Internationally Recognized Program Tracks Emerging HIV Strains

Although most of us might think that AIDS results from just one type of human immunodeficiency virus (HIV), there are actually a number of different strains of the virus.

In Canada, HIV-1 subtype B is the predominant strain. However, other strains have been reported and likely will continue to emerge - both through genetic mutation, and travel and migration from other countries.

Health Canada's Canadian HIV Strain and Drug Resistance Surveillance Program (CHSDRSP) monitors the frequency and distribution of the different strains and drug resistance patterns of the HIV virus.

The Program is recognized around the world as an effective approach to HIV strain and drug resistance surveillance. In fact, Health Canada's CHSDRSP has one of the world's most complete databases on HIV strains. The data are cited by many researchers and public health institutions, and the surveillance model is being copied by a number of health institutions worldwide, including the Centers for Disease Control and Prevention in Atlanta, Georgia.

The kind of work done by CHSDRSP to identify HIV strains and drug resistance is important for a number of reasons.

• Informing Vaccine Development: One of the most important reasons for monitoring HIV genetic variability is to inform vaccine development. The majority of vaccines in clinical trials were developed using strains of HIV-1 subtype B. However, it is unclear whether these vaccines are effective with other subtypes of the virus.
• Assessing Drug Resistance: There is concern that the widespread use of HIV drugs could result in drug-resistant viruses. CHSDRSP monitors drug resistance in different regions and in different populations; it also tracks changes in resistance over time.
• Enhancing the Safety of the Blood Supply: Blood tests must be able to detect all strains of HIV. For example, when HIV-2 and new strains of HIV-1 were discovered, blood tests needed to be adapted so that they could detect these new strains.
• Determining HIV Transmission and Progression: It is still uncertain whether differences in HIV strains affect transmission or progression of HIV. Knowing the distribution of HIV strains in Canada can help identify appropriate prevention and treatment strategies related to these questions.

Epidemiology Meets Laboratory Science

Health Canada's Canadian HIV Strain and Drug Resistance Surveillance Program has two components: laboratory-based genetic information and epidemiologic information. (Epidemiology is the study of the frequency and distribution of a disease)

The Program relies heavily on collaboration with the provinces and territories. They provide an essential contribution to the Program by sending serum samples from patients newly diagnosed as HIV positive.

The identity of the patient is removed and each sample is provided with a code so that no individuals can be identified. In this way, the patients remain completely anonymous. This is an essential aspect of the program.

The sample is then sent to the National Laboratory for HIV Genetics in Ottawa. Through sophisticated genetic analysis, the specific HIV strain is identified.

Multiple copies of the HIV genes are made and then the virus is sequenced. Once the sequence is determined, it is compared with all known sequences to identify the specific strain. This process also allows the researchers to match the samples for mutations which have already been linked to drug resistance.

Meanwhile, epidemiological data are recorded for each sample, such as the gender, age and ethnicity of the patient from whom the sample was taken. Together with the strain information identified in the lab, Health Canada is able to monitor the patterns of strain prevalence and drug resistance.

What We've Found So Far

• In Canada, the predominant strain of HIV virus is HIV-1 subtype B. However, other strains have been identified.
• Significantly higher proportions of other strains (non-subtype B) were detected in females, in those reporting heterosexual contact as their primary exposure factor, and in those of Black, Asian or mixed ethnicities.
• The prevalence of other strains varies according to geographic location. This is probably due to travel and migration from countries where other subtypes predominate.
• In the Canadian population, drug resistance to at least one antiretroviral drug is 7.1%.

As the Surveillance Program continues, knowledge about HIV strains will be useful in the development of effective vaccines. It will help Health Canada monitor the spread of the disease and ensure that all circulating strains are adequately detected. The Program's ongoing study of drug resistance will be useful for developing initial treatment options appropriate to different populations. It will also help us better understand the process of HIV transmission.