Seasonal variation in the vector competence of Culex tarsalis (Diptera:Culicidae) from the Coachella Valley of California for western equine encephalomyelitis and St. Louis encephalitis viruses.

This research paper examines how the vector competence, or ability to transmit diseases, of Culex tarsalis mosquitoes in Coachella Valley, California for Western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses changes across different seasons.

Research Background

• The study focuses on understanding changes in the ability of the mosquito species Culex tarsalis to transmit the Western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses over different seasons within a year. Both WEE and SLE are viral diseases that affect the central nervous system of humans and animals.
• The implications of such a study lie in the broader scope of disease control and prevention, where understanding seasonal changes in vector competence could potentially aid in formulating measures to control the spread of these diseases.

Methodology

• Researchers observed the mosquitoes monthly from February to November 1993 in the Coachella Valley region of California, testing the concentrations of WEE and SLE viruses and tracking infection and transmission rates across seasons.
• The concentration of the WEE virus necessary to infect 50% of females was measured and was found to increase during summer, correlating with rising ambient temperatures, and peaking in July.

Findings

• Transmission rates of the WEE virus were found to be high during March, lower during May-June, and high again from July-September. This suggests a pattern of seasonal variation in virus transmission.
• In the case of WEE, the mosquitoes exhibited internal barriers, impeding virus dissemination and lowering transmission rates. These barriers exist in the mosquito’s midgut (mesenteronal escape barrier) and salivary glands.
• Contrarily, SLE virus infection and dissemination rates did not exhibit such monthly variation. Even though the SLE infection rates were moderate, most infected female mosquitoes developed disseminated infections, indicating no internal limitations.
• Nevertheless, barriers in the salivary gland did have an impact on SLE virus transmission, preventing disease transmission in 16-100% of infected females.

Conclusion

• The research highlighted the importance of understanding seasonal variations in mosquito vector competence as a crucial piece of managing and preventing the spread of virus-based diseases.
• Findings from the study could have practical applications in formulating time-bound disease intervention and mosquito control strategies.