While the incidence of the human immunodeficiency virus (HIV) infection has leveled off somewhat in homosexual men, infection in women, children and adolescents is rising. Unless effective preventive measures are introduced, the number of pediatric patients with HIV and related illnesses will continue to increase. Animal models play a key role in the understanding of the pathogenesis and in the establishment of therapeutic approaches of infectious diseases. Ovine lentivirus (OvLV) comprises a subgenus of the lentivirus genus in the family Retroviridae, that shares genotypic, phenotypic and pathogenic features with HIV. Infection of sheep with OvLV results in a progressive chronic disease characterized by cachexia and chronic active inflammation in the lungs, lymph nodes, joints, mammary gland and the central nervous system. Pulmonary lesions in OvLV-affected sheep consist of lymphoid interstitial pneumonia (LIP) and lyphocytic alveolitis. Similarly, these pulmonary lesions also occur in up to 40% of HIV-infected children and in some adults with AIDS. Neonatal lambs experimentally inoculated intratracheally with OvLV develop LIP in 5 to 6 months, thus shortening by several years the natural incubation period and resembling the shorter incubation period observed in children with HIV-associated LIP. However, unlike HIV, OvLV does not infect CD4+T lymphocytes; OvLV only infects and replicates in macrophages. Recent studies indicate that macrophage tropic HIV plays an important role in disease progression. Similarities between HIV and OvLV argue for the use of ovine lentivirus infection as a model to advance in the understanding of some of the aspects of HIV infection.(ABSTRACT TRUNCATED AT 250 WORDS)