Consequently, the species is more likely to become extinct if environmental conditions change, even minimally. One such virus that can induce genetic changes is the West Nile virus (WNv), and it has the capacity to change the genetic sequencing of animal species, predominantly birds. WNv can be passed to humans and other mammals via mosquitoes and causes mild to severe illness, and in some cases death.
The investigators presented data that supported a phylogenetic conclusion that the MNv epidemic of North America already reached an epidemiological plateau. The conclusion that peak prevalence has been passed was based on the decline in the population growth of WNv in recent months.
Snapinn et al.'s method of trying to quantify the emergence of MNv in the USA contrasts with that of previous research, such as Hull et al. (2006) and Naugle et al. (2004) who observed antibody rates of birds to identify the prevalence of WNv infection. The results for Hull's study showed that antibodies to WNv were found across all raptor groups across two geographical regions. This supports the conclusion that many of the wild raptors had survived a WNv infection. In contrast, Naugle and colleagues observed that their sage-grouse sample did not exhibit WNv antibodies, suggesting that the species lacks resistance to infection. For both studies it appears that the summer months are times of increased infections, perhaps due to the increase in mosquito populations. These conclusions were drawn from evidence of statically different antibody rates across summer and winter regions used in each sample.
Statistical methods were used to track the WNv population, estimating a set of parameters; rate of evolutionary change; sequences divergence time; and rate of viral population growth. These factors were based on the changes observed in gene sequence data. This method of modeling estimates the level of new infections across all species that can be host to WNv. This is a reasonable conclusion given that a virus leaves an epidemiological 'history' on gene sequences.
The limitation of this study was that the statistical estimates used a viral sample from only one species - birds (corvids and raptors), and from only one geographical region - northeastern USA. It may be that species differences affect the lifespan of the virus, and that such a narrow geographical sample does not reflect random sampling of the entire population (which exists across the entire nation), and so is not representative. There may be confounding variables such as climate, pesticides, food availability or predators that impact on the health of the birds in this region that make them more resistant to MNv. Such a case would be of interest in developing a vaccine to the virus, but does not illuminate the true state of affairs with regard to the population growth, stagnation or decrease of MNv.
Hull's study drew plasma specimens from Red-tailed Hawks (Buteo jamaicensis), Red-shouldered Hawks (B. lineatus), and Cooper's Hawks (Accipiter cooperii) was
Whilst Naugle and colleagues collected the serum of 112 radio-marked sage grouse (Centrocercus