About Ticks and Disease
Ticks are an ancient arthropod race, rising to the floors of Carboniferous forests with six legs, teeming in some places so abundantly that layers of sap-sucking tick bodies now constitute thick measures of coal. Akin to spiders, mites, and other arthropods, modern adult ticks have 8 legs. An imago (adult) deer tick may measure 2-5 mm in length, unfed. In temperate zones, hungry six-legged larval ticks hatch in warmer, wetter months, and hunt host animals, crawling up to 6 feet on nearby weeds, grass or trees, on the lookout for warm-blooded prey.
Approaching animals send soil vibrations, changes in light, and rising temperatures received by the crouching larval ticks, which begin to "quest." A questing tick grasps its plant mount with its hind legs, extending its body toward the path, waving its two forelegs in the air. As the target animal brushes by, the questing legs catch fur or skin. The tick rides and crawls through host hair, finds the epidermis, pierces a host blood vessel with its lancet, and fills up with blood. Sated, the tick later drops into the forest undergrowth, molts, and becomes an 8-legged nymph.
The industry of ticks brings tick-borne disease, for in taking blood meals, they acquire and transmit blood-borne pathogens. Hæmatophagous, ectoparasitic, blood-sucking ticks serve as vectors for a number of disease agents, including viruses, rickettsii, bacteria, and protozoa. Sap-sucking ticks feed only on living and decomposing plant material and pose no threat to vertebrates. Ticks feed and travel on many host animals, including mice, deer, and birds. Arctic terns transport arbovirus-infected seabird ticks thousands of miles south to Macquarie Island, Australia where the ticks debark and attack Rockhopper penguins.
Females of some tick species release neurotoxin-laden saliva into the host bloodstream while feeding. The toxin causes an ascending paralysis, starting in the feet and legs, spreading to the arms, throat, and muscles of respiration, causing respiratory arrest-artificial ventilation proves life-saving. Finding and removing the tick cures the paralysis in a few hours to a day. "Tick paralysis," is a rare condition-the state of Colorado, an endemic area, reports one case per year on average. The long hair of young girls and the hunting habits of young men account for higher rates of tick paralysis seen in these two groups.
Hypothetical Case
Circa 1975: A white tail deer forages in the New England, carrying the spirochete Borrelia burgdorferii in its blood stream. An Ixodes scapularis (deer) tick larva quests and rides the deer; taking a blood meal, it acquires B. burgdorfeii infection. Filled, it later drops into the undergrowth, crawls under fern leaves, grows, molts, and emerges as an eight-legged nymph. This process repeats until the metamorphosis ends in an imago female. Infected with the spirochete, she now quests, anticipating an oncoming 7-year-old human in a wooded area near Lyme, Connecticut.
As the child walks under a stand of Queen Anne's Lace, the tick drops from its perch, landing on the child's head. It seeks shelter from light and descends blond hair shafts to the nape of the neck, crawls under the shirt, around the scapula, into the left axilla (armpit). It finds a crevice and attaches itself, taking a blood meal.
Its mission was accomplished without noise, pain, itching or "crawling sensation," in part by stealth, but also the child's focus on playing a game of hide and seek. As the tick feeds, fluids containing B. burdorferii begin to enter the child's blood stream. Two days later the child complains of itching under the arm. A parent finds the swollen female tick, the head firmly embedded in reddened skin. Using bare fingers, the parent pulls off the tick. Two weeks later, the child develops pain, swelling, and stiffness in the wrists, knees, ankles, and a rash surrounding the left axilla.
Lyme disease
In 1975, an epidemic of "juvenile rheumatoid arthritis" was observed in the vicinity of Lyme, Connecticut. Doctors noted an association between arthritis cases and recent history of deer tick attachments in the patients. A rash similar to that seen in diseases spread by arthropods led researchers to postulate a tick-borne disease. The microbiologist Willy Burgdorfer, PhD found a spirochete in blood samples in 1982 which proved causative of Lyme disease-it was later named Borrelia burgdorferii. See Image at http://www3.niaid.nih.gov/topics/lymeDisease/research/cause
The deer tick Ixodes scapularis carries B. burgdorferii. It transmits Lyme disease in the northeast, upper Midwest, and other parts of the eastern half of the US. I. scapularis unfed is about the size of a sesame seed. See Image 2 at http://bioweb.uwlax.edu/bio203/s2008/clarin_bria/ Ixodes pacificus, the western black-legged tick, found in the Pacific states, can also carry B. burgdorferii.
