How much does direct transmission between pigs contribute to Japanese Encephalitis virus circulation? A modelling approach in Cambodia

PLoS One. 2018 Aug 16;13(8):e0201209. doi: 10.1371/journal.pone.0201209. eCollection 2018.

Abstract

Japanese Encephalitis (JE) is the most important cause of human encephalitis throughout Asia and the Pacific. Although JE is a vector-borne disease, it has been demonstrated experimentally that transmission between pigs can occur through direct contact. Whether pig-to-pig transmission plays a role in the natural epidemiological cycle of JE remains unknown. To assess whether direct transmission between pigs may occur under field conditions, we built two mathematical models of JE transmission incorporating vector-borne transmission alone or a combination of vector-borne and direct transmission. We used Markov Chain Monte Carlo (MCMC) techniques to estimate the parameters of the models. We fitted the models to (i) two serological datasets collected longitudinally from two pig cohorts (C1 and C2) during two periods of four months on a farm on the outskirts of Phnom-Penh, Cambodia and to (ii) a cross-sectional (CS) serological survey dataset collected from 505 swine coming from eight different provinces of Cambodia. In both cases, the model incorporating both vector-borne and direct transmission better explained the data. We computed the value of the basic reproduction number R0 (2.93 for C1, 2.66 for C2 and 2.27 for CS), as well as the vector-borne reproduction number Rpv and the direct transmission reproduction number Rpp. We then determined the contribution of direct transmission on R0 (11.90% for C1, 11.62% for C2 and 7.51% for CS). According to our results, the existence of pig-to-pig transmission is consistent with our swine serological data. Thus, direct transmission may contribute to the epidemiological cycle of JE in Cambodia. These results need to be confirmed in other eco-climatic settings, in particular in temperate areas where pig-to-pig transmission may facilitate the persistence of JE virus (JEV) during cold seasons when there are no or few mosquitoes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Basic Reproduction Number / veterinary
  • Cambodia / epidemiology
  • Culex / virology
  • Encephalitis Virus, Japanese / immunology
  • Encephalitis, Japanese / epidemiology
  • Encephalitis, Japanese / transmission
  • Encephalitis, Japanese / veterinary*
  • Humans
  • Markov Chains
  • Models, Biological
  • Monte Carlo Method
  • Mosquito Vectors / virology
  • Seroepidemiologic Studies
  • Sus scrofa
  • Swine
  • Swine Diseases / epidemiology
  • Swine Diseases / transmission*

Grant support

This work was funded by CIRAD, Institut Pasteur de Paris, ComAcross project (www.onehealthsea.org/comacross) and Institut Pasteur du Cambodge. The salary of our PhD student, AO Diallo, was granted half by CIRAD, half by Institut Pasteur de Paris. Other costs were funded by ComAcross and Institut Pasteur du Cambodge (www.onehealthsea.org/comacross) project. SEAe project https://www.grease-network.org/main-projects/on-going/seae) funded the collection of pig incidence data (published in Cappelle et al). The specific roles of these authors are articulated in the ‘author contributions’ section.