LSTM Seminar Series: Why the details of heterogeneities in pathogen load and transmission matter for policy design

News article 18 Jun 2013
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LSTM’s seminar series continued today with a presentation by Dr Deirdre Hollingsworth, Deirdre joined LSTM in January 2013 as a joint appointment between LSTM and the University of Warwick (UoW).  Dr Hollingsworth works within LSTM’s Centre for Applied Health Research and Delivery(CAHRD) as an infectious disease modeller who uses mathematical and statistical methods to inform the design of more effective control programmes, for HIV and soil transmitted helminths (STH).

The presentation contained previous and ongoing research on estimating transmission rates for HIV and the implications for control, as well as work on the design of intervention programmes for STH in the current era of large-scale availability of treatments.

Research on estimating transmission rates for HIV, both in early infection and due to variability of viral load in later infection, has been highly cited and influential in HIV control policy. Large scale treatment can reduce transmission; however within that approach there are other factors to consider. For example, people with high viral loads have high transmission rates, infecting more people in a shorter timeframe, as their life expectancy is reduced. While people with low viral loads are less infectious, they will live longer and so over time may infect just as many people. Targeting people with intermediate viral loads may in fact be a more effective approach in reducing transmission. Targeting a particular load transmission group for treatment raises ethical concerns around the rights of the individual compared to a longer-term view of a wider population.

Dr Hollingsworth has been looking at new ways of estimating transmission rates from existing data. Her publications in this area are focussed on the dynamics of HIV in both sub-Saharan Africa and the northern hemisphere. The estimates from this research are directly informing the design of treatment programmes.

STH affect up to 1.2 billion people each year, with an annual death toll of 135,000. The question of how you maximise the impact of the drugs donated for treatment. STH are transmitted by eggs present in human faeces which in turn contaminate soil in areas where sanitation is poor. The eggs are ingested and in the case of many children, roundworms grow inside the body. Drug treatment (de-worming) is required and this tends to take place within schools. These children will need to be treated repeatedly due to the risks of reinfection from the environment. The impact of this repeated treatment in children is often measured, but the effect on the wider community is rarely studied. If you are only measuring impact on the people you are studying, then you will get a false impression of the wider population.

More recent work on the dynamics of STH is focussed around understanding the drivers of the speed and extent of ‘bounce-back’ in infections following a drop in infections due to mass treatment. An understanding of these processes allows researchers to address the policy question of who to treat and how often to treat to get the biggest impact.

Dr Hollingsworth is working with LSTM’s Professor Bertie Squire within CAHRD, developing methods for policy makers to understand and interpret the dynamics of epidemics. The presentation stimulated plenty of questions in relation to both HIV and STH from staff across LSTM. Professor Squire thanked Dr Hollingsworth for a fascinating seminar.