The rate of vector tick infection with B. burgdorferii in a given location may vary from 1% to 50% and is directly related to the risk of contracting Lyme disease. High rates of tick infection, as seen in Connecticut, contribute to the very high rate of Lyme disease in that state. See Map at http://www.aldf.com/usmap.shtml
During 1992--2006, a total of 248,074 cases of Lyme disease were reported to CDC by health departments in the 50 states, the District of Columbia, and U.S. territories; the annual count increased 101%, from 9,908 cases in 1992 to 19,931 cases in 2006. During this 15-year period, 93% of cases were reported from 10 states (Connecticut, Delaware, Massachusetts, Maryland, Minnesota, New Jersey, New York, Pennsylvania, Rhode Island, and Wisconsin). Incidence was highest among children aged 5--14 years. See Maps at http://www.aldf.com/usmap.shtml
The increasing rate of Lyme disease in the US may reflect increased recognition and reporting of the disease, but urban sprawl, where homeowner green space encroaches on wooded and tall grass areas s increasingly admits white tail deer from burgeoning cervine populations, moving tick territory closer to home.
Prevention
What can be done to prevent Lyme disease? Deny ticks access to your body. Avoidance of tick-infested areas is valuable, but if you hunt, hike, garden, fish, camp, garden, or partake in other outdoor activities from spring into late summer, even early fall, put on your guard: 1) chemical: insect repellant (DEET)-caution in children, 2) clothing: for heavily-infested areas, wear high-top socks, hiking boots, belted long pants, tucked into boot tops, long-sleeved shirt tucked into pants, nonporous hat, shades and gloves, 3)inspection: total skin check after outdoor activity, before shower.
If you find a non-attached tick, gently brush it safely away. If you find an attached tick, calmly use this method of safe tick removal: Wear nonporous gloves and goggles. Use high quality forceps. Grasp the hard part of the tick with the forceps (focus on the head or the head and the little shield-cephalothorax-of the tick). Slowly and continuously apply retractive force-do not jerk, which could break separate the head from mouth parts, leaving tick material in the skin, potentially becoming a "tick granuloma."
The tick has powerful muscles working its mouthparts, but the endurance capacity of human hands and arms will win-the tick's muscles will give out; it will release and come out clean.
Tick removal myths? Heat should not be applied in any form to an embedded tick-first, the tick will not back out from heat, but only try to dig in deeper, and second, the victim's skin near the tick will probably be burned. Lit cigarettes have been used in these attempts in the past, but are specifically contraindicated.
What about chemicals? The theory is to suffocate or poison the tick, so it will be "removable." White petrolatum has been used, and may work, but if not, the tick will be slippery, making a forceps extraction difficult.
Poison the tick? Chemicals poisonous to ticks are toxic to humans and absorbed through the skin. Do not try to poison an attached tick-the prognosis will deteriorate.
The Etiologic Agent
The cork-screw-shaped bacterium of Lyme disease, Borrelia burgdorferii, can persist for months to years in the body, affecting brain, heart, joints, and skin, and other organs and tissues. Treponema pallidum, the spirochete of syphilis, is not of the same genus as B. burgdorferii. See Dark Field Fluoresescent Micro Photograph below Willy'sPhoto at http://www3.niaid.nih.gov/topics/lymeDisease/research/cause
Clinical Features
If an infected tick is attached more than 2 to 3 days, the chance of transmission of B. burgdorferii into the host bloodstream is increased. The disease has flu-like symptoms initially, with some cases manifesting an annular ring-type rash called erythema migrans. Arthralgias (joint pains), myalgias (muscle pains), meningitis, neuropathy (such as Bell's palsy), and cardiac conduction defects may appear. Months later a chronic arthritis may develop in one or a few joints, usually involving one or both knees.
Diagnosis
Serological tests often give false positive or false negative results. Positive reactions may persist years after treatment.
The diagnosis largely rests on the patient history of the present illness and physical findings--rash, arthritis, neurological, or cardiovascular findings.
Treatment
Early medical care requires antibiotics, such as doxycycline. Later manifestations, such as arthritis, CNS findings (neuropathy, dementia), or first degree heart block may require administration of multiple antibiotics. Late stage disease often requires prolonged use of antibiotics, such as penicillin, cephalosporins, or tetracylines. NSAIDs, such as ibuprofen, help reduce arthritis symptoms.
Risk Management
Lyme disease is a highly preventable and treatable illness: First, protect yourself against tick attack, and second, check every inch of skin shortly after exposure to "tick turf," and third, properly remove attached ticks. If symptoms of Lyme disease appear, seek prompt medical attention. For questions, here's a FAQs resource with CDC data via Maine: http://www.maine.gov/dhhs/boh/ddc/epi/vector-borne/lyme/lyme-faq.shtml
A "safe and effective" vaccine (LYMErix) was developed but was withdrawn from the market by the manufacturer in February, 2002, due to "limited demand."
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