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-