Search tips
Search criteria

Results 1-7 (7)

Clipboard (0)

Select a Filter Below

Year of Publication
1.  The Role of Viral Introductions in Sustaining Community-Based HIV Epidemics in Rural Uganda: Evidence from Spatial Clustering, Phylogenetics, and Egocentric Transmission Models 
PLoS Medicine  2014;11(3):e1001610.
Using different approaches to investigate HIV transmission patterns, Justin Lessler and colleagues find that extra-community HIV introductions are frequent and likely play a role in sustaining the epidemic in the Rakai community.
Please see later in the article for the Editors' Summary
It is often assumed that local sexual networks play a dominant role in HIV spread in sub-Saharan Africa. The aim of this study was to determine the extent to which continued HIV transmission in rural communities—home to two-thirds of the African population—is driven by intra-community sexual networks versus viral introductions from outside of communities.
Methods and Findings
We analyzed the spatial dynamics of HIV transmission in rural Rakai District, Uganda, using data from a cohort of 14,594 individuals within 46 communities. We applied spatial clustering statistics, viral phylogenetics, and probabilistic transmission models to quantify the relative contribution of viral introductions into communities versus community- and household-based transmission to HIV incidence. Individuals living in households with HIV-incident (n = 189) or HIV-prevalent (n = 1,597) persons were 3.2 (95% CI: 2.7–3.7) times more likely to be HIV infected themselves compared to the population in general, but spatial clustering outside of households was relatively weak and was confined to distances <500 m. Phylogenetic analyses of gag and env genes suggest that chains of transmission frequently cross community boundaries. A total of 95 phylogenetic clusters were identified, of which 44% (42/95) were two individuals sharing a household. Among the remaining clusters, 72% (38/53) crossed community boundaries. Using the locations of self-reported sexual partners, we estimate that 39% (95% CI: 34%–42%) of new viral transmissions occur within stable household partnerships, and that among those infected by extra-household sexual partners, 62% (95% CI: 55%–70%) are infected by sexual partners from outside their community. These results rely on the representativeness of the sample and the quality of self-reported partnership data and may not reflect HIV transmission patterns outside of Rakai.
Our findings suggest that HIV introductions into communities are common and account for a significant proportion of new HIV infections acquired outside of households in rural Uganda, though the extent to which this is true elsewhere in Africa remains unknown. Our results also suggest that HIV prevention efforts should be implemented at spatial scales broader than the community and should target key populations likely responsible for introductions into communities.
Please see later in the article for the Editors' Summary
Editors' Summary
About 35 million people (25 million of whom live in sub-Saharan Africa) are currently infected with HIV, the virus that causes AIDS, and about 2.3 million people become newly infected every year. HIV destroys immune system cells, leaving infected individuals susceptible to other infections. HIV infection can be controlled by taking antiretroviral drugs (antiretroviral therapy, or ART) daily throughout life. Although originally available only to people living in wealthy countries, recent political efforts mean that 9.7 million people in low- and middle-income countries now have access to ART. However, ART does not cure HIV infection, so prevention of viral transmission remains extremely important. Because HIV is usually transmitted through unprotected sex with an infected partner, individuals can reduce their risk of infection by abstaining from sex, by having one or a few partners, and by using condoms. Male circumcision also reduces HIV transmission. In addition to reducing illness and death among HIV-positive people, ART also reduces HIV transmission.
Why Was This Study Done?
Effective HIV control requires an understanding of how HIV spreads through sexual networks. These networks include sexual partnerships between individuals in households, between community members in different households, and between individuals from different communities. Local sexual networks (household and intra-community sexual partnerships) are sometimes assumed to be the dominant driving force in HIV spread in sub-Saharan Africa, but are viral introductions from sexual partnerships with individuals outside the community also important? This question needs answering because the effectiveness of interventions such as ART as prevention partly depends on how many new infections in an intervention area are attributable to infection from partners residing in that area and how many are attributable to infection from partners living elsewhere. Here, the researchers use three analytical methods—spatial clustering statistics, viral phylogenetics, and egocentric transmission modeling—to ask whether HIV transmission in rural Uganda is driven predominantly by intra-community sexual networks. Spatial clustering analysis uses the geographical coordinates of households to measure the tendency of HIV-infected people to cluster spatially at scales consistent with community transmission. Viral phylogenetic analysis examines the genetic relatedness of viruses; if transmission is through local networks, viruses in newly infected individuals should more closely resemble viruses in other community members than those in people outside the community. Egocentric transmission modelling uses information on the locations of recent sexual partners to estimate the proportions of new transmissions from household, intra-community, and extra-community partners.
