Epidemiology of an avian malaria outbreak in a native bird species ( Mohoua ochrocephala ) in New Zealand

Emerging infectious diseases pose a considerable threat to wildlife globally. One such disease that has apparently emerged in recent years in New Zealand is avian malaria, with Plasmodium infections being detected in numerous species for the first time. Although the overall significance of this apparent emergence is not yet known, infection by Plasmodium has been diagnosed as a cause of mortality in several native species in captivity. Here we investigate the epidemiology of the most recently confirmed case, with our results having potentially important implications for native bird management. Avian malaria caused the death of five mohua or yellowheads (Mohoua ochrocephala) at Orana Wildlife Park in Canterbury during 2003–05, after their translocation from the Blue Mountains (Otago) in 2003. A lack of detectable Plasmodium infection in wild mohua in both the Blue Mountains and the nearby Catlins region, in contrast to an unusually high prevalence in wild bird populations at Orana Park at the time of the outbreak, indicates that infection was most likely acquired by the birds after translocation. This evidence, although not conclusive, strongly argues for assessment of the risk of greater (and potentially deleterious) exposure to malarial parasites to be undertaken prior to native bird translocation. A mosquito investigation carried out at Orana Wildlife Park identified the ubiquitous indigenous mosquito Culex pervigilans as the likely disease vector. Hence, management of this mosquito species (in addition to the exotic Cx. quinquefasciatus , a known vector of avian malaria in other countries) is a potentially useful preventative measure against disease outbreaks in native bird populations of conservation value in New Zealand.