Detection of Haemobartonella felis in cats with experimentally induced acute and chronic infections, using a polymerase chain reaction assay.

OBJECTIVE: To develop a test for detection of Haemobartonella felis, using a polymerase chain reaction (PCR) assay. ANIMALS: 4 adult cats seronegative for FeLV and feline immunodeficiency virus. PROCEDURE: Cats were infected with H felis by i.v. administration of 1 ml of blood obtained from an infected cat. Rectal temperature, PCV, and microscopic examination of blood smears for organisms were monitored daily. At peak of infection, doxycycline treatment was initiated for 21 days. Blood samples were collected at weekly intervals. Six months after treatment, 2 cats were given methylprednisolone (14 mg/kg of body weight, i.m.). Daily blood samples were collected for CBC, detection of organisms, and PCR evaluation. On the basis of the 16S rRNA gene sequence of H felis, specific PCR primers were created for a 393-basepair internal fragment.
RESULTS: The 393-basepair product was consistently amplified from blood samples obtained during peak parasitemia but not during the last week of or immediately after completion of doxycycline treatment. After treatment, PCV returned to the reference range, and organisms were not observed in blood samples; however, the PCR product could be consistently amplified. After administration of methylprednisolone, organisms were only rarely observed in blood smears but were consistently detected by PCR analysis. CLINICAL RELEVANCE: Using PCR analysis, it was possible to detect H felis in blood samples obtained from cats during peak parasitemia, during most of the carrier phase, and after challenge with immunosuppressive drugs. During and immediately after antibiotic treatment, this test may fail to detect the organisms.