AN EXPERIMENTAL-STUDY OF PRIMARY FELINE IMMUNODEFICIENCY VIRUS-INFECTION IN CATS AND A HISTORICAL COMPARISON TO ACUTE SIMIAN AND HUMAN-IMMUNODEFICIENCY-VIRUS DISEASES

Sixteen adolescent specific pathogen free cats were inoculated with th e Petaluma strain of feline immunodeficiency virus (FIV) and two cats were then necropsied at each of 5, 10, 21, 28, 42, 56, 70, and 84 day time points following infection. Lymphadenopathy gradually increased s tarting at Day 10 and persisted for the duration. Gross clinical signs of fever, mild to severe malaise, anorexia, diarrhea, dehydration, an d generalized soreness appeared around Day 42, peaked at Day 56, and d isappeared by Days 70-84 post-infection. Leukopenia, associated initia lly with a mild lymphopenia and later by both a mild lymphopenia and a severe neutropenia, appeared 14-28 days following infection, troughed at Day 56, and persisted thereafter. The CD4(+):CD8(+) T cell ratio s tarted to decrease around Day 28, reaching a nadir at Days 56-70. This decrease was due to a decline in the absolute numbers and percentage of CD4(+) T cells and an increase in the percentage of CD8(+) T cells. Significant histopathologic lesions included myeloid hyperplasia betw een Days 56-70 post-infection; thymitis with cortical involution and f ollicular hyperplasia starting at Day 42; lymphoid hyperplasia of peri pheral and mesenteric nodes, spleen and tonsils beginning around Day 4 2; typhlitis most evident from Day 56 onward, and an interstitial neph ritis and pneumonitis that was most intense after Day 42. Virus was is olated from peripheral blood mononuclear cells (PBMC) beginning 2 week s post-infection, and plasma viremia appeared 1 week later. Plasma and PBMC-associated viremia peaked at 42-56 days following infection and decreased abruptly thereafter. Proviral DNA was detectable as early as 5 days after infection in blood leukocytes and after 10 days in other organs. The central nervous system, lungs, thymus, tonsils and mesent eric lymph nodes were the earliest sites of virus localization. Antibo dies to the FIV capsid protein appeared 14 days following infection an d reached peak levels by Days 42-56. Abnormalities occurring during th e primary stage of FIV infection were consistent with those described for acute simian and human immunodeficiency virus-induced disease.