Serologic study of pig-associated viral zoonoses in Laos

Abstract

We conducted a serologic survey of four high-priority pig-associated viral zoonoses, Japanese encephalitis virus (JEV), hepatitis E virus (HEV), Nipah virus (NiV), and swine influenza virus (SIV), in Laos. We collected blood from pigs at slaughter during May 2008-January 2009 in four northern provinces. Japanese encephalitis virus hemagglutination inhibition seroprevalence was 74.7% (95% confidence interval [CI] = 71.5-77.9%), JEV IgM seroprevalence was 2.3% (95% CI = 1.2-3.2%), and HEV seroprevalence was 21.1% (95% CI = 18.1-24.0%). Antibodies to SIV were detected in 1.8% (95% CI = 0.8-2.8%) of pigs by screening enzyme-linked immunosorbent assay, and only subtype H3N2 was detected by hemagglutination inhibition in two animals with an inconclusive enzyme-linked immunosorbent assay result. No NiV antibody-positive pigs were detected. Our evidence indicates that peak JEV and HEV transmission coincides with the start of the monsoonal wet season and poses the greatest risk for human infection.

Figure 1.

Study sites in northern Laos. 1 = Xay District, Oudomxay Province; 2 = Luangprabang District, Luangprabang Province; 3 = Xiengngeun District, Luangprabang Province; 4 = Pek District, Xiengkhuang Province; 5 = Xamneua District, Huaphan Province; 6 = Viengxay District, Huaphan Province. Black dots indicate abattoirs or slaughterhouses (> 20 pigs per night) and black circles indicate slaughter points (< 5 pigs per night). The black dot in Luangprabang District (2) represents an amalgamation of home slaughter points caused by reconstruction of abattoir at the time of survey.