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West Nile virus

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West Nile virus,
Northeastern US
October 1999
Impact Worksheet




For the latest information on West Nile Virus please visit the APHIS West Nile Virus webpage.

Summary: An outbreak of arboviral encephalitis first occurred in New York City in late August and has since been identified in other New York, Connecticut, and New Jersey counties. As of September 28, there have been 17 confirmed, and 20 probable human cases, and 4 human deaths associated with West Nile-like virus (MMWR, 1999). Prior to and during this outbreak there have been mortalities in crows around the New York City area. The virus was initially identified from bird samples collected at the Bronx zoo. The virus was isolated at NVSL laboratories, and forwarded to the CDC for identification and characterization. Surveillance is ongoing, and wild bird death reports are being encouraged. As of October 5, 1999 the Veterinary Authorities of Hong Kong have stopped issuing permits for the importation of live poultry and hatching eggs from the U.S. due to the presence of West Nile virus.



Prepared by: Center for Emerging Issues, Centers for Epidemiology and Animal Health
Animal and Plant Health Inspection Service, USDA


How extensive is the situation?

An outbreak of arboviral encephalitis first occurred in New York City in late August and has since been identified in other New York, Connecticut, and New Jersey counties. As of September 28, there have been 17 confirmed, and 20 probable human cases, and 4 human deaths associated with West Nile-like virus (MMWR, 1999). Prior to and during this outbreak there have been mortalities in crows around the New York City area. The West Nile-like virus (WNV) was initially identified from bird samples collected at the Bronx zoo. The virus was isolated at NVSL laboratories, and forwarded to the CDC for identification and characterization. Surveillance is ongoing, and wild bird death reports are being encouraged.

WNV is a flavivirus with widespread distribution throughout Africa, the Mediterranean, and Eurasia (EID, 1999). Recent outbreaks have included a large one in Romania during 1996-1997, and one in Italy in 1998 prior to which there had never been any clinically or serologically confirmed cases in the country. During previous outbreaks and studies, the virus has been isolated from numerous vertebrate species including the following: horse, camel, dog, mouse, bat, hamster, chicken, pigeon, hooded crow, warbler, parrot, turtle dove, rook, European nuthatch, rook, Kikrichane thrush, Black Drongo, Squacco heron, white stork and blackbird (CRC, 1989). Perhaps the limits of whether or not the virus has been isolated from a particular bird species is dependent on whether that species has been tested. Chickens have been used as sentinels during surveillance efforts in countries with endemic infection. Typically the West Nile virus does not cause a high mortality in crows. That so many crows have been affected in this outbreak could be due to exposure of a naive bird population or a new, more virulent stain.

Information of signs of West Nile infection in naturally infected horses has been limited and, at times, contradictory. Based on reported signs from previous outbreaks in Egypt, France, and Italy these are some of the symptoms which may be associated with West Nile infection in horses: fever, weakness to paralysis of hind limbs, ataxia, tetraplegia, flaccid paralysis of the lower lip, coma, or death. The case fatality rate has been reported to be as high as 40-45%. One should note that clinical signs have not been well documented for West Nile, and this is still officially identified as a West Nile-like virus.

Virus has been isolated from crows in Suffolk, Nassau, Westchester, and Rockland counties of New York, and in Bergen, Union, Middlesex, and Essex counties of New Jersey, and in Fairfield County of Connecticut. Other than wild birds, current animal surveillance has been limited to police horses, dogs, and poultry within the New York City boroughs.

As of October 5, 1999 the Veterinary Authorities of Hong Kong have stopped issuing permits for the importation of live poultry and hatching eggs from the U.S. due to the presence of West Nile virus.

Source: MMWR 48(38);845-9, CRC The Arboviruses: Epidemiology and Ecology 1989 vol 5, Emerging Infectious Diseases Journal 1999 vol5(5), personal communication with CDC Fort Collins.

What is the US’s place in the international market for affected animals?

During the time period of January to July, 1999, the total US export of equine (horses, asses, mules, etc.) was 31,517 animals, valued at $79.5 million . The vast majority of these animals were exported to Canada. During the time period of January to September, 1999 the following numbers of equine were exported from northeastern US states. These states would be most susceptible to trade restrictions.

Table 1. Equine exported from Northeastern US, Jan-Sept, 1999

State exported from
Number of equine
New York
5,206
New Jersey
760
Connecticut
83
Rhode Island
8
Massachusetts
125
Pennsylvania
425
Source: World Trade Atlas, USDA:APHIS:VS Export Database

Live bird exports from the affected states, from January through September 1999, were 4,363,366 from New York, 27 from New Jersey, and 1,570,085 from Conneticut. The majority (62%) of these birds were exported to Canada. It has been unofficially reported that Hong Kong has stopped issuing import permits for live birds and hatching eggs, and it is feared that China will do the same in the near future.

Table 2. Potential impact of Hong Kong and China trade restrictions.

