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Journal of medical entomology1993; 30(1); 151-160; doi: 10.1093/jmedent/30.1.151

Effect of temperature on the transmission of western equine encephalomyelitis and St. Louis encephalitis viruses by Culex tarsalis (Diptera: Culicidae).

Abstract: The extrinsic incubation rate (inverse of the time in days from infection to median transmission) of western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses by laboratory strains of Culex tarsalis Coquillett increased as a linear function of incubation temperatures from 10 to 30 degrees C. The estimated temperatures for zero transmission thresholds (intercept of the X axis) were 10.9 and 14.9 degrees C, and the number of degree days above these thresholds required for median transmission (inverse of the slope) was 67.6 and 115.2, respectively. Although the bodies of most Cx. tarsalis females remained infected and the WEE viral titer did not decrease significantly throughout the incubation periods at all temperatures, transmission rates by females incubated at 20 to 30 degrees C decreased markedly after peaking at 7-10 d after infection. In contrast, midgut escape and salivary gland infection barriers limited the transmission rates of SLE virus at all temperatures, but these rates did not decrease markedly as a function of incubation time, indicating that virus modulation did not occur. Degree-day models were used to calculate monthly changes in the duration of the extrinsic incubation period for WEE and SLE viruses in the San Joaquin and Coachella valleys based on mosquito temperatures estimated by combining nocturnal air and diurnal resting site temperatures. Temperatures in the San Joaquin Valley averaged 5 degrees C cooler than in the Coachella Valley, proportionately shortening the duration of the potential transmission season for WEE virus from 10 to 8 mo and for SLE virus from 8 to 5 mo, respectively.
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Publication Date: 1993-01-01 PubMed ID: 8433322DOI: 10.1093/jmedent/30.1.151Google Scholar: Lookup
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  • U.S. Gov't
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article investigates how varying temperatures impact the transmission rates of two viruses, western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE), by Culex tarsalis, a type of mosquito.

Extrinsic Incubation Rate and Transmission Thresholds

  • The extrinsic incubation rate indicates the speed with which a virus can be spread by a carrier, in this case, the Culex tarsalis mosquito. The researchers found that this rate increased linearly as the incubation temperature rose between 10 to 30 degrees Celsius.
  • The zero transmission thresholds, the temperatures below which the viruses can’t be transmitted, were determined to be 10.9 degrees Celsius for WEE and 14.9 degrees Celsius for SLE.
  • The number of degree days (a measurement indicating how much and for how long the temperature was above a certain level) necessary for median transmission was found to be 67.6 for WEE and 115.2 for SLE.

Viral Titer and Transmission Rates

  • WEE viral titer, which is the concentration of the virus in the mosquito’s body, did not change significantly throughout all incubation temperatures. However, the transmission rates dropped significantly after 7-10 days of infection when mosquitoes were kept at 20-30 degrees Celsius.
  • For the SLE virus, barriers in the midgut and the salivary gland of the mosquitoes limited transmission rates at all temperatures. However, unlike WEE, the transmission rates did not decrease noticeably with time, which suggests that there was no virus modulation – a process where a virus changes its behavior or characteristics in response to the environment or host defenses.

Extrinsic Incubation Period and Potential Transmission Season

  • Using degree-day models, the researchers estimated the changes in the extrinsic incubation period for both WEE and SLE across months using estimated mosquito temperatures, derived from a combination of nocturnal air and diurnal resting site temperatures.
  • It was found that temperatures in the San Joaquin Valley averaged 5 degrees Celsius cooler than in the Coachella Valley, impacing the length of the potential transmission season for the two viruses: the season for WEE was shortened from 10 to 8 months and for SLE from 8 to 5 months.

Cite This Article

APA
Reisen WK, Meyer RP, Presser SB, Hardy JL. (1993). Effect of temperature on the transmission of western equine encephalomyelitis and St. Louis encephalitis viruses by Culex tarsalis (Diptera: Culicidae). J Med Entomol, 30(1), 151-160. https://doi.org/10.1093/jmedent/30.1.151

Publication

Journal of medical entomology
ISSN: 0022-2585
NlmUniqueID: 0375400
Country: England
Language: English
Volume: 30
Issue: 1
Pages: 151-160

Researcher Affiliations

Reisen, W K
  • Department of Biomedical and Environmental Health Sciences, School of Public Health, University of California, Berkeley 94720.
Meyer, R P
    Presser, S B
      Hardy, J L

        MeSH Terms

        • Animals
        • Culex / microbiology
        • Encephalitis Virus, St. Louis / growth & development
        • Encephalitis Virus, Western Equine / growth & development
        • Encephalitis, St. Louis / transmission
        • Encephalomyelitis, Equine / transmission
        • Female
        • Insect Vectors / microbiology
        • Temperature

        Grant Funding

        • 5-R22-AI-03028 / NIAID NIH HHS

        Citations

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