Relationship between avian malaria distribution and an exotic invasive mosquito in New Zealand

Although the mosquito vector responsible for the epizootic outbreaks of avian malaria in Hawaiian avifauna, Culex quinquelasciatus, has spread rapidly in New Zealand over the past three decades, no survey for malarial parasites has been conducted for more than 50 years. Avian malaria often causes extreme morbidity and mortality in novel hosts, and much of New Zealand's native avifauna has likely had no prior exposure, so the impact of this spread on native biodiversity is potentially serious. Wild non-native birds were surveyed for malarial parasites at multiple locations, to test the hypothesis that the prevalence of malarial infection is associated positively with the known distribution of C. quinquefasciatus. Blood samples collected were analysed using a Polymerase Chain Reaction (PCR) assay. There was a strong pattern of decreasing percentage of samples positive for the blood parasite PCR marker from north to south, closely matching the known distribution of C. quinquelasciatus. A subsample of 10 PCR products were sequenced, and all identified as the malarial parasite Plasmodium relictum. Since historical surveys found no malarial parasites in the New Zealand avifauna, with a few minor exceptions, this suggests that this invasive exotic vector may be one factor driving the emergence of avian malaria. Sampling of wild non-native birds at Orana Park, Christchurch, where a disease outbreak occurred recently in a captive native bird population, suggested that such outbreaks may spill-back into local wild bird populations. The high prevalence of malarial infection observed in certain non-native species, particularly blackbirds, indicates that they may act as reservoirs of infection to native species.