Journal Article

Transmission cycles, host range, evolution and emergence of arboviral disease

Barrett, Alan D. T., Weaver, Scott C.

2004

Overview

Key Points Many recent viral pandemics have been attributed to the ability of some RNA viruses, for example HIV, dengue virus and possibly the severe acute respiratory syndrome (SARS) coronavirus, to change their host range to include humans. The authors discuss the mechanisms of host-range alteration used by a selection of viruses, including Venezuelan equine and Japanese encephalitis viruses (VEEV and JEV, respectively), dengue virus and West Nile virus (WNV). Venezuelan equine encephalitis (VEE) was first recognized as a disease of horses, donkeys and mules in northern South America during the mid 1930s, but there has been renewed interest in this virus because of its potential as a biological weapon. Molecular analysis of epidemic strains — which exploit horses for amplification — and comparison with strains that do not cause epidemic disease, have shown that a few amino-acid mutations can affect host-range alteration. Changes on the surface of the VEE virion seem to be important for these host range changes. JEV causes epidemics of encephalitis in India, Korea, China, South-East Asia and Indonesia. The disease affects children, and is associated with a mortality rate of greater than 20%. However, unlike VEEV, there is no evidence that JEV undergoes mutation and selection to replicate in different hosts. Pigs amplify transmission in peridomestic settings, and migratory birds have a role in dispersion of JEV. Although different genotypes have been isolated, their relevance to pathology and host range is unclear. WNV is now endemic in the United States after first emerging in New York in 1999. WNV has a very broad host range. Forty-nine species of mosquitoes and ticks, and 225 species of birds are susceptible to infection. Other hosts include horses, cattle, llamas, alligators, cats, dogs, wolves and sheep. Transmission of WNV among these species has not been reported. Although humans are probably dead-end hosts, infection with WNV can cause severe disease. Dengue viruses are very important human arboviral pathogens and use humans as reservoir hosts. Aedes aegypti and Aedes albopictus mosquitoes are the most common vectors in urban settings. It is thought that the human epidemic form of dengue virus evolved in the last 2000 years, and genetic analysis indicates that mutations have resulted in adaptation to the urban mosquito host. However, links between mutations and human pathogenicity have not been established. Finally, the authors discuss how host-range changes can be studied experimentally. Cell-culture model systems can be used to find mutations that correlate with virus fitness and adaptation in different host strains. Viruses that replicate in useful laboratory animal models can also be studied in whole animal hosts. Many pandemics have been attributed to the ability of some RNA viruses to change their host range to include humans. Here, we review the mechanisms of disease emergence that are related to the host-range specificity of selected mosquito-borne alphaviruses and flaviviruses. We discuss viruses of medical importance, including Venezuelan equine and Japanese encephalitis viruses, dengue viruses and West Nile viruses.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: Adaptation / Aedes aegypti / Aedes albopictus / Alphavirus - genetics / Alphavirus - pathogenicity / Amino acids / Animal models / Animals / Aquatic animals / Aquatic insects / Aquatic reptiles / Arbovirus Infections - etiology / Arbovirus Infections - transmission / Arboviruses - genetics / Arboviruses - pathogenicity / Arthropods / Biological Evolution / Biomedical and Life Sciences / Birds / Cell culture / Coronaviruses / Culicidae / Dengue - etiology / Dengue - transmission / Dengue fever / Dengue virus / Dengue Virus - genetics / Dengue Virus - pathogenicity / Disease Outbreaks / Disease transmission / Encephalitis / Encephalitis Virus, Japanese - genetics / Encephalitis Virus, Japanese - pathogenicity / Encephalitis Virus, Venezuelan Equine - genetics / Encephalitis Virus, Venezuelan Equine - pathogenicity / Encephalitis, Japanese - etiology / Encephalitis, Japanese - transmission / Encephalomyelitis, Venezuelan Equine - etiology / Encephalomyelitis, Venezuelan Equine - transmission / Epidemics / Flavivirus - genetics / Flavivirus - pathogenicity / Genetic analysis / Genomes / Genotypes / Horses / Host range / Human immunodeficiency virus / Humans / Illnesses / Immunology / Infections / Infectious Diseases / Japanese encephalitis virus / Laboratory animals / Life Sciences / Medical importance / Medical Microbiology / Microbiology / Migratory birds / Mosquitoes / Mutation / Pandemics / Parasitology / Pathogenicity / Phylogeny / Proteins / Public health / Respiratory diseases / review-article / Ribonucleic acid / RNA / RNA viruses / SARS coronavirus / Severe acute respiratory syndrome / Strains (organisms) / Ticks / Tropical diseases / Urban areas / Urban environments / Vector-borne diseases / Vectors / Venezuelan equine encephalitis / Venezuelan equine encephalitis virus / Viral diseases / Virions / Virology / Viruses / West Nile Fever - etiology / West Nile Fever - transmission / West Nile virus / West Nile virus - genetics / West Nile virus - pathogenicity / Wolves