Signs and Symptoms of WNV


What are the symptoms of WNV infection?

The vast majority of people that become infected with the WNV have no illness or experience only a mild flu-like illness that includes fever, headache and body aches lasting only a few days. Some persons may also have a mild rash or swollen lymph glands.

Less than one percent of those infected may develop meningitis or encephalitis, the most severe forms of the disease, which occurs primarily in persons over 50 years of age. Symptoms of encephalitis or meningitis may include severe headache, high fever, neck stiffness, stupor, disorientation, tremors, convulsions, paralysis, coma and sometimes, death.

If I live in an area where birds or mosquitoes with WNV have been reported
and a mosquito bites me, am I likely to get sick?

No. Even in areas where mosquitoes do carry the virus, very few mosquitoes-much less than one percent-are infected. If the mosquito is infected, less than one percent of people who get bitten and become infected will get severely ill. The chances you will become severely ill from a mosquito bite are extremely small.

If a mosquito bites me, should I be tested for WNV?

No. However you should seek medical care if you develop symptoms such as high fever, body aches, confusion and severe headaches.

How soon after exposure do symptoms appear?

The symptoms generally appear about three to six days after exposure, but may appear as early as one day after exposure or as late as fifteen days.

What is the treatment for WNV infection?

There is no specific treatment for WNV infection. Doctors can treat the symptoms of encephalitis in a hospitalized patient. Most people recover from the illness. The mild flu-like symptoms generally do not require medical treatment.

Is there a vaccine for WNV?

There is no human vaccine for WNV. However there is a vaccine for horses (see WNV and equine).

What should a person do if he/she thinks they have West Nile encephalitis?

It is likely that a person with true WNV will be in the hospital with severe meningitis or encephalitis before a diagnosis of WNV is made. If a person has signs of encephalitis that include high fever, severe headache, possible muscle weakness along with confusion, or altered mental state, he or she should seek medical care as soon as possible.

Steps you can take to protect yourself from WNV

What can you do to protect yourself?

Even though the human risk of WNV is low, the best way to further protect yourself is to keep mosquitoes from biting you. During mosquito season (generally April through October), take the following precautions:

* Limit outdoor activities between dusk and dawn, since this is the time of greatest activity among the species of mosquitoes that carry WNV.
* If you are outside when mosquitoes are prevalent, wear protective clothing such as long pants, long-sleeved shirts and socks.
* Use a mosquito repellent that contains DEET (the chemical N-N-diethyl-meta-toluamide) and follow the directions on the label.

Avoid using products that contains more than 10 to 15 percent DEET on children and more than 30 percent DEET on adults. Do NOT use repellent containing any DEET on infants. Click here for more information about using insect repellent safely. (Please note: link will take you outside of the Tennessee Department of Health WNV website.)

What can I do around my home to help reduce exposure to mosquitoes?

To reduce mosquito populations around your home and neighborhood, get rid of standing water where mosquitoes can lay eggs. Weeds, tall grass and bushes also provide an outdoor home for mosquitoes. Any container with over ½ inch of standing water for five to seven days can hatch out mosquitoes.  You can take the following simple steps to reduce egg-laying sites for mosquitoes:

* Dispose of, regularly empty, or turn over any water holding containers on your property such as tires, cans, flowerpots, or trashcans.
* Drill holes in the bottom of recycling containers that are left outdoors.
* Make sure roof gutters drain properly and water doesn't stand in them.
* Change the water in birdbaths at least once a week.
* Turn over plastic wading pools and wheelbarrows when not in use.
* Keep swimming pools, outdoor saunas and hot tubs clean and properly chlorinated; remove standing water from pool covers.
* Eliminate any standing water that collects on your property.
* Remind or help neighbors to eliminate mosquito-breeding sites.
* Fix any holes in your screens and make sure they are tightly attached.

What types of mosquitoes in Tennessee are most likely to carry WNV?

Culex pipiens pipiens and the Culex pipiens quinquefasciatus are the most common mosquitoes in Tennessee that may carry WNV. They are often referred to as urban "house mosquitoes." These types of mosquitoes tend to lay eggs in man-made pools, water barrels, street gutters, clogged house gutters and birdbaths. To reduce your exposure to these types of mosquitoes, be sure to limit the amount of standing water near where you live. Also it is important to wear protective clothing (i.e. long sleeves) between dusk and dawn, since this is the time the Southern and Northern house mosquitoes are most active.

WNV and birds

Why should we be concerned with birds when discussing WNV?

Birds are infected by mosquitoes and serve as the natural host and reservoir for WNV. Although the virus usually does not make the birds ill, many birds can carry the virus in their blood for three or four days allowing more mosquitoes to feed on them and become infected. In nature,
WNV "cycles" between birds and mosquitoes only and does not involve humans unless the virus had built up in an area for a couple of months under favorable environmental conditions.

Can you get WNV directly from birds?

No. WNV cannot spread directly from birds to humans. However, dead birds should not be handled with bare hands. Use gloves to carefully place dead birds in a double plastic bag, and then place the birds in the outdoor trash.

Does a dead bird in my yard mean WNV is in the area?

Most birds do not become ill when infected with WNV. However, the virus is highly fatal in crows and blue jays. Thus, an increase in deaths of these two bird species can be an indication of WNV circulating in an area. The Tennessee Department of Health is testing fresh samples of crows and blue jays as part of their surveillance for WNV. Deaths of other kinds of birds are usually not associated with WNV. The testing of certain dead birds for WNV is the most accurate way to detect the early arrival of WNV in an area.  This type of surveillance demonstrated the spread of WNV to 27 states during 2001.

What types of birds will local health departments
across Tennessee be collecting to test for WNV?

