Lyme disease is by far the most common tick-borne disease in the United States, and spring and summer are when you need to be most wary, since the ticks that spread the disease are most active in May, June, and July.
Between 20,000 and 30,000 cases of Lyme disease have been reported in most of the past several years, and health officials suspect many more go unreported. The incidence is highest in New England, the Mid-Atlantic states and Wisconsin.
Deer ticks are responsible for the vast majority of Lyme disease cases, because they're able to harbor a disease-causing organism acquired at an earlier stage, which they transmit in their saliva as they enjoy a blood meal during their next one.
Deer ticks shouldn't be confused with dog ticks (which are sometimes called wood ticks: Dermacentor variabilis). One way you can tell the two species apart is by their size: Adult dog ticks are more than 10 times larger than tiny deer tick nymphs, which are about the size of a poppy seed.
Deer ticks in this country transmit pathogens that cause two other diseases besides Lyme: babesiosis, an illness that resembles malaria, and human granulocytic anaplasmosis (often shortened to just anaplasmosis), which causes flulike symptoms. Some studies have shown that people can get one of these other diseases and Lyme disease simultaneously.
Dog ticks aren't a cause of Lyme disease. However, they can infect people with the Rickettsia rickettsii bacterium that causes Rocky Mountain spotted fever, which is lethal in a small percentage of cases. The name is now a bit misleading: Most of the 1,000 or so cases of Rocky Mountain spotted fever that occur each year affect people living in a swath of south-central states that includes Oklahoma, Arkansas, Tennessee, and North and South Carolina.
The first time many of us heard about a bull's-eye rash was in the mid-1970s, when Lyme disease was first recognized. The red rash with a clear center was supposed to be the calling card of the new disease. That turned out to be misleading. The rash may take on the bull's-eye appearance, but not right away; early on, it's usually uniformly red or, occasionally, blotchy. The telltale feature is that it gets larger. If you mark the border in pen and it doesn't grow outside the pen mark in 24 hours, then it's probably not Lyme-related.
Common locations include hard-to-see places like the groin and the armpits. The rash may not appear until weeks after the tick has detached and is long gone, and people with Lyme disease often miss the tick bite that initiated the disease. Early on, Lyme disease also makes people feel sick, like they have the flu.
If the infection spreads beyond the site of the bite, the bacteria can cause arthritis and get into nervous tissue, resulting in a number of neurological symptoms, including numbness and pain in the arms and legs, facial paralysis on one side, a stiff neck, and severe headaches. Very rarely, the heart is affected.
Lyme disease is diagnosed based on symptoms and a history of possible exposure to infectious ticks. Lab tests for antibodies to the infection can help clinch the diagnosis but need to be interpreted carefully. If blood is tested during the early part of the infection, when the rash is the main symptom, then the test is likely to be negative for antibodies. A second follow-up test about a month later should be ordered. But if antibiotics are started early, there's a good chance that the second test may be negative.
Antibiotics effectively treat most cases of Lyme disease. Most doctors won't give someone antibiotics for just a tick bite, but current guidelines say a single dose of the antibiotic doxycycline may be appropriate if the tick has been attached for 36 hours and came from an area with a lot of Lyme disease.
The big controversy
Some doctors and Lyme disease patients have argued that Lyme disease can evade courses of antibiotics and become a chronic infection that needs long-term antibiotic treatment, even though conventional antibody tests are negative. Chronic Lyme disease has been blamed for causing pain, fatigue, muscle aches, cognitive shortcomings, and a host of other problems.
But many Lyme disease experts don't believe active infection persists after antibiotic treatment and once blood tests are negative for antibodies. They've been critical of what they see as unreliable tests for infection and unwarranted, possibly harmful, long-term antibiotic therapy.
Post-Lyme disease syndrome has been proposed as an alternative explanation - and label - for some of these cases of lingering illness. The notion is that some people are sick because their immune system has become dysfunctional or they've developed some other abnormality. Others may be ill for reasons unrelated to Lyme.