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Geology topics

Robert G. McLean

Publications and source records attributed to Robert G. McLean.

4 recordsLinked to original sources
USGS2016

Fluid spatial dynamics of West Nile virus in the USA: Rapid spread in a permissive host environment

The introduction of West Nile virus (WNV) into North America in 1999 is a classical example of viral emergence in a new environment, with its subsequent dispersion across the continent having a major impact on local bird populations. Despite the importance of this epizootic, the pattern, dynamics and determinants of WNV spread in its natural hosts remain uncertain. In particular, it is unclear whether the virus encountered major barriers to transmission, or spread in an unconstrained manner, and if specific viral lineages were favored over others indicative of intrinsic differences in fitness. To address these key questions in WNV evolution and ecology we sequenced the complete genomes of approximately 300 avian isolates sampled across the USA between 2001-2012. Phylogenetic analysis revealed a relatively ‘star-like' tree structure, indicative of explosive viral spread in US, although with some replacement of viral genotypes through time. These data are striking in that viral sequences exhibit relatively limited clustering according to geographic region, particularly for those viruses sampled from birds, and no strong phylogenetic association with well sampled avian species. The genome sequence data analysed here also contain relatively little evidence for adaptive evolution, particularly on structural proteins, suggesting that most viral lineages are of similar fitness, and that WNV is well adapted to the ecology of mosquito vectors and diverse avian hosts in the USA. In sum, the molecular evolution of WNV in North America depicts a largely unfettered expansion within a permissive host and geographic population with little evidence of major adaptive barriers.

Journal of Virology↗
USGS2001

The role of native birds and other wildlife on the emergence of zoonotic diseases

Wildlife can be an important source of transmission of infectious disease to humans. One potential transmission route involves hunting and fishing, both common activities in the United States and worldwide. For example, during 1996, approximately 11 million Americans, about 40 percent of the total population 16 years of age and older, took part in some recreational activity relating to wildlife and fish. Another potential route of infection focuses on urban and suburban environments. These locations are of special concern because of their increasing role as wildlife habitat, the greater interface between humans and wildlife that takes place within those environments, the paucity of knowledge about disease in those wildlife populations, and the general lack of orderly management for wildlife within those environments. In the wild, several trends are contributing to the growing importance of zoonotic diseases. First, the spectrum of infectious diseases affecting wildlife today is greater than at any time during the previous century. Second, the occurrence of infectious diseases has changed, from sporadic, self-limiting outbreaks that generally resulted in minor losses to frequently occurring events that generally result in major losses of wildlife. Third, disease emergence has occurred on a worldwide scale in a broad spectrum of wildlife species and habitats. Given the scope of the problem, current disease surveillance efforts are inadequate. Few state wildlife agencies allocate personnel and resources to address wildlife disease, despite their statutory responsibility for managing nonmigratory wildlife. Some state agencies provide minimal support for regional programs based at universities. At the federal level, the primary surveillance effort is conducted by the National Wildlife Health Center, operated by the U.S. Geological Survey. Outside of government, some veterinary schools, agriculture diagnostic laboratories, and other programs provide additional information on animal diseases, primarily by examining carcasses of dead wildlife submitted for analysis, and individual university-based researchers carry out a variety of studies. Typically, information about the occurrence of disease in free-ranging wildlife is derived from surveys and mortality events in areas where wildlife observations by agencies and the public are frequent enough to detect their occurrence before carcasses are removed by scavengers and predatory animals. The result is that disease occurrence is grossly underreported, heavily biased toward mortality events, and biased toward species of special concern and interest, such as game and endangered species. Therefore, the available information should be viewed as the “proverbial tip of the iceberg” relative to disease activity within wildlife populations.

National Academy of Science.↗