West Nile Virus
September 12, 2017
The Windsor-Essex County Health Unit is investigating higher than normal rates of West Nile Virus (WNV) in Windsor-Essex County (WEC). We would like to take this opportunity to provide a brief update to clinicians and remind them to consider WNV as a differential diagnosis for clients that may present with compatible symptoms.
Notification: West Nile Virus is a mandatory reportable disease, according to the Health Protection and Promotion Act, R.S.O., 1990. All clinically diagnosed, probable and confirmed cases are reportable to the health unit.
To date, the Health Unit has confirmed 11 cases of WNV for this season, which includes two separate reports of WNV-associated deaths. No deaths related to WNV have been reported since 2012.
So far this year, 29 mosquito pools throughout WEC have tested positive for WNV, which is significantly higher than prior years. WNV continues to be a concern until WEC experiences temperatures below freezing. It is important to educate patients on preventative measures.
DIAGNOSIS AND MANAGEMENT OF WEST NILE VIRUS CASES
Diagnosis: All symptomatic patients with potential exposure must be confirmed with laboratory evidence.
Clinical Evidence: Most people with WNV never develop symptoms and will not know that they have the virus. Individuals (about 20%) who do become sick, develop what is referred to as “West Nile Fever”. With a typical incubation period of 2 to 15 days, patients may present with the following mild flu-like symptoms:
- Muscle pain or aches
- Nausea, vomiting
- Eye pain or photophobia
- Occasionally, a skin rash and swollen lymph nodes
A small number of infected people (less than 1%) develop a more severe manifestation of WNV called neuroinvasive disease. This typically manifests as meningitis, encephalitis, or acute flaccid paralysis, and can be fatal. Symptoms may include:
- Rapid onset of a severe headache
- High fever
- Altered mental status
- Stiff neck
- Focal neurological deficits
- Loss of consciousness
- Lack of coordination
- Muscle weakness
Consider WNV as a differential diagnosis of acute neurologic or febrile illnesses associated with recent exposure to mosquitoes, blood transfusion, or organ transplantation. Most patients with WNV fever or meningitis recover, but fatigue, malaise, and weakness may persist for weeks or months.
Lab Evidence: For suspected cases, please ensure the following:
- Collect a minimum of 5.0 mL of blood, using a clotted blood-vacutainer.
- If sending cerebral spinal fluid (CSF) for molecular testing (minimum of 400 µL), it must be submitted together with a serum sample.
- Submit specimen for West Nile virus-(WNV) IgG and IgM serology to Public Health Ontario laboratory.
- Indicate whether the test is for acute or convalescent serology testing. If serum was collected within 10 days of illness and it lacks detectable IgM, consider sending a convalescent sample for testing.
- Ensure the following information is provided: mosquito bite history, symptoms, onset date, relevant travel history, and history of Japanese encephalitis virus vaccination or yellow fever vaccination.
- Note: Plaque reduction neutralizing testing (PRNT) will not be conducted on remaining samples sent this year, as WNV season has already been established within our region. If further investigation is required, please contact the Public Health Ontario Laboratory.
Public Health Ontario Laboratory is available for consultation on laboratory testing with health care providers as needed at (toll free) 1-877-604-4567.
- Primary treatment for WNV disease is supportive care.
- The Health Unit will collaborate with physicians upon receipt of a lab notification for additional investigation and confirmation of the diagnosis.
Prevention: Educate patients to prevent mosquito bites by doing the following:
- Using insect repellents that contain DEET, Icaridin or other approved ingredients on clothing as well as exposed skins. Always read and follow label directions.
- Wear long-sleeved shirts, long pants, and a hat when outdoors. Light-coloured clothing is best.
- Limit the time you spend outdoors at dawn and dusk, when mosquitoes are most active.
- Make sure that door and window screens fit securely and are free of holes.
- Remove nearby standing water.
Our website (www.wechu.org) is a reference for health care providers and patients. For additional information or consultation, please call the Health Unit during regular office hours at 519-258-246 ext. 1420. During after hours and weekends, please call 519-973-4510.
For more information, visit:
- Infectious Diseases Protocol for West Nile Virus Illness
- Provincial Case Definition for West Nile Virus Illness
- Public Health Agency of Canada – West Nile virus
- Public Health Ontario Laboratories: West Nile Virus Specimen Requirements
- Public Health Ontario Laboratories Labstract: West Nile Virus Update – Interpretation of serology results and investigation of cases with neurological involvement