What is Lyme disease?
Investigators studying unusual human arthritis cases in Lyme, Connecticut in 1975 uncovered a puzzling disease that affects both children and adults. This disease, which came to be called Lyme disease, was found to share some symptoms with an undefined malady in Europe known to be associated with bites of the sheep tick, Ixodes ricinus. Studies in Connecticut led to the discovery that the arthritis cases were linked with the bites of ticks of that region, now known as the deer tick, Ixodes scapularis. In 1982 researchers isolated from this tick a new bacterium described as the spirochete Borrelia burgdorferi. Later the same bacterium was found in patients with Lyme disease and was recognized as the cause of the disease. Further studies have shown that the corkscrew-shaped bacterium also can infect domestic animals such as dogs, cats, horses and cattle, as well as numerous wildlife species, and that these animals may possibly serve as reservoirs. Research continues in the areas of diagnosis, treatment, epidemiology and vector ecology.
Lyme disease patients respond to antibiotic treatments of tetracyclines and certain penicillins, especially when the disease is diagnosed early. However, left undiagnosed and untreated it can become extremely debilitating, affecting the joints, nervous system and heart. Preventive measures such as avoiding tick bites and getting an early diagnosis are important.
Where has Lyme disease been diagnosed?
Lyme disease, also called Lyme borreliosis, is now considered the most prevalent tick-borne disease in the U.S., with more than 5,000 human cases reported in 1988. It has been diagnosed in humans in 43 states. The majority of cases have occurred in Connecticut, Rhode Island, Massachusetts, New York, New Jersey, Wisconsin, Minnesota and along the northern California coast (Fig. 1). It also has been reported in at least 20 other countries, including Canada, Australia, China, Austria, Germany and the Soviet Union. Evidence of Lyme disease in Texas was discovered in serological studies in 1984. From 1986 through 1988, 67 cases were reported in the state. In the first 10 months of 1989 more than 60 cases were reported. Although the highest incidence occurred in northeast Texas, these cases are widely distributed and the disease may be spreading (Fig. 2). The number of reported cases is expected to increase as people become more aware of it.
What is my risk of becoming infected?
The primary risk of acquiring Lyme disease is associated with outdoor activities in habitats where ticks are found, such as in woods, brushy areas or thickets. In Texas there are many tick species which will attack man. However, not all tick species are effective vectors of the disease and not all individuals of an effective vector species are infected with the disease agent. Thus, being bitten by a tick does not necessarily mean you will contract Lyme disease. In states where important animal vectors have been identified, the seasonal risk of infection can be determined by the tick life cycle. In Texas, this information is not yet available. Even so, following a few simple guidelines for preventing tick bites and knowing the symptoms of Lyme disease can reduce the risks considerably.
What are the symptoms?
Lyme disease in humans
Lyme disease in humans is often called a “great imitator” because of its ability to mimic a wide variety of illnesses including influenza, arthritis, syphilis, multiple sclerosis and Alzheimer’s disease. People living in or visiting Lyme disease endemic areas, who are bitten by ticks, are advised to watch for symptoms of the disease. If any of the following symptoms develop, seek medical attention. If you recall having been bitten by a tick or have been on outings in tick habitat, alert your physician that you may have been exposed to Lyme disease.
1. A characteristic rash (called erythema migrans) may develop on the skin from 3 days to several weeks after the bite of an infected tick. The rash may look like an expanding red ring or bull’s eye with a clear center, but its appearance can vary from blotchy to circular or oblong. It may be large or small. If a single patch occurs it may or may not otcur at the site of the tick bite. Multiple red patches also may occur. The rash may even include blisters which later burst and form a heavy, dark scab. The rash can also appear as a bruise. Detection of the bruise on dark-skinned patients requires close examination. The rash occurs in less than 60 percent of cases; thus, its absence in the presence of other symptoms does not rule out Lyme disease.
2. A flu-like illness may develop With symptoms such as fever, chill, headache, stiff neck, backache and profound fatigue. These symptoms can occur before, during or after the appearance of skin rash ‘ Some patients apparently have no further symptoms, especially if they received early treatment. However, for others later complications can be quite severe.
Early symptoms of Lyme disease, which occur at the site of the tick bite, include (below, top to bottom) a rash which forms a single ring, a rash which forms a large ring with crusted center, and a rash which forms a double ring.
