Tick Borne Diseases
There are over 800 species of ticks worldwide, of which about 100 transmit diseases (Furman and Loomis 1984). Of the fourteen species we have identified in Maine, only one, I. scapularis, is responsible for the vast majority of tick-borne illnesses affecting humans or domestic animals in the state. In order of frequency they are:
Lyme Disease is an illness caused by a corkscrew-shaped spirochete bacterium (Borrelia burgdorferi) that is transmitted to humans, dogs, horses, and other animals by tick bites.
In 70-80% of infected individuals, a rash expanding from the tick bite and exceeding two inches in diameter will appear within a few days up to three weeks after the tick bite. As the rash expands it may develop paler bands, giving it a "target" appearance. Occasionally, similar satellite rashes may appear on other parts of the body. The initial symptoms of Lyme disease are fatigue, malaise, muscle aches and pains, headache, chills, fever. Untreated, additional symptoms may occur including hot swollen joints, paralysis of one side of the face (Bell's palsy), shooting pains and dizziness caused by disturbances in cardiac rhythm. Most symptoms of Lyme disease respond to antibiotic treatment. Ten to 20% of treated Lyme disease patients may continue to have muscle and joint pains and fatigue that persist for weeks or months despite eradication of the spirochete. The cause of these symptoms is unknown, but may in part reflect an autoimmune response in which residual antibodies attack tissues. If Lyme disease is suspected, it is important to get treated early; antibiotic treatment is very effective and can prevent later, more serious complications.
Examples of rashes from tick bite
It has been estimated recently (2013) that as few as one in ten cases of Lyme disease is reported by physicians; thus, with over 1,000 cases reported to the state in 2012, the actual number of infected individuals may have exceeded 10,000.
Since first introduced in Maine in the 1980's, vector deer ticks have become abundant in coastal counties and, with the exception of higher elevations, are now established throughout southern and central Maine. They are less abundant in northern counties where white-tailed deer, the primary host for mated female deer ticks, are sparse and temperatures are cooler. The distribution of Lyme disease cases across the state mirrors that of deer ticks that have been submitted to our lab for identification since 1989.
The The greatest risk of humans contracting Lyme disease is during the seasonal peak of deer tick nymphs, which in Maine is reached in late June and July. Approximately two-thirds of Maine cases are reported in June, July and August. Because deer tick nymphs are tiny and their bite painless, they frequently go undetected beyond the ~36 hours they usually need after attaching to transmit the Lyme spirochete.
[Image: Seasonal peaks of adult and nymphal deer ticks.]
Adult deer ticks also transmit B. burdorferi during their season, which is in the late fall and early spring. Their size frequently leads to their being removed prior to the transmission of disease for humans; less likely on furred animals, hence adults are the primary transmitters of Lyme spirochetes to dogs and other domestic animals. With one extra opportunity to feed on an infected host, the prevalence of infection in questing adult ticks is generally twice that in nymphs. Male deer ticks, however, rarely feed and do not cause infection. Where deer ticks are firmly established in southern and mid-coastal counties, typically at least half the adults and one quarter of nymphs are infected. Infection prevalence, however, may vary sharply within a community.
The agent of this disease, Anaplasma phagocytophylum, was first detected in Maine deer ticks in the mid 1990's. It is a rickettsial bacterium that invades certain white blood cells (granulocytes).
First symptoms occur within a few days of the tick bite and include, as with Lyme disease, chills, fever, headache, malaise, nausea, cough, and confusion. But Lyme-typical rashes, inflamed joints or neurological problems are not part of the symptom complex. Blood studies may show low platelets, low white cells, and elevated liver enzyme levels, and under the microscope bacteria may be visible within the granulocytes. Unlike Lyme disease, which is almost never fatal, more serious complications may develop with anaplasmosis including respiratory failure, renal failure, and hemorrhage. Approximately one percent of cases will end fatally, although this is likely an overestimate as many persons infected with Anaplasma have no symptoms at all. Therefore, it is very important to be seen early by a physician. As with Lyme disease, early treatment with doxycycline is extremely effective.
Single cases of anaplasmosis were reported in Maine from 2000 through 2004, but have since been increasing, reaching 52 in 2012. A statewide serosurvey of dogs in 2010 showed exposure to the pathogen was extremely high in south coastal towns and widespread, throughout the southern half of the state. Anaplasmosis is a growing veterinary problem as well. Dogs develop fever, joint pains, and lack of appetite, while fever, depression, lack of appetite and occasionally ataxia are seen in horses. Anaplasmosis is increasing and continues to spread in Maine.
This disease, also transmitted by deer ticks, is caused by a protozoon, Babesia microti, which invades red blood cells, similar to the parasites that cause malaria.
Babesiosis has been fairly common along the southern New England coast and on Long Island for decades. The pathogen was first identified in a Maine tick in 2004. Incidence of the disease has been increasing in the last few years, with 10 cases reported in 2012. Many people who become infected have very mild symptoms or none at all. In others, particularly those who have had their spleens removed, are immunocompromised or elderly, the disease can become rapidly fatal. Symptoms, beyond the "flu-like" symptoms typical of the previous two diseases, include the high fevers, sweating, and jaundice, followed by failure of the kidneys and other organs. The disease is treatable, however, so again, early recognition is imperative.
This is usually a serious viral infection of the brain and the tissues surrounding it which leaves half its victims with permanent neurological damage and is fatal for 10%-15%. There is no specific treatment. The chances of contracting this disease, however, are very low. So far, Maine has recorded five cases, including the first reported case in 2000. A similar disease is caused by two strains of the same virus: one (Powassan virus) that is transmitted by the woodchuck tick (I. cookei) and the squirrel tick (I. marxi), and a newly recognized strain (deer tick virus) that is transmitted by the deer tick. Unlike the transmission of B. burgdorferi and A. phagocytophilum, there is no delay between the tick bite and transmission of these viruses. Symptoms may come on suddenly within 2 days to two weeks following tick bite and include headaches, fever, nausea and vomiting, stiff neck, sleepiness, confusion, breathing distress, seizures and coma. Although no specific treatment exists, hospitalization with supportive care may be life-saving.