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Dynamics of Japanese Encephalitis Virus Transmission Among Pigs in Northwest Bangladesh and the Potential Impact of Pig Vaccination

Salah Uddin Khan
Centre for Communicable Diseases, i,cddr,b, Dhaka, Bangladesh, / College of Public Health and Health Professions - Department of Environmental and Global Health, University of Florida, Gainesville, Florida, United States of America

Henrik Salje
Department of Epidemiology, Johns Hopkins School of Public Health, Baltimore, Maryland, United States of America,

A. Hannan
Department of Livestock Services, Ministry of Fisheries and Livestock, Dhaka, Bangladesh,

Md. Atiqul Islam
Centre for Communicable Diseases, i,cddr,b, Dhaka, Bangladesh

A. A. Mamun Bhuyan
Centre for Communicable Diseases, i,cddr,b, Dhaka, Bangladesh

Md. Ariful Islam
Centre for Communicable Diseases, i,cddr,b, Dhaka, Bangladesh

M. Ziaur Rahman
Centre for Communicable Diseases, i,cddr,b, Dhaka, Bangladesh

Nazmun Nahar
Centre for Communicable Diseases, i,cddr,b, Dhaka, Bangladesh

M. Jahangir Hossain
Centre for Communicable Diseases, i,cddr,b, Dhaka, Bangladesh

Stephen P. Luby
Centre for Communicable Diseases, i,cddr,b, Dhaka, Bangladesh/5 Global Disease Detection Branch, Division of Global Health Protection, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America

Emily S. Gurley
Centre for Communicable Diseases, i,cddr,b, Dhaka, Bangladesh

Abstract/ Executive Summary:

The objectives of this study were to describe the transmission dynamics of Japanese encephalitis virus (JEV) among pigs in northwestern Bangladesh and estimate the potential impact of vaccination to reduce incidence among pigs and therby control the incidence of transmission to human. Infection could cause severe disease in humans, resulting in death or permanent neurologic deficits among survivors. Studies indicated that the incidence of JEV is high in northwestern Bangladesh. Pigs are amplifying hosts for JEV and a potentially important source of virus in the environment. A comprehensive census was conducted on pigs in three JE endemic districts and tested a sample of them for evidence of previous JEV infection. Then built a compartmental model to describe JEV transmission dynamics in this region and to estimate the potential impact of pig vaccination. It identified 11,364 pigs in the study area. Previous JEV infection was identified in 30% of pigs with no spatial differences in the proportion of pigs that were seropositive across the study area. It estimated that JEV infects 20% of susceptible pigs each year and the basic reproductive number among pigs was 1.2. The model suggest that vaccinating 50% of pigs each year resulted in an estimated 82% reduction in annual incidence in pigs. The widespread distribution of historic JEV infection in pigs suggests they might play an important role in virus transmission in this area.

Keywords: Japanese encephalitis virus, Transmission, Pigs, Northwest Bangladesh, Pig vaccination

Location: Northwestern part of Bangladesh (Rajshahi, Nawabgonj, and Naogaon Districts)

Start Date: 00-05-2009

End Date: 00-09-2009

Program Area: Pest Management

Commodity: Pig

Objectives:

To document the transmission dynamics of Japanese Encephalitis Virus (JEV ) among pigs in the northwestern part of Bangladesh
To determine relationship of JEV with that of tranmission to human

Methodology:

Pig census and sampling from May through September 2009 was used. Snowball sampling done to identify all pig-raisers in Rajshahi, Nawabgonj, and Naogaon Districts and their counting. Initially 10 pigraisers were identified who previously participated in a study of other diseases in 2007–2008. In addition, collected a list of 100 pigraisers identified through a local livestock office’s preliminary survey. All identified pig-raising households were listed,visited and asked to identify other households. This process was continued until no additional pig-raisers were found. The researchers visited 20 randomly selected unions (smallest administrative unit consisting of multiple villages) where no pig-raising was reported and went to places where residents congregate, such as markets, tea stalls and shops, to ask if they knew about any pig-raising communities in those areas. The presence of pigs reported through these interviews was confirmed by household visits. At each pig-raising household, then recorded the number of pigs, their age, sex, and location. The researchers then collected blood samples from pigs over six months of age for JE IgG antibody testing. Then approached the first pig raising household in the village and sampled a pig after obtaining an informed consent. It continued the sampling in the nearest households until they sampled 10 pigs per village. If no more than 10 pig raising households were identified in a village, collected samples from multiple pigs from a household. If there were less than 10 pigs in a village, then sampled all of the pigs. The sampling continued until reached a sample size of 260. Regardless their health status, it was recorded the number of pigs in each herd and collected blood from at least three pigs but no more than 10. The serum samples were tested by using a commercially available enzyme-linked immunosorbent assay (ELISA) according to manufacturer’s protocol (GENTAUR BVBA – Genoprice, Belgium. http://www.genoprice.com/). With guidance from herders from each herd, longitude and latitude of the grazing locations and travelling paths of nine pig herds located. These herds were particularly chosen for mapping because their grazing covered the majority of the nomadic pig herds feeding sites, and represented geographical variation of the feeding sites for the three districts. Also conducted informal interviews with all nomadic pig herders to explore the commercial trade of pigs at markets and backyard raisers. Visited commercial pig traders at the markets and some backyard pig-raisers to verify the frequency and timing of the sale. Mapping done of the locations of pig-raising households, nomadic pigraising routes, and sampled pigs by JE IgG status. To assess spatial heterogeneity of seropositive pigs, at first constructed intensity maps by placing a fine grid over the study area and estimating the probability of pigs within each grid segment being seropositive, using a Gaussian kernel with a bandwidth that minimized the cross-validated error. Then used a resampling method to test the null hypothesis of no spatial heterogeneity in the proportion of seropositive pigs. In the resampling method, randomly assigned serostatus of each tested pig, keeping the total number of seropositive and seronegative pigs the same.

Source of Information: PLoS Negl Trop Dis 8(9): e3166. doi:10.1371/journal.pntd.0003166

Article Link (Online Journal): file:///C:/Users/barc/Downloads/journal.pntd.0003166%20(2).PDF

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The widespread distribution of historic JEV infection in pigs suggests they might play an important role in virus transmission in the area.

Knowledge Management: Journal