From the Guidelines
West Nile virus is a single-stranded RNA flavivirus primarily transmitted to humans through the bites of infected mosquitoes, with potential to cause severe neurological illnesses in less than 1% of infected individuals. The virus has antigenic similarities to Japanese encephalitis and St. Louis encephalitis viruses, and its transmission is mainly through the bite of infected mosquitoes, particularly those of the Culex species 1. Some key points about West Nile virus include:
- It can cause illness ranging from mild to severe in humans
- Most people (about 80%) infected with West Nile virus don't develop any symptoms
- Approximately 20% experience mild symptoms including fever, headache, body aches, joint pain, vomiting, diarrhea, or rash
- Less than 1% of infected individuals develop serious neurological illnesses such as encephalitis or meningitis, which can be life-threatening, as reported in the Morbidity and Mortality Weekly Report 1. The elderly and those with compromised immune systems face the highest risk of severe disease. Some of the key prevention strategies for West Nile virus include:
- Avoiding mosquito bites through using insect repellent
- Wearing long sleeves and pants
- Staying indoors during peak mosquito activity times (dawn and dusk)
- Eliminating standing water where mosquitoes breed. There is no specific treatment or vaccine for West Nile virus; management focuses on supportive care for symptoms, as noted in the study published in the Morbidity and Mortality Weekly Report 1.
From the Research
Definition and Characteristics of West Nile Virus
- West Nile virus (WNV) is a mosquito-borne, single-stranded, positive-sense RNA virus belonging to the Flaviviridae family 2.
- It is transmitted to humans by infected mosquitoes of the genus Culex 3.
- WNV is a member of the Flaviviridae family, genus Flavivirus, with wild birds as its reservoir hosts 3.
Symptoms and Effects of West Nile Virus
- The majority of infected individuals remain asymptomatic, but symptoms can range from a mild fever to severe neurological disorder with high morbidity and mortality 2.
- Typical symptoms include fever above 39 degrees C, chills, headache, arthralgia, myalgia, back ache, cough, and sore throat 3.
- Gastrointestinal symptoms and generalized lymphadenopathy may also occur, and in some cases, the infection can progress to meningoencephalitis 3.
- People older than 50 years are at highest risk of severe disease, which may include encephalomyelitis 4.
Transmission and Epidemiology of West Nile Virus
- WNV was first recognized in the United States in 1999 and has since become the most common mosquito-borne virus in North America 2.
- The virus has been steadily moving westward, with human cases reported in 39 states and the District of Columbia in 2002 4.
- In 2021,49 states and the District of Columbia reported 3,035 cases of domestic arboviral disease, including 2,911 cases of West Nile virus 5.
- West Nile virus is the leading cause of domestically acquired arboviral disease in the United States, mainly transmitted by Culex species mosquitos 6.
Diagnosis and Prevention of West Nile Virus
- Diagnosis is currently based on detection of IgM antibodies in blood and cerebrospinal fluid or direct detection of WNV RNA 3.
- There are no approved vaccines or specific treatments for humans, and prevention depends on community and household efforts to reduce vector populations and personal protective measures to prevent mosquito and tick bites 2, 5.
- Health care providers should consider arboviral infections in the differential diagnosis of aseptic meningitis and encephalitis, obtain appropriate specimens for laboratory testing, and promptly report cases to public health authorities 5, 6.