Analysis of yearly changes in levels of antibodies to Japanese encephalitis virus nonstructural 1 protein in racehorses in central Japan shows high levels of natural virus activity still exist.

This research investigates the prevalence of the Japanese Encephalitis (JE) virus in horse populations in central Japan from 1998 to 2003. Despite reduced occurrences of JE in humans and horses in Japan that prompted calls to end immunization, the researchers found high occurrences of the virus in horses, indicating continued significant natural activity of the virus.

Methodology

• The researchers carried out their analysis by studying variations in the natural activity of the JE virus annually. This was achieved by using sera collected serially from 1998 to 2003. The sera were sampled from racehorses that lived in either of two prefectures in central Japan: Ibaraki and Shiga.
• A combined total of 467 sera were examined. This included 208 samples from 24 individuals in Ibaraki and 259 samples from 27 individuals in Shiga.
• The team scrutinized these sera for antibodies to the JE virus nonstructural 1 (NS1) protein. Notably, these antibodies are markers of natural infection, meaning that their presence in the sera would indicate that the horses had been naturally infected with the JE virus.

Findings

• The researchers found that there were significant variances in the natural infection rate during the epizootic seasons. These rates were determined through observation of a significant boost in NS1 antibody level.
• In Ibaraki, the infection rate oscillated between 4.2% and 26.7%. In Shiga, the rate ranged from 0% to as high as 41.7%.
• This variation indicates that there is still a high level of JE virus activity in the regions where the racehorses resided. Hence, in spite of the declines in the number of JE cases in humans and horses, the study suggests that the virus has not been eradicated in these areas.

Implications

• The study’s results have significant implications in shaping public health policy. They challenge the calls to end JW vaccination after the observed reduction in human and horse cases. The virus’ natural infection rates in these horse populations suggest that the JE virus is still widely active.
• The study stresses the importance of continued vigilance against the JE virus, and suggests that ending vaccination might not be advisable at this stage, given these high levels of viral activity.