Tick Borne Diseases
There are over 800 species of ticks in existence worldwide. Of those 800, only about 100 species are capable of carrying disease. In the United States, three genera (Ixodes, Dermacentor, and Amblyomma) are known to be capable of transmitting diseases to humans. These diseases are not caused by the ticks themselves, but rather by pathogens, such as bacteria, protozoa, and viruses, carried by the ticks. There are a number of diseases caused by these tick-borne pathogens.
Lyme Disease is an illness caused by a corkscrew-shaped bacterium called a spirochete that is transmitted to humans, dogs, horses, and other animals by tick bites. Frequently starting with a rash and flu-like symptoms, Lyme disease, if untreated, may progress to cause arthritis and neurological problems.
The spirochete bacteria that
causes Lyme disease.
The first symptom of Lyme disease in humans is usually an expanding red rash at the site of the tick bite, which may occur within a few days or several weeks later. The rash may be preceded or accompanied by flu-like symptoms such as fever, headache, chills, nausea, facial paralysis, or pain in the muscles and joints. If Lyme disease is suspected, call your doctor immediately. Early antibiotic treatment is very effective and can prevent later, more serious complications. Not all patients develop the rash, however, and many do not recall a tick bite.
In animals the rash apparently does not occur. Lameness, loss of appetite, fever, and lethargy may be the first indications. Animals usually respond to prompt antibiotic therapy. Consult your veterinarian.
Over 800 cases of Maine-acquired Lyme disease have now been officially recognized. The tick that transmits Lyme disease is the deer tick Ixodes scapularis (previously I. dammini). This tick is well established in coastal areas, particularly in York, Cumberland, and Knox Counties. Increasing numbers are being found in inland areas often along rivers. Ticks are routinely found in Androscoggin, Sagadahoc, Kennebec, Lincoln, Waldo, Hancock, and Penobscot Counties. Dear ticks are occasionally found in other areas of Maine; they are carried by some species of birds. Map of tick distribution in Maine.
For completion of its two-year life cycle, each consecutive stage of the deer tick -- larva, nymph, and adult --must take one blood meal. The tiny larvae active from June to September, are seldom found, and become infected when they take their first blood meal from a mouse or other small mammal. The risk of humans contracting Lyme disease is greatest from the bite of the inconspicuous nymphs which are most active in June and July. Adult ticks, which can also transmit Lyme disease, are found most often in the late fall as they search for larger hosts, primarily deer. Those that are unsuccessful may overwinter, to reappear in early spring or even during periods of mild winter weather. The larger reddish females can also transmit the Lyme bacteria, but the smaller, black males do not attach long enough to do so.
The seasonal appearances of the larval, nymphal and adult stages of the deer tick in Maine are shown in a bar graph developed from ticks submitted for identification over the last fifteen years.
Not all deer ticks contain the spirochete. Limited studies in Maine have shown that although in one site more than half the adult ticks sampled were infected, infection rates may vary considerably, even between adjacent areas at the same location.
Other tick borne pathogens
The organisms that cause two other tick-transmitted diseases, human granulocytic ehrlichiosis (HGE) and babesiosis, have been found in Maine. There have been several locally-acquired cases of each confirmed in Maine residents during the last few years. These infections may start with headaches, fever, and other flu-like symptoms, but without the characteristic rash of Lyme disease. HGE may cause severe illness, but responds well to doxycycline and a few other antibiotics. Babesiosis is an infection that invades red blood cells. It is most common in older individuals or those with immune deficiencies (i.e. without a spleen, etc.) and may cause persistent fever, anemia or other blood abnormalities. HGE may also affect dogs and horses. Powassan virus has also been found in Maine and to date has resulted in four human cases. Powassan virus has been isolated from Ixodes cookei, "the woodchuck tick", which is thought to be the primary vector.