What Did the Researchers Do and Find?
The researchers applied their three analytical methods to data collected from 14,594 individuals living in 46 communities (governmental administrative units) in Rakai District, Uganda. Spatial clustering analysis indicated that individuals who lived in households with individuals with incident HIV (newly diagnosed) or prevalent HIV (previously diagnosed) were 3.2 times more likely than the general population to be HIV-positive themselves. Spatial clustering outside households was relatively weak, however, and was confined to distances of less than half a kilometer. Viral phylogenetic analysis indicated that 44% of phylogenetic clusters (viruses with related genetic sequences found in more than one individual) were within households, but that 40% of clusters crossed community borders. Finally, analysis of the locations of self-reported sexual partners indicated that 39% of new viral transmissions occurred within stable household partnerships, but that among people newly infected by extra-household partners, nearly two-thirds were infected by partners from outside their community.
What Do These Findings Mean?
The results of all three analyses suggest that HIV introductions into communities are frequent and are likely to play an important role in sustaining HIV transmission in the Rakai District. Specifically, within this rural HIV-endemic region (a region where HIV infection is always present), viral introductions combined with intra-household transmission account for the majority of new infections, although community-based sexual networks also play a critical role in HIV transmission. These findings may not be generalizable to the broader Ugandan population or to other regions of Africa, and their accuracy is likely to be limited by the use of self-reported sexual partner data. Nevertheless, these findings indicate that the dynamics of HIV transmission in rural Uganda (and probably elsewhere) are complex. Consequently, to halt the spread of HIV, prevention efforts will need to be implemented at spatial scales broader than individual communities, and key populations that are likely to introduce HIV into communities will need to be targeted.
Additional Information
Please access these websites via the online version of this summary at
Information is available from the US National Institute of Allergy and Infectious Diseases on HIV infection and AIDS
NAM/aidsmap provides basic information about HIV/AIDS, and summaries of recent research findings on HIV care and treatment
Information is available from Avert, an international AIDS charity, on many aspects of HIV/AIDS, including information on HIV and AIDS in Uganda and on HIV prevention strategies (in English and Spanish)
The UNAIDS Report on the Global AIDS Epidemic 2013 provides up-to-date information about the AIDS epidemic and efforts to halt it
The Center for AIDS Prevention Studies (University of California, San Francisco) has a fact sheet about sexual networks and HIV prevention
Wikipedia provides information on spatial clustering analysis (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
A PLOS Computational Biology Topic Page (a review article that is a published copy of record of a dynamic version of the article as found in Wikipedia) about viral phylodynamics is available
Personal stories about living with HIV/AIDS are available through Avert, NAM/aidsmap, and Healthtalkonline
PMCID: PMC3942316  PMID: 24595023
3.  Previously Transmitted HIV-1 Strains Are Preferentially Selected During Subsequent Sexual Transmissions 
The Journal of Infectious Diseases  2012;206(9):1433-1442.
Background. A genetic bottleneck is known to exist for human immunodeficiency virus (HIV) at the point of sexual transmission. However, the nature of this bottleneck and its effect on viral diversity over time is unclear.
Methods. Interhost and intrahost HIV diversity was analyzed in a stable population in Rakai, Uganda, from 1994 to 2002. HIV-1 envelope sequences from both individuals in initially HIV-discordant relationships in which transmission occurred later were examined using Sanger sequencing of bulk polymerase chain reaction (PCR) products (for 22 couples), clonal analysis (for 3), and next-generation deep sequencing (for 9).
Results. Intrahost viral diversity was significantly higher than changes in interhost diversity (P < .01). The majority of HIV-1–discordant couples examined via bulk PCR (16 of 22 couples), clonal analysis (3 of 3), and next-generation deep sequencing (6 of 9) demonstrated that the viral populations present in the newly infected recipient were more closely related to the donor partner's HIV-1 variants found earlier during infection as compared to those circulating near the estimated time of transmission (P = .03).
