-Related Skin Lesions

Canine granulocytic anaplasmosis (CGA) is caused by Anaplasma phagocytophilum. This parasite is transmitted by several species of ixodid ticks in North America, Europe, and Asia. The clinical signs include fever, thrombocytopenia, lethargy, anorexia, arthropathy, and other nonspecific signs. Skin lesions have been reported in other species but not in dogs.

In this retrospective study, 52 skin biopsy specimens from 12 dogs seropositive for A phagocytophilum and responsive to doxycycline were compared with 2 specimens from 2 seronegative dogs and with 11 skin biopsy specimens from 10 dogs with unknown serologic status, compatible with tick-bite reactions. A phagocytophilum DNA was amplified in 4 of 12 seropositive dog samples. Skin lesions from the 12 dogs varied and included, but were not limited to, erythema, plaques, erosions, and crusts. Lesions were found on the head, ventral neck, ears, and ventral abdomen. Skin biopsy findings in all seropositive dogs included, but were not limited to, a perivascular-to-interstitial infiltrate of the superficial and deep dermis. A phagocytophilum was not amplified from seronegative and tick bite dogs. In 8 of the seropositive dogs, histologic findings included vasculopathy, fibrinoid necrosis of the vessel walls, and leuko-
cytoclastic changes.

The most common tick-borne illnesses are borreliosis, canine anaplasmosis, Rocky Mountain spotted fever, ehrlichiosis, babesiosis, and canine hepatozoonosis. Lack of adequate tick control is the most important risk factor for dogs. The clinical signs of these diseases overlap, and definitive diagnosis depends on laboratory diagnostics. It is likely that skin biopsy specimens were obtained in these cases because the lesions developed in close association with the onset of systemic illness. Although the histologic review did not identify a causative agent, the key finding was presence of histologic changes compatible with vasculitis. In addition, it was likely an unexpected finding because the gross clinical descriptions were not typical of classic vasculitis. From a practical perspective, it is important to remember that vasculitis is not a definitive diagnosis, but rather a reaction pattern, often a sign of systemic illness. If found during skin biopsy, a thorough search for the cause is warranted.—Karen A. Moriello, DVM, DACVD

Anaplasma phagocytophilum DNA isolated from lesional skin of seropositive dogs. Berzina I, Krudewig C, Silaghi C, et al. TICKS TICK BORNE DIS 5:329-335, 2014.