Seroprevalence of Japanese encephalitis virus in pigs and dogs in the Mekong Delta
Japanese encephalitis virus (JEV) is one of the leading causes of acute encephalitis in humans. The virus is spread by mosquitoes, mainly belonging to the Culex species. The main reservoirs are considered to be birds and pigs, with pigs constituting the most important reservoir in regard to human infection. During the last few decades the production of pork has increased significantly in Vietnam. With 90% of pigs being kept in households owning 10 pigs or less, pigs are widely spread across most parts of the country. Due to the ongoing urbanization of Vietnam, the need for urban agriculture and animal husbandry has increased, resulting in an increasing amount of pigs/reservoirs being kept in urban environments. In the city of Can Tho, located in the Mekong delta, almost 100 % of the pigs have been found to be JEV positive, and vectors needed for transmission of JEV have been shown to be present in the urban areas of the city. The objectives of this study was to examine the seroprevalence of JEV in dogs and pigs in an endemic region, and to evaluate if dogs make suitable sentinels and could be used to evaluate the risk that JEV may pose to humans living in urban areas. To do this, blood samples were collected from dogs and pigs. A total number of 127 dog samples and 176 pig samples were collected from Can Tho city province and 65 samples were collected for comparative purposes from dogs originating from Ho Chi Minh City. The samples from Can Tho were divided into two equal parts. One part was frozen and sent to Sweden to be tested for JEV antibodies, using a competitive IgG ELISA. One part of the samples from Can Tho was also tested at Can Tho University using an in house HI-test. Due to denaturation as a result of high temperature inactivation of the sera, none of the samples that were sent to Sweden could be tested using the competitive IgG ELISA. The HI-results showed that 27 of the 127 dog samples and 159 of the 176 pig samples, all originating from Can Tho city province, had measurable antibody titres against JEV. Twenty three per cent of the dogs originating from the urban district of Ninh Kieu had measurable antibody titres against JEV. Although the seroprevalence was much higher among dogs mainly kept outdoors than dogs mainly kept indoors, it is notable that more than 16% of the dogs mainly kept indoors were also seropositive for JEV. These results indicate not only that JEV does pose a risk to people living in the urban areas of Can Tho city, but also that dogs may be good sentinels for human infection and can be used for evaluating the risk that JEV poses to humans living in urban areas.