Serological evidence for Japanese encephalitis and West Nile virus infections in domestic birds in Cambodia

Mosquito-borne flaviviruses with an enzootic transmission cycle like Japanese encephalitis virus (JEV) and West Nile virus (WNV) are a major public health concern. The circulation of JEV in Southeast Asia is well-documented, and the important role of pigs as amplification hosts for the virus is long known. The influence of other domestic animals especially poultry that lives in high abundance and close proximity to humans is not intensively analyzed. Another understudied field in Asia is the presence of the closely related WNV. Such analyses are difficult to perform due to the intense antigenic cross-reactivity between these viruses and the lack of suitable standardized serological assays. The main objective of this study was to assess the prevalence of JEV and WNV flaviviruses in domestic birds, detailed in chickens and ducks, in three different Cambodian provinces. We determined the flavivirus seroprevalence using an hemagglutination inhibition assay (HIA). Additionally, we investigated in positive samples the presence of JEV and WNV neutralizing antibodies (nAb) using foci reduction neutralization test (FRNT). We found 29% (180/620) of the investigated birds positive for flavivirus antibodies with an age-depended increase of the seroprevalence (OR = 1.04) and a higher prevalence in ducks compared to chicken (OR = 3.01). Within the flavivirus-positive birds, we found 43% (28/65) with nAb against JEV. We also observed the expected cross-reactivity between JEV and WNV, by identifying 18.5% double-positive birds that had higher titers of nAb than single-positive birds. Additionally, seven domestic birds (10.7%) showed only nAb against WNV and no nAb against JEV. Our study provides evidence for an intense JEV circulation in domestic birds in Cambodia, and the first serological evidence for WNV presence in Southeast Asia since decades. These findings mark the need for a re-definition of areas at risk for JEV and WNV transmission, and the need for further and intensified surveillance of mosquito-transmitted diseases in domestic animals

Modelling Japanese encephalitis in Cambodia and predicting the consequences of its introduction to La Reunion Island

Malgré l'existence d'un vaccin, le virus de l'encéphalite japonaise (VEJ) reste la principale cause d'encéphalite humaine en Asie avec un taux de létalité pouvant atteindre 30%. Le cycle épidémiologique traditionnellement décrit de cette zoonose à transmission vectorielle est remis en question avec des preuves croissantes de l'implication de systèmes multi-hôtes plus complexes, dans les régions où les densités de porcs (principaux hôtes amplificateurs) ou d'Ardéidés (réservoir généralement décrit) sont faibles. Les porcs jouent un rôle central dans la transmission du VEJ mais des réservoirs secondaires comme les volailles pourraient exister et participer à la circulation du virus. Au Cambodge, le VEJ pourrait se maintenir dans un système multi-hôtes comprenant des porcs et des volailles comme hôtes compétents, mais aussi des chiens, des bovins et des humains comme hôtes non compétents. Nous avons développé un modèle dynamique de la transmission du VEJ dans un village traditionnel de la province de Kandal au Cambodge. Ce modèle a été calibré avec des données démographiques et sérologiques issues d'une enquête que nous avons réalisée en 2018 sur des porcs, des poulets et des canards, ainsi que des chiens dont les sérums avaient été prélevés lors d'une enquête précédente. Le modèle a permis d'analyser les variations du nombre de reproduction de base (R0), du taux d'incidence annuel des infections humaines et de l'impact clinique associé chez l'homme en fonction de la composition du système multi-hôtes. Dans le village modélisé, la circulation endémique du JEV pourrait être assurée par un système multi-hôtes complexe où les porcs domestiques sont essentiels à la persistance mais où les volailles pourraient agir comme réservoir secondaire. D'après les simulations, l'augmentation de la proportion d'hôtes compétents induisait une concentration des infections chez les enfants. Enfin, selon les prédictions du modèle, la probabilité annuelle d'exposition humaine était linéairement corrélée à la séroprévalence anti-VEJ canine, suggérant que dans notre zone d'étude, la séroprévalence anti-VEJ canine pourrait être un bon proxy de la probabilité annuelle d'exposition des hommes au VEJ. Les nombreux échanges commerciaux et humains dans l'Océan Indien font craindre une introduction du VEJ à l'île de La Réunion, où les vecteurs potentiels et les hôtes (compétents et non compétents) du VEJ sont présents et pourraient constituer un système multi-hôtes permettant la circulation du virus s'il venait à y être introduit. Nous avons adapté le modèle précédemment développé au contexte réunionnais afin d'analyser le risque de circulation du VEJ à La Réunion en cas d'introduction, en calculant des R0 autour des zones identifiées comme les plus à risque d'émergence : les élevages de porcs et leurs alentours. Le VEJ pourrait circuler au moins autour de certains élevages de porcs, et le risque d'introduction couplé au risque de circulation du VEJ le cas échéant, pose le problème d'une surveillance de l'EJ à La Réunion.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

Modélisation de l'encéphalite japonaise au Cambodge et prédiction des conséquences de son introduction à l'île de la Réunion

