Investigation of West Nile Virus infection from Japanese encephalitis patients in Shandong, China

Abstract

Objective To determine whether human infection with West Nile Virus in Shandong province. Methods 272 clinical samples(214 sera and cerebrospinal fluids of acute phase, 58 sera of convalescent phase) from 242 patients who were clinically diagnosed as Japanese encephalitis(JE) in parts of Shandong province were collected. RNAs of Japanese encephalitis virus(JEV) and WNV were detected by RT-PCR from acute phase samples, and positive samples were used for virus isolation, IgM and IgG antibodies to JEV and WNV of samples were detected by Enzyme-linked immunosorbent assay(ELISA). JEV-IgM and WNV-IgM, JEV-IgG and WNV-IgG cross-reacted samples were further detected antibody titers. The following two results were considered as potential WNV infected cases: ① Both antibody positive samples: For antibody titers, WNV-IgM /JEV-IgM≥4 or WNV-IgG/JEV-IgG≥4. ②WNV-IgM(+) and JEV-IgM(-), or WNV-IgG(+) and JEV-IgG(-) samples. Results 4 of 214 acute phase samples were positive to JEV RNA, but all samples were negative to WNV RNA by RT-PCR. No virus was isolated from the samples. In acute samples, JEV-IgM positive rate was 99.07%(212/214), WNV-IgM positive rate was 35.05%(75/214), cross-reaction rate was 34.58%(74/214). In convalescent samples, JEV-IgG positive rate was 55.17%(32/58), WNV-IgG positive rate was 46.55%(32/58), cross-reaction rate was 31.03%(18/58). 15 patients were considered as potential WNV infection. Conclusions Our study indicated there may be some cases infected with WNV from JE patients in Shandong Province of China, 2013, but the results can not fully support the epidemic of WNV in this area, surveillance of WNV should be strengthened meanwhile JE was prevented and controlled. Key words: Encephalitis virus Japanese; West Nile virus; Enzyme-linked immunosorbent assay; antibody titer