Abstract
Japanese encephalitis (JE) is a vaccine-preventable disease caused by the Japanese encephalitis virus (JEV), which is primarily prevalent in Asia. JEV is a Flavivirus, classified into a single serotype with five genetically distinct genotypes (I, II, III, IV, and V). JEV genotype III (GIII) had been the most dominant strain and caused numerous outbreaks in the JEV endemic countries until 1990. However, recent data shows the emergence of JEV genotype I (GI) as a dominant genotype and it is gradually displacing GIII. The exact mechanism of this genotype displacement is still unclear. The virus can replicate in mosquito vectors and vertebrate hosts to maintain its zoonotic life cycle; pigs and aquatic wading birds act as an amplifying/reservoir hosts, and the humans and equines are dead-end hosts. The important role of pigs as an amplifying host for the JEV is well known. However, the influence of other domestic animals, especially birds, that live in high abundance and close proximity to the human is not well studied. Here, we strive to briefly highlight the role of birds in the JEV zoonotic transmission, discovery of birds as a natural reservoirs and amplifying host for JEV, species of birds susceptible to the JEV infection, and the proposed effect of JEV on the poultry industry in the future, a perspective that has been neglected for a long time. We also discuss the recent in vitro and in vivo studies that show that the newly emerged GI viruses replicated more efficiently in bird-derived cells and ducklings/chicks than GIII, and an important role of birds in the JEV genotype shift from GIII to GI.
Highlights
Japanese encephalitis virus (JEV) causes neurological disease, which is one of the leading types of viral encephalitis in the world [1]
Because of the bird’s close association to humans and varying levels of seroprevalence observed in birds, their role in epidemiological cycle as secondary reservoirs for JEV may be of importance
These results suggest that the response and susceptibility of ducklings to JEV infection differed among JEV strains [66]
Summary
JEV causes neurological disease, which is one of the leading types of viral encephalitis in the world [1]. JEV GI strains were isolated and characterized from a nonsuppurative encephalomyelitis case of 141-day-old calf and 114-month-old cow from Japan, suggesting that JEV GI infection can lead to the development of neurological disorders in cows [40,41]. These animals do not act as a reservoir/amplification hosts for JEV but can play a potential role in future and continuous monitoring is required. The JEV genotype shift from GIII to GI has reported in some countries where pig-farming is not common, such as Malaysia [45], India [46], and Korea [42]. We can contain the JEV spread while taking possible countermeasures that can blunt their impact on public health as well as for veterinary concerns
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