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Epidemiology and infection1988; 101(3); 511-535; doi: 10.1017/s095026880002940x

Impact of climate on western equine encephalitis in Manitoba, Minnesota and North Dakota, 1980-1983.

Abstract: Information was collected on confirmed outbreaks of western equine encephalitis (WEE) in North America east of the Rockies for 1981 and 1983 (epidemic years) and 1980 and 1982 (non-epidemic years). The initial pattern of outbreaks in Manitoba, Minnesota and North Dakota was determined for each year. Backward (and in some instances forward) wind trajectories were computed for each day 4-15 days (incubation period) before the initial outbreaks of WEE in a given area of province or state. During these years the timing and location of WEE outbreaks in horses and man, seroconversion in chickens, the maximum Culex tarsalis counts at Winnipeg and first isolation of WEE virus from C. tarsalis could be correlated with trajectories of winds from states further south within acceptable intervals. It is suggested that C. tarsalis mosquitoes infected with WEE virus are carried on the wind from Texas on the Gulf of Mexico, where they continue to breed during the northern winter months, to northern Texas and Oklahoma in the spring. In May, June and July C. tarsalis are carried north on southerly winds from these states through Kansas and Nebraska to North Dakota, Minnesota, Wisconsin and Manitoba. Distances of 1250-1350 km are traversed in 18-24 h at heights up to 1.5 km with temperatures greater than or equal to 13 degrees C. Landing takes place where the warm southerly winds meet cold fronts associated with rain. Convergence leads to concentration of C. tarsalis and determines where outbreaks occur. It is possible that return of new generations of C. tarsalis to the south may occur later in the year. The development of an epidemic of WEE in the northern states and provinces would appear to depend on (i) suitable trajectories from the south in June and July with temperatures greater than or equal to 13 degrees C meeting cold fronts with rain, (ii) sufficient C. tarsalis infected with WEE virus at source, carried on the wind and locally, (iii) C. tarsalis biting horses and man, (iv) maintenance of local mosquito populations in August and (v) susceptible hosts (birds) at source and susceptible hosts (horses and man) locally. Possible methods of prediction involving determination of trajectories, identification of C. tarsalis blood meals, measuring seroconversion in calves are discussed in addition to the methods already in use.
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Publication Date: 1988-12-01 PubMed ID: 2905669PubMed Central: PMC2249417DOI: 10.1017/s095026880002940xGoogle Scholar: Lookup
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  • Journal Article

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 study explores the connection between climate elements like wind trajectories, temperatures, and seasonal changes and the outbreaks of the western equine encephalitis (WEE), particularly in Manitoba, Minnesota, and North Dakota over 1980 to 1983. The investigation suggests that the spread of infected mosquitoes from southern regions contributes to these outbreaks, which are further influenced by the presence of sufficient infected mosquito populations, local weather conditions, and availability of susceptible hosts in the locale.

Findings and Analysis

  • The research collected data on confirmed WEE outbreaks from 1980 to 1983 in different years of epidemic and non-epidemic phases. Backward and forward wind trajectories were computed to trace the pattern of these outbreaks.
  • The study revealed correlation between wind trajectories from the southern states and the timing and location of WEE outbreaks, seroconversion in chickens, maximum C. tarsalis counts at Winnipeg, and first isolation of the WEE virus.
  • The investigation postulates that mosquitoes infected with the WEE virus are carried by the wind from southern regions where they breed during the northern winter months, to northern regions during the spring and summer months.
  • The study further reveals that the infected mosquitoes traverse long distances within 18-24 hours at heights of up to 1.5 km and temperatures more than or equal to 13 degrees Celsius. They land where warm southern winds meet cold, rain-associated fronts.

Development of WEE Epidemics

  • According to the research, the evolution of a WEE epidemic depends on multiple elements. These include wind trajectories from the south with optimal temperatures, meeting with cold fronts and subsequent rainfall.
  • Presence of enough mosquitoes infected with the WEE virus at the source that are carried by the wind and also locally can instigate an outbreak.
  • Other factors include the mosquitoes biting horses and human, local mosquito populations in August and the presence of susceptible hosts at source and locally.

Methods of Prediction

  • The study discusses possible methods of predicting such outbreaks. Determining trajectories, identifying blood meals of C. tarsalis, and measuring seroconversion in calves are proposed methods apart from the ones already in use.

Cite This Article

APA
Sellers RF, Maarouf AR. (1988). Impact of climate on western equine encephalitis in Manitoba, Minnesota and North Dakota, 1980-1983. Epidemiol Infect, 101(3), 511-535. https://doi.org/10.1017/s095026880002940x

Publication

Epidemiology and infection
ISSN: 0950-2688
NlmUniqueID: 8703737
Country: England
Language: English
Volume: 101
Issue: 3
Pages: 511-535

Researcher Affiliations

Sellers, R F
  • Agriculture Canada, Health of Animals Laboratory Division, Ottawa, Ontario.
Maarouf, A R

    MeSH Terms

    • Animals
    • Chickens / microbiology
    • Climate
    • Culicidae
    • Disease Outbreaks
    • Encephalitis Virus, Western Equine
    • Encephalomyelitis, Equine / epidemiology
    • Encephalomyelitis, Equine / transmission
    • Horse Diseases / epidemiology
    • Horses
    • Humans
    • Insect Vectors
    • Manitoba
    • Minnesota
    • North Dakota

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    Citations

    This article has been cited 8 times.
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