Host risk factors in relation to the occurrence of Japanese encephalitis virus in pigs and dogs in northern Vietnam

Abstract: Japanese encephalitis is the leading cause of encephalitis in Asia. The disease is caused by Japanese encephalitis virus (JEV), a vector-borne virus that has an enzootic cycle involving mosquitoes, pigs and birds. Surveillance programs for detection of virus activity can function as an early warning system of increased risk of transmission and disease outbreak. Surveillance of JEV infection is often performed using sentinel animals like pigs. Dogs have recently been shown to be good sentinels as well. The objective of this study was to determine the seroprevalence and to assess the host factors in pigs and dogs favoring JEV infection in Vietnam. For this purpose, 114 blood samples were collected from dogs in rural areas in the provinces of Hai Duong and Thai Binh in northern Vietnam. Ten blood samples were retrieved from pigs in the same areas. In addition, 250 blood samples were collected from pigs originating from all over Vietnam, in a slaughterhouse in Hanoi. Blood samples were tested for antibodies against JEV using a competitive ELISA method. A total of 30% pigs (n =78) and 72% of dogs (n=82) were JEV seropositive. The seroprevalence in pigs found in this study is much lower than the previously found; in the range of 60-100%.This could be indicative of a reduced infection pressure due to the ongoing depopulation of pigs as a result of the recent outbreak of African swine fever in the country. Further, the seroprevalence was lower in the south and south-central areas (19-26%) compared to the north (87%). The seroprevalence among dogs was higher than in earlier studies suggesting that people in these areas are exposed to JEV in high extent. The results from the dog samples show a possible correlation between age and JEV seropositivity. Also breed seems to play a role for the risk of being seropositive.