Using HIV transmission patterns to design effective public health interventions

Thirty years after its emergence in the West, the global HIV pandemic is still a pressing public health concern. In many countries, infection with HIV still carries a significant stigma, which creates barriers that prevent infected individuals from accessing available treatment options.

In an ideal world, we would be able to design a ‘one size fits all’ approach to HIV prevention that would work for everyone. Sadly, HIV has such a vast spread that this simply isn’t possible. To make things even more complicated, HIV transmission follows different patterns in different regions around the world. These transmission patterns can vary from a local network of injecting drug users in a small town to country-specific networks that encompass different exposure routes, changing immigration patterns and changing behaviours in different population groups.  For example, the traditional picture of HIV infections in the UK showed two parallel epidemics. There was the epidemic seen in the men who have sex with men population, which was comprised of infections mainly acquired in the UK from other men who have sex with men, and there was the heterosexual epidemic, which was mainly composed of people who acquired their infections outside of the UK. In recent years, however, these patterns have been changing, and the current situation is that more HIV infections are acquired in the UK than abroad. When you couple this information with the knowledge that the rates in HIV infection are rising again after many years of decline, it becomes apparent that we need to understand how these transmission patterns are changing so that we can design effective public health interventions.

The HIV virus changes and mutates very easily, which is one of the reasons that it has proved so difficult to eradicate. However, this very plasticity offers us ways to understand regionally-specific transmission networks. One of the ways in which the virus can change is through a process known as recombination, in which different strains of the virus merge to form a new variant. If the new variant is transmitted to enough people, it is termed a circulating recombinant form (CRF) and named using the two parental types of virus e.g. A/B. By using DNA sequencing to characterise these new strains as they emerge, we can increase our understanding of local HIV transmission patterns.

Our project was performed in conjunction with the UK HIV Drug Resistance Database and involved characterising one such new strain of HIV, known as CRF50_A1D. We found that this strain emerged in Britain in the early 1990s and has been transmitted among men who have sex with men, heterosexual men and women and injecting drug users. Geographically, our investigation suggested that the strain was originally imported into the UK, and is most closely related to strains of HIV found in East Africa. We plotted the path of the virus across the UK using Google Earth and found that the strain emerged in Northwest England before spreading to London, which is where the greatest number of transmissions occurred; however, Northwest England remained the source of spread to regions such as Northeast England, Southwest England and Scotland.

In total, we identified 72 instances of this strain of HIV in the UK. Although the numbers seem small, identifying Northwest England as the source for spread to other regions of the UK suggests that there is scope for further research examining transmission patterns in this region. Should the results show that this region is significantly involved in national HIV transmission trends, public health interventions could be usefully targeted to this region. Extending these types of studies to countries in the developing world would allow the design and implementation of HIV prevention initiatives where they are most needed.

By Geraldine Foster – HEART Research Officer and Liverpool School of Tropical Medicine Research Co-ordinator

NB –  All information used in this study was anonymised to prevent the identification of individuals.

References and suggested further reading

Foster et al., 2014. Novel HIV-1 Recombinants Spreading across Multiple Risk Groups in the United Kingdom: The Identification and Phylogeography of Circulating Recombinant Form (CRF) 50_A1D.

HPA 2013, HIV in the United Kingdom: 2013 report. Health Protection Agency


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