All about HIV Types, Subtypes, Groups and Strains
I often get questions from people worried about having some ‘strange strain’ of HIV that cannot be picked up by tests.
Let’s take a step back and try to understand all this rather confusing terms of Types, Subtypes, Groups and Strains of HIV and see if it can shed any light on such concerns.
Scientist love to categorize things into neat little boxes. This is no different for living things. The science of taxonomy is an interesting one. Lets starts with viruses. We all know what viruses are. There are many different Families of viruses. What we are interested in is the Family Retroviridae. In this family, we further sub classify into Sub-Families like Orthoretroviridae. Which we then sub classify into Genus like Lentivirus and again into Species like the Primate Lentivirus Group. Into this neat little box that we have made, lies the HIV virus. i.e. HIV = Family Retroviridae, Sub-Family Orthoretroviridae, Genus Lentivirus, Species Primate Lentivirus Group. The Simian Immunodeficiency Virus also fits into this box but this is just trivia.
There are 2 Types of HIV, Type 1 and 2. They are similar in many ways except for geographical distribution, ease of transmission and speed of disease progression. HIV type 1 is further classified into Groups (M, N, O, P) and subtypes (A, B, C, D, F, G, H, J, K, CRFs). CRF is an acronym that stands for Circulating Recombinant Forms. They are basically products of different HIV subtypes combining together. HIV is classified as such according to their genetic makeup.
So aside from an overwhelming level of complexity that gives scientists a really big kick; what exactly is the use of classifying HIV down to such a degree? The real difference it makes is in people who live with the HIV virus. Knowing exactly the type, group and subtype of HIV we are dealing with makes a big difference in treatment and monitoring.
But what does it mean for people who do not have HIV? Or who have been exposed to HIV and are testing for it? The fact is types, groups and subtypes of HIV are rather geographically distinct. Knowing which predominates in a particular area will help policy makers decide on the appropriate HIV screening tools. Thankfully, most modern tests are able to pick up all forms of HIV. Our clinic uses the Determine and Oraquick rapid tests which are able to test for both HIV Type 1 and 2 and even the dreaded Type 1 O Group.
Although it looks all neat and nice now, the fact remains that science is an ever changing field. No doubt there will be more discoveries of new subtypes and CRFs. We can only hope that testing technology will be able to keep up.
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About Dr. Tan
Dr. Tan graduated from the National University of Singapore in 2001. His residency was in the two largest public hospitals in Singapore; Tan Tock Seng Hospital and Singapore General Hospital.