West Nile Virus

     Is there a West Nile mosquito who walks like an Egyptian? No. In fact, there isn't even a West Nile mosquito. However, the West Nile (WN) virus is transmitted by a tiny insect, the mosquito. The virus, carried by the Adedes, Anopheles and primarily the Culex mosquito, causes healthy birds to fall helplessly from their flight and once elegant racehorses to stagger in pain. First detected in a blood sample of a woman in the West Nile district of Uganda in 1937 and later isolated in birds, patients and mosquitoes in Egypt in the 1950's, the WN virus is considered to be the most geographically widespread of the flaviviruses. It has been detected on all continents that have temperate zones.

     The first recorded epidemic occurred in Israel (1951-1954) and later in 1957. Migratory birds, infected with the virus, are believed to be the principal factor in relocating WN virus to the Western Hemisphere. The center for Disease Control reports that "In 1999, 62 cases of severe disease, including 7 deaths, occurred in the New York area. In 2000, 17 cases have been reported through the September, including one death". Since the Culex species is capable of "overwintering" in temperate zones, there is concern that WN encephalitis may erupt again on the east coast of the United States during the summer or early fall.

     In the late summer months of 1999, an unusually large number of dead crows appeared in the New York City area. This was the first sign that the WN virus had arrived in the United States. Later, gulls, blue jays, pigeons, and red-tailed hawks were also found to be infected, although the American crow paid the highest death toll. A number of vertebrates can also be infected by the virus, but birds act as the amplifying host. An infected mosquito bites a bird. Within days, the virus multiplies in the bird's blood stream. The onset may be so severe that it kills the bird. If not, another mosquito may bite the infected bird and become a vector host for the WN virus. The virus is lodged in the mosquito's salivary glands. If the mosquito seeks another blood meal from a bird, horse or human the virus may be injected where it quickly multiplies. In humans, the result is "encephalitis" which the Center for Disease Control defines as "inflammation of the brain caused by virus and bacteria, including viruses transmitted as by mosquitoes."

     Once the WN virus has been transmitted by the bite of an infected mosquito, the virus multiplies in the person's blood stream and crosses the blood-brain barrier to reach the brain. The virus interferes with the normal central nervous system functioning and causes inflammation of brain tissue. It is not possible to contract the WN virus directly from another person, animal or bird. WN virus is transmitted by infectious mosquitoes. A female mosquito drinks about 5-millionths of a liter per serving. A mosquito's salivary glands contain anti-coagulants or chemicals that prevent blood from clotting as it punctures the skin and sucks blood into the mosquito's gut. If the mosquito is infected, the salivary glands also contain the WN virus. Together, this toxic mixture is a biological grenade to its new victim.

     Symptoms in humans of viral encephalitis may include the following:

Advanced symptoms may cause inflammation to the pancreas (pancreatis) and the heart (myocarditis).

     While human encephalitis is a concern, the threat of equine encephalitis is an ominous threat to horse and owner. Equus writer, Joanne Meszoy, calls the WN virus a "Deadly Import" in her March 2000 article commenting, " Most affected horses first exhibit signs of posterior weakness or paralysis and poor condition. In severe cases, horses develop tumors, convulsions, paddling of the limbs and paralysis." Since the outbreak of the WN virus on the east coast of America, European Union, Hong Kong, and other racing destinations have placed restrictions on the importation of horses from New York, New Jersey, or Connecticut. Aside from the economic impact of curtailed horse racing, breeding and show activities, owners are emotionally frayed. The incubation period for the equine virus is five to fifteen days and every spoonful of standing water from barn to field is a suspected mosquito breeding site.

     Whether equine or human the WN virus has no vaccine. The viral newcomer is a long way from an epidemic in the US, but it deserves careful monitoring. Even though a majority of mosquitoes die off in the Northeast's winters, some adult mosquitoes survive into the next season by camping out in trapped water pools and storm drains. Although a mosquito can fly up to 100 miles at a wing flapping speed of 1.5 miles per hour, the greater threat is the infected migratory bird population who can easily fly up to 200 miles. Both migratory range and WN viral potency spark alarm. The sphinx-like nature of the WN virus deserves a great deal more study to unravel its secrets.