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Lyme Disease

The major tick-borne diseases that we see in the United States are: Lyme disease, the rickettsial diseases, which now includes ehrlichiosis as well as Rocky Mountain Spotted Fever, babesiosis, which seems to live together with the causative agent of Lyme disease.

Lyme disease was first described in the mid 1970's during an epidemic of arthritis in Lyme, Connecticut. It was really recognized by a group of mothers of children who were affected with this disease that was initially diagnosed as juvenile rheumatoid arthritis. These mothers wondered why they were seeing a cluster of juvenile rheumatoid arthritis in Lyme, Connecticut and that led to the investigation of that as an outbreak and the discovery of Borrelia burgdorferi in the early 1980's as the causative agent of Lyme disease. This is a spirochetal bacteria. Lyme disease is the leading vector-borne disease in the United States. It has been reported in 48 states, although ninety percent of the cases occur in either the Northeastern coastal states, the upper Midwest.

The geographic distribution of cases of Lyme disease corresponds to the distribution of the ticks. The name of the tick has undergone a variety of different changes over the past three to five years. They are members of the Ixodes class of ticks. These are small ticks and the most common one is Ixodes scapularis, although in different parts of the country, it is a different species of the tick that causes the disease. Small mammals are important in the maintenance of the causative agent. Deer are the most important host for the adult tick. There is a cycle that is required for the maintenance of spirochete in the community that involves deer, small mammals - usually mice and in the Northeast it is the white-footed mouse.

Other ticks that feed on humans, such as some of the ticks we will talk about with some of these other diseases, particularly Rocky Mountain Spotted Fever, or dog ticks, don't appear to transmit infection. So the tick that transmits the disease is the deer tick which, when non-engorged, is about the size of the head of a pin. It can therefore be very easily missed. When we talk about the symptoms of infection, we will talk about why some people don't recognize the tick bite.

Most human infections occur in the period between May and August and that is when people are out and about and the ticks are around. Efficient transmission requires about 48 hours of feeing or attachment. This is why prevention can be an important part of anything when we talk about Lyme disease and its impact on the community, because it takes that long for the tick.

The nymphal forms of the tick are the most important, because of their small size and the ability to remain attached unrecognized. So that is the problem with prevention of tick removal, that again, these ticks are so small that when you do checks, particularly in the scalp, but in other areas as well, you may miss them and they can remain attached and unrecognized and they can transmit infection. However, overall, about fifty percent of infected patients remember the tick bite.

This will be reminiscent what we talked about with syphilis in terms of the stages of diseases. Lyme disease is a spirochetal disease that goes through stages the same way that the spirochetal disease syphilis does. Early localized disease occurs within days to weeks of infection. It begins as a macular dermatitis at the site of the tick bite, which is commonly called erythema.