Skip to main content Skip to navigation

Infection reservoirs/ Réservoirs d'infection

Assessing evidence for animal reservoirs that contribute to transmission of gHAT in the DRC

Support for the model with or without animals contributing to the transmission of gHAT

With gHAT targeted for elimination of transmission (EoT) to humans by 2030 there remain fundamental questions about the presence of non-human animal transmission cycles and their potential role in slowing progress towards, or even preventing, EoT. In this study we used two model variants, one with and one without animal transmission, to assess whether animals contribute to transmission in specific regions of the DRC, and if so, how their presence could impact the timing of EoT. We conclude that there are 24/158 health zones where there is moderate or high support for some animal transmission, however, even in these regions, we estimate that animals would be extremely unlikely to maintain transmission on their own. Animal transmission could hamper progress towards EoT in some settings, with projections under continuing interventions indicating that the number of health zones expected to achieve EoT by 2030 reduces from 68 to 61 if animals are included in the model. With supplementary vector control added to medical screening and treatment interventions, the expected number of health zones meeting the goal increases to 147 for the model including animals due to the impact of vector reduction on transmission to and from all hosts.

Click here to view our infographic.

Forthcoming paper: Crump RE, Huang C-I, Spencer SEF, Brown PE, Shampa C, Mwamba Miaka E & Rock KS (2021) Modelling to infer the role of animals in gHAT transmission and elimination in DRCLink opens in a new window PLOS Neglected Tropical Diseases Paper summaries: EnglishLink opens in a new window, FrenchLink opens in a new window

Potential impact of asymptomatic human infections on gHAT transmission

There is evidence of asymptomatic human gHAT infection but there is uncertainty around the role it plays in overall transmission and maintenance. To study this challenge, we developed a novel model by extending our established baseline framework for gHAT to account for asymptomatic infections including those in people with blood-dwelling trypanosomes, without discernible symptoms, and those with parasites only detectable in skin. Our new model adds extra parameters to the baseline model including different self-cure, recovery, transmission rate from skin-only infections, and the proportion of exposures resulting in initial skin or blood infection. Performing sensitivity analysis suggests the new parameters introduced in the asymptomatic model can impact the infection dynamics substantially. For some plausible parameterisations, an initial fall in infection prevalence - due to screening and treatment interventions - could subsequently stagnate even under continued screening due to the formation of a new, lower endemic equilibrium. Excluding this scenario, our results still highlight the possibility for asymptomatic infection to slow down progress towards elimination of transmission. Location-specific model fitting will be needed to determine if and where this could pose a threat.