Medicine for the Outdoors
Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Tick-Borne Illness

This is the next post based upon a presentation given at the Wilderness Medical Society Annual Meeting held in Snowmass, Colorado from July 24-29, 2009. The presentation was entitled “Lessons Re-learned: The US Army’s Experience with Tick –Borne Illness.” It was delivered by John Westhoff, MD, who is a Fellow of the American College of Emergency Physicians.

Dr. Westhoff made a number of great points, in a session that mentioned Rocky Mountain spotted fever, ehrlichiosis, Lyme disease, tularemia, Q fever, and southern tick-associated rash illness (STARI).

A case presentation format was used to highlight the varied way and severity in which some of these disorders can present to clinicians. For instance, a case was described in which the victim was a 49 year old with a 24 hour history of headache and chills, mildly elevated blood pressure – pulse – respirations – temperature – white blood cell count, and was initially given the diagnosis of sinusitis. One day later, the patient was seen with persistent problems, and informed of a working diagnosis of viral syndrome. Three days later, the patient had developed subjective numbness in the hands and feet, and still had a progressive low grade fever, but the white blood cell count had dropped to normal. The working diagnosis was still viral syndrome. On the fourth visit, the victim underwent a spinal tap (lumbar puncture) and was admitted to the hospital. A skin rash developed and blood testing revealed that the patient suffered from ehrlichiosis, from which there was a full recovery.

Ehrlichiosis can be severe. Dr. Westhoff described another case, in which a young man who initially presented with fever and chills and not much more deteriorated over three days sufficiently to be admitted to the hospital, and died after 8 days in the hospital, again with a diagnosis of ehrlichiosis. During his illness, he suffered from skin rash, muscle pain, high fever, infiltrates (consistent with pneumonia) in his lungs, low blood counts, and severe systemic infection with multi-organ failure. Ticks were found in his groin.

Human ehrlichiosis (there is also a canine form) is present in two forms, one caused by a rickettsial organism known as Ehrlichia chaffeensis, which is spread by Amblyomma americanum tick bites, and the other caused by the rickettsial organisms E. phagocytophila and E. equi, spread by Ixodes tick bites. Infection is usually acquired by a person who inhabits a rural environment. The average incubation period after a bite is approximately 7 to 10 days. The victims, who are more commonly middle-aged adults than children and young adults, complain of a flu-like syndrome with high fever, chills, fatigue, headache, muscle aches, vomiting, and a variety of skin rashes, which can be punctate, bumpy, like tiny bruises, or broad and reddened. A victim often has decreased counts of various types of blood cells, as well as liver dysfunction. The treatment is tetracycline 500 mg four times a day, or doxycycline 100 mg twice a day, for 10 days. The few children who have been diagnosed with ehrlichiosis have been treated with doxycycline 3 mg per kg of body weight in two divided doses per day. Untreated or treated after a delay in diagnosis, up to 15% of victims can develop severe infections, kidney failure, bleeding disorders, seizures, and/or coma.

Human anaplasmosis, which was formerly called human granulocytic ehrlichiosis, is caused by infection of white blood cells by a bacterium named Anaplasma phagocytophilum. Like ehrlichiosis, anaplasmosis is disseminated by bites of Ixodes ticks, the blacklegged tick (I. scapularis) in the Northeast and upper Midwest, and the western blacklegged tick (I. pacificus) on the West Coast. Infected persons have the onset of illness 5 to 21 days after a bite with symptoms of fever, headache, fatigue, and muscle aches, which may progress to more serious illness affecting the kidneys, central nervous system, lungs, and blood system. The treatment is the same as for ehrlichiosis.

We also learned about Rocky Mountain spotted fever (RMSF), which is most commonly seen during the months of April to September, when ticks and humans are most frequently in contact. The disease carries an incubation period of 5 to 10 days, and classically presents with fever (flu-like illness), typical rash 2 to 5 days after the fever, and a history of tick bite. Treatment is usually with doxycycline 100 mg by mouth every 12 hours (4 mg/kg/day for persons under the weight of 45 kg) for 10 days. Chloramphenicol is used for pregnant patients.

After a further discussion of features of ehrlichiosis and Lyme disease and brief discussion of tularemia, Q-fever, and STARI, the bulk of the remainder of the session was devoted to the most important topic – namely, prevention of tick-borne illnesses. The key features noted were personal skin inspection to locate and remove ticks, heightened awareness during tick season, use of appropriate insect repellents, such as DEET (33% controlled release lotion), permethrin treatment of clothing, proper wearing of clothing (long sleeves, tucked in shirts and pants), and so forth. It was emphasized that permethrin treatment of clothing is much more effective than is DEET treatment of clothing.

If you decide to apply permethrin spray to clothing, be certain to do the following:

1) Follow manufacturer’s instructions closely. Do not exceed recommended spraying times.
2) Treat clothing only. Do not apply to skin.
3) Apply the permethrin in a well-ventilated outdoor area, protected from the wind.
4) Only spray the permethrin on the outer surface of clothing and shoes.
5) In a concentration of 0.5%, it can be sprayed on both sides of clothing to lightly moisten the outer surface of the clothing item; it is not necessary to have the clothing soaked through (saturated).
6) Be certain to apply completely cover socks, trouser cuffs and shirt cuffs, where insects may attempt to crawl or fly through openings to your skin.
7) Hang treated clothing outdoors and allow to dry for at least 2 to 4 hours in non-humid conditions and for at least 4 hours in humid conditions.
8) Treat clothing no more often than every 2 weeks.
9) Launder treated clothing separately from other clothing at least once before re-treating.
10) Assume that your treated clothing is effective for repellency for 2 weeks or more. Wear it only when you need to repel insects and arthropods. Store it in a separate impermeable (to permethrin) bag when not in use.

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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.