Unsolved Questions over the Origin of HIV and AIDS

T he concept of AIDS as a zoonosis stems from studies that traced HIV origins to two simian species in West and Central Africa—an idea that was reinforced by reports in highprofile journals. Although the simian origin of HIV and other human retroviruses such as human T cell leukemia virus and human foamy viruses is not in dispute, the hypothesis that simian retroviral infections are zoonoses is. Simply put, a zoonosis is a disease that is acquired from a vertebrate animal. Some microbiologists also consider vector-borne diseases as zoonoses. But the central meaning of zoonosis is that the disease, and not just the infection, is acquired from an animal, not from another human being. In the 2003 edition of Zoonoses: Infectious Diseases Transmissible from Animals to Humans, an ASM publication, HIV is dismissed as a zoonosis on the first page. It contains no chapters on simian retroviral zoonoses because there are none. When we think of zoonosis, we should think of rabies, not AIDS. Some experts consider this debate semantic and thus of little importance. Thus, because every case of human AIDS is acquired from another human being, it cannot be a zoonosis and the discussion could end here. Yet the underlying question of what launches new diseases among humans, including not only AIDS but also avian flu, Ebola virus, and severe acquired respiratory syndrome (SARS), is critical to address because it so often remains a black box. While we know the origin of HIV and the avian influenza virus and have some leads on the Ebola and SARS viruses, the shocking fact is that we know next to nothing about the factors that launch animal viruses into epidemics, pandemics, or result in dead-end infections. The ecological events that led SIV to become HIV with epidemic potential remain completely unknown.