Date: Fri, 19 May 1995 11:40:14 +0500
From: ghmcleaf{CONTRACTOR/ASPEN/ghmcleaf}%NAC-GATEWAY.ASPEN@ace.aspensys.com
Subject: CDC Nat. AIDS Hotline Train. Bull. #136


           CENTERS FOR DISEASE CONTROL AND PREVENTION
                       HIV/AIDS PREVENTION
           CDC NATIONAL AIDS HOTLINE TRAINING BULLETIN
.................................................................
April 25, 1995                                              #136

These are answers from the Centers for Disease Control and
Prevention (CDC) to questions submitted by the CDC National AIDS
Hotline concerning strains of HIV.

NAH Questions:

There has been considerable press coverage about the possibility
that HIV strains from Africa and Asia are spread more easily
through heterosexual contact than North American/European strains
of HIV.  What does CDC know about this report?  What are the
differences among the terms subgroup, subtype, strain, and
variant when referring to HIV?

CDC Response:

The terms subgroup, subtype, strain, and variant, when used in
reference to HIV, have never been formally defined by CDC.
However, subgroup is not a term that is commonly used in HIV
terminology.  Strain and variant are generic words that are often
used to refer to individual viruses (HIV) either within a person
or within a subtype.  The word, subtype (or clade) refers to
phylogenetically distinct strains of HIV.  There are several
different subtypes found throughout the world.  They are
designated by upper case letters, approximately in alphabetical
order according to when they were identified (e.g., the most
recently discovered is subtype O).

A recent report suggested that if strains found in countries
where heterosexual transmission is commonly reported were
introduced into the United States, the heterosexual epidemic
would be accelerated here.  A researcher theorized that some
subtypes are more easily transmitted than others.

It is not known whether subtypes of HIV play a role in
facilitating any particular mode of transmission.  CDC studies
are underway in Thailand to look at the rates of transmission of
different subtype viruses from infected injecting drug users to
their sex partners.  These studies will take some time, and we do
not know when any results from these studies will be available.

Many biologic and behavioral factors appear to contribute to the
rapid spread of HIV in heterosexual populations in Africa and
Asia.  CDC does not believe that the introduction of other HIV
subtypes into the United States would be the major determinants
of the course of the heterosexual epidemic in this country.

The same measures that prevent transmission of HIV-1 subtype B
(the major subtype circulating in North America) also prevent all
other HIV-1 subtypes as well as HIV-2 and other sexually
transmitted diseases.