The rate of progression to AIDS is independent of virus dose in simian immunodeficiency virus-infected macaques

Of the viral factors that are proposed to influence the rate of progression to AIDS, the role of infectious dose remains unresolved. Intravenous infec tion of outbred Macaca mulatta with various doses of simian immunodeficienc y virus isolate 8980 (SIV8980) revealed an endpoint from which an infectiou s dose 50 (ID50) was defined, In the six infected animals, the time to deve lop AIDS was variable with a spectrum of rapid, intermediate and slow progr essors, High and sustained plasma viraemia with marked loss of CD4(+) T-cel ls was a distinguishing feature between rapid versus intermediate and slow progressors, Animals that received the highest doses did not develop the hi ghest sustained viral loads, nor did they progress more rapidly to disease. Similarly, animals infected with lower doses did not uniformly develop low er viral loads or progress more slowly to AIDS. Furthermore, compiled data from more than 21 animals infected with different doses of the same virus a dministered by the same route failed to reveal any correlation of infectiou s dose with survival. Indeed, host factors of these outbred animals, rather than dose of the initial inoculum, were probably an important factor influ encing the rate of disease progression in each individual animal. Compariso n of animals infected with SIV8670, from which SIV8980 was derived, reveale d marked differences in disease progression. Clearly, although dose did not influence viral loads nor disease progression, the virulence of the initia l inoculum was a major determinant of the rate of progression to AIDS.