Everything You Need To Know About The West Nile Virus

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). 

The most efficient & effective preventative measure is it to prevent being bitten by mosquitoes in the first place. (3)

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. 

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. 

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. 

Mosquito surveillance data report 

Surveillance Data for positive WNV in Wild Birds & Equine 

 MOSQUITO-BORNE DISEASES SURVEILLANCE REPORT SEPTEMBER 27 to OCTOBER 24, 2021 

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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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