Newswise — Summer brings insects such as ticks and mosquitoes, which can carry disease to humans. Dr. Katherine Feldman, a public health veterinarian at the University of Maryland campus of the Virginia-Maryland Regional College of Veterinary Medicine, is an expert on disease transmission between animals and humans. Here she talks about which insect-borne diseases we should be on the lookout for this summer and how we can reduce our exposure.
Dr. Feldman served as principal investigator in a landmark epidemiological study on Martha's Vineyard, MA, of primary pneumonic tularemia, a potentially fatal disease carried by ticks. It was only the second pneumonic tularemia outbreak in the U.S. and came at a time of heightened concern about the possible use of tularemia as a bioweapon. Dr. Feldman also investigated West Nile virus infection in New York City and Tickborne Relapsing Fever in Nevada. She received the 2006 James H. Steele award for outstanding contributions in the investigation, control, or prevention of zoonotic diseases or other animal-related human health problems.
What are the major insect-borne diseases we should be aware of this summer?
Dr. Feldman: Ticks and mosquitoes can transmit many different diseases. Mosquitoes can transmit diseases including West Nile virus and other viruses that can cause encephalitis. The most common tick-borne disease in Maryland and other states in the northeast is Lyme disease, caused by the bacterium Borrelia burgdorferi, but ticks can harbor other diseases as well, such as ehrlichiosis and Rocky Mountain Spotted Fever. Both Lyme disease and West Nile virus can infect humans and animals. The good news is that by preventing a mosquito or a tick bite, more than one disease is stopped in its tracks.
What are the effects of these diseases on humans?
Dr. Feldman: In 70 to 80 percent of people infected with Lyme disease, the first sign of infection is a circular "bull's eye" rash that begins at the site of a tick bite and gradually expands, reaching up to 12 inches across. It is called a "bull's eye" rash because it often has a central area of clearing. Other symptoms may include fatigue, chills, fever, headache, muscle and joint aches, and swollen lymph nodes. The infection can spread if it is not treated, and may cause severe headaches and neck stiffness, joint pain that shifts from joint to joint, heart symptoms, or droopiness of facial muscles. Some patients, if their infection is never treated, may develop chronic disease, including arthritis and neurologic disease. For patients with Lyme disease, arthritis, large joints, the knees in particular, may swell significantly and be painful. Patients with neurologic complications may experience numbness and tingling in their hands or feet or difficulty concentrating.
Approximately 80 percent of people infected with West Nile virus do not have any symptoms, and most of the remaining people infected have relatively mild symptoms including fever, headache, body aches, nausea, and vomiting. However, approximately one in 150 people infected with West Nile virus will develop more serious disease, and their symptoms can include high fever, headache, neck stiffness, convulsions, muscle weakness, paralysis and other neurologic effects.
Should you experience any of these symptoms, especially after having been bitten by a mosquito or a tick, you should seek medical attention promptly.
Which diseases present the highest likelihood of being contracted?
Dr. Feldman: In 2003, nearly 700 cases of Lyme disease in Maryland and over 21,000 cases nationwide were reported to the federal Centers for Disease Control and Prevention, more than any other insect-borne disease.
It seems like we're hearing about more cases of Lyme disease and in more areas of the country. Why is the number of cases increasing?
Dr. Feldman: There are many reasons why the number of reported cases of Lyme disease has increased over time. A primary reason is that there is increased contact between people and high risk areas due to recreational activities and housing developments that encroach on more suburban/rural areas. In addition, re-forestation of many areas has led to an increased deer population (the host of the tick that transmits Lyme disease) with increased habitat for tick populations. Finally, as the awareness of Lyme disease increases, it is more likely to be recognized and diagnosed by health care providers.
What steps can we take to reduce our exposure to Lyme disease?
Dr. Feldman: For all vector-borne diseases, prevention is the key to protecting yourself from disease. To prevent diseases transmitted by ticks, avoid areas where ticks live, such as wooded areas with lots of leaf litter, bushes or tall grasses. Wear long-sleeved shirts, long pants, and long socks when you are outside in areas where ticks live. Tucking shirts into pants and pants into socks helps prevent ticks from getting inside your clothing. Wearing light colored clothing allows you to better see if there are ticks on you. Use insect repellent according to the manufacturer's label, and most important, perform a thorough tick check when you come in from the outside. If you should find a tick on you, remove it promptly using fine tipped tweezers. The ticks that cause Lyme disease can be very small, but they require at least 24-48 hours of attachment to transmit the infection.
How can we reduce the risk of contracting the other insect-borne diseases you mentioned?
Dr. Feldman: To prevent mosquito-borne diseases, use insect repellent appropriately, avoid the outdoors at dusk and dawn, the highest risk times, and wear long pants and long-sleeved shirts. Eliminate mosquito breeding sites by changing the water in pet dishes and bird baths weekly and emptying standing water from containers on your property. Make sure screens on windows and doors are in good repair.
There are many great resources to learn more about Lyme disease, West Nile virus and other diseases transmitted by insects, including details on insect repellent and tick removal. For a great starting point, visit the Centers for Disease Control and Prevention's website: http://www.cdc.gov.
Contact: Ellen Ternes, 301-405-4627, [email protected]
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