HAT tip: researchers map African sleeping sickness

Above: One of the maps produced by the study. The map shows the distribution of HAT risk in Congo, with five deepening shades of colour representing five categories of risk from ‘very low’ to ‘very high’.

In the 1960s, we very nearly eliminated ‘Sleeping Sickness’, known today as Human African trypanosomiasis (HAT) (1). But in the latter half of the 20th Century there was a marked resurgence, and although cases are now falling once again, an estimated 70 million people are still thought to be at risk (2).

Knowing exactly how many people have the disease, or are at risk of contracting it, is difficult, as cases tend to be concentrated in areas with little or no access to health services. But researchers from the World Health Organization (WHO), the United Nations and Edinburgh University, have been working to map the levels of HAT risk in affected populations in sub-Saharan Africa. Their study, published in October 2012, provides both a striking visual representation of the reach of HAT and a mine of information for those working to eliminate the disease.

HAT is one of 17 neglected tropical diseases identified by the World Health Organisation. The disease, which is unique to Africa, is caused by two sub-species of the blood parasite Trypanosoma and is transmitted to both animals and humans by the bite of the tsetse fly. In its advanced stages it causes neurological disorders and, if left untreated, is ultimately fatal.

Advances in GPS technology have prompted the development of new methodologies to map the risk of disease. In 2011, as part of the WHO’s Programme to Eliminate Sleeping Sickness, scientists pioneered a way of combining epidemiological data with human population figures. The result was a series of maps showing estimated levels of HAT risk in six Central African countries. Now, the same team of researchers has applied this methodology at a continental level to all HAT endemic countries.

The researchers combined data on sleeping sickness cases from the latest Atlas of HAT report with that from Landscan™ databases on how the population is distributed across sub-Saharan Africa. Based on the resulting maps, they estimate that an area of 1.55 million square kilometres – that’s six times the size of the United Kingdom – is at some risk of HAT.

When tackling disease on this scale, the ability to accurately target appropriate response to different areas according to how they are affected is a great advantage. The maps clearly show, for instance, that the Democratic Republic of the Congo is the country with both the highest number of people at risk and the largest at-risk area, accounting for half of the total population at risk of HAT.

The maps could also allow us to target interventions according to the level of risk in a given area: “intensive control measures” for the 21 million people at moderate to very high risk, “cost-effective and adapted measures” to control infection in areas where there the risk of infection is low.

As well as informing their action on the ground, the bold, colourful maps could help the WHO to raise awareness of disease risk and garner support for their Programme. If regular updates can be made using the latest data, these maps will be a useful tool for those who are working to monitor, control and eradicate the disease.

References

(1) The WHO Programme to Eliminate Sleeping Sickness:
Building a Global Alliance Ref: WHO/CDS/CSR/EPH/2002.13

(2) Pere P.Simarro et al. (2012). Estimating and Mapping the Population at Risk of Sleeping Sickness. PLOS Neglected Tropical Diseases 6 (10) PMID: 23145192