June 26 , 2007
Tics and Bugs
A brief word on West Nile, and a bit more on Lyme Disease)
Jonathan Wood, MD
Summer is here! And with summer comes all the necessary but unwanted bugs the crawl and fly around our yards, fields, and woods.
Q: Should we be worried about diseases carried by these bugs?
A: Yes and No
Q: How severe is the threat of these diseases?
Q: Are there simple measures we can take to reduce our risk?
Two diseases seem to have captured the main interest of the world in recent years:
West Nile Virus infection and Lyme Disease.
A few brief words on West Nile Virus:
There has never been a case of human disease from West Nile Virus in Maine.
There have been 3 cases in New Hampshire, all 3 occurring in 2003.
Every year some animals or birds in Maine are discovered to have the virus, but the numbers are very low and the risk to humans continues to be very low.
Still, use of DEET-containing insect repellants is recommended to further lower the risk of this and other diseases transmitted by insects and arthropods.
(see Dr Movius’ on WABI from 2005 (“Bugged in Maine”) for more info on DEET: http://healthyliving.emmc.org/archive/05.04.2005.asp)
Now how about Lyme Disease?
The incidence of LD in Maine has been steadily increasing for the past 10 years.
The incidence in Maine last year was 18.7 cases per 100,000. That compares to 20.2 in New Hampshire, 8.7 in Vermont, 36.5 in Massachusetts, and 51.6 in Connecticut.
LD is caused by a bacteria transmitted to humans by the tiny deer tick
The deer tick is truly tiny compared with the more common dog tick.
Lyme Disease Transmission
The Lyme disease bacterium, Borrelia burgdorferi, normally lives in mice, squirrels and other small animals. It is transmitted among these animals – and to humans -- through the bites of certain species of ticks.
In the northeastern and north-central United States, the blacklegged tick (or deer tick, Ixodes scapularis) transmits Lyme disease. In the Pacific coastal United States, the disease is spread by the western blacklegged tick (Ixodes pacificus). Other tick species found in the United States have not been shown to transmit Borrelia burgdorferi.
Blacklegged ticks live for two years and have three feeding stages: larvae, nymph, and adult. When a young tick feeds on an infected animal, the tick takes the bacterium into its body along with the blood meal. The bacterium then lives in the gut of the tick. If the tick feeds again, it can transmit the bacterium to its new host. Usually the new host is another small rodent, but sometimes the new host is a human.
Most cases of human illness occur in the late spring and summer when the tiny nymphs are most active and human outdoor activity is greatest.
Although adult ticks often feed on deer, these animals do not become infected. Deer are nevertheless important in transporting ticks and maintaining tick populations.
Other Modes of Transmission
There is no evidence that Lyme disease is transmitted from person-to-person. For example, a person cannot get infected from touching, kissing or having sex with a person who has Lyme disease.
During Pregnancy & While Breastfeeding
Lyme disease acquired during pregnancy may lead to infection of the placenta and possible stillbirth, however, no negative effects on the fetus have been found when the mother receives appropriate antibiotic treatment. There are no reports of Lyme disease transmission from breast milk.
Although no cases of Lyme disease have been linked to blood transfusion, scientists have found that the Lyme disease bacteria can live in blood that is stored for donation. Individuals being treated for Lyme disease with an antibiotic should not donate blood. Individuals who have completed antibiotic treatment for Lyme disease may be considered as potential blood donors. Information on the current criteria for blood donation is available on the Red Cross website http://www.redcross.org/donate/give/.
Although dogs and cats can get Lyme disease, there is no evidence that they spread the disease directly to their owners. However, pets can bring infected ticks into your home or yard. Consider protecting your pet, and possibly yourself, through the use of tick control products for animals.
You will not get Lyme disease from eating venison or squirrel meat, but in keeping with general food safety principles meat should always be cooked thoroughly. Note that hunting and dressing deer or squirrels may bring you into close contact with infected ticks.
There is no credible evidence that Lyme disease can be transmitted through air, food, water, or from the bites of mosquitoes, flies, fleas, or lice.
Lyme Disease Symptoms
The Lyme disease bacterium can infect several parts of the body, producing different symptoms at different times. Not all patients with Lyme disease will have all symptoms, and many of the symptoms can occur with other diseases as well. If you believe you may have Lyme disease, it is important that you consult your health care provider for proper diagnosis.
The first sign of infection is usually a circular rash called erythemamigrans or EM. This rash occurs in approximately 70-80% of infected persons and begins at the site of a tick bite after a delay of 3-30 days. A distinctive feature of the rash is that it gradually expands over a period of several days, reaching up to 12 inches (30 cm) across. The center of the rash may clear as it enlarges, resulting in a bull’s-eye appearance. It may be warm but is not usually painful. Some patients develop additional EM lesions in other areas of the body after several days. Patients also experience symptoms of fatigue, chills, fever, headache, and muscle and joint aches, and swollen lymph nodes. In some cases, these may be the only symptoms of infection.
