Factors favoring pigs as being the main amplifying host for JEV are a high birth rate and a rapid population turnover, resulting in constant generation of an immunologically naive population. Furthermore, an important JEV vectorCulex tritaeniorhynchus preferentially feeds on pigs. Fortunately, viraemia in humans and horses is probably insufficient to infect mosquitoes, and they are considered to be dead-end hosts.
Authors in the journal Nature Communications questioned if vector-free transmission might be possible and, if so, could help explain some of the observations made in temperate regions.
Therefore, in the frame of a pathogenesis study with pigs, they placed sentinels with intravenously (i.v.) infected pigs and found vector-free transmission of JEV in pigs.
This finding was confirmed and further supported by demonstrating efficient oronasal infection with low doses of virus. Pigs shed virus in oronasal secretions and are highly susceptible to oronasal infection. Clinical symptoms, virus tropism and central nervous system histological lesions are similar in pigs infected through needle, contact or oronasal inoculation.
In all cases, a particularly important site of replication are the tonsils, in which JEV is found to persist for at least 25 days despite the presence of high levels of neutralizing antibodies.
These findings could have a major impact on the ecology of JEV in temperate regions with short mosquito seasons.