Everything You Need To Know About The West Nile Virus
Written by: Sulayman Mehboob, B.Sc., M.Sc. - Microbiologist
History
The West Nile Virus (WNV) was first identified in 1937 from the blood of a woman showing illness symptoms in the West Nile region of Uganda. (1,2,3). WNV is now known to be enzootic in most African countries, India, the Middle East, southern Europe, Southern and western Asia, Australia , and North America. (4,5,2,6) WNV was first discovered in North America in 1999, having an outbreak in New York City. (5) Since the virus has spread across the United States, Central America, southward into The Caribbean, and Central America northward into Canada. (5,3,7) This has resulted in the largest epidemics of neuroinvasive WNV fever ever known. (5,3) In subtropical & temperate regions, most infections in humans occur in summer or in the early fall. Infections in tropical regions occur in the rainy season when mosquito populations are in most abundant. (8)
Pathogenicity
Many people infected with WNV remain asymptomatic. (9,3,10) West Nile (WN) fever caused by West Nile Virus is a mild illness lasting for 3 to 6 days. (4,9,10). The typical symptoms are sudden onset of fever along with chills, malaise, rash, backache, headache along with arthralgia, myalgia and the eye pain. (4,3,10) Other general manifestations include vomiting, nausea, loss of appetite, rhinorrhoea, diarrhea, and/or a sore throat, with a cough. (4,3) Some patients have generalized lymphadenopathy (swollen lymph nodes), with macular, papular, or morbilliform erythematous rash on the whole body. (4,9,3) Meningitis, encephalitis, with or without acute flaccid paralysis may develop in less than 1% of the WNV-infected individuals. (11,3,12) Patients having neurological disease typically have a fever (>38.3°C) from 1 to 7 days, which may come in two phases, before they develop neurological disease symptoms. (4) Patients will also display fever, headache, stiff neck, weak muscles, tremors, gastrointestinal symptoms, disorientation, convulsions, and even paralysis. (4,9,3) Mode of Transmission
The main route of WNV infection is through the bite of the mosquito that is infected by feeding on birds infected with WNV. (4,13,14,2)
Humans and most other mammals are dead-end hosts as they do not produce sufficient amounts of viraemia to infect mosquitoes and therefore do not significantly contribute to the transmission cycle. (3,10)
Other possible routes for infection may include blood transfusions, breast milk, vertical transmission (in utero) & organ transplantation. (7)
WNV has been known to also occur through contact of the conjunctiva with contaminated bodily secretions of the infected birds. (15), and incidents in laboratory settings involving injury with sharp objects. (16)
The incubation period ranges from 2 to 6 days but can extend to 14 days, or as long as 21 days for the patients following organ transplantation. (4,12)
Birds, particularly passerine species (jays, finches, grackles, sparrows, and crows (13,14,7)), are the main source vectors. Humans can contract WNV from the exposure of conjunctival membranes (15) and/or percutaneous injury to the body fluids or tissues of WNV-infected birds(16) as well as indirectly by the bite of an infected mosquito. (9,6 8).
Treatment
Currently, there is no treatment for WNV fever. (3,7). Supportive therapy for encephalitis cases may include intravenous fluid, electrolyte management, assisted respiration therapy (if needed), management of cerebral edema, anti-convulsant, and the prevention of secondary bacterial infections. (4,11)
Studies have assessed antivirals like ribavirin, interferon, osmotic agents, gamma globulins, and the steroids for treatment of WN fever, but more evidence is needed to determine their efficacy. (4,11,9)
Immunization
There is currently no available vaccine for immunization. An inactivated-type vaccine is available for horses, but vaccines for humans are won’t be available for many years, even though a number of the possible vaccines are in clinical trials. (10)
IF CONTRACTED WITH INFECTION
If you believe you have possibly contracted the West Nile Virus, monitor for symptoms. Confirmation is through the virus isolation from blood(,11) or from the cerebrospinal fluid(7) during the viraemic phase of infection. Other methods include detection through PCR(9), haemagglutinin inhibition tests, (15) a plaque reduction neutralization test, (12), a complement fixation test, indirect immunofluorescence assay, (10), and the IgM capture ELISA. (12).
