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West Nile Virus


Disease: West Nile Virus West Nile Virus
Category: Infectious diseases

Disease Definition:

The west Nile virus, which is transmitted by mosquitoes, is common in areas such as West Asia, Africa and the Middle East. In some cases, a person infected with this virus might not experience any signs or symptoms, or he/she may experience only minor symptoms, such as a skin rash and headache. But in other cases, a life-threatening illness could be developed, which includes inflammation of the brain.The risk of getting West Nile virus increases by exposure to mosquitoes where this virus exists. To reduce this risk, people should wear clothing that covers their skin, or they could use mosquito repellent.

Work Group:

Symptoms, Causes


As mentioned before, most people infected with this virus have no signs or symptoms. However, about 20% of infected people develop a mild infection called West Nile fever. Some of the common signs and symptoms of this fever include:

  • Nausea
  • Skin rash
  • Vomiting
  • Fever
  • Lack of appetite
  • Diarrhea
  • Muscle aches
  • Swollen lymph glands
  • Backache
  • Headache


The virus can cause a serious neurological infection in less than 1% of infected people, which includes inflammation of the brain (encephalitis), inflammation of the brain and surrounding membranes (meningoencephalitis) or infection and inflammation of the spinal cord (West Nile poliomyelitis) as well as acute flaccid paralysis, which is a sudden weakness in the arms, legs or breathing muscles. These diseases cause some of these signs and symptoms:

  • Severe headache
  • Pain
  • Stiff neck
  • High fever
  • Convulsions
  • Tremors or muscle jerking
  • Lack of coordination
  • Disorientation or confusion
  • Signs and symptoms similar to Parkinson’s disease
  • Partial paralysis or sudden weakness
  • Stupor or coma


Although the symptoms of West Nile fever usually last no longer than three or six days, however, the symptoms of meningitis or encephalitis can last for weeks, and some neurological effects, such as muscle weakness, could be permanent.


The virus enters the mosquito’s bloodstream when this mosquito bites a bird infected with the virus, and it circulates for a few days before settling in the salivary glands, so that when this infected mosquito bites an animal or a human, the virus enters the host’s bloodstream where it could cause serious illness.


Potentially, the West Nile virus enters the host’s bloodstream where it multiplies and crossing the blood-brain barrier, moves on to the brain. The blood-brain barrier separates the blood from the central nervous system. The brain tissue becomes inflamed and symptoms arise once the virus crosses this barrier and infects the brain or its linings.


The West Nile transmission most commonly occurs when the mosquito populations are active during warm weather. The incubation period ranges between 2 to 14 days; this is the period between when a person is bitten by an infected mosquito and the appearance of signs and symptoms of the illness. In some rare cases, the West Nile virus could spread through other routes, such as:


From mother to unborn child:

A mother can pass this virus to her unborn child, however, whether this can result in abnormalities in the child or not is not yet known.


Organ transplantation and blood transfusion:

Even though blood donors are screened for the West Nile virus which reduces the risk of infection from blood transfusions, however, donated organs are not yet screened for this virus.


Laboratory acquisition:

Some laboratory workers involved in West Nile surveillance and research have contracted the disease from infected animals.



Even though in some cases the West Nile virus has been transmitted from mothers to their babies through their breast milk, however, experts at the Centers for Disease Control and Prevention say that these cases are extremely rare and that it shouldn’t affect a woman’s decision to breast-feed.






Interferon therapy, which is a sort of immune cell therapy, is being investigated to be used as a treatment for encephalitis caused by West Nile virus. Although more studies are needed, however, one research shows that people receiving interferon could recover better than those who don’t receive this drug.



Usually, people with this virus recover without treatment, even those who develop meningitis or encephalitis might only need supportive therapy with pain relievers and intravenous fluids.


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