Antiretrovirals could stop HIV epidemic – optimism or realism?

Widespread use of currently available antiretrovirals could reduce the HIV epidemic, a group of mathematicians claims, but their paper may open a debate on the value of mathematical models in predicting disease trends.

Treatment of HIV infection with antiretroviral agents can increase the life expectancy of HIV-positive individuals. However, the impact of drugs on the HIV epidemic is hard to measure since any reduction in transmission of HIV resulting from lower plasma levels of the virus may be off-set by increases in risky behaviour. A study published in The Lancet Infectious Diseases this month attempts to weigh up the risks and benefits of treatment at the epidemic level, using a mathematical equation.

Velasco-Hernandez and colleagues, working in the San Francisco gay community, calculated the average number of new infections generated by one HIV case during his lifetime. The probability that sexual transmission of HIV occurs during a sexual partnership, the average number of new sexual partners, and the average duration of infectiousness, were all taken into account. Antiretrovirals were assumed to be available for all individuals, and strains resistant to these drugs were able to evolve and be transmitted.

The authors conclude that even in a high-prevalence epidemic, HIV could be eradicated using currently available antiretrovirals. If risky sexual behaviour decreased, the average number of new infections generated by each HIV-positive individual would be less than one, meaning that the epidemic would eventually peter out.

Some may decide to take the results of the equation with a pinch of salt because the assumption made by Velasco-Hernandez and colleagues – that antiretroviral treatment lowers the amount of virus in the bloodstream by at least half, and up to 100-fold – may not be realistic. Similarly, the supposition that drug resistant strains of HIV will be less infectious needs to be verified in clinical practice.

Despite these potential flaws, the overall message from the study is that the use of antiretroviral agents should be tightly coupled with effective behavioural strategies to reduce the risk of transmission, a claim that even the most hardened critic could not challenge.