Human immunodeficiency virus type-2 (HIV-2) is a close relative of the prototype acquired immunodeficiency syndrome (AIDS) virus, HIV-1. HIV-2 is biologically similar to HIV-1, but information is lacking concerning clinical outcomes of HIV-2-infected individuals. From 1985 to 1993, a prospective clinical study was conducted in women with HIV-2 and HIV-1 infection to determine and compare rates of disease development. HIV-1-infected women had a 67% probability of AIDS-free survival 5 years after seroconversion in contrast with 100% for HIV-2-infected women. In addition to having significantly less HIV-related disease outcome in HIV-2 enrollees compared to HIV-1 enrollees, the rate of developing abnormal CD4+ lymphocyte counts with HIV-2 infection was also significantly reduced. This natural history study demonstrates that HIV-2 has a reduced virulence compared to HIV-1.

At least 10 different genetic human immunodeficiency virus type 1 (HIV-1) subtypes (A-J) are responsible for the AIDS pandemic. Much of the understanding of HIV-1 disease progression derives from studies in the developed world where HIV infection is almost exclusively subtype B. This has led many to question whether the properties and consequences of HIV-1 infection can be generalized across subtypes that afflict the majority of infected persons in the developing world. From 1985 to 1997, a prospective study of registered female sex workers in Senegal tracked the introduction and spread of HIV-1 subtypes A, C, D, and G. In clinical follow-up, the AIDS-free survival curves differed by HIV-1 subtype. Women infected with a non-A subtype were 8 times more likely to develop AIDS than were those infected with subtype A (hazard ratio=8.23; P=. 009), the predominant subtype in the study. These data suggest that HIV-1 subtypes may differ in rates of progression to AIDS.

Men who have sex with men in Senegal are highly infected with HIV and other STI. Intervention programs targeting this population are urgently needed, given their particular vulnerability and because infections are likely to disseminate into the general population given the high proportion of bisexual activity in this community.

This study shows that HAART is feasible and well tolerated in African patients. Clinical and biological results were comparable to those seen in western cohorts, despite differences in the HIV-1 subtype distribution and an advanced disease stage when the treatment was initiated. Contrary to other recent studies in Africa, viral resistance rarely emerged.

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The tropical legume Sesbania rostrata can be nodulated by Azorhizobium caulinodans on both its stem and its root system. Here we investigate in detail the process of root nodulation and show that nodules develop exclusively at the base of secondary roots. Intercellular infection leads to the formation of infection pockets, which then give rise to infection threads. Concomitantly with infection, cortical cells of the secondary roots dedifferentiate, forming a meristem which has an "open-basket" configuration and which surrounds the initial infection site. Bacteria are released from the tips of infection threads into plant cells via "infection droplets," each containing several bacteria. Initially, nodule differentiation is comparable to that of indeterminate nodules, with the youngest meristematic cells being located at the periphery and the nitrogen-fixing cells being located at the nodule center. Because of the peculiar form of the meristem, Sesbania root nodules develop uniformly around a central axis. Nitrogen fixation is detected as early as 3 days following inoculation, while the nodule meristem is still active. Two weeks after inoculation, meristematic activity ceases, and nodules then show the typical histology of determinate nodules. Thus, root nodule organogenesis in S. rostrata appears to be intermediate between indeterminate and determinate types.

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We could not find evidence that concurrent sexual partnerships were a major determinant of the rate of spread of HIV in five cities in sub-Saharan Africa. HIV epidemics are the result of many factors, behavioural as well as biological, of which concurrent sexual partnerships are only one.