The health departments will only collect freshly dead crows and blue jays.  Click here to see descriptions and pictures of the type of birds local health departments will collect for testing.

What if I notice a dead crow or blue jay?

If you notice a freshly dead crow or blue jay, you should contact your local health department's environmental or vector control section to see if it is needed for testing. To keep it from deteriorating in the heat, you should place it in a plastic bag ( place hand in bag, grasp bird, pull bag over hand), double bag and refrigerate, freeze or keep on ice until delivered or picked up. Not every bird reported will be submitted for testing, especially after WNV is already known to be in the area.

When will my local health department NOT accept birds for testing?

Local health departments will not accept birds other than blue jays and crows, and they will not accept birds that are decomposed. Also, once WNV has been determined to be in a certain area, birds will no longer be collected for testing.

WNV and equine (horses)

Can horses be infected with WNV?

Yes. Cases of WNV disease in horses were documented in 1999 and 2000. With the spread of WNV to 27 states in 2001, the number of horses with confirmed West Nile Encephalitis rose to over 730. Nearly one-third of these horses died or were euthanized. There was only one horse with West Nile virus in Tennessee in 2001.

How are horses infected with WNV?

The horses most likely became infected with WNV in the same way humans become infected, by the bite of infected mosquitoes. The virus is located in the mosquito's salivary glands. When the mosquito bites or feeds on the animal, the virus is injected into the blood system of the horse. The virus then multiplies and may cause illness.

Can humans or other animals contract WNV from infected horses?

Although there is no documented evidence of animal-to-person transmission of WNV, normal veterinary infection control precautions should be followed when caring for a horse suspected to have this or any viral infection.

There is no documented evidence that WNV is transmitted between horses.  Also, horses do not produce high enough virus levels in their blood to pass the virus on to additional mosquitoes.

Are horses that are vaccinated against eastern equine encephalitis (EEE),
western equine encephalitis (WEE), and Venezuelan equine encephalitis (VEE)
protected at all against WNV infection?

No, they are not.

Is there a WNV vaccine for horses?

The USDA conditionally released a WNV vaccine for horses; but its level of effectiveness is unknown. However in early tests, the vaccine appears to be effective. It is recommended that if you already vaccinate your horses against EEE, WEE and VEE, you should consider vaccinating for WNV also. The risk of WNV disease in horses in Tennessee is low and about the same for
EEE. The vaccination of your horse for WNV should be discussed with your veterinarian.

Should I destroy my horse if it has been infected with WNV?

There is no reason to destroy a horse just because it has been infected with WNV. Most horses recover from the infection, especially if young and healthy. Treatment would be supportive and would depend upon the advice of your veterinarian.

If a horse in my community is infected with WNV, are my horses at risk?

Not necessarily. This may indicate that WNV is in the area and precautions should be taken. However it has been proven that a horse cannot infect a mosquito, which in turn can infect other horses. In most US cases, WNV in horses has been sporadic, and rarely have multiple horses in the same area become infected with WNV. This is especially true in areas where the virus is found at low to moderate levels, as expected in Tennessee.

WNV and household pets

Can WNV affect my pets?

West Nile virus does not appear to cause noticeable illness in dogs or cats. Although WNV was isolated from a couple of dead pets in New York City in 1999 and 2000, there was no indication that it caused their death.  Studies showed that there was a low infection rate for dogs and cats.
According to the Centers for Disease Control and Prevention, prior reports of small mammals becoming seriously ill from WNV were further reviewed and it was determined that WNV was not the cause of the illness.

If my dog or cat chewed or ate a bird that died of WNV, would they become ill?

No, not from WNV.

Can infected pets transmit WNV to human or other animals?

No. There is no documented evidence of person-to-person or animal-to-person transmission of WNV. Infectious mosquitoes may transmit the virus to dogs and cats as they can to any animal. However, dogs and cats do not usually have any symptoms. Also the transient virus level in their blood would be too low to transmit the virus back to mosquitoes or to any other animal.

Other mosquito-borne diseases

What other mosquito-borne diseases should I be aware of?

St. Louis encephalitis and La Crosse encephalitis are two mosquito-borne diseases that have affected people in Tennessee.

How are St. Louis encephalitis and La Crosse encephalitis transmitted?

Both diseases are transmitted to humans through certain species of mosquitoes who have become infected by birds or small mammals.

What are the symptoms of St. Louis encephalitis and La Crosse encephalitis?

Mild infections occur without apparent symptoms other than fever with headache. The majority of infections result in mild illness. Headache, high fever, neck stiffness, stupor, disorientation, tremors and occasional convulsions mark more severe infection.

Who is at risk of contracting St. Louis encephalitis and La Crosse encephalitis?

The elderly are at highest risk of contracting St. Louis encephalitis and children under 16 are at highest risk of contracting La Crosse encephalitis.

When and where have mosquito-borne disease been a problem in Tennessee?

St. Louis encephalitis occurs in sporadic outbreaks anywhere in the country (usually in urban areas). During the mid 1960s and again in the mid 1970s, there were outbreaks lasting two to three years each in West Tennessee, especially in Shelby County. There were over 100 cases of encephalitis with each outbreak. Improved mosquito control should lessen the risk from St. Louis encephalitis, as well as the similar WNV encephalitis.

East Tennessee in one of the areas where La Crosse encephalitis has been most prevalent in recent years. There were 19 cases in 2000 and 17 cases in 2001; there were no deaths.

Where can I learn more about St. Louis encephalitis and La Crosse encephalitis?

Visit the CDC website to learn more about these mosquito-borne diseases and others.

This information has been reproduced from the State Health Dept. Website on infectious diseases.