Tracking a scourge

HIV-1 and HIV-2 are the two main types of the virus. While new subtypes for HIV-1 are being constantly discovered, the dominant ones are subtype A in sub-Saharan Africa; subtype B in the Americas, Japan, Australia, the Caribbean and Europe; subtype C in India, South Africa, Brazil and China; subtype E in Central Africa, Thailand, North-east India and South-east Asia. HIV-2 with five subtypes is prevalent mostly in sub-Saharan and West Africa.

Though HIV-1 subtype C is the dominant virus in India—involved in 85 per cent of cases—other subtypes of HIV-1 (including a recombinant B subtype known as the Thai variety) and HIV-2 infections have been detected in India. ‘‘Viral subtypes are like human races. As various human races differ from one another in small details but still belong to the same species, HIV strains also differ from one another at genetic or molecular levels yet retain their viral identity,’’ says Dr Udaykumar Ranga, head, molecular virology department at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) in Bangalore.

Over the past two years, Ranga and his colleagues have been trying to establish what sub-type of HIV is spreading in the south. ‘‘The need for such analysis is more pronounced for countries like India where the interplay between the genetics of a host and the virus is least explored. There is also a need to understand the socio-economic factors involved in the differences in distribution of virus subtypes,’’ says Ranga.

The JNCASR studies have found that the majority of infections in south India involve the HIV-1 subtype C virus. The researchers have also found a small but perturbing emergence for a new subtype that is a combination of the B and C subtypes. In two separate studies of infected people in 35 towns and cities in Andhra Pradesh, Karnataka, Kerala and Tamil Nadu, the researchers looked at the molecular signatures of over 350 HIV samples. In one study involving 256 samples the researchers found that the A, B and B-C combination type popped up in three of the samples with the remainder all being the C subtype.

In the second study of around 115 samples the researchers found a predominance of subtype C infection and three of B-C combination type. To the surprise of the researchers two of the three B/C recombinants found were similar to subtype B strains reported from USA. ‘‘Subtype C has been documented since the early days of the epidemic in India, the reason is not known. Now the determination of the real incidence of the recombinant viruses is also of importance,’’ says Ranga who now hopes to carry out a nationwide study to look at the pattern of HIV subtype spread. ‘‘No evidence linking genetic subtypes with differences in disease progression is available, but the link cannot be ruled out. Subtype differences are also expected to impact strongly on the efficacy of a vaccine and are relevant to resource-poor countries,’’ he says.