West Nile Virus: Transmission, Symptoms, Treatment, Diagnosis
About West Nile Virus
The West Nile virus was first detected in a woman in Uganda in the West Nile district in the late 1930s, after which it was identified to infect crows and Columbiformes (birds) in the Nile delta region in early 1950s. Owing to this detection in the West Nile region, it was named as West Nile Virus. Although this virus is mostly found in the regions of Africa, West Asia, and Europe, this virus has created havoc in the present time in the continental United States due to the transmission of the virus from these places by the carrier mosquitos. Massive outbreaks of this virus have been recorded in Israel, Greece, and Russia to name a few.
According to the Centers for Disease Control and Prevention (CDC), West Nile Virus or WNV for short has become one of the leading causes of mosquito-borne disease in the United States. It was first detected in the United States in the year 1999 after which every state in the US except Hawaii and Alaska have shown a considerable increase in the number of such cases every year1,2. It is transmitted by a carrier mosquito that has been previously infected with the virus. A bite of this mosquito is enough to transfer it to the host body. The cases of infestation by this virus increase in summer and fall owing to the massive growth of the mosquito population.
Fortunately, CDC maintains that not more than 20 percent of people who get infected by West Nile Virus develop a fever and some primary symptoms while the chance of a fatality is almost close to 0.67 percent3. Also, if adequate measures are taken to prevent it, the spread of this virus can be easily prevented.
The World Health Organisation (WHO) categorizes this virus in the genus Flavivirus making it a member of the family Flaviviridae. West Nile Virus in its deadliest form is capable of causing neurological imbalances and even death in humans. The cycle of transmission of West Nile Virus is mainly restricted to birds and mosquitos but recent trends have shown an infestation of humans and other mammals like horses and cows as well.
Transmission of West Nile Virus
The main line of transmission of the West Nile Virus follows a bite from an infected mosquito. Mosquitos feed on birds which may be infected leading to their own infestation due to the circulation of the virus within their bloodstreams. When this infected mosquito comes in contact with either a human or a mammal for its future blood meals, it incidentally transmits the West Nile Virus to the host body which leads to their multiplication inside the host cells. Even though the mosquito bite is the main cause of this transmission but this West Nile Virus can also be transmitted by coming in contact with the blood or tissue of an infected animal. This contact can be in the form of organ transplant, milk or blood transfusion as far as the human infestation is concerned. Till now only a unique case of transplacental transmission has been observed between a mother and her child.
Other mammals like horses behave just like humans in terms of West Nile Virus transmission. Being a dead-end host like humans they are usually not the ones responsible for spreading of this virus.
While discussing the transmission aspect the West Nile Virus is not spread by any of the following actions:
- Physical touching of a mammal
- Coming in contact with a cough stain or sneezing
- Handling of dead infected birds
- Ingestion of infected organisms.
Symptoms of West Nile Virus
According to Center for Disease Control and Prevention (CDC), almost 80 percent of the West Nile Virus infected people do not develop any visible symptoms. Only about 20 percent of the people infected with West Nile Virus have shown a visible symptom in the form of fever, headache, joint pains, and vomiting. Even after the infestation, the recovery period of the people from West Nile Disease is very less, even though they can develop fatigue or weakness in the body which might take weeks if not months to wither away completely. As observed by the Centers for Disease Control and Prevention (CDC), only about 0.67 percent of all the patients are subjected to inflammation of their neurological system either in the form of encephalitis or meningitis leading to increased pressure on the membrane of the brain as well as the spinal cord4.
Some of the severe symptoms as shown by the people infected with West Nile Disease include neck stiffness, stupor, disorientation, tremors, coma, muscle weakness, loss of vision, paralysis as well as high fever. Although this disease is not fatal for the young adults it can be life-threatening to people who are older than the age of 60 years as well as for the people who have a history of diseases such as cancer, kidney disease or high blood pressure. In addition to these, the people who have undergone surgery in the recent past have to take extra care to prevent the infestation.
The recovery from West Nile Disease may take several weeks or months but cases have shown permanent damage to the neurological system as well. Death from this illness is fairly rare, leading to the death of only about 1 in 10 patient who develops a severe infection.
Diagnosis of West Nile Virus
The World Health Organisation (WHO) has laid down several parameters to detect the West Nile Virus through a myriad of tests:
- Reverse transcription polymerase chain reaction or RT-PCR to detect the virus.
- Cell culture shall be used for virus isolation.
- Collection of two serial specimens at a week’s interval by enzyme-linked immunosorbent assay or ELISA for the detection of IgG antibody seroconversion.
- Capturing IgM antibody by ELISA neutralization assays.
Treatment of West Nile Virus
Hospitalization of the patient is the first treatment to be given to the patient. This would ensure proper respiratory support, intravenous fluids, and prevention of secondary infections. Adequate treatment shall be provided as directed by the physician but there is no vaccine available to destroy the virus completely as of now.
Centers for Disease Control and Prevention (CDC) offers the following guidelines for the treatment of the patient with West Nile Virus:
West Nile antivirus vaccine is not available as of now but other relevant medicines can be opted for as directed by the respected physician in order to relieve the pain in the patients’ body.
Pain relievers can be used to reduce fever and body pain symptoms.
Patients with a severe case of West Nile Virus infection are advised to be hospitalized for a supportive treatment which must include respiratory support, nursing care, pain medication, and intravenous fluids.
For further support, the patient must talk to his healthcare provider as soon as he observes some symptoms relating to the West Nile Disease.
Other Measures To Prevent West Nile Disease Include:
- Cleaning of the roof of gutters.
- Maintaining a hygienic swimming pool and birdbath.
- Cleaning the pet bowls at a regular interval.
- Repairing the windows and screens inside the house.
- Avoid unnecessary outdoor activity during the summer and fall season.
- Covering the whole body by wearing full sleeved shirts as well as pants when outdoors.
- Installation of mosquito repellents as well as mosquito nets at night.
- Application of mosquito repellent lotion when there is a need to go outdoors at night.
It is rightly said that prevention is better than cure. The best practice to be followed in order to prevent the infestation with this disease is to prevent the exposure to the carrier mosquitoes by eliminating the potential sites of stagnant water. This would otherwise act as a breeding ground for mosquitoes.
- Outbreak of West Nile-like viral encephalitis -- New York, 1999. MMWR Morb Mortal Wkly Rep 1999;48:845-849
- Asnis DS, Conetta R, Teixeira AA, Waldman G, Sampson BA. The West Nile virus outbreak of 1999 in New York: the Flushing Hospital experience. Clin Infect Dis 2000;30:413-418[Erratum, Clin Infect Dis 2000;30:841.]
- C. W. Morin, A. C. Comrie. Regional and seasonal response of a West Nile virus vector to climate change. Proceedings of the National Academy of Sciences, 2013; DOI: 10.1073/pnas.1307135110