TICK SUPPLEMENT: Lyme Disease: The No. 1 Tick-Borne Disease In The U.S.

Ageographical name can often become an integral part of a product name. For instance, if you think of Epsom Salts, you may think of Epsom, England. Perhaps less proudly, an affliction diagnosed in a region can also carry that geographical name, such as Lyme disease from Old Lyme, Conn.

According to Marc Dolan, a senior research biologist/medical entomologist for the Lyme Disease Vector Section of the Centers for Disease Control (CDC) in Fort Collins, Colo., a cluster of juvenile rheumatoid arthritis cases was discovered around Old Lyme, Conn., in 1975. “Two housewives became concerned about the number of cases of juvenile arthritis in their family histories as well as in the surrounding area. They contacted the health department,” Dolan said. “Studies were conducted and it was later discovered that this disease responded well to antibiotic treatment.”

This illness was named Lyme disease in 1977, and in 1982, the etiologic agent, Borrelia burgdorferi was identified. This bacterium was transmitted to humans through the bite of Ixodes scapularis, the black-footed (or deer) tick. At that time, the CDC began surveillance for Lyme disease, and officially designated it as a nationally notifiable disease in 1990.

“Physicians were required by law to report diagnosed cases to the local health department and the CDC,” Dolan said. With this information, CDC could start determining geographic regions with the most activity, the age groups most affected, and the peak months of Lyme disease onset. This information, in turn, could be used to develop strategies to help control the disease.

LYME DISEASE DETAILS. Even though Lyme disease has been reported in 49 states and the District of Columbia, there is a definite band of concentrated activity in the northeastern and mid-Atlantic seaboard region (Connecticut, Rhode Island, New York, Pennsylvania, Delaware, New Jersey, Maryland and Massachusetts). For instance, Connecticut reported 3,215 cases of Lyme disease in 1999, or 98.30 incidence cases per 100,000 population, the highest incidence rate reported in a state.

But Lyme disease reporting has extended to the upper north-central region (primarily Wisconsin and Minnesota) and is gradually on the rise in northern California. The western black-legged tick (Ixodes pacificus) transmits the bacteria in the states bordering the Pacific Ocean.

Lyme disease now constitutes more than 95 percent of all vector-borne diseases in the United States, far outpacing Rocky Mountain spotted fever, tularemia, arboviral encephalitis and plague.

Based on the reported cases, the age groups most affected by Lyme disease are children ages 5 to 14 and adults ages 35 to 59. Children playing in wooded areas with ample leaf cover, which is the natural habitat of ticks, and adults who hike, camp or work in this environment, are most susceptible.

June and July have the most cases reported and that is, perhaps, due to the life cycle of the tick. Adult females lay eggs in the early spring. The eggs hatch into larvae by summer and start to feed on mice, other small mammals, birds and deer. The larvae become infected with B. burgdorferi bacteria when they feed on small rodents and mice that are already infected. These animals act as reservoirs for the bacteria, allowing the bacteria to live and grow without killing the host animal. Large deer populations provide the opportunity for the tick populations to expand and migrate.

By fall, the larvae molt into nymphs and remain dormant until the following spring. Nymphs feed on the same animals as larvae, but also include humans. Because their small size can allow them to go undetected, the nymphs are most responsible for the transmission of Lyme disease. By the fall, the nymphs molt into adults, continue to feed on large mammals and mate. Adult ticks may bite humans, but they are more easily seen and removed. The female ticks then leave the animals and lay eggs in the spring to complete the two-year life cycle.

“A tick will attach itself to a human by piercing the human’s epidermis and dermis with its mouthparts. For the first 12 hours, the tick secretes a cement-like substance to anchor itself to the skin, so it cannot be easily dislodged,” said Dolan. “At that point, the tick starts to draw blood from the human’s capillaries. Because of the tick’s anatomy, the B. burgdorferi bacteria are not immediately transferred to the human. The transmission usually would occur about 48 hours after the tick first lands on the human.”

SYMPTOMS. If Lyme disease does develop, the first characteristic symptom seen is erythema migrans, or a rash that looks like a bulls-eye, usually greater than or equal to five centimeters in diameter (see photo above). This typically appears about seven to 14 days following the tick bite. Also accompanying the rash can be fever, fatigue, headache, and muscle and joint aches. In rare cases, no outward signs appear, but the individual suffers from fever, headaches and fatigue.

If untreated, or undertreated, the disease may enter the early disseminated disease stage, which includes additional erythema migrans lesions. The neurologic and musculoskeletal systems are also affected. People can suffer from facial nerve paralysis and joint and muscle pain, including joint swelling. In rare cases, the cardiovascular system may be affected. This stage can start as early as several days or as late as a few weeks following the first erythema migrans.

In the late disseminated disease stage, additional stresses are placed on the musculoskeletal and neurologic systems. Arthritis can attack one or more joints, usually the knees, shoulders, ankles, elbows and wrists, and the pain can range from intermittent flare-ups to a chronic condition. An individual can also suffer from memory and concentration loss, and experience tingling or a burning sensation in his or her legs, arms or fingers. These symptoms can appear weeks or even months following the infection. In the most extreme cases, the disease can be chronic and disabling, but Lyme disease is rarely fatal.

Based on the reporting of Lyme disease cases, peak occurrences and geographic locale, a vaccine called LYMErix™ was developed, and in 1995 during the Phase III trials, nearly 11,000 people were tested using vaccine and placebo groups. “The vaccine efficacy ran about 50 percent after two doses, and rose to 76 percent after three doses,” Dolan said, “and the only side effects of the vaccine are those typical to any injection site – pain and swelling, and mild headache, fever and muscle/joint pain.”

The FDA approved the vaccine in 1998, with a three-dose schedule. An individual receives the first shot in the early spring (usually in March), the second shot a month later, and the third shot is 12 months after the first shot.

There are, however, certain individuals who do not respond to this vaccine. Among those groups are children under the age of 15 and adults over the age of 70, pregnant women, anyone with an existing musculoskeletal disease, pre-existing Lyme arthritis or neuroborreliosis, anyone showing a hypersensitivity to a previous inoculation, and anyone whose immune system is compromised.

However, according to a report by the Associated Press, GlaxoSmithKline, the maker of LYMErix (the nation’s only Lyme disease vaccine) pulled it off the market Feb. 26, citing poor sales. LYMErix caused some controversy in recent years, as patients who argued they were sickened by the vaccine asked the government to restrict sales and also filed numerous lawsuits against its maker.

OTHER MEASURES. Pest management professionals and their clients can practice Lyme disease prevention by avoiding wooded or overgrown grassy areas, particularly in the spring and summer. Light-colored clothing should be worn so ticks can be seen more easily; shirts should be long-sleeved and pants should be tucked into socks or boots so ticks can’t reach the skin. Insect repellents can be applied to humans and pets; and after exposure to the environment, a thorough examination of the skin for ticks should be conducted.

If a tick is found, tweezers should be placed as near to the skin as possible, and the tick should be pulled straight out. Even if the mouthparts remains in the skin, they don’t pose a risk of the transmission of Lyme disease, since the feeding process hasn’t begun. A topical antiseptic should be applied.
“A microbiologist in the Lyme Disease Vector Section has just recently completed mapping the I. scapularis tick genome,” Dolan said. “Of possible interest for future research would be to pursue those genes that are implicated in pesticide/acaricide resistance.” 

The author is a freelance writer from Cleveland, Ohio. She can be reached at dtaylor@pctonline.com.