Identification of salivary gland escape barriers to western equine encephalitis virus in the natural vector, Culex tarsalis.
Authors: Stauft Charles B, Phillips Aaron T, Wang Tony T, Olson Kenneth E
Journal: PloS one
Summary
Western equine encephalitis virus (WEEV) transmission dynamics depend not just on viral replication within mosquito vectors, but critically on the virus's ability to cross a salivary gland escape barrier (SEB)—a previously uncharacterised restriction that limits passage from the insect's body into saliva where transmission to horses occurs. Using Culex tarsalis mosquitoes experimentally infected with two WEEV strains (one originally from mosquitoes, one from a human case), researchers demonstrated that whilst both viruses successfully reached the salivary glands following direct injection, the mosquito-derived IMP181 strain achieved substantially higher salivary titres and transmission rates than the human-derived McMillan strain, indicating differential adaptation to crossing the SEB. Through chimeric virus construction, the authors identified that the structural proteins of the IMP181 strain conferred partial ability to circumvent this barrier, suggesting the salivary gland escape mechanism involves specific viral protein interactions rather than non-specific replication capacity. These findings have important implications for understanding why certain WEEV isolates pose greater epidemiological risk to equine populations: variants naturally circulating in mosquito populations may be inherently more transmissible due to structural adaptations that facilitate salivary secretion, even if multiple strains can establish infection within the vector. Equine practitioners managing WEEV risk should recognise that vector competence varies significantly between strains, meaning epidemiological surveillance and vaccine development strategies should account for this heterogeneity in transmission potential.
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Practical Takeaways
- •Understanding vector competence barriers to WEEV may inform epidemiological risk assessment for western equine encephalitis in equine populations
- •Virus strain origin (mosquito-adapted versus human-isolated) affects transmission efficiency, which has implications for disease outbreak patterns
- •Structural proteins play a key role in overcoming salivary gland barriers, potentially relevant to understanding natural transmission cycles
Key Findings
- •Culex tarsalis mosquitoes possess a salivary gland escape barrier (SEB) that restricts WEEV transmission
- •IMP181 strain (mosquito-isolated) achieved higher virus titers in saliva and better transmission rates compared to McMillan strain (human-isolated)
- •IMP181-derived structural genes can partially circumvent the salivary gland escape barrier in chimeric recombinant WEEV strains