Acute Anaplasma phagocytophilum infection in a pediatric domestic cat

Case summary A domestic shorthair cat estimated to be 4–6 weeks old was presented to a referral center for evaluation of lethargy, anorexia and diarrhea for a duration of 24 h. A feline vector-borne PCR panel, as well as a blood smear, examined by a board-certified pathologist, confirmed an Anaplasma phagocytophilum infection. Morulae were identified in both feline neutrophils and eosinophils. Treatment consisted of a 21-day course of liquid doxycycline. Clinical signs rapidly resolved and were not noted to recur. Relevance and novel information This case demonstrates that A phagocytophilum can infect cats as young as 4–6 weeks old. Doxycycline, as the antibiotic of choice for the treatment of A phagocytophilum infections, was used. Consistent with the literature, a rapid clinical improvement was detected. Anaplasmosis should be listed as a differential diagnosis in pediatric cats suffering from acute febrile illness with potential previous tick exposure (history of living outdoors) in order to provide proper treatment.