Background: AIDS is caused by infection with pathogenic strains of HIV-1 or 2. HIV-2 is broken into 9 groups, A-I. Groups A and B are epidemic in West Africa while the remaining groups are individual cases and are not known to be pathogenic. HIV-2F is an exception being both pathogenic and found in 2 persons, suggesting transmissibility. HIV's origins have been widely studied, however, questions remain. The simian ancestry of HIV is well established yet exactly how SIV adapted to HIV in humans is still unknown. Several theories have been put forth to explain HIV emergence from SIV including the serial passage theory of HIV emergence. Here we conduct an HIV survey in northern Sierra Leone (SL) to assess the public health threat of HIV-2F and also model the serial passage theory of emergence both in vivo and in vitro to elucidate mechanisms of adaptation.
Materials and methods: For the human HIV study in northern SL, we enrolled persons presenting for a voluntarily HIV test following education and outreach activities and those referred for an HIV test. This is a targeted, higher risk population than the general population. Commercial HIV-1/2 rapid tests were used in the field. Proviral DNA was amplified with PCR methods and sequenced with Sanger methods. Parallel pigtailed (PTM) and rhesus macaque in vivo and in vitro models were used to test the serial passage theory of HIV emergence. Virus was detected with an HIV-2F specific qPCR and commercial SIV p27 Antigen ELISA. Illumina methods were used to deep sequence day 3 samples with peak virus loads. A SNP analysis was conducted to investigate virus variation over serial passage.
Results: To date we have found the prevalence of HIV in the targeted sample population to be 6.36%. HIV-2 rates in the targeted sample were 0.50%, HIV-1 was 4.81% and apparent co-infections were seen in 1.06% of those tested. Two HIV-1 samples have been sequenced and typed to CRF02_AG. Attempts to PCR amplify proviral DNA from HIV-2 antibody positives were negative, possibly due to low virus load. In vitro, over serial passage, peak virus load decreased to undetectable, the opposite of what was expected. In fact, the in vitro serial passage results exactly contradict what was observed in a parallel in vivo serial passage experiment. In vivo we saw an increase in PVL over serial passage in the PTMs and viral escape in passages 2 and 3. SNP analysis showed mutations over serial passage allowing the virus to adapt to a new host in vivo.
Conclusion: In this study we asked two main research questions. First, is HIV-2F a public health threat? This question remains unanswered due to our inability to sequence the HIV-2 samples collected in this study. However, the samples remain preserved for applying different techniques. We described HIV burden in a self-selected, at risk population in northern Sierra Leone providing the first HIV-2 data in 20 years. We also provided the first HIV-1 sequence data from Sierra Leoneans living in Sierra Leone, all previous data are from SL immigrants to Europe or the USA. The second question was, can the serial passage hypothesis of HIV emergence be modeled to elucidate the role of serial passage in HIV cross-species transmission, adaptation and diversity? We successfully showed that this can be done through the in vivo serial passage experiment in pigtailed macaques. Together the data from the field studies along with the in vivo and in vitro models presented in this thesis provide a better understanding of mechanisms of HIV emergence as well as much needed information about HIV distribution and genetic diversity in northern Sierra Leone.
|Advisor:||Marx, Preston A.|
|Commitee:||Maness, Nicholas J., Oberhelman, Richard A., Schieffelin, John S., Wesson, Dawn D.|
|School:||Tulane University, School of Public Health and Tropical Medicine|
|School Location:||United States -- Louisiana|
|Source:||DAI-B 77/04(E), Dissertation Abstracts International|
|Subjects:||Health sciences, Public health, Virology|
|Keywords:||Disease emergence, HIV, Public health, Sierra leone, Tropical medicine|
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