Malgré l'existence d'un vaccin, le virus de l'encéphalite japonaise (VEJ) reste la principale cause d'encéphalite humaine en Asie avec un taux de létalité pouvant atteindre 30%. Le cycle épidémiologique traditionnellement décrit de cette zoonose à transmission vectorielle est remis en question avec des preuves croissantes de l'implication de systèmes multi-hôtes plus complexes, dans les régions où les densités de porcs (principaux hôtes amplificateurs) ou d'Ardéidés (réservoir généralement décrit) sont faibles. Les porcs jouent un rôle central dans la transmission du VEJ mais des réservoirs secondaires comme les volailles pourraient exister et participer à la circulation du virus. Au Cambodge, le VEJ pourrait se maintenir dans un système multi-hôtes comprenant des porcs et des volailles comme hôtes compétents, mais aussi des chiens, des bovins et des humains comme hôtes non compétents. Nous avons développé un modèle dynamique de la transmission du VEJ dans un village traditionnel de la province de Kandal au Cambodge. Ce modèle a été calibré avec des données démographiques et sérologiques issues d'une enquête que nous avons réalisée en 2018 sur des porcs, des poulets et des canards, ainsi que des chiens dont les sérums avaient été prélevés lors d'une enquête précédente. Le modèle a permis d'analyser les variations du nombre de reproduction de base (R0), du taux d'incidence annuel des infections humaines et de l'impact clinique associé chez l'homme en fonction de la composition du système multi-hôtes. Dans le village modélisé, la circulation endémique du VEJ pourrait être assurée par un système multi-hôtes complexe où les porcs domestiques sont essentiels à la persistance mais où les volailles pourraient agir comme réservoir secondaire. D'après les simulations, l'augmentation de la proportion d'hôtes compétents induisait une concentration des infections chez les enfants. Enfin, selon les prédictions du modèle, la probabilité annuelle d'exposition humaine était linéairement corrélée à la séroprévalence anti-VEJ canine, suggérant que dans notre zone d'étude, la séroprévalence anti-VEJ canine pourrait être un bon proxy de la probabilité annuelle d'exposition des hommes au VEJ. Les nombreux échanges commerciaux et humains dans l'Océan Indien font craindre une introduction du VEJ à l'île de La Réunion, où les vecteurs potentiels et les hôtes (compétents et non compétents) du VEJ sont présents et pourraient constituer un système multi-hôtes permettant la circulation du virus s'il venait à y être introduit. Nous avons adapté le modèle précédemment développé au contexte réunionnais afin d'analyser le risque de circulation du VEJ à La Réunion en cas d'introduction, en calculant des R0 autour des zones identifiées comme les plus à risque d'émergence : les élevages de porcs et leurs alentours. Le VEJ pourrait circuler au moins autour de certains élevages de porcs, et le risque d'introduction couplé au risque de circulation du VEJ le cas échéant, pose le problème d'une surveillance de l'EJ à La Réunion

In silico Comparison of test-and-cull protocols for bovine tuberculosis control in France

Whole depopulation of cattle herds (WHD) confirmed infected by bovine tuberculosis (bTB) has led since the 1950s to a drop of herd incidence in France below 0.1% in 2000, justifying the current officially bTB free (OTF) status of the country. However, this protocol is expensive, ethically questionable, and difficult for breeders to accept because the number of confirmed animals in an infected herd is often very low. A test-and-cull protocol combining at least three screening sessions of the entire herd followed by the slaughter of all the non-negative animals has been used for some years. The aim of this work was to evaluate in silico the epidemiological effectiveness, the public costs and the acceptability to farmers of this test-and-cull protocol as well as of several ones. A stochastic compartmental model of within-herd bTB spread was used. Six test-and-cull protocols were compared: two versions of the official protocol and four alternatives with varying delays between screenings, and varying tests used. Protocols were simulated for an average French beef herd, and compared to WHD. Three key indicators were computed: the failure probability of the protocol (a failure being defined as an herd recovering its OTF status recovery while still infected, indicator of epidemiological effectiveness), its overall public cost and the percentage of farmers who would have dropped it to switch to WHD (indicator of acceptability to farmers). Failure probability ranged from 1.4 to 12.4% and was null (by definition) for WHD. The median cost varied between 2.7 and 78 K€ for the test-and-cull protocols, vs. 120 K€ for WHD. The percentage of dropout ranged from 7.8 to 22%. The optimal tradeoff between epidemiological effectiveness, public costs, and acceptability to farmers was obtained for protocols with an increased delay (6 months instead of 2 in the currently used protocol) between the last two screening sessions, with either 3 or 2 screening sessions. This study may help improving the official test-and-cull protocol applied in France under European Union regulation, by suggesting alternative protocols, very effective, cheaper, and more acceptable than WHD

Modelling Japanese encephalitis virus transmission dynamics and human exposure in a Cambodian rural multi-host system

