Impact of West Nile virus on Canada's health care infrastructure

Information Note Number: IN03-002
17 September 2003

Purpose

To provide OCIPEP partners with background information on the West Nile virus, as well as an assessment of the current threat level being posed to Canadian critical infrastructure (CI) by the virus. This analysis is based on publicly available information and was produced in consultation with Health Canada (HC).

Information

In 1937, the West Nile (WN) virus was first isolated in an adult woman who lived in the West Nile district of Uganda. In Canada, the virus was first detected in birds during August 2001. The first human case of WN virus contracted in Canada was reported in August 2002.

West Nile virus is spread by infected female mosquitoes. Most species breed on standing or stagnant water and require a blood diet to produce eggs. Mosquitoes may become infected with WN virus after feeding on the blood of infected birds. Approximately two weeks after ingesting an infected blood meal, the virus is in the salivary glands of the mosquito and may be injected into humans during blood feeding.

Many people infected with WN virus have no symptoms and do not get sick, or have only mild symptoms. When infection does cause illness, symptoms will usually appear within two to 15 days. The extent and severity of symptoms vary widely from person to person. In mild cases, there may be flu-like symptoms including fever, headache, fatigue and body aches. Some people may also develop a mild rash or swollen lymph glands.

While persons of any age or health status can be at risk of serious health effects associated with WN virus infection, the overall risk of serious health effects increases with age. These serious health effects include meningitis and encephalitis, both of which are potentially fatal. Meningitis is an inflammation of the lining of the brain or spinal cord, and encephalitis is an inflammation of the brain itself. In such cases, symptoms could include the rapid onset of high fever, severe headache, stiff neck, nausea, difficulty swallowing, vomiting, drowsiness, blurred vision or deteriorating eyesight, confusion, loss of consciousness, lack of coordination, muscle weakness and paralysis. During 2002, several other symptoms of WN virus infection were identified including movement disorders, Parkinsonism, acute flaccid paralysis (poliomyelitis-like syndrome) and muscle degeneration. Anyone who has a sudden onset of these symptoms should seek immediate medical attention.

At this time, there is no licensed human vaccine for WN virus, although recent reports state that one may be available within the next few years. There is no specific treatment, medication or cure for WN virus. Serious cases are treated with supportive therapies to ease symptoms and prevent secondary infections. These cases may require hospital or nursing care.

The U.S. Centers for Disease Control and Prevention (CDC) has confirmed that the virus can be transmitted by organs/tissues during organ/tissue transplantation, by blood during blood transfusions, and possibly through breast milk during breast-feeding. It was also confirmed that WN virus can be passed transplacentally, infecting the unborn fetus of a WN virus-infected woman. In December 2002, a U.S. woman, confirmed as having WN virus infection during her pregnancy, gave birth to a full-term infant with significant brain abnormalities, who also tested positive for the virus. However, it has not been confirmed whether WN virus caused the abnormalities. Several laboratory workers have been infected via needle punctures or cuts in the process of handling infected specimens. It should be noted that these alternative methods of WN virus transmission represent a very small percentage of the total reported cases. There have been no recorded cases of animals passing WN virus infection to humans, except in a laboratory setting.

As of 5 September 2003, HC reported that there were 20 confirmed positive cases of the WN virus in Canada, but no deaths were attributed to the virus. As of 10 June 2003, HC reported that 20 Canadian residents infected with WN virus during the 2002 mosquito season had died . Influenza results in approximately 500-1500 deaths per year in Canada. Therefore, with respect to mortality, the threat from WN virus is assessed to be lower than from influenza. While persons of any age or health status can be at risk of serious health effects associated with WN virus infection, the overall risk of serious health effects increases with age. People with weaker immune systems and people with chronic diseases are also thought to be at greater risk for serious health effects, and a weakened immune system is thought to increase susceptibility to the virus. For example, the first two people to die from WN virus in Canada were elderly persons. On 25 September 1999, a 75 year old man from Ontario died of complications associated with infection with WN virus; however, he did not contract the virus in Canada, but during a visit to New York City. On 16 September 2002, a 70 year old man from Mississauga, Ontario, died due to complications from WN virus, which he contracted in Canada.

