Recognising the HIV
sdfhindia Updated: Dec 01, 2003 18:55 IST
There are two types of AIDS virus: HIV-1 and HIV-2. The predominant virus is HIV-1. Though the transmission route and the clinical symptoms of both strains are the same, but HIV-2 is less easily transmitted, and the period between initial infection and illness is longer. HIV-1 is the common strain in India.
HIV-1 subtype mutates easily and has many strains, which are classified in groups and subtypes. The basic difference between the subtypes is their genetic composition. Routine HIV antibody tests used for blood screening and diagnostic purposes detect all subtypes of the HIV.
There are two groups, M and O. In 1998, French researchers discovered a new strain of HIV in a woman from Cameroon in West Africa. The strain does not belong to either group M or group O, and has only been found in only three other people in the Cameroon.Within group M, there are at least 10 genetically distinct subtypes of HIV-1.
THE DISTRIBUTION OF SUBTYPES
In the predominant M group of HIV-1, 10 subtypes A through J have been identified to date. While most subtypes are found in different regions of Africa, three strains - B. C and E - predominate the rest of the world.
Subtypes A and D: Sub-Saharan Africa
Subtype B: Europe, North, Central and South Americas, Australia, New Zealand, Japan and the Caribbean. This subtype is spread more easily through homosexual contact, but a people have been infected through heterosexual contact in Europe, countries of the former Soviet Union, Indonesia, the Philippines and Taiwan. This subtype is also found in small numbers in drug users in India, Myanmar, Malaysia and southeast China.
Subtype C: This is the dominant strain in South Africa and India, which also has a sprinkling of A and B infections. Brazil also has some strains of subtype C.
Subtype E: Predominant in Thailand and other south-east Asian countries, and central Africa.
Others: These are the low prevalence strains whose distribution is are largely localised so far. Subtypes F (Brazil and Romania), G and H (Russia and Central Africa), I (Cyprus), and group O (Cameroon).
A Harvard School of Public Health study demonstrated that subtypes C and E infect and replicate more efficiently than subtype B in cells present in the vaginal mucosa, cervix and the foreskin of the penis but not on the wall of the rectum. This suggests that subtypes C and E have a higher potential for heterosexual transmission than subtype B.
First Published: Dec 01, 2003 18:55 IST