West Nile Virus Monitoring Update

West Nile virus was only recently introduced to North America, but in that time it has had dramatic impacts on both humans and wildlife. The first reported appearance of this virus was in New York in 1999; since then, it has spread rapidly across North America (Figure 2).

Figure 2. The spread of West Nile virus in the United States during a five year period 1999-2005. The relative role of localized vs. long-distance transmission in this spread is currently unknown. Maps adapted from CDC website.

West Nile virus must have a vector to transmit to either a bird or mammal, and in North America, these vectors are primarily mosquitoes of the Culex sp. group. Understanding how virus, vector, and host population movements affect the transmission dynamics of this infectious disease is of paramount importance in mitigating and preventing its effects. Recent research has suggested that birds are likely still able to migrate even if carrying an active infection of West Nile virus, and this could mean a rapid and long-distance transmission of the disease to new locations at stopover sites and on wintering grounds. This may be particularly harmful for Central and South American year-round residents, as they may not have been previously exposed to the virus.

UCLA’s Center for Tropical Research received funding from EPA in 2008 to examine the spatial and temporal patterns of West Nile virus (WNV) in neotropical passerines. Based on the prevalence across selected species, we will also determine whether particular species are acting as WNV “superspreaders”. We will then determine the environmental variables that may affect infection using bioclimatic and satellite remote sensing data and examine the effects of changes in climate on its distribution. We will also be examining possible correlation between geographical WNV hotspots and areas where human activity has altered the environment. We have selected 10 target species for the WNV study: American Robin, House Finch, Gray Catbird, Brownheaded Cowbird, Swainson’s Thrush, Hermit Thrush, Wilson’s Warbler, Yellow-breasted Chat, Common Yellowthroat and Yellow Warbler. The American Robin is currently thought to be particularly susceptible to mosquito bites and virus infection, and as a migrant or partial migrant across most of North America, represents a potential long-distance spreader of West Nile virus.

Recent studies have indicated that vascular pulp of feathers (the small amount of tissue material left in the quill of the feather when it is pulled from a bird) can contain remnants of the WNV virus that are detectable by genetic testing methods. UCLA is investigating whether feathers can be a useful sample for testing WNV and is asking the banding community and banders in the LaMNA network to consider participating in our ongoing neotropical migrant feather sampling collection efforts (described in more detail at Feather Sampling from Neotropical Passerines). The list of target species in our call for feather sampling includes the 10 target species for our WNV study.

No host-to-host WNV transmission (e.g. birds-to-humans) has been reported, but banders should again follow USGS/USDA recommended procedures and precautions in handling wild birds. Note that WNV is transmitted by a vector (mosquitoes), so banders should take precautions against mosquito bites, especially in localities where WNV cases have been reported in birds and/or humans.

-John Pollinger, UCLA Center for Tropical Research
May 2010