West Nile Virus – Causes and Symptoms of West Nile Virus

WNV belongs to the Flaviviridae family of virus. WMV denotes West Nile Virus. This virus is found in tropical regions and temperate regions. This virus is observed to infect mostly birds, but humans and animals like dogs, horses, bats, cats, domestic rabbits, chipmunks and squirrels are also found to have infected by this. WMV can cause inflammation of the brain (encephalitis) and inflammation on the lining of the brain and spinal cord (meningitis).

Causes of infection by West Nile Virus

It spreads through the mosquito bite. Hence WMV is also popularly named as a mosquito-borne virus. Generally a mosquito gets infected after biting an infected bird. Else this virus does not spread through a person carrying the disease. It does not spread through caring, touching or kissing an infected person. The period of incubation is generally 5-15 days. This is the time from the start of the infection to the onset of the disease.

How this virus entered the New York city, is still not clear. But most researchers believe that the infection was imported either from an infected bird or an infected human being who returned from some place with lots of infected birds. WMV infection was common in Africa, Middle East countries, Asia but the outbreak in the US was seen in the year 1999. But this infection is rarely found in Europe.

Symptoms of infection by West Nile Virus

Usually three different effects are observed in humans following the infection. These are

  • asymptomatic infection (the infected person has no symptoms)
  • mild febrile syndrome (infected person with symptoms of fever; also termed as Wets Nile Fever)
  • neuroinvasive disease (also known as West Nile Meningitis or West Nile Encephalitis; the infected person shows some inflammation in the brain and spinal cords)

The ratio of people showing the above symptoms counts for 110:30:1. The febrile stage often takes an incubation period of 2-8 days followed by the following symptoms –

  • chills
  • drowsiness
  • excessive sweating (diaphoresis)
  • fever
  • gastro-intestinal symptoms (with nausea, vomiting, diarrhoea and loss of appetite)
  • headache
  • pain behind the eyes
  • pains in joints
  • occasional occurrence of rashes
  • symptoms of flu or influenza
  • swelling in lymph glands (lymphadenopathy, lasting for about 2 months)
  • and weakness (or fatigue lasting for about some weeks)

Most of the symptoms mentioned above tend to subside within 7-10 days. Most people show no symptoms while a few experience mild illness associated with body aches, fever and headaches. Some also complain of swelling in lymph glands and appearance of mild rashes. In a few, particularly in the elderly patients, even serious disease may occur affecting brain tissues.
If left untreated, severity can cause permanent neurological damages in the patient and can show fatal results. Encephalitis can even cause death. Symptoms of Encephalitis caused by West Nile Virus include-

  • rapid onset of severe headache
  • muscle weakness
  • high fever
  • coma (loss of consciousness)
  • stiff neck
  • confusion
  • sensitivity to light

Patients with mild or no symptoms recover fast requiring any specific medication or laboratory testing, while if any of the above symptoms are observed, then immediate medical help must be looked for. The ratio of people with the above symptoms have been counted to be

  • fever (90%)
  • headache (46%)
  • joint aches (17%)
  • muscle weakness (54%)
  • altered mental status (44%)
  • stiff neck (19%)
  • rash (22%)
  • sensitivity to light (15%)
  • body aches (14%)

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