Photographs copyrighted by Dr. Alan B. MacDonald
1. Arthritis, usually of the knees, hips and ankles, may develop from a few weeks to more than a year after the tick bite, and can recur several times over the following years.
2. Meningitis, with fever, severe headache and stiff neck, may develop weeks to months after the tick bite.
3. There may also be neurological problems such as numbness, tingling in the extremities, loss of concentration and memory, loss of hearing, double vision, loss of confidence and withdrawal, lethargy and paralysis of facial muscles, and cardiac symptoms such as heart palpitation or heart block.
It is more difficult to treat later symptoms than early symptoms, and often less successful.
Later symptoms include swelling and pain in the joints, especially in the knees, which resembles arthritis (below). Photographs copyrighted by Dr. Alan B. MacDonald
Lyme disease in domestic animals
In dogs the predominant symptoms appear to be fever, pain of the joints and migrating lameness. Cats exhibit low-grade fever, locomotion problems, fatigue, stiffness and sometimes neuralogic problems. Symptoms in horses have included fever, lameness and or encephalitic signs. Cows may experience fever, swollen joints, arthritis and abortion.
(Tick markings and color may vary.)
How do I recognize a tick?
Ticks are not insects but are closely related to mites, spiders and scorpions. Most ticks are parasites of warm-blooded animals and must take one or more blood meals in order to survive and reproduce. Transmission of diseasecausing organisms primarily occurs during tick feeding.
Adult ticks have eight legs and a single body region rather than the three-part body typical of insects. Ticks are grouped into two families:
- the “hard ticks” (Ixodidae), which have hard, smooth skin and apparent heads; and
- the “soft ticks” (Argasidae), which have tough, leathery, often pitted skin and no distinguishable heads.
Certain species of “hard ticks” are responsible for transmitting Lyme disease. These ticks have four developmental stages consisting of the eggs, six-legged larvae, eight-legged nymphs and adults. The female deposits eggs on the ground, usually in a single mass containing more than 3,000 eggs. The eggs hatch into larvae or “seed ticks.” The larvae may cluster on grass or remain in leaf litter while waiting for a host to pass by. Larvae cling to the clothing, hair or feathers of a host, attach to its skin, feed and then drop off. The fed larvae molt to nymphs on the ground. Nymphs repeat the sequence of waiting, attacking and feeding on a second host. Then they drop to the ground and molt to adults. Adult ticks repeat the sequence a third time, usually selecting larger hosts. After a blood meal the engorged female will weigh up to 250 times her unfed weight.
Figure 4. Areas of Texas where most of the blacklegged ticks and other hard ticks are found.
What are the tick vectors?
Knowledge of the ticks involved in Lyme disease, their biology, habitat and distribution, as well as methods of control, can help you avoid the problem.
There is no evidence that all ticks transmit Lyme disease. The hard ticks of the Ixodes ricinus complex appear to be the primary vectors of Lyme disease spirochetes around the world, and several species occur in the U.S. The deer tick, Ixodes scapularis, is responsible for most cases of Lyme disease in the northeastern and north central United States. They also occur in a second area in eastern Minnesota and western Wisconsin. Ixodes scapularis does not occur in Texas. The western black-legged tick, Ixodes pacificus, is a close cousin of Ixodes scapularis and an important vector of Lyme disease in California, particularly along the coast north of San Francisco and into the coastal regions of Oregon. In Texas and throughout most of the southern U.S. there is a close relative of this complex, Ixodes scapularis, the blacklegged tick. The black-legged tick has been found throughout the eastern half of Texas (Fig. 3); its hosts include cattle, horses, whitetailed deer, domestic dogs and cats, coyotes, bobcats, lynx, fox and javelina, as well as small rodents and reptiles. While all stages of the tick may attack man, the incidence of humans being bitten by larvae and nymphs of the blacklegged tick has not been measured. Laboratory studies suggest that the black-legged tick may be an effective vector of the Lyme disease organism. Many other ticks are found in the eastern half of Texas, some of which bite humans more frequently than the black-legged tick.
Spirochetes have been isolated from certain non-Ixodes ticks such as the lone star tick, Amblyomma americanum, and the American dog tick, Dermacentor variabilis, suggesting that these ticks also may play some role in Lyme epidemiology. More research is needed to clarify the roles of these ticks in Lyme transmission. It should be kept in mind that ticks also transmit other diseases such as Rocky Mountain spotted fever and tularemia.
