Visceral leishmaniasis is an infectious disease which causes significant numbers of deaths in the Indian sub-continent every year. Kala azar, or “black fever”, as it is known, is characterized by fever followed by potentially severe symptoms such as a swollen spleen. Untreated it is believed to be almost uniformly fatal. Currently there is a large international effort to eliminate kala azar, but there is a need to consider strategies which will prevent a resurgence of infection when these controls are lifted.

Results published in Nature today suggest that reductions in time from when fever develops to diagnosis and effective treatment could be enough to reduce onward transmission and reduce the number of cases. Currently in Bihar state in northern India, it can take 90 days to be diagnosed, whereas diagnosis times are shorter in Bangladesh and Nepal, where incidence is also lower.

The research, which was a collaboration across four institutions, used mathematical models to investigate the dynamics of infection in areas with different diagnosis times and suggested that reducing time to diagnosis by weeks or months may be an effective control strategy. By using simple models, informed by the limited data available on this neglected tropical disease, we can get an understanding of the dynamics of transmission.

The analysis also highlighted the potential use of a new diagnostic that would identify infections early in their development, before serious symptoms. Even at a moderately low probability of detecting a case, this would have the potential to identify enough cases early enough to reduce transmission. However, the researchers also highlighted that such a diagnostic would have to be very specific to visceral leishmaniasis, otherwise there would be many false positives, particularly as cases of visceral leishmaniasis become rarer.