Prevention
The most efficient & effective preventative measure is it to prevent being bitten by mosquitoes in the first place. (3)
Epidemiology In Canada
According to the “Mosquito-Borne Diseases Surveillance Report (20) (September 27 to October 24, 2021, Week 39 to 42)”, a total of 17, 229 mosquito pools were tested for West Nile Virus (WNV) in Canada. There were 10 positive mosquito pools identified in Québec, 104 in Ontario, 116 in Manitoba , and 9 pools tested positive in Saskatchewan.
A total of 22 wild birds have tested positive WNV WNV by the Canadian Wildlife Health Cooperative, 14 in Québec and 8 in Ontario), however, Quebec reported additional bird infections and Manitoba reported 3 birds that tested positive for WNV.
When the session started, the Canadian Food Inspection Agency (CFIA) had identified equine cases which tested positive for the WNV in Saskatchewan (8), Alberta (1), Ontario (3) & Manitoba (6). Saskatchewan reported 2 additional horses that tested positive for WNV.
Figure A. West Nile virus (WNV) human clinical cases and the asymptomatic infections
*Human cases including clinical cases and asymptomatic infection.
*Human cases including clinical cases and asymptomatic infection.
Figure B. Positive Case WNV equine
B: Episode week is based upon the symptoms onset or the best available date which includes: diagnosis, lab sample or the date reported.
B: Episode week is based upon the symptoms onset or the best available date which includes: diagnosis, lab sample or the date reported.
Figure C. Percentage of positive mosquito pools
Episode week is based on the death date or the best available date including the date found, submitted , or received.
Episode week is based on the death date or the best available date including the date found, submitted , or received.
Mosquito surveillance data report
|
WNV- positive pools and percentage of positive by province and nationally (January 1 - October 24, 2021)
|
|||
|
Province
|
Positive pools
|
Total pools tested
|
Percent positive
|
|
Saskatchewan
|
9
|
360
|
2.50%
|
|
Manitoba
|
116
|
1,446
|
8.02%
|
|
Ontario
|
104
|
13,436
|
0.77%
|
|
Québec
|
10
|
1,987
|
0.50%
|
|
Total
|
239
|
17,229
|
1.39%
|
Surveillance Data for positive WNV in Wild Birds & Equine
|
Number of WNV positive birds and equine by province (January 1 - October 24, 2021)
|
||
|
Province
|
Wild Birds
|
Equine
|
|
Ontario
|
8
|
3
|
|
Quebec
|
15
|
0
|
|
Saskatchewan
|
0
|
10
|
|
Manitoba
|
3
|
6
|
|
Alberta
|
0
|
1
|
|
National Total
|
26
|
20
|
MOSQUITO-BORNE DISEASES SURVEILLANCE REPORT SEPTEMBER 27 to OCTOBER 24, 2021
|
Province
|
Clinical Cases
|
Total Clinical Cases
|
Asymptomatic Infections
|
Rate (Per (100,000)
|
||
|
Neurological
|
Non-Neurological
|
Unclassified
|
||||
|
Ontario
|
9
|
7
|
1
|
17
|
2
|
0.12
|
|
Québec
|
9
|
2
|
1
|
12
|
2
|
0.14
|
|
Alberta
|
2
|
0
|
0
|
2
|
0
|
0.15
|
|
Manitoba
|
0
|
1
|
1
|
2
|
0
|
0.05
|
|
Canada
|
20
|
10
|
3
|
33
|
4
|
0.09
|
About The Author:
Sulayman Mehboob, B.Sc., M.Sc. - Microbiologist
Sulayman has done research on various science projects and has been published in well reputed journals. Currently, he is doing research on animals and insects on various topics and some of his research projects have been completed and under review in the top journals. He loves researching plants and animals, and his aim is to continue deep study in this field.
References
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