1998
Jan - July, 1999
$ Million
Quantity (number)
$ Million
Quantity (number)
Hong Kong
Chickens, live, breeding stock, whether or not purebred, weighing not over 185 g each, broiler-type (meat-type) 0105110020
0.33
44,332
0.25
60,452
Birds’ eggs, in shell, for hatching 0407000020
0.11
118,860 (dozen)
0.08
88962 (dozen)
Turkeys, ducks, geese and guineas, live, weighing over 185 g each 0105990000
0.03
7,464
0
0
Chickens, weighing more than 2,000 g each 0105930000
0.01
5,777
0
0
China
Chickens, live, breeding stock, whether or not purebred, weighing not over 185 g each, broiler-type (meat-type) 0105110020
3
333,215
2.31
238,912
Chickens, live, breeding stock, whether or not purebred, weighing not over 185 g each, layer-type (egg-type) 0105110010
1.3
935,461
0.7
363,552
Other live poultry, weighing not over

185 g each 0105190000

0.04
53,145
0
0
Birds’ eggs, in shell, for hatching 0407000020
0.02
20,896 (dozen)
0.2
370 (dozen)
Source: World Trade Atlas

What are the involved states’s production in affected animals?

Table 3. Number of chickens and turkeys and the value of chicken and turkey production in New York, 1997 and 1998.

Number (thousands)
Year
1997
1998
Layers
Pullets (not of laying age)
Broilers
Turkeys
Grand Total
Value (thousands)
Layers and pullets (not of laying age)
Broilers
Turkeys
Grand Total
NA = no data available.

Table 4. Number of chickens and turkeys and the value of chicken and turkey production in New Jersey, 1997 and 1998.

Number (thousands)
Year
1997
1998
Layers
Pullets (not of laying age)
Broilers
Turkeys
Grand Total
2,202
2,097
Value (thousands)
Layers and pullets (not of laying age)
Broilers
Turkeys
Grand Total
6,660
6,291
NA = no data available.

Table 5. Number of chickens and turkeys and the value of chicken and turkey production in Connecticut, 1997 and 1998.

Number (thousands)
Year
1997
1998
Layers
Pullets (not of laying age)
Broilers
Turkeys
Grand Total
Value (thousands)
Layers and pullets (not of laying age)
Broilers
Turkeys
Grand Total
NA = no data available.

Table 6. Number of eggs produced and the value of egg production in New York, New Jersey and Connecticut, 1997 and 1998.

Number (millions)
Year
1997
1998
New York
New Jersey
Connecticut
Grand Total
Value (thousands)
New York
New Jersey
Connecticut
Grand Total
NA = no data available.

Source: Agricultural Statistics 1999. United States Department of Agriculture.

What are the U.S. imports of affected animals from countries where West Nile virus can be found?

If imported birds were the source of the virus, they would most likely have been imported during the months of April to July, 1999. This is based on the dates of the first reported deaths of birds in NYC due to West Nile virus and the length of viremia in birds as reported in the literature. During this time period, 446 birds were imported and released from the ports of JFK airport and the NY Animal Import Center. Of these 446 birds, 45% were destined for NY, NJ, or CT. No birds destined for these three states were imported during this time period through other ports. It should be noted that birds of US origin can leave the country and reenter in less than 60 days under a health certificate issued prior to departure from the US. In this situation, such birds would not be included in the importation data, yet could be at risk of bringing the virus into the US.

Table 7. Avian imports via JFK airport or the NY Animal Import Center that were destined for NY, NJ, or CT.

Month
Country of Origin
Type of Bird
Number Released
April
Hungary Pigeon (Ghana)
8
Poland Pigeon (Ghana)
10
Spain unspecified
6
May
Bangladesh Budgerigar
3
Spain unspecified breeding bird
1
Belgium Pigeon (Ghana)
51
Hungary Pigeon (Ghana)
8
Turkey Macaw
1
June
unspecified lovebird
2
Guyana Amazon
1
Guyana unspecified pet bird
1
Bulgaria cockatiel
1
unspecified Pigeon (Ghana)
1
July
Belgium Pigeon (Ghana)
108

If imported horses were the source of the virus, they would most likely have been imported during the months of June or July, 1999. This is based on the dates of the first reported deaths of birds in NYC due to West Nile virus and the length of viremia in horses as reported in the literature. During this time period, 356 equine were imported via the ports of JFK airport and the NY Animal Import Center. Of these 356 equine, approximately 40% were destined for NY, NJ, or CT. No equine destined for these three states were imported during this time period through other ports.

Table 8. Equine imports via JFK airport or the NY Animal Import Center that were destined for NY, NJ, or CT.

Country of Origin
Number Imported
June
July
Belgium
8
6
Denmark
6
0
France
8
6
Germany
73
103
Israel
2
0
Lebanon
1
0
Netherlands
65
63
Russia
5
2
Spain
0
1
Switzerland
3
0
Ukraine
1
0
United Arab Emirates
0
3
Source: USDA:AHIS:VS Import Database

CEI’s plans for follow up:

CEI will continue to monitor the outbreak, and, should relevant information arise, an update to this impact worksheet will be issued.


If you seek more information or wish to comment on this worksheet, please reply to this message or contact Katherine Marshall, Vicki Bridges, or Reg Johnson at (970) 490-8000.



Additional Information