Early haematological and pathological abnormalities of pathogen-free cats experimentally infected with feline immunodeficiency virus (FIV).
Twelve 8-12-week-old specific-pathogen-free (SPF) cats were inoculated intraperitoneally with feline immunodeficiency virus, or with blood from inoculated cats. Three cats of the same age were used as controls. All animals were sacrificed 10 weeks after inoculation. The inoculated cats seroconverted between the 3rd and 6th weeks after inoculation. For 6 infected cats, a decrease in the CD4/CD8 lymphocyte ratio was observed as early as the 6th to the 10th week after inoculation. Granular lymphocytes and atypical cells with cytoplasmic vacuoles and very irregular nuclei were observed in the blood from the 1st to the 10th weeks after inoculation. The only statistically significant differences were obtained 10 weeks after inoculation. Mean leucocyte and lymphocyte numbers were decreased (8000 and 3200 per microliter respectively compared with 14500 and 7200 per microliter before inoculation). The mean CD4/CD8 ratio was also decreased (from 2.60 to 1.50). The percentage of lymphocytes in the bone marrow was increased, reaching 34% as a mean for infected cats as opposed to 20% for control animals. The atypical cells found in the blood were not observed in the marrow. The sternebral bone marrow did not contain lymphoid follicles, as described for HIV infection. Severe follicular hyperplasia was only found in the lymph nodes, but no viral particles could be observed in them.