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Background
West Nile virus was first isolated in the West Nile District of Uganda in 1937. In recent years it has spread to the temperate regions of Europe and North America, presenting a threat to public, equine and animal health. In it's most serious form it causes fatal encephalitis (inflammation of the brain) in humans and horses, as well as mortality in certain domestic and wild birds.

In 1957 there was an outbreak in elderly patients in Israel. Equine disease was first noted in Egypt and France in the early 60's. In 1999, WNV spread to the eastern North America where 62 cases, with 7 deaths occurred in the New York Area. Scientists do not know how the virus was spread to the United States, but suspect that it came to New York City from Israel. Just a few weeks prior to its appearance in NYC, over 10,000 geese had to be euthanized in Israel due to WNV. This is the same strain of WNV that we have. The other Mediterranean strain has not yet been found in this country.

Transmission
The principal transmission cycle of West Nile Virus involves at least 26 species of mosquitoes and over 120 species of birds. The Culex spp. is however the most prolific. Mosquitoes become infected with WNV when they feed on a bird carrying the virus in its blood. After 10-14 days, the virus can be transmitted to another bird, person, or other animal that the mosquito bites. During the female blood feeding (males don't feed on blood) the mosquito injects the virus, contained in its saliva, into the bird, animal, or person-where the virus replicates and may cause illness.

People and horses are actually incidental hosts. That is, they are thought not to develop enough virus in their bloodstream to infect mosquitoes, despite the possibility that they may become ill. The main role that people play in contributing to the continuing cycle of West Nile virus is by maintaining environments (especially standing water) in which mosquitoes can lay eggs. WNV cannot be spread from person to person.

Although some species of mosquitoes die during the winter, one species, the Culex species, can overwinter. This means that in the adult stage, the mosquito survives. Other species of mosquitoes lay eggs, which survive the winter, and carry the virus.

Symptoms
Most people who are infected with West Nile virus will not develop symptoms. Some however, will develop symptoms within 3-15 days after the bite of an infected mosquito. Generally the illness is mild-fever, headaches, body aches and sometimes a skin rash and swollen glands.

Infrequently the virus infection results in a severe illness known as West Nile encephalitis. Encephalitis is an inflammation of the brain that may be marked by severe headaches, high fever, still neck, stupor, disorientation, coma, tremors, convulsions, muscle weakness and paralysis. This can be fatal. There is no specific treatment for the virus, however, supportive therapy may be required- hospitalization, intravenous fluids, respiratory support, good nursing care, and prevention of secondary infections.

Who is at Risk
As with most diseases, the elderly and those with chronic diseases or are immuno-compromised, and the very young have a higher risk of contracting the disease. There is no documented evidence that a pregnancy is at risk in the event that a mother would be infected with WNV. Transmission in this area is only during the summer months, when mosquitoes are active. In the south, transmission may occur year round. A study carried out in 1999 among residents in the most affected areas of New York City showed that only 2.6% of residents had been infected. Studies elsewhere have shown a lower infection rate.

Nationally:
To date, there have been a total of 1355 people infected with WNV in the United States in 33 states. There have been 19 deaths.
In 2002, there were a total of 4156 people infected with WNV in the United States in 40 states. There have been 284 deaths.

State Statistics in 2002:

Veterinary- 756 Horse cases in 2002 on 763 farms in 104 counties
Of the 756 horses, status in known on 396
Of those 396 horses, 37% died.
In Randolph Co. the infection rate was 6.8-10/1000 horses
10 horses that were reported as vaccinated died. Of those 5-8 were properly vaccinated. In herds that had one positive horse, 1/3rd of the others were seropositive, but had no symptoms.

Mosquito- positive mosquito pools in 17 counties
Bird- 278 dead birds from 81 counties
Human-To date there has been 169 human cases of WNV in MO (2002) and 5 deaths.
In St. Louis County all human cases were investigated. In every instance, there was a breeding site with a positive pool of mosquitoes either on the property or within 100'. Not one of the human cases used any type of preventative measures.

Randolph Co. Statistics
As of 08/26/03, Randolph County has had 1 horses that tested positive for WNV and two Blue Jays.

Prevention and Control

The Integrated Pest Management Approach

• Survey and Mapping of the area
  Locate and define the sources
  Map the sources
  Categorize the sources-ie: catch basin, stagnant water, containers, tire piles, etc.
  Record and measure the acres/miles of the source
  
  
• Surveillance
  Record every dead bird for surveillance by location or address
  Record every reported animal case
  Record every human case and investigate
  
  
• Larval control
  Not every treatment works at every site.
  Treat landfills, wastewater treatment plants, tire sites, catch basins, railroad tracks, ditches, depressions-anywhere where water stands.
  The City of Moberly will be providing larval control this year.
  
  
• Adult control-based on surveillance rather than delaying until human cases are reported.
  Adulticiding should occur:
  when there is an emergency;
  when larviciding fails;
  when there is an increase in human cases
  utilize barrier sprays during fairs, etc.
  

PERSONAL & HOUSEHOLD PREVENTION

• Try to avoid or limit time spent outdoors between dusk and dawn and to avoid activities in areas where mosquitoes are plentiful.
  
• Whenever possible, wear protective clothing-long-sleeves, long pants, socks
  
• Apply insect repellent to exposed skin. The most effective repellents contain 35% DEET. Higher concentrations of DEET are no more effective.
  
• Avoid applying repellent to children less than 2 years old. Use care with repellents, and do not put it on their hands, as it may get into their mouth or eyes and cause irritation.
  
• Spray clothing with products containing DEET.
  
• Maintain or install window and door screens to keep mosquitoes out of buildings.
  
  Note: "Ultrasonic" devices and Vitamin B are not effective in preventing mosquito bites.
  
  
• AVOID BREEDING MOSQUITOS-mosquitoes lay their eggs in standing water. To avoid helping mosquitoes breed, drain standing water. Empty water from flowerpots, pet bowls, clogged rain gutters, swimming pools and pool covers, discarded tires, buckets, barrels, cans, and other items that collect water.
  

COMMUNITY PREVENTION

• Watch for mosquito-breeding areas. These include storm sewers, ditches, and abandoned properties with standing water.
  
• Support disease-tracking activities-report dead and dying birds and horses that are suspected of being infected with WNV.
  

If you have any questions or need additional information please contact us. We'll be glad to help.