Search

Introduction & Objectives: The canine population is remarkably abundant in Malagasy communities, with the majority of dogs roaming freely without any restriction. Given the country's limited investment in the health sector, this study aims to investigate dogs as indicators of potential zoonotic pathogen circulation, contributing to the enhancement of early warning systems. Rift Valley fever virus (RVFV) and West Nile virus (WNV) were considered as first models. Methodology: Blood samples were collected from dogs in the Ifanadiana and Fianarantsoa I districts and analysed at the Virology Unit of the Institut Pasteur de Madagascar. ID Screen WNV ELISA Competition Multi-species kit was used for the detection of antibodies directed against Flaviviruses and ID Screen RVFV ELISA Competition Multi-species kit for the detection of antibodies directed against RVFV. A first identification of factors influencing dogs' exposure to these pathogens was then carried out using logistic regression. Results: These screenings revealed a flavivirus seroprevalence of 56.55%, significantly higher in rural areas (410/577) than in urban areas (56/247): p = 2.2e-16. RVFV seroprevalence was 3.39%, notably higher in rural areas (27/578) than in urban ones (1/247): p = 0.001. Dogs' exposure to these pathogens increased with age, suggesting an endemic transmission. Further serological analysis based on Luminex technology will enable to distinguish results specific to WNV from other flaviviruses. Furthermore, calculating force of infection and comparing the results with human serological data in the same study area will enable to assess dogs' utility as sentinel animals for monitoring these zoonotic pathogens.

Japanese 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.

Japanese 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 km2), 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, R0 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 R0 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 R0 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 poult

Rift Valley fever (RVF) is a zoonotic disease caused by a virus mainly transmitted by Aedes and Culex mosquitoes. Infection leads to high abortion rates and considerable mortality in domestic livestock. The combination of viral circulation in Egypt and Libya and the existence of unregulated live animal trade routes through endemic areas raise concerns that the virus may spread to other Mediterranean countries, where there are mosquitoes potentially competent for RVF virus (RVFV) transmission. The competence of vectors for a given pathogen can be assessed through laboratory experiments, but results may vary greatly with the study design. This research aims to quantify the competence of five major potential RVFV vectors in the Mediterranean Basin, namely Aedes detritus, Ae. caspius, Ae. vexans, Culex pipiens and Cx. theileri, through a systematic literature review and meta-analysis. We first computed the infection rate, the dissemination rate among infected mosquitoes, the overall dissemination rate, the transmission rate among mosquitoes with a disseminated infection and the overall transmission rate for these five mosquito species. We next assessed the influence of laboratory study designs on the variability of these five parameters. According to experimental results and our analysis, Aedes caspius may be the most competent vector among the five species considered.

Background and objectives: Rabies is endemic in Cambodia where the transmission chained is maintained in free-roaming owned dogs. Due to the current lack of national vaccination program, there is a need to inform authorities on the best strategies for implementation. Recent pilot vaccination campaigns have surveyed the canine population of several Cambodian villages and collected detailed demographic information. We aimed to model the impact of population turnover on vaccination coverage and the effectiveness of different levels of annual vaccination drives on rabies transmission using locally specific dog demography data. Methods: We used demographic and spatial data from pilot dog vaccination campaigns to parametrize and construct a spatially explicit agent-based model in five villages of Kandal Province, Cambodia. Infection parameters were sourced from the literature, with reported basic reproduction number (R0) values used to calibrate key transmission parameters, including probability and distance of infectious contact. Calibration was accomplished through 48,000 simulations testing a range of parameter values with a target R0 between 1 and 2. Another 75,000 simulations were used to test various vaccination coverage scenarios within this R0 range. Results: We observed a 40% reduction in vaccination coverage one year after vaccination. Annual vaccination with a target coverage of 70% maintained the average coverage over six years at 65% and reduced the mean R0 under one in every infection scenario. However, 8% of simulations led to outbreaks of 10 dogs or more in higher R0 scenarios. A target coverage of 90% reduced the number of outbreaks of 10 dogs or more to below 1% of simulations with the same scenarios. Conclusion: We provide evidence that dogs need to be vaccinated annually due to the impact of rapid population turnover, and that annual vaccination coverage should be at least 70% of the whole dog population to control rabies in this setting.

Japanese encephalitis virus (JEV) is a vector-borne zoonotic virus and leading cause of human acute encephalitis in Asia. Some vector-borne diseases have been introduced to Reunion island located in the Indian Ocean, and have posed or are posing serious public health problems such as Dengue or Chikungunya. The numerous commercial and human exchanges between Southeast Asia and Reunion raise concerns about the introduction of JEV on the island where known vectors of JEV and amplifying hosts such as pigs are present. We used a deterministic compartmental model, developed in Cambodia (where JE is endemic) and adapted to Reunion context in order to investigate whether multi-host systems, composed of pigs, poultry, and non-competent hosts as human, dogs and cattle, would allow a local circulation of JEV (based on R0 calculations) if introduced. Field and literature data were collected to adapt model parameters to the specific context of Reunion, including vector (estimated from mosquito trapping data) and host population sizes in areas of 1km radius (average flight distance of a Culex spp.) around pig farms. As the comparison between trapping data from Cambodia and La Reunion showed discordant effects of the type of trap, we studied 4 scenarios according to the trap type and to the season. For each scenario, R0 value was used to identify the areas most at risk for JEV circulation if introduced. The calculated R0s were low in all scenarios, but was > 1 in 12 areas in 2 scenarios. Regardless of the scenario, the ranks of the areas according to R0 value did not change: ranks thus allowed identifying the most at-risk areas, one of which was located a few kilometers from the large port area of Reunion, which could be a gateway for JEV-infected vectors (Figure 1).