A preliminary study of Japanese encephalitis vector mosquitoes in the field without pigs in Dhaka, Bangladesh

The infection pathway of Japanese encephalitis was originally investigated in Japan, and it was found that herons carry the pathogen and that zoophilic Culex tritaeniorhynchus plays an important role in transmitting the virus from birds to pigs and then human. This scenario was thought to be applicable to Southeast Asian countries where rice paddy cultivation and pig breeding are common. However, there are Asian countries where pig breeding is rare. We asked if it is possible to follow any infection route of Japanese encephalitis without pigs as amplifying host in Bangladesh. We collected mosquitoes at night in places where pigs are not raised, including places where only humans are present as larger mammals. As a result, the occurrence of Cx. tritaeniorhynchus peaked in the winter when rice paddy cultivation is carried out and with abundant migrating birds. Culex tritaeniorhynchus was most frequently collected in cow sheds, but not a few were also collected in dormitory rooms where only humans sleep and wake up. Under these circumstances, we discuss effective measures to prevent Japanese encephalitis.