Are there non-tick vectors of Lyme disease?
There are reports of the Lyme organism being found in fleas, horseflies and mosquitoes, and possible associations between fleas and Lyme cases. Further research is needed on the role of these insects as vectors for the Lyme spirochete.
Where are ticks found?
Most ticks are found in shrub and woodland habitats, but may be as close as your home landscape or your pets. Ticks are numerous in underbrush along creeks and river bottoms and near animal resting places. They become excited and attracted by the shadow, vibration and scent of animals. Humans most often encounter ticks near roads, paths, trails and recreational areas.
How can I minimize the risk of infection?
When in habitats likely to be infested with ticks, certain precautions can be taken to avoid tick bites. There is no reason for panic if you are bitten. Contracting Lyme disease from a tick bite depends on whether or not that tick was a carrier of the infectious agent and on how long the tick had been feeding on you.
Because the movement and bites of ticks are seldom felt, careful and frequent examination of the body and clothing is imperative. Periodically inspect yourself, your children and your pets.
Use tweezers or protected fingers, not your bare fingers, to remove attached ticks. Grasp the tick firmly, without crushing it, as near the skin as you can and remove it with a slow, steady pull away from your body. Hasty removal of an attached tick can break off the mouthparts and lead to prolonged inflammation, irritation and possibly secondary infection. Treating the bite with first aid antiseptic will prevent secondary infection. It is advisable to save the tick for identification in the event you later suspect signs of disease. Ticks can be kept alive by placing them in a small bottle with moistened (not wet) paper towel pieces; or they can be killed and preserved in a small container of rubbing alcohol. It will also help if you date the collection and note the geographic location the tick came from. Live ticks can be submitted for examination to determine the presence of Lyme spirochetes. Contact the Texas Department of Health, Bureau of Laboratories, (512) 458-7605, for information on collection and shipping.
To obtain some degree of protection against ticks and make their detection easier, wear lightcolored clothing, a long-sleeved shirt, trousers and socks. Keep clothing buttoned, shirttail inside trousers and trouser legs inside tops of socks. A ring of masking tape with the sticky side out placed around the tops of boots or shoes will often trap ticks that are ascending to look for an attachment site. Do not sit on the ground or on logs in brushy areas.
Permanone®, a tick repellent containing permethrin, may be applied to clothing only (avoid skin contact). This product may provide protection for a day or longer. Repellents containing Deet will protect exposed skin but will not stop ticks from crawling under clothing to reach untreated portions of the body. Applying repellents to the entire body might prevent tick bites for awhile, but such extensive treatments often are impractical and may be hazardous to health. Always read and follow the pesticide label instructions.
Active children old enough to play outdoors are prime candidates for tick bites. It is best to keep children indoors or in a tick free environment such as an enclosed playground if the area is known to be infested with ticks. Teach children to avoid tall grass and low brush areas, to check each other for “small moving spots” and remove ticks only with tweezers or protected fingers. Examine children closely after they have been in infested areas.
Dogs and cats
Pets often frequent tick habitats and bring the parasites into contact with people. Dogs are probably more likely to get Lyme disease than their owners. Cats are generally less likely to be attacked by ticks than dogs. These animals should be inspected periodically and after each outing to suspected tick-infested areas. Ticks can be removed from pets as previously described and with the same precautions. Avoid sleeping with pets likely to have ticks. Flea and tick collars, sprays, dips and shampoos containing permethrin, pyrethrins, chlorpyrifos or other approved acaricides will give small animals some protection. Dealing with heavy or persistent infestations may require the advice of your local veterinarian.
It may be necessary to treat heavily infested yards and structures with an approved acaricide containing permethrin, chlorpyrifos, propoxur or diazinon, or to obtain the service of your local pest control operator. Animal testing by your veterinarian and early treatment can save infected animals.
Remember to follow all pesticide label instructions.
Pets should be examined frequently for attached ticks. There are various products available which give small animals some protection from ticks.
Garland Mcllveen, Jr., Pete D. Teel and Philip J. Hamman
Extension entomologist, associate professor of entomology and Extension urban entomologist, The Texas A&M University System.