Arthropod Bites



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Am Fam Physician. 2013 Dec 15;88(12):841-847.

This clinical content conforms to AAFP criteria for continuing medical education (CME). See CME Quiz Questions.

  Related letter: Identifying Erythema Migrans Rash in Patients with Lyme Disease

Author disclosure: No relevant financial affiliations.

The phylum Arthropoda includes arachnids and insects. Although their bites typically cause only local reactions, some species are venomous or transmit disease. The two medically important spiders in the United States are widow spiders (Latrodectus), the bite of which causes intense muscle spasms, and the brown recluse (Loxosceles), which may cause skin necrosis. Widow bites usually respond to narcotics, benzodiazepines, or, when necessary, antivenom. Most recluse bites resolve uneventfully without aggressive therapy and require only wound care and minor debridement. Tick bites can transmit diseases only after prolonged attachment to the host. Treatment of clothing with permethrin and proper tick removal greatly reduce the risk of infection. Ticks of medical importance in the United States include the black-legged tick, the Lone Star tick, and the American dog tick. The prophylactic use of a single dose of doxycycline for Lyme disease may be justified in high-risk areas of the country when an attached, engorged black-legged tick is removed. Bites from fleas, bedbugs, biting flies, and mosquitoes present as nonspecific pruritic pink papules, but the history and location of the bite can assist with diagnosis. Flea bites are usually on ankles, whereas mosquito bites are on exposed skin, and chigger bites tend to be along the sock and belt lines. Antihistamines are usually the only treatment required for insect bites; however, severe mosquito reactions (skeeter syndrome) may require prednisone. Applying insect repellent containing diethyltoluamide (DEET) 10% to 35% or picaridin 20% is the best method for preventing bites.

Arthropods comprise a vast invertebrate phylum that includes arachnids (those with eight legs, such as spiders, mites, and ticks) and insects (those with six legs [subphylum Hexapoda], such as mosquitoes, gnats, and flies). Most arachnid and insect bites are summertime nuisances, but several species' bites are toxic and others are vectors of disease. This article focuses on spider, mite, tick, and insect bites of medical importance.

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendation Evidence rating References

Consider methicillin-resistant Staphylococcus aureus infection in a patient presenting with a suspected spider bite. Many purported spider bites are bacterial pyodermas or other skin conditions.

C

2, 3

Black widow spider bites should be treated with intravenous benzodiazepines for muscle spasm and narcotics for pain.

C

4, 5

Black widow antivenom should be reserved for patients with significant pain that has not responded to conventional treatment with benzodiazepines and narcotics.

C

4, 5

Wound cleansing and minor debridement are the mainstays for managing necrotic brown recluse bites.

C

68

Tick bites should be treated with prophylactic doxycycline (200 mg in a single dose) only when an engorged black-legged tick is acquired in a high-risk area for Lyme disease. Antibiotics are effective if given within 72 hours of tick removal.

C

11

Antihistamines are the best first-line therapy for most insect bites.

C

21


A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to http://www.aafp.org/afpsort.

SORT: KEY RECOMMENDATIONS FOR PRACTICE

View Table

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendation Evidence rating References

Consider methicillin-resistant Staphylococcus aureus infection in a patient presenting with a suspected spider bite. Many purported spider bites are bacterial pyodermas or other skin conditions.

C

2, 3

Black widow spider bites should be treated with intravenous benzodiazepines for muscle spasm and narcotics for pain.

C

4, 5

Black widow antivenom should be reserved for patients with significant pain that has not responded to conventional treatment with benzodiazepines and narcotics.

C

4, 5

Wound cleansing and minor debridement are the mainstays for managing necrotic brown recluse bites.

C

68

Tick bites should be treated with prophylactic doxycycline (200 mg in a single dose) only when an engorged black-legged tick is acquired in a high-risk area for Lyme disease. Antibiotics are effective if given within 72 hours of tick removal.

C

11

Antihistamines are the best first-line therapy for most insect bites.

C

21


A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to http://www.aafp.org/afpsort.

The Author

GREGORY JUCKETT, MD, MPH, is a professor of family medicine and director of the international travel clinic at West Virginia University School of Medicine, Morgantown.

Address correspondence to Gregory Juckett, MD, MPH, West Virginia University School of Medicine, 1 Medical Center Dr., Box 9247, Robert C. Byrd Health Science Center, Morgantown, WV 26506 (e-mail: gjuckett@hsc.wvu.edu). Reprints are not available from the author.


Figures 1,3 through 5,7, and 8 provided by the Centers for Disease Control and Prevention's Public Health Image Library, Atlanta, Ga.

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