Weather factors in the prediction of western equine encephalitis epidemics in Manitoba.
Abstract: Cases of western equine encephalitis in horses in 1987 in western USA and Manitoba, Canada were examined by backward trajectory analysis of winds. Culex tarsalis mosquitoes infected with western equine encephalitis virus could have been carried on southerly winds from Texas and Oklahoma to northern USA and from there to Manitoba. The presence of the Polar front over North Dakota and Minnesota at the end of July would have led to the landing of Cx. tarsalis in Montana and Wisconsin and prevented further carriage into Manitoba. Temperatures in southern Texas during the winter months (average daily maximum temperatures 19.7 degrees C and higher) would have permitted continuous transmission of western equine encephalitis virus by Cx. tarsalis in this area. Weather factors involved in outbreaks from 1975-88 were analysed to see if epidemics in Manitoba (23 or more cases in horses) could be predicted. The conditions for epidemics could be defined as follows: (a) the number of cases in horses in USA was 98 or more, (b) winds were southerly with speeds 45 kmh-1 or higher, and (c) counts of Cx. tarsalis females/light trap per day were 3.2 or higher. There were 3 or fewer cases in Manitoba, when the number of cases in USA was 27 or less, even when Cx. tarsalis counts were higher than 3.2. With Cx. tarsalis counts below 3 and/or unsuitable winds, or the Polar front further south, the number of cases in Manitoba was between 0 and 17, even when the number of cases in USA was from 38-172. Without information on the extent of infection further south, the weather variables would probably be more useful in excluding the possibility of an epidemic in Manitoba than in predicting one.
Publication Date: 1993-10-01 PubMed ID: 8405163PubMed Central: PMC2271377DOI: 10.1017/s0950268800057071Google Scholar: Lookup
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- Journal Article
- Animal Health
- Animal Science
- Climate
- Disease
- Disease control
- Disease Outbreaks
- Disease Prevalence
- Disease Surveillance
- Disease Transmission
- Epidemiology
- Equine Diseases
- Equine Health
- Horses
- Infectious Disease
- Mosquito-borne Diseases
- Public Health
- Vector-borne disease
- Veterinary Science
- Weather
- Western Equine Encephalitis
Summary
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The research investigates how weather factors, mosquito populations, and equine encephalitis outbreaks in the United States can be used to predict epidemics of the disease in Manitoba, Canada.
Research Method
- The researchers studied cases of western equine encephalitis (WEE) in horses that occurred in the western USA and Manitoba, Canada in 1987.
- They used backward trajectory analysis, a method used to trace the path taken by an entity (in this case, mosquitoes) based on wind patterns, to theorize likely transportation routes of the virus-carrying mosquitoes.
Findings
- They suggest that Culex tarsalis mosquitoes, which carry the WEE virus, could have been transported by southerly winds from Texas and Oklahoma to the northern USA and from there to Manitoba.
- The researchers found that the presence of the Polar front over North Dakota and Minnesota would prevent continuation of the insects’ journey into Manitoba.
- The study also noted that winter temperatures in southern Texas would allow for year-round transmission of the WEE virus by these mosquitoes.
Conditions for Epidemics
- The researchers established certain conditions under which an epidemic in Manitoba could occur and be predicted: if there were 98 or more cases in the US, southerly winds with speeds of 45 km/h or higher, and a higher female Culex tarsalis count.
- However, even when female Culex tarsalis counts were high, three or fewer cases appeared in Manitoba if the number of cases in the US was 27 or less.
- Furthermore, with low mosquito counts and/or unsuitable winds, or a southern Polar front, Manitoba saw between 0 and 17 cases even when the US had between 38 and 172.
Limits of Predictive Power
- Despite these findings, the authors concluded that without information about the degree of infection further south, these weather and mosquito population variables might be more useful for excluding the possibility of an epidemic in Manitoba than for predicting one.
Cite This Article
APA
Sellers RF, Maarouf AR.
(1993).
Weather factors in the prediction of western equine encephalitis epidemics in Manitoba.
Epidemiol Infect, 111(2), 373-390.
https://doi.org/10.1017/s0950268800057071 Publication
Researcher Affiliations
- Agriculture Canada, Health of Animals Laboratory Division, Ottawa, Ontario.
MeSH Terms
- Animals
- Culex / microbiology
- Disease Outbreaks / veterinary
- Encephalitis Virus, Western Equine
- Encephalomyelitis, Equine / epidemiology
- Encephalomyelitis, Equine / transmission
- Encephalomyelitis, Equine / veterinary
- Female
- Horse Diseases / epidemiology
- Horse Diseases / transmission
- Horses
- Insect Vectors / microbiology
- Manitoba / epidemiology
- Risk Factors
- Temperature
- United States / epidemiology
- Weather
- Wind
References
This article includes 15 references
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