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West Nile Virus_ Florida 7_24_01

CEI LogoWest Nile Virus, Florida

Impact Worksheet, July 24, 2001


Summary:

The first equine case of West Nile virus (WNV) in the United States in 2001was confirmed on July 20 in a Florida horse by USDA-APHIS National Veterinary Services Laboratories. The positive horse was located in Jefferson County, Florida (green area on map below). In addition, two other ill horses on two separate premises in Jefferson County were classified as probable cases of WNV infection.

This is the farthest south that WNV has been found in the US. In 2000, WNV cases in equids were found in the northeastern US only as far south as Delaware, although WNV-infected birds were reported as far south as North Carolina. This is also the earliest onset of equine WNV in the US. In 2000, the earliest onset of clinical disease due to WNV was in mid-August.

West Nile virus-positive crows were reported in Jefferson County in June 2001 and later in adjacent Madison County. Although mosquitoes have been collected in the area, no WNV-positive pools have been detected.

West Nile - Florida

The total US equine inventory on January 1, 1999 was 5.3 million. Florida, with 170,000 head, accounted for 3.2 percent of the US total. Equine exports from Florida totalled $8.3 million in 2000.

Florida has also had recent cases of eastern equine encephalitis (EEE) in relatively close proximity to the WNV cases. Although clinical signs of WNV and EEE in equids are similar, the two diseases can be differentiated by serologic testing.

How extensive is the situation?

The first equine case of West Nile virus (WNV) in the United States in 2001was confirmed on July 20 in a Florida horse by USDA-APHIS National Veterinary Services Laboratories (NVSL) in Ames, IA. The positive horse was located in Jefferson County, Florida. In addition, two other ill horses on two separate premises in the same county have been classified as probable cases of WNV infection.

WNV activity was recently reported in this area of Florida, including the finding of WNV positive crows in June in Jefferson County and later in adjacent Madison County. Although mosquitoes have been collected in the area, no WNV positive pools have been detected.

The confirmed case was an adult male horse that was euthanized on or about July 12. Serum and brain samples were collected prior to death and sent to the Florida Department of Agriculture and Consumer Services' laboratory in Kissimmee. A positive hemagglutination inhibition (HI) test result was obtained at that lab and serum and brain were forwarded to NVSL for WNV confirmation. NVSL confirmed the diagnosis by positive results on an IgM-capture enzyme-linked immunosorbent assay (ELISA) on serum, and by a positive reverse transcriptase nested polymerase chain reaction (RT-nPCR) on brain tissue.

Serum from the other two horses with signs of WNV infection also tested positive on HI testing in Kissimmee, FL. Serum from these two horses was then forwarded to NVSL. Both horses had positive IgM-capture ELISA test results at NVSL. Onset of illness in one of the horses was late June and the other horse in early July. These probable cases may be reclassified as confirmed cases based on the results of additional serological testing currently being conducted at NVSL.

Source: USDA:APHIS:VS, Emergency Programs

What is the equine population in Florida and the US?

The total US equine inventory on January 1, 1999 was 5.3 million. Florida, with 170,000 head, accounted for 3.2 percent of the US total. These numbers include horses, ponies, mules, burros, and donkeys. According to the 1997 US Census of Agriculture, which included only on-farm animals, Jefferson County was not a major horse county, accounting for only 0.9 percent of Florida’s horses and ponies on farms.

Source: USDA:NASS

What are Florida’s and the US’s exports of Equids?

The United States exported a total of 77,089 live horses, asses, and mules in 2000, amounting to $423.4 million (Table A). The highest number of horses (26,573) were exported to Canada, but the greatest dollar amount ($90.5 million) went to Ireland. Exports via Florida ports were $8.3 million dollars in 2000, a significant drop from $23.5 million in 1999 (Table B). The greatest dollar amount of exports from Florida went to Brazil in 2000 and Ireland in 1999. These data included horses travelling to races and breeding horses that will return to the U.S. It should also be noted that Table B shows exports from Florida ports: these animals may or may not have originated in Florida. Number quantities were not available for exports via Florida. The tables below show total exports and the top ten export destinations.

Table A: U.S. Exports of Horses, Asses and Mules

Quantity (Number)

Millions of Dollars

1999

2000

1999

2000

World

Canada

Japan

Ireland

United Kingdom

Australia

United Arab Emirates

Mexico

Hong Kong

Sweden

France

Source: World Trade Atlas

Table B: U.S. Exports of Horses, Asses, and Mules via Florida

Millions of Dollars

1999

2000

World

Brazil

Canada

Venezuela

Argentina

Ireland

Colombia

Japan

Turkey

Netherlands

Panama

Source: World Trade Atlas

Are there any other considerations regarding this event?

Based on the geographic spread of WNV from 1999 to 2000, further expansion in 2001 was not unexpected. In 2000, WNV cases in equids were found in the northeastern US only as far south as Delaware, although WNV-infected birds were reported as far south as North Carolina.

A factor which may confound the clinical detection of WNV in equids is the presence of eastern equine encephalitis (EEE) in Florida’s panhandle. As of late June 2001, more than 20 cases of EEE were reported in 2 counties (Holmes and Jackson) which are less than 100 miles west of Jefferson county. Additional suspect cases were under investigation in surrounding counties. Thus, the areas with equine cases of EEE and WNV appear to be in relatively close proximity.

Clinical signs of WNV and EEE in equids are similar, i.e., neurologic signs. However, the two diseases can be differentiated by serologic testing.

Based on the observation that most WNV-positive premises in 2000 had only one infected equid, it appears that WNV does not transmit easily between equids. Evidence to date has not shown movement of horses to be a factor to contributing to spread of WNV. Thus, movement of horses probably does not present a significant risk for spreading WNV.

Sources: Florida Dept of Agriculture and Consumer Services, Press release, 06-29-01; USDA:APHIS:VS

CEI’s plans for follow up:

CEI has no plans for further reports regarding this event. If you seek additional information, please contact Ken Geter at (970) 490-7817 or Chris Kopral at (970) 490-7819.



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