West Nile virus is a microorganism belonging to the Flavivirus genus. West Nile virus has been commonly found in humans, birds and other animals in Africa, Eastern Europe, West Asia and the Middle East. Only recently the virus has been detected in North America.
West Nile virus is spread to humans by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then transmit West Nile virus to humans and animals while biting to take blood. A recent investigation has confirmed West Nile virus transmission through blood transfusions and organ transplants. There is also evidence that pregnant women can pass the virus to their babies and that the virus can be passed through breast milk. In addition, laboratory workers can get the West Nile virus through needle stick injuries. There is no evidence to indicate that the virus is transmitted from person-to-person contact. There is also no evidence that a person can get the virus from handling infected birds or other animals such as cats, dogs and horses.
The West Nile virus has been found in more than 150 bird species in North America. Some species may have no obvious signs of illness when infected. Others, such as crows, blue jays, and ravens get sick more often and can die. People who find a dead bird should contact their local public health unit office. For information about submitting a dead bird in your area contact the Canadian Cooperative Wildlife Health Centre.
There is no evidence that a person can get the virus by handling a dead infected bird. However, it may be prudent to avoid barehanded contact with dead animals. People handling dead birds should wear gloves and double bag the bird. After handling dead birds it is advisable to wash hands with soap and water.
The symptoms of West Nile virus infection can begin 3 to 15 days following the bite of an infected mosquito. The majority of infections are mild and most people who become infected have no symptoms at all. Some people may experience mild flu-like symptoms, such as fever, headache, and body aches. Some may also develop a skin rash and swollen lymph glands.
People of any age can be at risk of adverse health effects from West Nile virus infection. However, the elderly, and those with weak immune systems may develop severe infection. The severe infection can affect the brain (encephalitis) or the lining of the brain or spinal cord (meningitis). In these cases, the symptoms can include severe headache, high fever, neck stiffness, vomiting, disorientation, muscle weakness, coma, and in some cases, death.
Because West Nile virus is an emerging disease the long-term effects are not fully understood. Studies to date show that some people with serious symptoms and health effects recover completely. Others experience prolonged health problems including muscle weakness, fatigue and headache, confusion, depression, problems with concentration and memory loss. It is not known why some people recover while others continue to have varying degrees of health problems.
There is no specific treatment for West Nile virus infection. However, many of the symptoms and complications of the infection can be treated.
There is no human vaccine for West Nile virus. People contracting the infection develop immunity assumed to be lifelong.
The first thing doctors look for are symptoms of West Nile virus infection. Blood tests confirm the infection. They are done on two separate blood samples taken about three weeks apart.
Persons whose occupation may place them at risk for West Nile virus infection include:
Outdoors workers should wear long sleeved shirts and long pants. They should spray clothing with insect repellent since mosquitoes may bite through thin clothing. Always read the entire label carefully before using insect repellents. Persons involved in collecting dead birds should use gloves and double bag the specimen. After handling dead birds people should wash their hands with soap and water.
Veterinarians are advised to use their usual personal protective equipment such as gowns, gloves, masks and eye protection. Laboratory workers should follow the recommendations of the Biosafety Advisory on WN Virus produced by the Office of Laboratory Security, Centre for Emergency Preparedness and Response, Public Health Agency of Canada, Health Canada.
Prevention and control of West Nile virus is best accomplished by implementing appropriate mosquito control measures and taking appropriate personal precautions.
Provincial and local health authorities are responsible for deciding whether to use pesticides to control the number of mosquitoes in the area. Many municipalities have planned to use larvicides in standing water and catch basins where mosquitoes lay their eggs. Methoprene, a chemical larvicide will be used in catch basins. Bti (bacillus thuringiensis israelensis) a biological larvicide will be used in standing water. With this strategy officials hope to drammatically reduce the number of mosquitoes.
The Pest Management Regulatory Agency (PMRA) Health Canada has registered both methoprene and Bti for use in Canada. As part of the registration process the products undergo a strict scientific assessment to determine whether they are safe.
Mosquitoes lay their eggs in standing water. Here are some ways to reduce mosquito breeding sites around homes:
People should consider staying indoors at dawn, dusk and in the early evening, which are peak mosquito biting times. If you are outdoors during these times, wear long-sleeved shirts and long pants. Wear light colored clothing as it is less attractive to mosquitoes.
If you choose to use an insect repellent always read the entire label carefully and follow the label directions. The Pest Management Registry Agency has registered five different active ingredients for use in Canada as personal insect repellents.
p-Menthane-3,8-diol: This is a new product that provides up to two hours of protection against mosquitoes. This product cannot be used on children under three years of age. It can be applied two times per day.
Soybean oil: Products containing soybean oil provide between one to 3.5 hours of protection against mosquitoes.
Citronella and lavender: These products provide between 30 minutes to two hours protection against mosquitoes. These products cannot be used on infants under two years of age.
DEET (N,N-diethyl-meta-toluamide): DEET was re-evaluated recently to ensure acceptable use and protection. The following safety tips are based on the Pest Management Regulatory Agency evaluation of DEET:
Studies show that products with lower concentrations of DEET are as effective as the high concentration products, but they remain so for shorter periods of time.
Examples of protection times based on DEET concentration are as follows:
|Concentration of DEET||Protection Time|
For more information about West Nile virus, mosquito control, and safety tips on using personal insect repellents visit the Health Canada web site.
Document last updated on August 30, 2006