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WNV_ USA 9_11_01

CEI LogoWest Nile Virus in the United States

Impact Worksheet, September 11, 2001


Summary: As of 11 September 2001, at least one case of equine or avian West Nile Virus in 2001 (WNV) was confirmed in 18 states east of the Mississippi River, District of Columbia, and Louisiana. Eight states have reported a total of 67 confirmed WNV cases in horses in July, August, and September 2001. Evidence to date has not shown movement of horses to be a factor contributing to spread of WNV. A conclusion that WNV does not transmit between equine is supported by observations that most WNV-positive premises in 2000 had only one infected horse, and by results of studies involving (1) horse innoculation and (2) transmission by mosquitoes. Results from a recent USDA:APHIS:VS case-control study of WNV cases in 2000 suggest that equine cases may be associated with proximity to avian habitats.

Total US equine inventory in 1999 was 5.3 million. States east of the Mississippi River, plus Louisiana, had combined inventory of 2.4 million, or 45 percent of the US total. Equine exports from eastern states, primarily Kentucky and New York, were valued at about $378 million dollars in 2000, an increase from $257 million in 1999. The United States exported a total of 77,089 live horses, asses and mules in 2000, valued at $423.4 million.

West Nile US

How extensive is the situation?

As of 11 September 2001, at least one case of equine or avian West Nile Virus (WNV) had been confirmed in 18 states east of the Mississippi River, plus District of Columbia and Louisiana. Eight states have reported a total of 67 confirmed WNV cases in equine, all horses: Connnecticut, Florida, Georgia, Kentucky, Louisiana, New York, Pennsylvania, and Virginia. Fifty-four of the 67 equine cases were in Florida. Equine cases began appearing in Florida, Georgia, and Pennsylvania in July 2001, which was earlier than the first US equine cases were seen in 2000 (mid-August). Estimated dates of onset of the disease in the other five states with equine cases were in August.

Avian cases have been confirmed in 17 states east of the Mississippi River, plus Louisiana. Kentucky (which samples wild birds for WNV) was the only state with a confirmed WNV equine case that had not reported any confirmed WNV cases in birds as of 11 September 2001. The geographic range of states with avian cases stretches from Michigan and Wisconsin in the north, to New Hampshire and Massachusetts in the east, to Louisiana and Florida in the south.

Sources: USDA:APHIS:VS, Emergency Programs; CT Dept of Environmental Protection web site; New York State Department of Health web site; United States Geological Survey

What is the equine population in the Eastern United States and Louisiana?

Total US equine inventory in 1999 was 5.3 million. The 27 eastern states (including Louisiana), had 2.4 million head, which is about 45 percent of the US total (Table B). These numbers include horses, ponies, mules, burros, and donkeys.

Table A: Equine inventory*, Eastern US and Louisiana, 1999

State

Number (1,000)

Alabama

130

Connecticut

26

Delaware

10

Florida

170

Georgia

70

Illinois

100

Indiana

140

Kentucky

155

Louisiana

65

Maine

17

Maryland

45

Massachusetts

35

Michigan

130

Mississippi

75

New Hampshire

8

New Jersey

45

New York

155

North Carolina

140

Ohio

160

Pennsylvania

170

Rhode Island

2

South Carolina

65

Tennesee

190

Vermont

20

Virginia

150

West Virginia

43

Wisconsin

120

Subtotal

2,436

Total US

5,317

* Equids include horses, ponies, mules, burros, and donkeys

Source: USDA:NASS

What are the quantities and values of equine exports from the US and the eastern states?

The United States exported a total of 77,089 live horses, asses and mules in 2000, amounting to $423.4 million (Table B). The highest number of horses (26,573) were exported to Canada, but the greatest dollar amount ($90.5 million) went to Ireland. Exports via eastern states’ ports were $377.6 million dollars in 2000, an increase from $256.7 million in 1999 (Table C). Kentucky and New York accounted for the greatest dollar amounts with $294 million and $48.5 million respectively. Kentucky’s highest value horse exports went to Ireland, United Arab Emirates, and the United Kingdom. New York’s highest value exports went chiefly to Japan.

Tables B and C include short-term exports of horses for races or breeding. Table B shows total US exports and the top ten export destinations. Table C shows exports from the eastern states’ ports (although the animals may not have originated in these states). Number of head were not available for exports from the eastern states.

Table B: U.S. Exports of Horses, Asses and Mules, by Importing Country

Quantity (Number)

Millions of Dollars

1999

2000

1999

2000

World

Canada

Japan

Ireland

United Kingdom

Australia

United Arab Emirates

Mexico

Hong Kong

Sweden

France

Table C: Exports of Horses, Asses, and Mules from the Eastern States

Millions of US Dollars

1999

2000

Connecticut

Delaware

Florida

Georgia

Illinois

Indiana

Kentucky

Louisiana

0.0

0.0

Maine

Maryland

Massachusetts

Michigan

New Hampshire

New Jersey

New York

North Carolina

Ohio

Pennsylvania

Puerto Rico

Rhode Island

South Carolina

Tennessee

Vermont

Virginia

West Virginia

Wisconsin

Total

Source for Tables B and C: World Trade Atlas

Are there any other considerations regarding this event?

A conclusion that WNV does not transmit between equids is supported by observations that most WNV-positive premises in 2000 had only one infected horse, and by results of studies conducted by Centers for Disease Control and Colorado State University involving (1) horse innoculation and (2) mosquito transmission. Evidence to date has not shown movement of horses to be a factor contributing to WNV spread. In 2000, WNV cases in US horses were found only as far south as Delaware, although WNV-infected birds were reported as far south as North Carolina.

A case-control study coordinated by USDA:APHIS:VS was conducted in seven eastern states with confirmed equine WNV cases in 2000. The study used spatial analysis to describe geographic and ecological characteristics of case premises. Study results suggested that equine cases may be associated with proximity to blackbird roosts and waterfowl habitats. The report also noted that exposure of equids to WNV was a geographically clustered event. This report is available from the VS Centers for Epidemiology and Animal Health: http://www.aphis.usda.gov/vs/ceah/wnvhighlights.pdf (summary and highlights), and http://www.aphis.usda.gov/vs/ceah/wnvreport (full report).

A West Nile Virus vaccine for horses was conditionally licensed for manufacture, distribution and use for one year beginning August 2001. The Animal and Plant Health Inspection Service issued the license for the killed virus vaccine to American Home Products, Inc. of Fort Dodge, Iowa. The product is restricted to use by a veterinarian in those states where use of the product has been approved by state regulators. Horse owners planning to ship their animals to other countries should be aware that vaccinated animals may not meet the import requirements of those countries due to the presence of certain antibodies in their blood. While the presence of antibodies from the vaccine is not permanent, complications in shipping the horse may result.

Conditional licenses are generally issued with restrictions and for a limited period. At the end of the conditional license period, data on a product’s efficacy, potency, and performance are evaluated to determine if the license should be renewed or extended.

Sources: Florida Dept of Agriculture and Consumer Services, Press release, 29 June 2001; USDA:APHIS:VS press release, 1 Aug 2001; USA Today, 4 Sept 2001

CEI’s plans for follow up:

As of 11 September 2001, CEI has no plans for further reporting on WNV. If you have questions or comments on this worksheet, please contact David Cummings at (970) 490-7895 or Ken Geter at (970) 490-7817.



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