Disease Review_ West Nile Virus

West Nile Virus

The majority of infectious diseases are known to be attacking and proliferating in underdeveloped countries. Easily, these diseases can attack people if the country has a poor health system, unsanitary conditions, no access to clean water and foods, and uninformed citizens. People in developed countries can just boost their immune system or easily diagnose their illness through CT scans to fight against these diseases.

But some diseases can still manage to proliferate in developed countries. As per the Centers for Disease Control and Prevention (CDC), West Nile virus (WNV) is the leading cause of mosquito-borne disease in the United States. West Nile virus can cause neurological disease and death in people.

Start of West Nile Virus

West Nile virus was first isolated from an infected woman from the West Nile district of Northern Uganda in 1937. The patient was part of an epidemiologic study for the yellow fever virus. However, the isolated virus has different physical and pathological properties from the yellow fever virus. It is more similar to two known encephalitis viruses. Encephalitis viruses cause inflammation of the brain. Although the infected woman only has a fever, the study on the newly discovered virus suggested the pathological nature of it.

Details on the epidemiology and ecology of West Nile virus were learned during several outbreaks in the Mediterranean in the early 1950s and 1960s. The first recognized epidemic occurred in 1951 in a small town of Haifa, Israel.

Outbreaks in Egypt between 1951 and 1954 led to several breakthroughs. Based on their study, they have found that younger children seemed to have a more symptomatic illness. Infections were self-limited, fever illness with rare occurrences of meningitis or encephalitis.

They found out that the virus was infectious in a wide range of species including birds and non-human mammals. They found out that the virus is more prevalent in birds, particularly in crows. In addition, the vector-borne nature of the virus has been established.

West Nile Virus on the USA

In October 1999, CDC reported an outbreak of human encephalitis in New York City. At the same time during the outbreak, there was an increase in bird mortality around New York City. These were initially thought to be unrelated. Assessment of the dead birds showed the involvement of multiple organs and encephalitis.

It is still unknown how the virus was introduced to North America but based on the study, the virus strain found in New York originated in the Middle East.

After it was identified in New York City, WNV spread progressively throughout the United States. The spread of human cases seemed to follow bird deaths so avian death and mosquito pool surveillance were being done to track the virus.

In 2002, West Nile virus caused the largest epidemic of neuroinvasive illness in the Western Hemisphere. 39 states and the District of Columbia reported 4,156 human West Nile virus. 2,942 (71%) of them showed neuroinvasive illness such as meningitis, encephalitis, or meningoencephalitis. The factors contributing to the outbreak is still unknown but males appeared to have a higher risk of severe illness and death.

Nature of The Virus 

The West Nile virus is a single-stranded RNA virus. It is part of the family Flaviviridae genus Flavivirus which includes other human pathogens such as dengue, yellow fever, and Japanese encephalitis. It is a spherical virus enveloped by a smooth protein shell that is used for several functions such as viral attachment.

West Nile virus is commonly spread to people by infected mosquitoes. Culex mosquitoes are said to be the primary vector.  Culex tarsalis is the main vector of WNV in the western United States. It can feed on a variety of birds and mammals. Mosquitoes acquire WNV after taking blood from infected animals, usually birds.

The virus is maintained in nature through the transmission cycle between the bird reservoir and the mosquito vector. Some birds become ill, show symptoms, and die while others become infected without symptoms and serve as carriers. Bird to bird transmission was also observed. Humans are considered “dead-end” hosts for the West Nile virus because the chance of virus from humans getting transferred to another mosquito is low. Thereby ending the transmission cycle.


Most people, around 80%, infected with the West Nile virus are asymptomatic or do not develop any symptoms. Some people develop West Nile fever. Symptoms, which usually appear 3 to 14 days upon being infected, include fever, headaches, joint pains, vomiting, diarrhea, and rash.

About 1 out of 150 people who are infected develop a serious illness such as inflammation of the brain (encephalitis) or inflammation of the membranes that surround the brain and spinal cord (meningitis). Severe symptoms also include high fever, headache, neck stiffness, coma, vision loss, numbness, and paralysis.

People who are aged 60 years old above are at higher risk of contracting the severe illness. Also, people with existing medical complications such as cancer, diabetes, and kidney disease are at higher risk.

West Nile can also cause vision problems if optic neuritis develops as one of the symptoms. The inflammation of the optic nerve can even cause psychological trauma. Both of which are preventable in cases that receive proper treatment.

Treatment and Prevention

Unfortunately, there are no specific antiviral treatments for West Nile virus. Most people recover from mild illness without treatment. But over-the-counter pain relievers are available to reduce fever and help ease the pain from muscle aches and headaches.

People with severe symptoms need to be hospitalized to receive proper treatment. Patients are given intravenous fluids, respiratory support, and pain medication. About 1 out of 10 people with severe illness affecting the nervous system die.

Up to this day, there is still no human vaccine against WNV. So the best treatment is prevention. The most effective way to prevent

WNV infection is to prevent mosquito bites.

The focus should be on personal and community protection against mosquitoes. We can use mosquito nets, insect repellant, and maintain our surroundings to stop mosquitoes from laying eggs.

A good way to reduce infection in people is to raise awareness and educate people about the ways they can do to reduce exposure to these types of diseases. Diseases do not exclude anyone or any country. It is best that we help each other to eliminate diseases.


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