Lyme disease poses risk for patients visiting or living in the Northeast

For patients and their families who might be spending time this summer camping, hunting, fishing or hiking, particularly in the Northeast region of the US, discussions about how to prevent Lyme disease can be beneficial. In this Ask the Experts feature, Paul Lantos, MD, a pediatric infectious disease specialist and attending physician in the departments of internal and pediatric medicine at Duke University Medical Center, discusses the latest in Lyme disease.

Paul M. Lantos

There is a general awareness that Lyme disease is caused by a bite from a deer tick (Ixodes scapularis) infected with Borrelia burgdorferi, but what role, if any, do deer themselves play in the transmission of the disease?

Deer are an important part of the ecology of Lyme disease, but it’s not through direct contact with deer that people get the disease. Adult ticks preferentially feed and mate on deer. The female adults lay eggs, which hatch into larval ticks. The larvae usually bite small mammals, most importantly the white-footed mouse, which is the natural reservoir for B. burgdorferi, the bacterium that causes Lyme disease. The larvae mature to their next life-cycle stage, the nymph, which is the stage most likely to bite a human and transmit the disease.

Deer are not thought to be a natural reservoir for B. burgdorferi, and deer contact is not in itself a means by which humans contract Lyme disease. Environments with lots of deer, however, are likely to have deer ticks as well. Spending time outdoors, especially in the highly endemic coastal Northeast, is the primary risk factor for Lyme disease.

What are the mediating factors in the increased Lyme disease case load during the past few decades?

There is evidence that expanding deer populations in coastal New England is responsible for the expansion of Lyme disease in the last 30 to 40 years. This is often attributed to the conversion of northeastern farmland to forest, which affects surrounding communities. It is possible to contract Lyme disease even in urban parks in the Northeast, so one need not live in or near the woods. Some communities, especially on offshore islands, have attempted to control Lyme disease and the other two infections borne by the deer tick, babesiosis and anaplasmosis, by encouraging deer hunting. Having a fence around your yard can possibly lower the risk of Lyme disease — presumably because it keeps the deer out and prevents the adult ticks from leaving eggs in your yard.

Tick bites are quite common, but how often do these bites lead to infection?

A very high-risk bite, ie, a bite from a confirmed deer tick, acquired only in the coastal Northeast, where more than 30% of deer ticks carry the bacteria that cause Lyme disease, in which the tick has been attached for more than 48 hours or if the tick has become engorged, gives a risk of Lyme disease of no more than 3%. This has been studied in several prospective trials, and the highest rate described was just over 3% (3.2% more or less).

In practical terms, many bites will be lower risk than this because most people cannot tell a deer tick from several other major kinds of ticks; the tick has not been attached for long enough to transmit the germ; or deer ticks in other regions of the country, such as North Carolina, have much lower carriage rates for the Lyme disease bacterium.

Where are infections most prevalent?

Around 90% of all Lyme disease cases are in the northeastern United States, generally from northern Virginia up to northern New England. The Appalachians roughly form the western border of this range. Of the remaining 10% to 15%, nearly all reported cases are in Minnesota and Wisconsin. A scattering of cases occurs in northern California. Elsewhere in the United States, most cases of Lyme disease are imported from the Northeast or the upper Midwest and not acquired locally. Parenthetically, Lyme disease is quite common in some parts of Europe as well.

Should physicians offer patients and their families prophylactic treatment?

There is evidence that a single dose of doxycycline will prevent Lyme disease if given to an adult with a high-risk tick bite (high risk as described above). Doxycycline is not an appropriate medication for children under around 7 years of age, though, and the alternatives that we use in young children would probably require more doses. Thus, we do not recommend prophylactic treatment for children, even with high-risk tick bites, because in the end, no more than 3% will develop Lyme disease, which in turn is readily treatable.

If infection occurs, how does it present and how serious can it be?

Lyme disease causes a rather defined collection of symptoms. About 80% get a large, round rash called erythema migrans, which sometimes looks like a bull’s-eye. Of those who do not get treated for erythema migrans (which is an early manifestation of the infection), most of the remainder will get Lyme arthritis (usually causing swelling and stiffness of one or two large joints, like the knee or ankle) or neurologic Lyme disease (usually causing a mild meningitis with headache and neck ache, or causing weakness of some of the nerves that supply the face and head, often causing a facial droop or double vision). A minority will get “heart block,” where the electrical impulses over the heart are not conducted efficiently and in very rare cases necessitate a pacemaker (though temporarily). All of these manifestations are treatable, generally with 4 weeks of antibiotics or less. Virtually no one has died from Lyme disease, although it is certainly disabling.

What is chronic, persistent Lyme disease, and why is there no specific reference to it in the Infectious Diseases Society of America guidelines for Lyme disease treatment?

Chronic Lyme disease is a term that does not have any accepted clinical or microbiological definition — even from people who espouse it. Thus, the term ‘chronic Lyme disease’ doesn’t really mean anything. It’s a term that’s usually applied to patients with chronic, nonspecific symptoms such as fatigue or joint pains or memory problems, regardless of whether they have other manifestations of Lyme disease.

When these patients are evaluated, it’s seldom that they are found to have any evidence of Lyme disease, either active or in the past. These symptoms are extremely common in the general population and do not appear to be any more common in patients with a past history of Lyme disease. So in all likelihood, Lyme disease is not an independent risk factor for developing these chronic complaints.

In fact, many trials show that outcomes are excellent months or years following treatment for Lyme disease. Several trials have looked at prolonged antibiotic courses for patients who have 1) a history of confirmed and appropriately treated Lyme disease, and 2) prolonged symptoms for months following treatment. In these trials, prolonged antibiotics have not been found to help their symptoms and, in fact, can cause life-threatening side effects.

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