H. felis is a rickettsial parasite that causes hemolysis and sequestration of feline erythrocytes. It should be considered as a potential primary pathogen or opportunist in any cat presented with signs ranging from episodic malaise to acute anemic collapse. Diagnosis requires visualization of the organism in properly prepared blood smears. Treatment uses antirickettsial drugs, corticosteroids, and supportive measures. Clinical recovery requires immune containment of the organism. Treatment does not eliminate the organism from the host. Carrier cats may relapse when their immunity is severely compromised by other diseases such as FeLV. Transmission is presumed to be by blood-sucking parasites and possibly bite wounds between cats. Prevention requires prudent health management of cats. Future advances in the knowledge of the disease will relate mainly to the development of a diagnostic technique that will allow identification of all infected cats.