As we approach elimination, it is important to understand persitance and extinction of gHAT infection in a population. Regional elimination rests on the dynamics and persistence at the village scale, therefore we have investigated this potential by developing a stochastic model of gHAT infection dynamics. A stochastic framework means chance events are directly captured and true elimination - when the infected population falls to zero - can be observed in model simulations.
The Warwick gHAT model, which is underpinned by screening and incidence data of gHAT in villages within Kwilu province, Democratic Republic of Congo, shows that in contrast to other commonly-studied infections, we predict the long-term persistence of gHAT. This is even true in small isolated populations, despite the low prevalence, indicating that rapid re-emergence of the disease is possible if not adequately controlled. In addition, we separate what it means to detect no gHAT cases and to have no gHAT infection in a population, by simulating the model to inform on probabilities of local elimination when failing to detect any cases on consecutive active screening events. These quantitative results provide insights for public health policy in this region, particularly highlighting the difficulties in achieving and measuring gHAT elimination.
The graph opposite shows the probability of elimination in a settlement, given consecutive zero-detections in active screenings with no detected passive cases in between. Each point represents a single settlement in the health zones Yasa-Bonga or Mosango, in the DRC, where the reported pattern of active screenings has been replayed in simulating the infection dynamics; the lines represent a weighted local regression fit. A case reporting rate of 26% is assumed in the points and solid lines, while the dashed and dotted lines show reporting rates of 0% and 100%, respectively.
Publication: Davis, CN, Rock, KS, Miaka, EM, Keeling, MJ (2019). Village-scale persistence and elimination of gambiense human African trypanosomiasis. PLoS neglected tropical diseases, 13(10), e0007838. doi:10.1371/journal.pntd.0007838