Conclusions. These findings suggest that sexual transmission constrains viral diversity at the population level, partially because of the preferential transmission of ancestral as opposed to contemporary strains circulating in the transmitting partner. Future successful vaccine strategies may need to target these transmitted ancestral strains.
PMCID: PMC3466994  PMID: 22997233
4.  HIV Type 1 Genetic Variation in Foreskin and Blood from Subjects in Rakai, Uganda 
The foreskin contains a subset of dendritic cells, macrophages, and CD4+ and CD8+ T cells that may be targets for initial HIV infection in female-to-male sexual transmission of HIV-1. We present analyses comparing HIV-1 sequences isolated from foreskin DNA and serum RNA in 12 heterosexual men enrolled in an adult male circumcision trial performed in Rakai, Uganda. Phylogenetic analysis demonstrated three topologies: (1) little divergence between foreskin and serum, (2) multiple genetic bottlenecks occurring in both foreskin and serum, and (3) complete separation of foreskin and serum populations. The latter tree topology provided evidence that foreskin may serve as a reservoir for distinct HIV-1 strains. Distance and recombination analysis also demonstrated that viral genotypes in the foreskin might segregate independently from the circulating pool of viruses.
PMCID: PMC3380386  PMID: 21902587
5.  Molecular Epidemiology of HIV Type 1 in Singapore and Identification of Novel CRF01_AE/B Recombinant Forms 
AIDS Research and Human Retroviruses  2011;27(10):1135-1137.
To investigate HIV-1 molecular epidemiology in Singapore, we sequenced portions of three regions of the HIV-1 genome (protease HXB2: 2163 to 2620, gp120 HXB2: 6904 to 7628, and gp41 HXB2: 7817 to 8264) from 212 plasma samples collected between February 2008 and August 2009. From these samples, 109 (51.4%) generated interpretable data in all regions. Sixty-one (56.0%) were identified as CRF01_AE, 26 (23.9%) as subtype B and 14 (12.8%) as possible novel recombinant forms. The main novel recombinant pattern, detected in 13 sequences, had subtype B in protease and gp41 and CRF01_AE in gp120. There was intermixing of subtypes within transmission risk groups. However, 85% of subjects infected with the novel recombinant forms self-identified as men who have sex with men or bisexuals compared with only 41% of individuals infected with CRF01_AE and 62% infected with subtype B (p = 0.001).
PMCID: PMC3186691  PMID: 21235306
6.  Identification of HIV Superinfection in Seroconcordant Couples in Rakai, Uganda, by Use of Next-Generation Deep Sequencing ▿ †  
Journal of Clinical Microbiology  2011;49(8):2859-2867.
HIV superinfection, which occurs when a previously infected individual acquires a new distinct HIV strain, has been described in a number of populations. Previous methods to detect superinfection have involved a combination of labor-intensive assays with various rates of success. We designed and tested a next-generation sequencing (NGS) protocol to identify HIV superinfection by targeting two regions of the HIV viral genome, p24 and gp41. The method was validated by mixing control samples infected with HIV subtype A or D at different ratios to determine the inter- and intrasubtype sensitivity by NGS. This amplicon-based NGS protocol was able to consistently identify distinct intersubtype strains at ratios of 1% and intrasubtype variants at ratios of 5%. By using stored samples from the Rakai Community Cohort Study (RCCS) in Uganda, 11 individuals who were HIV seroconcordant but virally unlinked from their spouses were then tested by this method to detect superinfection between 2002 and 2005. Two female cases of HIV intersubtype superinfection (18.2%) were identified. These results are consistent with other African studies and support the hypothesis that HIV superinfection occurs at a relatively high rate. Our results indicate that NGS can be used for detection of HIV superinfection within large cohorts, which could assist in determining the incidence and the epidemiologic, virologic, and immunological correlates of this phenomenon.
PMCID: PMC3147722  PMID: 21697329
7.  Disulfiram Reactivates Latent HIV-1 in a Bcl-2-Transduced Primary CD4+ T Cell Model without Inducing Global T Cell Activation▿† 
Journal of Virology  2011;85(12):6060-6064.
Highly active antiretroviral therapy (HAART) can reduce plasma HIV-1 levels to below the detection limit. However, due to the latent reservoir in resting CD4+ cells, HAART is not curative. Elimination of this reservoir is critical to curing HIV-1 infection. Agents that reactivate latent HIV-1 through nonspecific T cell activation are toxic. Here we demonstrate in a primary CD4+ T cell model that the FDA-approved drug disulfiram reactivates latent HIV-1 without global T cell activation. The extent to which disulfiram reactivates latent HIV-1 in patient cells is unclear, but the drug alone or in combination may be useful in future eradication strategies.
PMCID: PMC3126325  PMID: 21471244

Results 1-7 (7)