Last month, we talked about how to properly remove ticks and when to seek medical attention. Here's a more indepth look at tick borne dieases specific to our area.
As warmer weather approaches, ticks begin to appear in wooded areas. These insects adhere to both people and pets. A small percentage of ticks carry bacteria, viruses and protozoa that produce disease in humans. There are a myriad of diseases, but they are typically limited geographically based on the ticks endemic to any given region. Several tick borne diseases occur in the greater Philadelphia area.
Borrelia burgdorferi, the bacteria that causes Lyme disease, is transmitted by small deer ticks that feed on infected rodents. In endemic areas, only a small percentage of ticks are actively infected with the bacteria and therefore capable of transmitting the disease.
Human infection follows a prolonged bite from an infected tick, although the bite is not recognized in many cases. The earliest manifestation of infection is a rash called erythema migrans. This red rash begins around the site of the bite and gradually expands symmetrically. At its peak, the rash can be more than three inches in diameter. The rash usually lasts for several weeks to months, does not itch and is not painful.
The early stage of infection is associated with the spread of the bacteria from the bite to the bloodstream and may be accompanied by flu-like symptoms and multiple rashes. Involvement of the facial nerve may also occur at this stage of the disease. These patients develop weakness of the facial muscles on one side of the face (Bell’s palsy). Inability to close one eye and raise the corner of the mouth on the same side is characteristic of this complication. If the disease is left untreated, many patients will go on to develop arthritis. Redness, swelling and tenderness of large joints, mainly the knees, are typical of this stage of the disease.
Patients with symptoms specific for Lyme disease may be diagnosed with a simple blood test. Unfortunately, this test may also be positive among patients without the disease so screening of patients without Lyme specific symptoms is not recommended. Lyme disease is treated with a two to four week course of antibiotics, depending on the clinical stage of the disease at diagnosis.
Rocky Mountain Spotted Fever
This disease is caused by a bacteria called Rickettsiae ricketsii and is transmitted by a dog tick. Following an incubation period of about a week, infected patients develop a flu-like illness with fever and muscle aches. Many patients will develop headache and some may develop confusion and disorientation. It is difficult to identify at first since early symptoms are non-specific. Then the vast majority of patients develop a characteristic non-blanching, pinpoint, red rash typically limited to the hands and feet and involving the palms and soles.
The disease may be diagnosed using one of several blood tests, however, in many cases the test may not become positive for several weeks after the onset of illness. Rocky Mountain Spotted Fever is often treated in hospital and before the results of the diagnostic test are known because the disease carries a significant mortality rate, particularly among school aged children. Antibiotic therapy, administered for seven to 10 days, is recommended for the treatment of this infections.
Infections caused by Anaplasma phagocytophilum are transmitted by the same tick that transmits Lyme disease. The clinical appearance, excluding the rash, is similar to Rocky Mountain Spotted Fever. In addition, patients with anaplasmosis have abnormalities in liver function and reduced numbers of white blood cells and platelets. Antibiotics are effective in the treatment of anaplasmosis.
Unlike the other illnesses associated with ticks, tick paralysis is not caused by an infectious agent. In our area, the American dog tick carries a toxin that produces paralysis. After several days to a week of continuous exposure to the tick, patients develop weakness and paralysis that begins in the lower extremities and gradually progresses to involve the upper extremities. Fever is absent. The diagnosis is often missed because these symptoms are shared with other neurological diseases. Removal of the tick will end the paralysis.
The best way to avoid tickborne illness is to avoid tick bites. Avoiding tick infested woodlands and wearing light colored clothing that covers exposed areas if woodlands cannot be avoided is recommended. Insect repellents containing 10 to 30 percent DEET may be applied to the skin of children two months of age and older and will reduce the risk of tick bite. Finally, close and frequent inspection of the skin should be performed during the summer months for children and adults with extended outdoor exposure. If a tick is found, it should be removed and your child’s healthcare provider should be notified.
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