Characteristics of an outbreak of West Nile virus encephalomyelitis in a previously uninfected population of horses.
Abstract: Equine West Nile virus (WNV) encephalomyelitis cases - based on clinical signs and ELISA serology test results - reported to Texas disease control authorities during 2002 were analyzed to provide insights into the epidemiology of the disease within a previously disease-free population. The epidemic occurred between June 27 and December 17 (peaking in early October) and 1,698 cases were reported. Three distinct epidemic phases were identified, occurring mostly in southeast, northwest and then central Texas. Significant (P<0.05) disease clusters were identified in northwest and northern Texas. Most (91.1%) cases had no recent travel history, and most (68.9%) cases had not been vaccinated within the previous 12 months. One-third of cases did not survive, 71.2% of which were euthanatized. The most commonly reported presenting signs included ataxia (69%), abnormal gait (52%), muscle fasciculations (49%), depression (32%) and recumbency (28%). Vaccination status, ataxia, falling down, recumbency and lip droop best explained the risk of not surviving WNV disease. Results suggest that the peak risk period for encephalomyelitis caused by WNV may vary substantially among regions within Texas. Recumbent horses have a poor prognosis for survival. Vaccines, even if not administered sufficiently in advance of WNV infection within a district, may reduce the risk of death by at least 44%.
Publication Date: 2006-07-26 PubMed ID: 16971067DOI: 10.1016/j.vetmic.2006.07.016Google Scholar: Lookup
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Summary
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This research paper assesses and provides insight into an outbreak of West Nile virus (WNV) encephalomyelitis in a horse population in Texas during 2002 that had not been previously exposed to the virus. The study uncovers various aspects of the outbreak, including the phases of the epidemic, disease clusters, recent travel history of affected horses, vaccination status, survival rate, and commonly reported signs of the disease.
Epidemiological Analysis of WNV Encephalomyelitis Outbreak
This study undertakes a comprehensive analysis of equine West Nile virus (WNV) encephalomyelitis cases reported in Texas in 2002, which is based on clinical signs and ELISA serology tests.
- The epidemic occurred between June 27 to December 17, peaking in early October and affecting around 1,698 horses.
- The study identifies three distinct phases of the epidemic that majorly occurred in southeast, northwest, and central Texas.
- Two significant disease clusters were identified in northwest and northern Texas.
Travel and Vaccination History of Affected Horses
The research also delves into the travel and vaccination history of the affected horses, as these factors could potentially influence the spread and severity of the disease.
- It is noted that a majority (91.1%) of the horses afflicted by the disease had no recent travel history.
- About 68.9% of the afflicted horses had not been vaccinated within the previous 12 months.
Survival Rate and Clinical Signs
The survival rate and the symptoms presented by afflicted horses were also scrutinized.
- The study reports a low survival rate with one-third of the horses not surviving the outbreak.
- The majority of the horses that died (71.2%) were actually euthanized.
- The most common clinical signs observed in horses included ataxia (lack of muscle control – 69%), abnormal gait (52%), muscle fasciculations (involuntary muscle twitching – 49%), depression (32%), and recumbency (lying down – 28%).
Disease Risk Factors and Prognosis
In terms of risk factors and prognosis, the paper illustrates the impact of specific variables on disease progression and mortality.
- Vaccination status, ataxia, falling down, recumbency and lip droop were found to have significant influence on the chances of a horse not surviving the disease.
- The study also asserts the varying peak risk period for encephalomyelitis caused by WNV across different regions within Texas.
- The prognosis for recumbent horses was observed to be poor.
Role of Vaccination
The role of vaccinations in potentially mitigating the risk of death was also examined.
- Even if not administered adequately in advance of WNV infection within a district, vaccines were found to reduce the risk of death by at least 44%.
Cite This Article
APA
Ward MP, Schuermann JA, Highfield LD, Murray KO.
(2006).
Characteristics of an outbreak of West Nile virus encephalomyelitis in a previously uninfected population of horses.
Vet Microbiol, 118(3-4), 255-259.
https://doi.org/10.1016/j.vetmic.2006.07.016 Publication
Researcher Affiliations
- Department of Veterinary Integrative Biosciences, MS 4458, Texas A&M University, College Station, TX 77843-4458, USA. mward@cvm.tamu.edu
MeSH Terms
- Animals
- Cluster Analysis
- Disease Outbreaks / veterinary
- Encephalomyelitis / epidemiology
- Encephalomyelitis / mortality
- Encephalomyelitis / veterinary
- Encephalomyelitis / virology
- Female
- Geography
- Horse Diseases / epidemiology
- Horse Diseases / mortality
- Horse Diseases / virology
- Horses
- Male
- Prognosis
- Risk Factors
- Seasons
- Texas / epidemiology
- Time Factors
- West Nile Fever / epidemiology
- West Nile Fever / mortality
- West Nile Fever / veterinary
- West Nile Fever / virology
- West Nile Virus Vaccines / administration & dosage
- West Nile Virus Vaccines / immunology
- West Nile virus / isolation & purification
Citations
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