Modelling Japanese encephalitis in Cambodia and predicting the consequences of its introduction to La Reunion Island
Author: Ladreyt, Héléna
Under the direction of: Benoît Durand and Véronique Chevalier
Paris 12 University
Texte français
Keywords: Epidemiology, Cambodia, Japanese encephalitis, Multi-host system, Cambodia, Reunion Island, Modeling, Infectious diseases - Mathematical models.
Abstract
Despite the existence of a vaccine, Japanese encephalitis virus (JEV) remains the leading cause of human encephalitis in Asia with a case fatality rate of up to 30%. The traditionally described epidemiological cycle of this vector-borne zoonosis is being challenged with increasing evidence of the involvement of more complex multi-host systems, in areas with low densities of pigs (the main amplifying host) or Ardeids (the commonly described reservoir). Pigs are central in JEV transmission, but secondary reservoirs such as poultry could exist and participate in virus circulation. In Cambodia, JEV could therefore be maintained in a multi-host system including pigs and poultry as competent hosts, but also dogs, cattle and humans as non-competent hosts (not able to infect back mosquitoes). We developed a dynamic model of JEV transmission in a traditional village in Kandal province, Cambodia. This model was calibrated with demographic and serological data from a survey we conducted in 2018 in pigs, chickens, and ducks, as well as dogs whose sera were collected during a previous survey. The model was used to analyze variations in the basic reproduction number (R0), the annual incidence rate of human infections, and associated clinical impact in humans as a function of the composition of the multi-host system. In the modeled village, endemic JEV circulation could be supported by a complex multi-host system where domestic pigs are essential for persistence but poultry could act as a secondary reservoir. Simulations indicated that increasing the proportion of competent hosts induced a concentration of infections in children. Finally, the model predicted that the annual probability of human exposure was linearly correlated with canine JEV seroprevalence, suggesting that in our study area, canine JEV seroprevalence may be a good proxy for the annual probability of human exposure to JEV. The extensive trade and human exchanges in the Indian Ocean raise concerns about the introduction of JEV to La Reunion Island, where potential vectors and hosts (competent and non-competent) of JEV are present and could constitute a multi-host system allowing the circulation of the virus should it be introduced. We adapted the previously developed model to the Reunion context in order to analyze the risk of circulation of JEV in case of introduction, by calculating R0 around the areas identified as the most at risk of emergence : pig farms and their surroundings. JEV could circulate at least around some pig farms, and the risk of introduction combined with the risk of JEV circulation, raise the question of JE surveillance in La Reunion.
