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Session 5
Oral Abstract Session
Epidemiology and Infection Control Session Time: Monday, 10 am - 12:30 pm Room 6C |
Methods: Phylogenetic trees were used to analyze the evolution of the subtype C epidemic. The year of origin of the African and Indian subtype C epidemics were estimated using methods refined by Korber et al. Results: Only a few African subtype C form clear subclusters and few inferences can be made from them. However, in Ethiopia the availability of a large number (>250) of samples from several cities has led to the identification of a distinct local subtype C sub-clade. The introduction of subtype C into Ethiopia was dated to the early 1980s, concordant with epidemiological data. The recent origin of this sub-epidemic may have contributed to the ease with which the Ethiopian sub-epidemic could be traced. In Asia, the subtype C epidemic shows clear epidemiological patterns. The variant that is spreading in India is distinct from all African sequences. Another sub-epidemic is seen in south-central China, driven by drug use and drug trafficking. A third distinct sub-epidemic, clearly branching off from the Indian subtype C, is currently invading Nepal. Reports of subtype C infections emanate from other countries surrounding the Golden Triangle (Myanmar, Vietnam, Thailand, Cambodia), but few subtype C sequences are available from those regions. Our estimate for the beginning of the Indian subtype C sub-epidemic is 1986 (95% CI 1973-1988), which is consistent with epidemiological data. The best estimate for the origin of subtype C in Africa (1933, 95% CI 1571-1967) is more problematic, because due to the scarcity of longer sequences from early strains it is heavily influenced by a few data points. More early samples are needed before a more stable estimate can be obtained. Conclusions: While in Africa the overall pattern in the subtype C epidemic appears to be chaotic, there are regions where distinct sub-epidemics can be identified. It is possible that patterns will emerge when the sampling density increases. The Asian epidemic is probably much younger (dating from the mid-1980s) and tracing the spread of the virus here appears to be very feasible. While the number of well-annotated sequences is small, increased awareness and interest in designing an appropriate vaccine should lead to a rapid accumulation of data. |
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©2002 9th Conference on Retroviruses and Opportunistic Infections |