Untreated, the infection may spread to other parts of the body within a few days to weeks, producing an array of discrete symptoms. These include loss of muscle tone on one or both sides of the face (called facial or “Bell’s palsy), severe headaches and neck stiffness due to meningitis, shooting pains that may interfere with sleep, heart palpitations and dizziness due to changes in heartbeat, and pain that moves from joint to joint. Many of these symptoms will resolve, even without treatment.
After several months, approximately 60% of patients with untreated infection will begin to have intermittent bouts of arthritis, with severe joint pain and swelling. Large joints are most often effected, particularly the knees. In addition, up to 5% of untreated patients may develop chronic neurological complaints months to years after infection. These include shooting pains, numbness or tingling in the hands or feet, and problems with concentration and short term memory.
Most cases of Lyme disease can be cured with antibiotics, especially if treatment is begun early in the course of illness. However, a small percentage of patients with Lyme disease have symptoms that last months to years after treatment with antibiotics. These symptoms can include muscle and joint pains, arthritis, cognitive defects, sleep disturbance, or fatigue. The cause of these symptoms is not known. There is some evidence that they result from an autoimmune response, in which a person’s immune system continues to respond even after the infection has been cleared.
Lyme Disease Diagnosis
Lyme disease is diagnosed based on symptoms, objective physical findings (such as erythema migrans, facial palsy, or arthritis), and a history of possible exposure to infected ticks. Validated laboratory tests can be very helpful but are not generally recommended when a patient has erythema migrans. For detailed recommendations on serologic testing, click here.
When making a diagnosis of Lyme disease, health care providers should consider other diseases that may cause similar illness. Not all patients with Lyme disease will develop the characteristic bulls-eye rash, and many may not recall a tick bite. Laboratory testing is not recommended for persons who do not have symptoms of Lyme disease.
Several forms of laboratory testing for Lyme disease are available, some of which have not been adequately validated. Most recommended tests are blood tests that measure antibodies made in response to the infection. These tests may be falsely negative in patients with early disease, but they are quite reliable for diagnosing later stages of disease.
CDC recommends a two-step process when testing blood for evidence of Lyme disease. Both steps can be done using the same blood sample.
1) The first step uses an ELISA or IFA test. These tests are designed to be very “sensitive,” meaning that almost everyone with Lyme disease, and some people who don’t have Lyme disease, will test positive. If the ELISA or IFA is negative, it is highly unlikely that the person has Lyme disease, and no further testing is recommended. If the ELISA or IFA is positive or indeterminate (sometimes called "equivocal"), a second step should be performed to confirm the results.
2) The second step uses a Western blot test. Used appropriately, this test is designed to be “specific,” meaning that it will usually be positive only if a person has been truly infected. If the Western blot is negative, it suggests that the first test was a false positive, which can occur for several reasons. Sometimes two types of Western blot are performed, “IgM” and “IgG.” Patients who are positive by IgM but not IgG should have the test repeated a few weeks later if they remain ill. If they are still positive only by IgM and have been ill longer than one month, this is likely a false positive.
CDC does not recommend testing blood by Western blot without first testing it by ELISA or IFA. Doing so increases the potential for false positive results. Such results may lead to patients being treated for Lyme disease when they don’t have it and not getting appropriate treatment for the true cause of their illness. For detailed recommendations for test performance and interpretation of serologic tests for Lyme disease, click here.
Other Types of Laboratory Testing
Some laboratories offer Lyme disease testing using assays whose accuracy and clinical usefulness have not been adequately established. These tests include urine antigen tests, immunofluorescent staining for cell wall-deficient forms of Borrelia burgdorferi, and lymphocyte transformation tests. In general, CDC does not recommend these tests. Click here for more information. Patients are encouraged to ask their physicians whether their testing for Lyme disease was performed using validated methods and whether results were interpreted using appropriate guidelines.
Patients who have removed a tick often wonder if they should have it tested. In general, the identification and testing of individual ticks is not useful for deciding if a person should get antibiotics following a tick bite. Nevertheless, some state or local health departments offer tick identification and testing as a community service or for research purposes. Check with your health department; the phone number is usually found in the government pages of the telephone book. REMEMBER: Prevention is the best approach…
For more information on safe and reliable use of DEET-containing insect repellents, please refer to Amy Movius’ excellent synopsis in the Healthy Living archive from May 2005: http://healthyliving.emmc.org/archive/05.04.2005.asp)
How to Remove a Tick
Use tweezers to grab tick's head as close to the skin as possible. Do not squeeze the tick's body.
Gently pull straight out. Make sure you remove all of the tick.
Save the tick in rubbing alcohol for identification in case symptoms develop.
Clean the area with antiseptic.