Acute feline leukemia virus infection causes altered energy balance and growth inhibition in weanling cats

Naturally occurring retroviral infections cause progressive weight loss, immune suppression, invasion by opportunistic organisms, and eventual death. Feline leukemia virus (FeLV) inhibited growth and decreased energy intake in seven experimentally infected weanling cats compared with age- and sex-matched controls. Remarkably, changes in energy intake, energy expenditure, and weight gain occurred in the acute phase of infection prior to the systemic/productive bone marrow phase of FeLV infection. In other words, growth inhibition developed before FeLV infection was clinically detectable with use of standard enzyme-linked immunosorbent assay or fixed-cell immunofluorescence assays of circulating neutrophils and platelets. Acutely infected, previremic cats consumed 25% less energy [Day 4 postinoculation to Day 16 postinoculation (p < 0.05)] and expended 20% less energy [Day 8 postinoculation to Day 18 postinoculation (p < 0.05)] compared with control cats. Growth stunting of inoculated cats began by Day 11 postinoculation (p < 0.05) and was not corrected during the remaining 4 months of the study. Thus, experimental FeLV infection causes perturbations of metabolism and energy balance resulting in permanent growth impairment. Secondly, detrimental metabolic effects begin in the acute phase of retroviral infection, prior to the clinically detectable phase of FeLV infection.