来源： Gleeson, D., and Tompkins, D., pers. comm., 2005
There is no evidence yet for or against Plasmodium relictum being either alien or invasive in New Zealand. All we can currently say for sure is that it is established, based on blood smear analysis and incidences of native bird fatalities in captivity. Avian malaria was identified as the cause of bird deaths at Auckland Zoo and at Orana Park, Christchurch. Until recently, no widespread survey had been undertaken. Dianne Gleeson and Dan Tompkins, from Manaaki Whenua Landcare Research, used a combination of PCR (Polymerase chain reaction) using primers designed from Plasmodium mtDNA cytB sequences & blood smear analysis to detect avian malaria in non-native wild bird populations at 7 sites spread throughout New Zealand, using a minimum sample size of 60 birds. They detected the presence of avian malaria at all 7 sites and identified a north-to-south gradient in detection rates (48% of birds tested in the north compared to 6% in the far south). While the results closely match the New Zealand distribution of the Culex quinquefasciatus vector, there were some anomalies, which are being investigated. Phylogenetic analysis can test hypotheses regarding origin and numbers of separate invasions and the possibility of host-specific strains, and PCR can be used to track & monitor spread. The researchers also wish to confirm which mosquito species are the key vectors for the different strains (Tompkins and Gleeson 2006).
The Culex quinquefasciatus vector of avian malaria is established in New Zealand and it continues to be intercepted at ports. In March 2005 it was found in an imported car which had been discharged at the port of Auckland. Its distribution in New Zealand has increased to cover most of the North Island and substantial parts of the South Island. Options for responding to the threat of avian malaria include depriving the mosquito vector of habitat, mosquito contol, control of non-native birds that are reservoirs of infection, and application of anti-malarial drugs to native populations at risk.
This work is important because New Zealand’s unique avifauna is currently considered the most ‘extinction-prone’ in the world. In addition, New Zealand’s terrestrial ecosystems are especially sensitive to losses in native biodiversity due to the higher proportion of bird-pollinated plants than in other parts of the world. Finally, this work can be used as a model system for effects of climate change on other vector-borne disease of concern such as Dengue fever, West Nile virus, canine heartworm, Ross River virus, and avian pox (Gleeson, D., and Tompkins, D., pers. comm., 2005)
寄生: "At Auckland Zoo, 60% of a captive population of New Zealand dotterel (Charadrius obscurus) were killed by infection with Plasmodium sp. parasites in 1996 (Reed 1997 in Tompkins and Gleeson 2006). At Orana Park, Christchurch, 80% of a group of native mohua (Mohoua ochrocephala) were killed by infection with Plasmodium sp. parasites after being translocated there from the wild in 2003 (Tara Atkinson-Renton, Orana Park, pers. comm. in Tompkins and Gleeson, 2006)" (Tompkins and Gleeson 2006).
Historical surveys revealed no malarial parasites present in wild New Zealand avifauna (Bennett et al. 1993 in Tompkins and Gleeson 2006). However a recent survey of non-native wild bird populations by Tompkins and Gleeson (2006) found that avian malaria (Plasmodium relictum) was present in bird populations at 7 sites throughout New Zealand. They determined a north-to-south gradient in detection. rates which closely match the distribution of the vector Culex quinquefasciatus (although there were some anomalies which require further investigation). This positive association between P. relictum and Cx. quinquefasciatus suggests that this mosquito may be a cause of disease emergence, although there is evidence that other mosquito species can be vectors such as Cx. pervigilans (Holder et al. 1999 in Tompkins and Gleeson 2006) This is of great concern if P. relictum is introduced to populations of native birds with no history of exposure. “A high degree of susceptibility to infection is likely in many species, given the historical absence of such parasites in much of the New Zealand avifauna” (Tompkins and Gleeson 2006).
最后修改 ： 30/03/2010 11:47:34 a.m.