WEST NILE VIRUS (WNR): Transmission, Symptoms, and Risks

How can you catch the West Nile virus?

West Nile virus (WNV) spreads through infected mosquitoes. These mosquitoes pick up the virus by feeding on infected birds. Thankfully, they can’t transmit it directly between people.

In rare cases, WNV can spread through blood transfusions or organ transplants. However, strict testing in the U.S. makes the blood supply very safe.

What are the signs of West Nile infection?

Most people (around 80%) infected with WNV show no symptoms at all. Some may experience mild, flu-like symptoms that fade on their own.

For a smaller group (about 20%), WNV causes West Nile fever. This can bring fever, headache, fatigue, and a rash. It can take weeks or months to fully recover, even though the illness itself isn’t severe.

What happens in severe cases?

In very rare instances (roughly 1 in 150 infections), WNV reaches the brain or spinal cord, causing encephalitis or meningitis. These can be life-threatening.

Symptoms of severe WNV infection include:

• High fever and severe headache
• Stiff neck
• Confusion, coma, or seizures
• Muscle weakness or paralysis

What are the risks for pregnant women?

While the risk seems low, some miscarriages have occurred in pregnant women with WNV. Most infected pregnant women, however, deliver healthy babies. It’s still important for pregnant and breastfeeding women to be extra careful about mosquito bites.

Can breastfeeding spread WNV?

One case suggests a possible, but very rare, transmission through breast milk. The benefits of breastfeeding far outweigh this minimal risk.

How likely is death from WNV?

The chances of severe WNV disease are about 1 in 150, with a 10% mortality rate in those cases. This brings the overall death rate from WNV infection to around 1 in 1,500. However, this risk increases significantly for people over 50, especially the elderly.

How does WNV cause serious illness?

WNV crosses the blood-brain barrier, attacking the brain and spinal cord. This disrupts normal brain function, including breathing control, which can be fatal.

Blood donation and transplants: Safe or risky?

Blood donation is crucial and safe. The benefits of blood transfusions and organ transplants far outweigh the minimal risk of WNV infection, which is thoroughly screened for.

How do doctors diagnose WNV?

A blood test checks for antibodies against the virus, indicating a recent infection. In severe cases, a spinal tap might be used to analyze spinal fluid.

Who’s most at risk of WNV infection?

Anyone can be infected, but those who spend a lot of time outdoors, particularly at dawn and dusk when mosquitoes carrying WNV are most active, are at higher risk. People over 50 seem more susceptible to severe illness from WNV infection. Age, however, doesn’t appear to affect the likelihood of getting infected.

Is WNV contagious between people?

No, WNV cannot spread from person to person through touch, kissing, or even contact with healthcare workers treating infected patients.

Where did WNV come from?

First detected in the U.S. in 1999, WNV likely originated in the Middle East.

Is WNV seasonal?

WNV activity peaks in late summer and early fall in most areas. In warmer climates, it can circulate year-round.

Is there a WNV vaccine?

No vaccine exists yet, but research into similar viruses suggests its potential.

Should I worry about a single mosquito bite?

Even in areas with WNV, very few mosquitoes carry the virus. And even if bitten by an infected mosquito, less than 1% of people develop severe illness.

Does WNV infection provide immunity?

Immunity is likely lifelong, although it might weaken over time.

Can pets spread WNV to humans?

No, although cats and dogs can contract WNV, they cannot transmit it to people or other animals.

Sources:

• CDC website
• CDC news conferences, August 2012
• CDC provisional data, “Characteristics of Reported Cases of Arboviral Disease, United States,” Aug 28, 2012
• Samuel, M.A. and Diamond, M.S. Journal of Virology, October 2006.