Serological surveillance of Japanese encephalitis virus infection among pigs in the Philippines

Japanese encephalitis virus (JEV) belongs to Genus Flavivirus, Family Flaviviridae and is the causative agent of Japanese encephalitis, a mosquito-borne disease transmitted by Culex spp. It infects mainly certain species of mosquitoes and animals. Pigs are an important vertebrate amplifying host; man is infected through the bite of an infected mosquito. In recent years, no serological and virological survey on JEV has been done in the Philippines. This study aims to determine the prevalence of this disease and to monitor the seasonality of JEV infection among domestic pigs in the Philippines. This will provide valuable information on the potential risks of exposure of the human population. IgM and IgG levels against JEV in pig sera were monitored by using the St. Luke_s in-house IgM _capture and IgG ELISA, respectively. Healthy pig serum samples collected in 2001 from the three major areas of the Philippines (Luzon-65, Visayas-29, Mindanao-27) were examined. Out of 121 samples, 7 (5.8%) were IgM-positive; 1/65 (1.5%) from Luzon, 4/29 (13.8%) from Visayas, and 2/27 (7.4%) from Mindanao. Furthermore, out of 117 pig sera examined by IgG ELISA, 54 (46.2%) were IgG-positive; 25/64 (39.1%) from Luzon, 14/29 (48.3%) from Visayas, and 15/24 (62.5%) from Mindanao. Results showed that more than anti-JEV IgG was present in more than 40% of pigs sampled from the 3 areas. In 2002-2004, fixed-point sampling in pigs in Tanay, Rizal [Philippines] was also done to check for IgM and IgG levels. Sampling was done from May to December of 2002, January to October of 2003, and July to October of 2004. Monthly IgM levels detected ranged from 0-27.5%, the highest level obtained in the month of July, 2002 (27.5% anti-JEV IgM). Anti-JEV IgG levels ranged from 4.8-80% for the same period, with the highest obtained in August 2003 (80% anti-JEV IgG). These findings indicate that JEV infection in pigs in Tanay, Rizal peaked in July to September of each year. The results of this serological surveillance show that JE is present in domestic pigs in all the areas sampled. This may indicate the occurrence of possible transmission to the human population. Public medical awareness against JEV infection is important to prevent and management of outbreaks. Virological confirmation through culture of JEV is being developed.