National Wildlife Refuge System

The West Nile Virus Threat to Hawai'i and the Pacific Islands

      — Jeff Burgett, USFWS

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The invading West Nile virus (WNV) is having severe impacts on birds and other wildlife as it moves westward from its point of introduction in New York. Birds in many taxonomic groups suffer fatal infections, including corvids, other passerines, and raptors, with some groups having nearly 100 percent mortality rates. Because WNV is apparently carried by migrating birds, wildlife managers in North America have few options but to watch and wait for its arrival, and hope that stricken bird populations can recover with time.

Alala bird
The 'Alala (pop. 39) could
not recover if WNV reaches
The Pacific islands cannot, and need not, watch and wait. There is a good chance that pathways that could introduce WNV to Hawai'i and other Pacific islands can be controlled, and WNV kept out of the islands. In addition to the human health benefits of preventing WNV introduction, there is a compelling need to prevent a major loss of global biodiversity.

The rich avifauna of Hawai'i and other Pacific islands have already been severely depleted by introduced avian diseases. The introduction of WNV into Hawai'i would have catastrophic consequences for the native avifauna and would likely produce losses similar to or greater than other previously introduced pathogens. We would expect that most endangered passerines, with populations ranging from three to a few thousand, eventually would be either rendered extinct or have their recovery precluded. The vulnerability of other endangered bird taxa, as well as non-listed endemics, is unknown but probably high due to their insular evolutionary history. In total, 41 of the 92 listed species of birds in the U.S. could face extinction if WNV were to become established in the islands.

The mosquito vectors are widespread in Hawai'i and there is no disease-free winter. Once established in competent host populations of alien birds, WNV could not be eradicated and would spread to other islands by the same pathways by which it reached Hawai'i. Mitigation strategies, while important for public health, would not prevent the spread of the disease to native birds. Therefore, efforts must be focused on preventing the introduction and establishment of WNV in Hawai'i and other Pacific islands. Indeed, this may be the most important action that can be taken globally to protect wildlife from this disease. Pie chart showing 44% of listed bird species at risk from WNV introduction to Hawaii. Three main potential routes of entry exist. Importation of infected birds has been prevented for the present by a postal embargo and state and territorial quarantines. Migratory birds are thought to be low-risk due to the stress of migrating over 2500 miles nonstop, which could be fatal to birds ill with the virus. Accidental importation of infected mosquitoes is a little-researched pathway that may be a significant threat. Research is needed to determine these risks, and if necessary resources will be needed to devise and carry out a strategy to close this pathway.

Point of Contact - Mike Higgins, Mosquito Coordinator
Providing Support - Raye Nilius, Refuge Liaison to Migratory Birds

Last updated: November 7, 2012