The ecology of Whataroa virus, an alphavirus, in South Westland, New Zealand

The findings of a survey on the ecology of an alphavirus over the years 1964–9 are reviewed. Evidence is presented to show that wild birds constitute a vertebrate reservoir of the virus and that mosquitoes, primarily Culiseta tonnoiri and Culex pervigilans, which are both endemic New Zealand species, are responsible for summer transmission. Serological evidence of infection was obtained in all years and evidence is presented to indicate that the virus is enzootic rather than being reintroduced each spring. The number of birds with antibody increased before mosquitoes became active in the spring and possible explanations of this are discussed. The mean temperature in the hottest month in the study area is substantially below that in other areas with enzootic mosquito-borne viruses and experimental studies showed that Whataroa virus was able to replicate more rapidly in mosquitoes at low temperatures than any arboviruses previously studied. The main natural focus of infection appeared to be in a modified habitat and the introduced song thrush (Turdus philomelos) to be the main vertebrate reservoir host.