The incubation period for West Nile Virus (WNv) ranges from 3 to 14 days. WNv Illness can be considered to consist of two clinical pictures, WNv Fever and WNv Neurological Manifestations. Data from the U.S.A. indicate that most WNv infections are often clinically unapparent or mild. Approximately 20% of those infected develop a mild illness (WNv Fever). Approximately 1 in 150 (0.7 %) infections will result in severe neurological disease. The most significant risk factor for developing severe neurological disease is advanced age.

WNv Fever - WNv Fever is the milder form of WNv Illness. Clinical symptoms include a febrile illness of sudden onset plus one or more of the following; malaise, anorexia, nausea, vomiting, headache, eye pain, photophobia, arthralgia, myalgia, maculopapular rash, and lymphadenopathy. The complete clinical spectrum may not yet be recognized, however.

WNv Neurological Manifestations - The clinical picture of WNv Neurological Manifestations may include the symptoms of WNv Fever. Symptoms of encephalitis are more commonly reported than meningitis. Symptoms may include change in mental status, severe muscle weakness, flaccid paralysis, myelitis, seizures, polyradiculitis, cranial nerve abnormalities including optic neuritis, ataxia and extrapyramidal signs. In addition, the occurrence of acute flaccid paralysis and poliomyelitis-like syndrome has increased and/or been documented for the first time during the 2002 outbreak.

Encephalitis/meningitis due to WNv cannot be clinically distinguished from other etiologic causes of encephalitis/meningitis. The following diagnostic specimens should be collected if the diagnosis of WNv encephalitis/meningitis is suspected.

Note : In most cases, West Nile infection can be diagnosed serologically. However, in immunocompromised individuals, the examination of cerebrospinal fluid by polymerase chain reaction (PCR) may be helpful to detect the presence of virus in cases where antibody production may be delayed. Note, however, that PCR will be positive in only approximately 50% of infected patients.

(1)  Collect the following specimens using standard universal precautions :

(a)  Blood

A single serum sample should be collected in a red-top tube (5-10 ml per tube) and forwarded to the Central Public Health Laboratory (CPHL) (see below for contact information).

OR

Paired sera (i.e., acute and convalescent serum) should be collected in red-top tubes (5-10 ml per tube) and forwarded to the Central Public Health Laboratory (CPHL) (see below for contact information). Acute phase samples should be collected 1-8 days post-onset of encephalitic symptoms, while convalescent phase samples should be collected 10-14 days after symptom onset. Practically, this may be best achieved by collecting samples upon hospital admission and discharge. However, if hospital discharge occurs less than 10-14 days after the onset of symptoms, a subsequent appropriately timed specimen should be collected.

Note : A single blood sample should be required for the majority of cases. Certain circumstances may require acute and convalescent blood samples. The attending physician will be notified if a convalescent blood sample is required.

(b) Cerebrospinal Fluid (CSF) (if collected - see note above)

1 to 2 ml of CSF remaining after routine microbiological and biochemical testing to rule out a bacterial etiology should be placed in each of two tubes without preservatives. The tubes should be kept frozen on dry ice or in a -70C freezer until picked up for transport to the CPHL (see below for contact information).

(c) Heart blood, CSF and tissue samples

Brain biopsies taken on persons with viral encephalitis should be tested for West Nile Virus. For fatal cases, every attempt should be made to collect heart blood and brain samples, especially the brainstem, for PCR and immunohistochemistry testing and from the spleen and liver for immunohistochemistry testing. These specimens should not be formalin-fixed but should be transported fresh to the CPHL (see below for contact information).

(2) Carefully and completely fill out the Public Health Laboratory Test Requisition form for each sample, with particular attention to :

• Patient Information : Complete entire section
• Physician/Referring Laboratory : Provide a contact telephone and pager number for follow-up by the Provincial Lab and Minister of Health
• Test(s) Requested : Enter code V 02 for Arbovirus Testing
• Specimen type and site : Clearly indicate the type of sample (i.e. CSF or blood, etc ). For serum specimens, indicate if the sample was drawn in the actue or convalescent phase of illness and the corresponding dates of collection.
• Reason for test : Under "Other", please specify that testing is for suspect West Nile virus Illness.
• Clinical Information : Clearly specify any symptoms consistent with the suspect case definition as well as the date when symptoms first occurred. Useful items to indicate on the form with respect to West Nile virus include :
1. any known history of recent travel within, or out of, Ontario,
2. recent activities which could lead to increased exposure to vectors of arboviral illnesses (e.g. camping, outdoor work, gardening, known recent exposure to mosquitoes),
3. whether the person has had prior immunization against Japanese encephalitis and/or Yellow Fever, as these antibodies may cause "false-positive results", and/or
4. whether the individual resided in south-west or south-central Ontario in 2002.

All specimens collected in Ontario for testing must be sent to the Central Public Health Laboratory by the usual route used by the physician [via a Regional Public Health Laboratory or the laboratory service normally used by the physician]. Specimens sent to the Public Health Laboratory should include a Public Health Laboratory test requisition with a detailed clinical history and noting a specific request for West Nile virus testing.

Central Public Health Laboratory
Ontario Ministry of Health and Long-Term Care
81 Resources Road
Toronto ON
M9P 3T1

If you have questions, telephone the Medical Microbiologist (416) 235-5725. For emergencies contact the after hours duty officer (416) 605-3113 after business hours.

Call the ministry INFOline at 1-866-532-3161 (Toll-free in Ontario only) TTY 1-800-387-5559 Hours of operation : 8:30am - 5:00pm	For information about surveillance activities in specific regions of the province, please refer to your local public health unit.

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