International audienceJapanese encephalitis (JE) is a vector-borne zoonosis and the leading cause of human viral encephalitis in Asia. Its transmission cycle is usually described as involving wild birds as reservoirs and pigs as amplifying hosts. JE is endemic in Cambodia, where it circulates in areas with low pig densities (<70 pigs per km 2 ), and could be maintained in a multi-host system composed of pigs, but also poultry as competent hosts, and dogs, cattle and humans as non-competent hosts. We used a mathematical model representing Japanese encephalitis virus (JEV) transmission in a traditional Cambodian village that we calibrated with field data collected in 3 districts of Kandal province, Cambodia. First, R 0 calculations allowed us to assess the capacity of the epidemiological system to be invaded by JEV and sustain virus transmission in villages in the 3 districts, and we predicted human exposure at the epidemiological equilibrium, based on simulations. Changes in spatial density of livestock, in agricultural practices, and epizootics (e.g., African swine fever), can profoundly alter the composition of host communities, which could affect JEV transmission and its impact on human health. In a second step, we then used the model to analyse how host community composition affected R 0 and the predicted human exposure. Lastly, we evaluated the potential use of dog JE seroprevalence as an indicator of human exposure to JEV. In the modeled villages, the calculated R 0 ranged from 1.07 to 1.38. Once the equilibrium reached, predicted annual probability of human exposure ranged from 9% to 47%, and predicted average age at infection was low, between 2 and 11 years old, highlighting the risk of severe forms of JEV infection and the need to intensify child immunization. According to the model, increasing the proportion of competent hosts induced a decrease in age at infection. The simulations also showed that JEV could invade a multi-host system with no pigs, reinforcing the assumption of poultry acting as reservoirs. Finally, the annual human exposure probability appeared linearly correlated with dog seroprevalence, suggesting that in our specific study area, dog seroprevalence would be a good proxy for human exposure

Modelling the Potential Human Exposure to Japanese Encephalitis Virus (JEV) in Case of Introduction into Reunion Island

International audienceJapanese encephalitis virus (JEV) is a vector-borne zoonotic virus and the leading cause of human acute encephalitis in Asia. Continuous human and commercial exchanges between Southeast Asia where JE is endemic and Reunion Island increase the risk of introducing JEV on the island, where putative vectors of JEV such as Culex quinquefasciatus and amplifying hosts such as pigs are present. Each of the 255 Reunionese pig farms was assumed to harbor a Cx. quinquefasciatus population and, together with the competent hosts: pigs and poultry and noncompetent hosts: humans, dogs, and cattle, located within a radius of 1 km, formed an epidemiological unit. We used a deterministic compartmental model to investigate whether these epidemiological units could be invaded by JEV in the event of an introduction. Since the vector population size changes seasonally, we computed the basic reproduction number (R0) using vector population sizes ranging from 100 to 100,000 vectors for each of the 255 epidemiological units. The size of the potentially exposed human population was calculated in the case where the virus would be introduced in a single epidemiological unit and in the extreme case where the virus would have spread over the whole island. For a vector population of 1,000 vectors per unit, 2 out of 255 units had an R0 ≥ 1. With 50,000 vectors per unit, more than 75% (193/255) of the units had an estimated R0 ≥ 1, representing a median of approximately 2,500 potentially exposed people if JEV was introduced in a single unit, and about 140,000 potentially exposed people if JEV had expanded throughout the island. The unit located a few kilometers from the large port area of Reunion Island had an estimated R0 ≥ 1 with at least 10,000 vectors, making it a potential gateway to JEV given a virus introduction of infected vectors

Comparison of Japanese Encephalitis Force of Infection in Pigs, Poultry and Dogs in Cambodian Villages

International audienceJapanese encephalitis virus (JEV) is the main cause of human viral encephalitis in Asia, with a mortality rate reaching 30%, mostly affecting children. The traditionally described cycle involving wild birds as reservoirs, pigs as amplifying hosts and Culex mosquitoes as vectors is questioned, with increasing evidence of a more complex multi-host system involved in areas where densities of pigs are low, such as in Cambodia. In 2018, we examined pigs, chickens, ducks and dogs from Kandal province, Cambodia, for antibody response against JEV by hemagglutination inhibition and virus neutralization assays. Forces of infection (FOI) for flaviviruses and JEV were estimated per species and per unit of body surface area (BSA). JEV seroprevalence reached 31% (95% CI: 23–41%) in pigs, 1% (95% CI: 0.1–3%) in chickens, 12% (95% CI: 7–19%) in ducks and 35% (95% CI: 28–42%) in dogs. Pigs were most likely to be infected (FOI: 0.09 per month), but the FOI was higher in ducks than in pigs for a given BSA (ratio of 0.13). Dogs had a lower FOI than ducks but a higher FOI than chickens (0.01 per month). For a given BSA, dogs were less likely to be infected than pigs (ratio of 1.9). In Cambodia, the virus may be circulating between multiple hosts. Dogs live in close contact with humans, and estimating their exposure to JEV infection could be a relevant indicator of the risk for humans to get infected, which is poorly known due to underdiagnosis. Understanding the JEV cycle and developing tools to quantify the exposure of humans is essential to adapt and support control measures for this vaccine-preventable disease