Arboviral Encephalitides

The Centers for Disease Control and Prevention (CDC) says arboviral viruses are viruses that can be spread to humans by infected arthropods, including mosquitoes and ticks. (Read about "Animal & Insect Borne Diseases") Infection occurs when you are bitten.

Some of these viruses have the potential to cause a serious complication called encephalitis, which is an inflammation of the brain. (Read about "Encephalitis and Meningitis" "The Brain") These are called arboviral encephalitides. Although many cases of encephalitis are not severe, these diseases are cause for concern, because sometimes encephalitis does have severe complications. It can result in damage to the nervous system (Read about "Nervous System") and in some cases, it can be deadly.

CDC says most cases of arboviral encephalitis occur from June through September, when arthropods are most active. In warmer parts of the country, where arthropods are active late into the year, cases can occur into the winter months.

According to CDC, arboviral encephalitides found in the United States include:

• West Nile virus - West Nile encephalitis is encephalitis caused by West Nile virus (Read about "West Nile Virus"), which is commonly found in Africa, West Asia and the Middle East. It is closely related to the St. Louis encephalitis virus (see below) CDC say the first recorded outbreak of West Nile encephalitis in the United States was in 1999, although the virus may have been present in this part of the world even before that. You can get the disease if you're bitten by an infected mosquito. West Nile virus infects people, horses, many types of birds and some other animals. CDC says most people who become infected with West Nile virus will have either no symptoms or only mild ones, including fever, headache and nausea. On rare occasions, symptoms can include more serious complications and can even be fatal. The risk of severe disease is higher for persons 50 years of age and older. According to CDC, there is no evidence to suggest that West Nile virus can be spread directly from person to person or from animal to person the way the flu or a cold is transmitted. Organ transplantation and/or blood transfusion from an infected person is suspected as a possible means of transmission. (Read about "Transplants" "Blood Donation Guidelines")
• Eastern equine encephalitis virus - CDC says it takes from 4-10 days after the bite of an infected mosquito for an individual to develop symptoms from eastern equine encephalitis virus. These symptoms begin with a sudden onset of fever, general muscle pains and a headache of increasing severity. Many individuals will progress to more severe symptoms such as seizures and coma. (Read about "Seizures") Eastern equine encephalitis virus causes disease in humans, horses and some bird species. It is transmitted to humans through the bite of an infected mosquito. Because of the high mortality rate, it is regarded as one of the most serious mosquito-borne diseases in the United States, according to CDC.
• Western equine encephalitis virus - Western equine encephalitis is a disease that is spread to horses and humans by infected mosquitoes. Infection can cause a range of illnesses. Sometimes there are no symptoms. People with mild illness may have only a headache and sometimes fever. People with more severe disease can have sudden high fever, headache, drowsiness, irritability, nausea and vomiting, followed by confusion, weakness and coma. Young infants often suffer seizures. (Read about "Seizures") Children, especially those under 1 year old, are affected more severely than adults.
• St. Louis encephalitis virus - St. Louis encephalitis is an infection that comes from the bite of the mosquito that is infected with the virus. Feeding on birds infected with the virus infects mosquitoes. St. Louis encephalitis grows both in the infected mosquito and the infected bird, but does not make either one sick, according to CDC. Symptoms of St. Louis encephalitis may be mild, like a fever and headache. Headache, high fever, stiff neck, disorientation, coma, tremors, occasional convulsions and spastic paralysis mark a more severe infection. The infection can be deadly. CDC says there's an average of 128 cases reported each year in this country. Outbreaks can occur throughout most of the United States.
• La Crosse encephalitis - CDC says most cases of La Crosse encephalitis occur in children. Many times, according to CDC, there are no symptoms. If symptoms are present, they usually occur three to 15 days after a bite from an infected mosquito. It often starts with symptoms of fever, headache, nausea, vomiting and lethargy. In young children, it can cause more serious complications.

Treatment and prevention

Healthcare providers will usually attempt to relieve the symptoms of the illness, but there is no specific treatment available for arboviral infections, nor is there a vaccine.

If you're concerned, CDC says you can take precautions to avoid mosquito bites, for example:

• Stay indoors at dawn, dusk, and in the early evening.
• Avoid sweet fragrances, which tend to attract insects, such as perfumes, colognes and hair sprays.
• Keep food and open beverage containers covered as much as possible when eating outdoors.
• Don't let standing water remain on your property.
• Wear long-sleeved shirts and long pants when possible, tucking pants into boots or socks when hiking.

You can also ask your doctor about using repellents containing permethrin or DEET to protect against mosquitoes biting through thin clothing. Insect repellents are available in different forms and concentrations. The Centers for Disease Control and Prevention (CDC) recommend three types of repellents. They are:

• DEET
• picaridin
• oil of lemon eucalyptus

All three have been shown to offer long-lasting protection against mosquito bites, according to CDC.

Products containing DEET have been on the market for many years. CDC says they are a highly effective repellent option. Picaridin, also known as KBR 3023, is an ingredient found in many mosquito repellents used in Europe, Australia, Latin America and Asia for some time. CDC says evidence indicates that it works very well, often comparable with DEET products of similar concentration. One product, containing 7 percent picaridin, is relatively new to the market in the United States. Oil of lemon eucalyptus (also known as p-menthane 3,8-diol or PMD), is a plant-based mosquito repellent that provided protection time similar to low concentration DEET products in two recent studies, according to CDC. It is available in a variety of formulations throughout the United States. CDC says DEET may be effective against ticks as well.

If you must use a repellent, it's important to remember that repellents contain powerful chemicals that must be used cautiously.

Some suggestions from the US Environmental Protection Agency:

• Never use repellents on open cuts or irritated skin.
• Consult your pediatrician about using repellents on very young children.
• Do not let children handle repellents.
• Avoid spraying repellents directly on children's hands when they're likely to be handling food or if they have a tendency to put their fingers in their mouths.
• Do not spray in an enclosed area.
• Do not use excessively or at higher concentrations than necessary.
• After returning inside, wash treated skin with soap and water.

If you develop suspicious symptoms, see your healthcare provider at once.

Related Information:

    Microorganisms

    Insect Bites