Statistics show that approximately one percent of those infected with WN virus develop serious, adverse health effects, and the mortality rate among cases involving serious complications from the virus is approximately 3-15 percent. Cases with more serious health effects involve prolonged periods of hospitalization and many endure prolonged recoveries. Of the 66 WN virus cases reported in the U.S. in 2001, the vast majority showed significant neurological sequelae and profound weakness. Severe muscle weakness was also a prominent feature among human cases during the 1999 outbreak in New York City, and occurred among 40 percent of confirmed cases. In a follow-up study of the cases from the New York City outbreak, it was noted that long-term sequelae included physical (poliomyelitis-like paralysis, muscle weakness, difficulty walking, fatigue, headache), cognitive (confusion, depression, loss of concentration and memory), and functional (difficulty with meals, leaving home, shopping, transportation) characteristics.

At this time, it is determined that WN virus does not pose a significant threat to Canada's critical infrastructure, including the health care infrastructure. The virus has not seriously impacted Canada's health care infrastructure since its arrival, partially due to Canada's relatively short mosquito season, compared to the mosquito season in other North American regions where the virus has been prevalent, and partially due to the relatively limited geographic distribution of human cases to date. Overall, the threat posed to Canadians by infected mosquitoes is considered to be low. During the summer and early autumn in Canada, hospitals will admit some people with flu-like symptoms due to WN virus, and some with more serious health effects, but the majority of these cases are likely to be remedied fairly quickly and without major or long lasting consequences for the patient. These cases are not likely to overwhelm hospitals to the point of adversely affecting their ability to provide health care.

One aspect of the health care infrastructure that has experienced an impact due to WN virus is Canadian laboratories. In 2002, some provincial laboratories reported receiving a high volume of WN virus test requests, which was overwhelming their capacity and causing all other test requests and activities to fall behind schedule. In the winter of 2003, HC outlined several steps to be followed to prepare for WN virus activity during the coming mosquito season. One of these steps involves measures to assist provincial labs with the anticipated increase in testing required for WN virus diagnosis. HC's National Microbiology Laboratory is providing provincial laboratories with testing technology and training, which will result in a faster turnaround time for test results. Laboratories in Newfoundland and Labrador, Nova Scotia, Quebec, Ontario, Manitoba, Saskatchewan, Alberta and British Columbia have been equipped and trained, and discussions are ongoing with other provinces and territories.

Suggested Action

Although the overall threat from WN virus in Canada is low, Canadians should take precautions to reduce their exposure to mosquito bites. Precautionary measures include eliminating standing water from around homes, cottages, cabins and camps (where mosquitoes breed), as well as protecting exposed skin from mosquito bites. When outdoors, Canadians should use insect repellent, preferably one containing DEET (N, N-diethyl-meta-toluamide) or other approved ingredients, read the label and follow the instructions carefully. Covering skin with light-coloured clothing is also recommended, as mosquitoes are most attracted to dark objects.

For more information, Public Health Agency of Canada's site (www.phac-aspc.gc.ca) offers information on WN virus, including surveillance data and maps, and a list of steps Canadians can take to reduce the risk of infection. The site will be regularly updated throughout the upcoming mosquito season. Information can also be obtained by calling the Health Canada West Nile virus Information Line (1-800-816-7292).

Note to Readers

The Canadian Cyber Incident Response Centre (CCIRC) provides a focal point for Canada's cyber threat and vulnerability warning, analysis and response. CCIRC is responsible for assuring the resilience of national critical infrastructure through monitoring threats and coordinating a federal response to cyber security incidents of national interest. CCIRC operates in conjunction with the Government Operations Centre (GOC) within Public Safety Canada and is a key component of the government's all-hazards approach to emergency management and national security.

For general information, please contact Public Safety Canada's Public Affairs division at:

Telephone: 613-944-4875 or 1-800-830-3118
Fax: 613-998-9589
E-mail: communications@ps-sp.gc.ca