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West Nile Virus

Published in the Autumn 1999 Issue of the N.B. Naturalist, Vol. 26, Issue 3, pages 76-77 The N.B. Naturalist is the publication of the New Brunswick Federation of Naturalists

AMERICAN CROWS:
SENTINELS OF DISEASE
by James P. Goltz

      A good friend often teases me by stating that the American Crow should be the provincial bird of New Brunswick. When asked why, he replies that they are the most conspicuous and distinctive bird species in the province, by virtue of their vocalizations and their abundance, especially along highways where they serve as a clean up crew for road-killed animals of all sizes from insects through mammals.

      Many New Brunswickers don't share my friend's opinions about crows. Unfortunately, these intelligent and highly successful birds are often considered to be ‘nuisance' wildlife, particularly when huge numbers flock together to roost, raid fields of grain or perform a raucous symphony. However, thanks to the American Crow, we have been alerted to the presence of a new virus in North America.

      In mid August, some wild crows were found dead on the grounds of the Bronx Zoo in New York city, but phone reports of dead crows elsewhere in the city had begun earlier in the summer. Around the same time, there were reports of encephalitis, originally thought to be St. Louis encephalitis, in humans. By late August, crow deaths were reported in multiple areas in New York state. Deaths in captive birds began in the Bronx Zoo in early September and continued over a three-week period. Horse deaths, initially attributed to a parasitic infection transmitted by opossums, began in New York state in late August. West Nile Virus has been isolated from crows, other wild birds, zoo birds, humans, horses and mosquitoes, and is believed to be the cause of these disease problems and mortality.

      What is West Nile Virus and why is it cause for concern? It is a virus that may cause encephalitis (inflammation of the brain) and is spread only by the bites of infected arthropods, mainly mosquitoes (at least 43 species worldwide) and, to a lesser extent, ticks. There is no evidence of direct animal to animal, or animal to human transmission.

      Wild birds are the primary hosts but the virus may also infect humans, domestic fowl, large domestic animals, and non-human primates.

      In humans, West Nile Virus may cause mild disease with fever, frontal headache, muscle aches, swollen lymph nodes and skin rash, and less commonly may result in severe disease that is marked by headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions, paralysis and death. Disease is usually more severe in the elderly. The incubation period (between infection and the onset of disease) in humans is usually 5 to 15 days. No approved vaccines against this virus are available for use in humans or animals.

      Prior to 1999, the virus was only reported from Africa, Asia and Europe, and had never been found in the Western Hemisphere.

      The 1999 New York area outbreak of West Nile Virus caused disease in at least 60 people and resulted in 7 human deaths, including one Canadian who visited New York from Toronto. It likely killed at least 5000 wild birds, mainly American Crows, but also caused deaths in at least 17 other species of native wild (Blue Jay, Fish Crow, Ring-billed Gull, Herring Gull, Yellow-billed Cuckoo, Rock Dove, American Robin, Red-tailed Hawk, Broad-winged Hawk, Cooper's Hawk, American Kestrel, Belted Kingfisher) and captive (Bald Eagle, Laughing Gull, Sandhill Crane, Black-crowned Night Heron, Mallard) birds, as well as Chilean flamingos and unspecified species of pheasants and cormorants. The virus caused disease in at least 22 horses (at least 10 of which died or had to be euthanized), while at least 21 other horses became infected without showing any sign of disease. Although most cases of disease and death in humans and animals occurred in New York state, some bird mortality was also detected in nearby New Jersey and Connecticut.

      Health officials responded to the West Nile Virus outbreak with public education campaigns, surveillance of mosquitoes and dead birds, and mosquito control programs. It is not known how the virus arrived in the New York area but it is hypothesized that it may have been introduced by migrating birds, legal or illegal imports of birds, a viremic person, or the transport of infected mosquitoes via aircraft. Consequently, several countries have adopted measures to prevent importation of the virus from New York.

      Canadian public health officials fear that this virus may be brought to eastern Canada next spring by migrating birds infected with the virus. As in mammals, not all infected birds will become sick or die. No one really knows what will happen next year, but wildlife agencies and entomologists in the southern United States have been organized to help with surveillance of wild birds and mosquitoes this winter, and similar efforts for eastern Canada will likely be carried out in the spring and summer.

      What can we naturalists do to safeguard against and prepare for West Nile Virus? It is important to be well informed, and to avoid being bitten by mosquitoes by adopting personal protective measures when engaging in outdoor activities where mosquitoes are likely to be encountered, especially at dawn, at dusk and at night (and especially if traveling to areas where the virus is known to occur).

      In addition, please keep watch for any warning signs that our American Crow population may provide. Remember, if not for the American Crow, West Nile Virus may not have been detected and identified as soon as it was. Unusual outbreaks of crow mortality should be reported to Dr. Jim Goltz at the Provincial Veterinary Laboratory [(506) 453-5412] or Dr. Pierre-Yves Daoust at the Atlantic Veterinary College [(902) 566-0667], especially if neurologic disease is suspected. Suspect dead birds should be placed in leakproof plastic bags and promptly refrigerated until they can be delivered to a laboratory for testing. Remember, there's no need to worry about catching the West Nile Virus directly from wild birds; however, avoiding handling any sick or dead animal with your bare hands will help prevent the transmission of other possible diseases.

      The following Internet links are provided for those who would like additional information on West Nile Virus: http://www.cdc.gov/ncidod/eid/vol5no5/hubalek.htm#20 http://www.cdc.gov/ncidod/dvbid/arbor/arboinfo.htm http://www.cdc.gov/od/oc/media/pressrel/r990924.htm http://www.umesc.usgs.gov/nwhchome.html

West Nile Virus Update

      West Nile virus was recently found in a dead Red-tailed Hawk in Connecticut and in overwintering mosquitoes in New York city. There is no doubt that it has survived the winter and it is possible that it may spread to New Brunswick via migrating birds.

      Your help would be very much appreciated in monitoring local crow populations for mortality. Please report any observations of crow deaths to Dr. Jim Goltz at the Provincial Veterinary Laboratory [(506) 453-5412] or Dr. Pierre-Yves Daoust of the Canadian Cooperative Wildlife Health Centre (located at the Atlantic Veterinary College) [(902) 566-0667]