Vaccination is a potential method of controlling P. relictum. A study by McCutchan et al. (2004) looked at the effects of vaccinating canaries in Baltimore Zoo with a DNA vaccine plasmid encoding the circumsporozoite protein of P. relictum. In the first year after vaccination birds “exhibited a moderate degree of protection against natural infection” with non-vaccinated birds dying in significantly greater numbers than vaccinated birds. In the second year “vaccinated birds were no longer statistically distinguishable for protection against malaria from cages of naïve birds”. Vaccination also had a surprising effect in that it “seemed to interfere with the acquisition of reinfection immunity because in the follow-up year all birds that died were ones that had previously been vaccinated, while those that had acquired immunity as a result of exposure were fully protected”. It seems that the vaccine may have cause a total elimination or significant reduction in parasite load, which interferes with the acquisition of natural immunity. Indeed the introduction of vaccine into areas of avian malaria could actually worsen malaria conditions. This study has particular significance for human malaria (McCutchan et al. 2004) and for high value birds such as African black-footed penguins (Spheniscus demersus). Grim et al. (2004) determined the impact of the same vaccine on penguins in Baltimore Zoo. “Among the vaccinated penguins, the parasitemia rate dropped from approximately 50% to approximately 17% despite intense parasite pressure, as determined by mosquito infection rate. During the year of the vaccine trial, no mortalities due to malaria occurred and no undesirable vaccination side effects occurred” (Grim et al. 2004).
There have been concerns that other mosquitoes in addition to Cx. quinquefasciatus are important vectors of avian malaria including Aedes albopictus and Wyeomyia mitchellii. However Lapointe et al (2005) conclude that "In light of the present susceptibility data and ecological profiles for the 3 forest-dwelling mosquitoes occurring in Hawai’i, it is concluded that Cx. quinquefasciatus is the primary vector of P. relictum and that concerns over important secondary or yet unknown vectors are largely unfounded. Future strategies to reduce the transmission of avian disease through vector control should focus on this species (Lapointe et al. 2005).
"The most feasible method for reducing transmission is by a reduction of mosquito populations through treatment or elimination of larval habitats on the refuge and adjacent lands." However this will be challenging due to steep slopes and presence of feral pigs Sus scroaf which create larval habitat by felling trees which create troughs which hold rainwater. Vector control is the most feasible option in this area because of the steep slopes of the volcano which drain water, meaning that the only water bodies are created by feral animals or human infrastructure. (Atkinson et al. 2005).
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)
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摘要： Available from: http://www.veterinaria.uchile.cl/publicacion/congresoxi/prafesional/exo/4.doc [Accessed 6 April 2006]
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