■ SUBMITTED BY DR. LAUREN M. HANA MD
BOCA GRANDE HEALTH CLINIC
The Florida Department of Health has issued a mosquito-borne illness advisory for residents and visitors. The first U.S. cases were reported in New York City in 1999, and the first reported case in Florida was in 2001. All 48 contiguous states have now had human cases of West Nile virus infection.
West Nile virus affects birds as the primary host. Humans (and other animals) are infected after being bitten by an infected mosquito that previously bit an infected bird. The life cycle of the virus involves several species of Culex mosquitos (primarily C. nigripalpus and C. quinquefasciatus), and wild birds – mainly jays and crows, but also osprey and many others. An infected bird has circulating virus for several days. A mosquito feeds on the infected bird and becomes a carrier. That mosquito can then bite a person and inject the virus through its salivary glands into the person’s bloodstream. These carrier mosquitos can also infect other birds the same way.
West Nile virus produces seasonal infections from summer through fall, but the season can be longer in areas with warmer climates, where mosquitos can live longer. Infection rates generally peak in mid-August to early September. One of every four infected persons becomes ill, but only one in about 200 will develop severe symptoms. Those with chronic diseases such as chronic kidney disease and diabetes, those with immune system problems (due either to disease or to taking immunosuppressive medications) and those over 50 years old are at higher risk for severe symptoms should they become infected. Persons in these categories should take extra precautions to avoid contracting the disease.
As the primary hosts, birds carry high levels of the virus, and contact with ill or dead birds should be avoided. Dead birds should be reported to the Florida Department of Health. Pregnant women should immediately contact their doctor if they believe they may have been infected, because fetal abnormalities have been associated with maternal infection. Routine testing is not recommended for women who have no symptoms.
West Nile virus is not transmitted person to person and cannot be spread by touching, kissing or sharing utensils. Transmission through blood transfusion and organ transplant is possible but very unlikely, due to the routine testing for West Nile virus in the blood of donors since 2003. It is not possible to contract the virus by donating blood.
Most people who become infected never develop symptoms. The virus stays in the system for a few days while the immune system does its job and eliminates it. Those who show symptoms do so in the first 15 days after infection. Symptoms include fever, headache, rash, muscle aches and fatigue. Less commonly, nausea, vomiting, diarrhea and abdominal pain may also occur. These symptoms can last a few days to several weeks and are self-limited, or go away on their own, with time. Sometimes fatigue can persist longer.
Less than one percent of those infected will develop severe symptoms when the virus travels through the bloodstream and infects the central nervous system (brain and spinal cord). Symptoms of severe disease include fever and headache but also confusion, muscle weakness and even paralysis, coma and seizures. These conditions can last for several weeks, and in some cases neurologic damage is permanent. Death may occur in rare cases.
If you suspect that you may have West Nile virus (e.g., you have symptoms and have been in a region where West Nile virus has been found), see your doctor right away. Your physician or an urgent care clinic will review your symptoms and history and do an exam that will include blood testing for West Nile virus, if appropriate. The testing may be negative in the first week of illness, because the blood test is for antibodies to the virus that take time to develop. If infection is strongly suspected, follow-up testing at a later date may be necessary to confirm the diagnosis. If severe disease is suspected, a lumbar puncture or spinal tap may be necessary. If the virus is present, the cerebrospinal fluid that surrounds the brain and spinal cord will test positive for the antibodies.
There is no specific medication or treatment available to treat West Nile virus infection. Mild disease generally improves on its own. Severe disease may require hospitalization for supportive treatment (intravenous fluids, monitoring, breathing assistance and nursing care) while the body recovers.
There is currently no vaccine available for West Nile virus, but there are steps you can take to avoid the disease. The Florida Department of Health’s campaign for prevention of West Nile virus and other mosquito-borne illnesses is called “drain and cover”:
- Drain all standing water (in gutters, flowerpots, wading pools, tires, etc.). Standing water is where the mosquitos lay their eggs.
- Empty the water in outside pet bowls and birdbaths, and replace the water at least every week.
- Check boats and other outside vehicles for any areas that may collect water. (Shake standing pools of water off tarps.)
- Maintain swimming pools with appropriately chlorinated water even when not in use.
- Wear protective clothing (long pants, long sleeves and shoes).
- Use insect repellant with DEET, picaridin, oil of lemon eucalyptus, para-menthane-diol and IR3535. Be sure to follow the directions regarding the use of insect repellants on children. Permethrin may be applied to clothing but not to skin. Use mosquito netting to protect infants less than two months old.
- Repair any holes or tears in door and window screens.
- Report dead birds to the Florida Department of Health.
Remember, mosquitos are most active at dawn and dusk. Be sure to take extra precautions at these times.
Our mosquito control program in Boca Grande is overseen by Lee County. For surveillance of mosquito-borne illnesses, the County uses both chicken coops and mosquito “pools.” The chickens and mosquitos are both routinely tested for West Nile virus and other mosquito-borne diseases. If any test positive, the surrounding areas are aggressively treated. Lee County boasts the only “in-house” testing for West Nile virus, allowing for quicker treatment of affected areas. Other counties have to wait up to a week for return of results from the state lab. As one of the more southern counties, we are also able to watch the infected birds from the more northern counties to know when they will reach our area in their southward migration. Treatment of affected areas consists of a truck-based spraying of permethrin at 1 oz/acre (about the size of a football field). This kills adult mosquitos. It is the same chemical that is applied to clothing as an insect repellant and is also used for treatment of lice, so at such low concentrations it is safe to humans. The West Nile virus has to replicate and circulate in the infected mosquito before it can be transmitted in a bite. Therefore, mature mosquitos are the threat. Areas may also be treated with a naturally occurring bacterium (Bacillus sphaericus) that will kill larvae before they have a chance to mature and become carriers.