History of the West Nile Virus

A summertime guest has taken up residence

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Culex Mosquito. "CulexNil"

The doctor on the phone described a man in his later years confused with maybe a slight fever. It wasn't a surprising story; sometimes the elderly are confused, but he had been hiking vigorously the weekend before. His decline had been rapid without any other particular symptoms. The doctor knew what he had: West Nile.

It wouldn't be any easy case for an elderly man who now had a nervous system infection from West Nile.

West Nile first arrived in the US in 1999, surprising New York City. It is a flavivirus spread by mosquitoes. It was first described in 1937 in the West Nile region of Uganda. In the 1990s, it spread to Algeria and later Romania. It then likely hopped from an Israeli outbreak to New York City in 1999. Within 5 years, it had spread throughout the US and Canada. By 2013, over 1500 deaths and over 15,000 neuroinvasive cases (affecting the brain and nervous system) had been reported. It is thought more than 780,000 cases have occurred in the US.

There is no specific treatment. Instead, prevention and supportive care are what are important.

How does this disease start?

Fortunately, most people - up to 70%-80% - have no symptoms. Those who develop symptoms usually do in 2-6 days (2-14 days) after a mosquito bite.

Blood transfusions and organ transplants have led to infections. All blood is tested for WNV in the US; not all organs are.

Some infants are infected in utero, at birth, or through breastfeeding.

West Nile is not transmitted person-to-person. Many animals are infected, primarily birds - especially crows. Infections occur in horses and to a lesser extent, dogs and cats. People are not infected by simple contact with an infected animal alive or dead or from eating meat from infected animals.

What carries West Nile?

West Nile Virus is largely transmitted by mosquitoes biting us - after biting a bird. 

Many, actually 43, different mosquito species can carry West Nile. These species vary from different Culex species to Aedes Aegypti and Aedes Albopictus that can carry Dengue and Chikungunya. A common mosquito responsible is the Culex Pipiens, found in cities and much of the Central and Eastern US. The mosquito breeds in storm drains, pools, ditches, and sewage treatment plants. 

With so many varieties of mosquitoes able to transmit West Nile, it is hard to avoid them. Their breeding habitats range from gutters, tires, buckets, and vases to birdbaths and wading pools. Some bite during the day, others at dusk, others at night, inside or outside. 

Outside of Americas, deaths of birds from West Nile is very rare; in the Americas, members of over 250 species have died, often in notable numbers. Certain birds, especially crows develop high virus levels, associated with poor bird outcomes.

Biting these birds can make a mosquito infectious. Humans and other animals do not develop high viral levels and cannot transmit infection through mosquitoes.

What is bad about West Nile?

About 1 in 5 infected will have a fever - and maybe a headache, body ache, joint pain, rash, nausea/vomiting, diarrhea, lymph node swelling. The rash is often on the torso, red, slightly raised. Fatigue may continue for weeks and months, but generally completely resolves

What is more worrisome is that 1 in 100 will develop neuroinvasive disease. This includes meningitis (inflammation of membranes surrounding the brain, spinal cord), encephalitis (inflammation of the brain), and acute flaccid (floppy) paralysis. The neuroinvasive disease leads to death in 1 in 10 affected. Some may have prolonged impairments post-encephalitis and many with paralysis (likely 2 in 3) have substantial, residual weakness.

Acute Flaccid paralysis resembles polio. It can involve isolated limb weakness or paralysis, without fever or a viral syndrome. It can also progress rarely to weakened breathing muscles and a need for ventilation for patients to breathe.

Other rare effects include cardiac dysrhythmias, myocarditis, rhabdomyolysis, optic neuritis, uveitis, chorioretinitis, orchitis, pancreatitis, hepatitis. Infants can rarely have birth defects.

How can we prevent West Nile?

Most infections occur in the summer, especially August and September:

a) Spray with insect repellant containing DEET

b) Avoid areas, times of the day with mosquitoes

c) Wear long sleeves and pants when possible

d) Eliminate mosquito breeding grounds by draining standing water

e) Mosquito-proof your home with screens. Air-conditioning reduces risk.

f) Report dead birds 

Droughts may spread West Nile. Water pockets may shrink to amount needed for mosquito breeding.

There is a vaccine available for horses, but not for humans.

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