What is West Nile Virus? Symptoms, Diagnosis & Treatment
As the world is dealing with the emergence and circulation of viruses such as COVID-19 and monkeypox, Greece has reported increasing numbers of infections with the West Nile Virus (WNV) infections. On August 30, the National Public Health Organization in Greece (EODY) reported 123 cases of West Nile Virus (WNV) infections with 11 deaths. According to the weekly epidemiological report, 74 of the infected cases demonstrated neuro-invasive diseases such as encephalitis, meningitis, or acute flaccid paralysis, whereas the rest experienced mild symptoms. Most of the reported cases were recorded in Chalkidiki, Thessaloniki, Imathia, Kilkis, Pella, Pieria, Larissa, and Trikala. Although further surveillance efforts are required to determine the exact size and urgency of the outbreak, the increasing number of infected cases with a significant level of mortality has caused major concern regarding the risks posed by the West Nile Virus (WNV). Read along to learn more about the West Nile Virus (WNV), along with its transmission, symptoms, diagnosis, prevention, and treatment.
What is West Nile Virus (WNV)?
West Nile Virus (WNV) is a mosquito-borne single-stranded RNA virus from the genus Flavivirus, of the family Flaviviridae. Thus, West Nile Virus (WNV) shares the same family with the Zika virus, dengue virus, and yellow fever virus. As a neurotropic pathogen, West Nile Virus (WNV) belongs to the Japanese encephalitis antigenic complex and thus, is also closely related to other viruses causing encephalitis. Although the transmission cycle of the West Nile Virus (WNV) mainly involves mosquitos and birds, West Nile Virus (WNV) is known to affect horses, humans, and other mammals.
How common is West Nile Virus (WNV) infection?
West Nile Virus (WNV) is commonly found in many regions around the world, including Africa, Europe, the Middle East, North America, and West Asia. Following its initial discovery in a woman in the West Nile province of Uganda in 1937, the West Nile Virus (WNV) has rapidly spread to many other parts of the world and caused major outbreaks in Greece, Israel, Romania, Russia, and the USA.
How does West Nile Virus (WNV) transmit?
West Nile Virus (WNV) is known to circulate in nature in a mosquito-bird-mosquito transmission cycle. Birds act as the natural reservoir of the West Nile Virus (WNV), while mosquitoes of the genus Culex, most commonly C. pipiens, are generally considered to be its primary vectors. On the other hand, humans and horses are most often dead-end hosts, which means that although they get infected, they usually do not transmit the infection.
West Nile Virus (WNV) transmits to mosquitoes when they feed on infected birds. Once the virus reaches the salivary glands, it can transmit to humans and other animals through the bite of the infected mosquito. After its injection into a host, the virus can multiply and lead to disease. In case of infection, West Nile Virus (WNV) can cause severe neuro-invasive disease in humans and horses.
Apart from mosquito bites, the virus can also spread through direct contact with infected animals, along with their blood, bodily fluids, and other tissues. Although West Nile Virus (WNV) transmits to humans most commonly through mosquito bites, human infections have occasionally been reported to occur through organ transplantations, blood transfusions, and breast milk. While there is also one documented case of transplacental transmission, there is currently no evidence for the human-to-human transmission of the West Nile Virus (WNV) through direct contact.
What are the signs and symptoms of West Nile Virus (WNV) infection?
According to World Health Organization (WHO), approximately 80% of those infected with the West Nile Virus (WNV) do not experience any symptoms. Around 20% of the infected people, on the other hand, develop West Nile fever. Common symptoms associated with West Nile fever include fever, headache, fatigue, nausea, vomiting, body aches, and less frequent, skin rash and swollen lymph glands.
Unfortunately, around 1 in 150 people infected with the West Nile virus (WNV) develop a more severe, typically neuro-invasive form of diseases such as encephalitis and meningitis. Severe disease caused by West Nile virus (WNV) may be life-threatening with symptoms such as severe headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. Although older adults, immunocompromised people, and those suffering from certain medical conditions including cancer, diabetes, hypertension, and kidney disease are at higher risk for developing severe symptoms, neuro-invasive forms of West Nile virus (WNV) infections may occur in anybody regardless of age. According to the Centers for Disease Control and Prevention (CDC), 10% of neuro-invasive infections with the West Nile virus (WNV) result in death.
How can West Nile Virus (WNV) infection be prevented?
Avoiding mosquito bites is the best possible way to reduce the risk of infection with the West Nile virus (WNV). When mosquitoes cannot be avoided, the use of mosquito nets, insect repellents, window screens, and protective clothing can help reduce the risk of animal-to-human transmission. It is also recommended to remove standing water and refrain from outdoor activity as much as possible at peak biting times. In addition to personal precautions, experts encourage the elimination of mosquito breeding sites in residential areas. Finally, additional restrictions could be implemented in affected regions to reduce the risk of transmission through blood transfusions and organ transplantations.
How can West Nile Virus (WNV) infection be diagnosed?
The screening and diagnosis of West Nile Virus (WNV) infections are possible through RT-PCR assays, neutralization assays, virus isolation, or ELISA-based IgG and IgM tests. Moreover, when required, the diagnosis of West Nile virus infection can be confirmed with a blood or cerebrospinal fluid test.
Which treatment options are available for West Nile Virus (WNV)?
According to the World Health Organization (WHO), there is currently no specific treatment for West Nile Virus (WNV). Likewise, although there is a vaccine available for use in horses, there is currently no human vaccine targeting the West Nile Virus (WNV). Still, supportive treatments involving anti-inflammatory medication, nursing care, intravenous fluids, respiratory support, and prevention of secondary infections are available for neuro-invasive cases of infection.
Ciota, A., & Kramer, L. (2013). Vector-Virus Interactions and Transmission Dynamics of West Nile Virus. Viruses, 5(12), 3021–3047. https://doi.org/10.3390/v5123021