- Epidemiology: Ticks are important carriers of vector-borne diseases (e.g., Lyme disease, babesiosis, anaplasmosis, ehrlichiosis) in the United States.
- Etiology: While ticks feed on blood from their hosts, their secretions may produce local reactions, transmit diverse pathogens, induce a febrile illness, or cause paralysis. Soft ticks attach for <1 h; hard ticks can feed for >1 week.
- Clinical features: Except for tick-borne diseases, most manifestations of tick bites are self-limited following tick removal.
- Tick-induced fever, in the absence of pathogen transmission, is associated with headache, nausea, and malaise and usually resolves ≤36 h after the tick is removed.
- Tick paralysis is an ascending flaccid paralysis due to a toxin in tick saliva that causes neuromuscular block and decreased nerve conduction.
- Weakness begins symmetrically in the lower extremities ≤6 days after the tick's attachment and ascends symmetrically, causing complete paralysis of the extremities and cranial nerves.
- Deep tendon reflexes are decreased or absent, but sensory examination and lumbar puncture (LP) yield normal findings.
- Tick removal results in improvement within hours; failure to remove the tick may lead ultimately to respiratory paralysis and death.
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Tick Bites and Tick Paralysis
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Recluse Spider Bites
- Epidemiology: Brown recluse spiders occur mainly in the south-central United States, and their close relatives are found in the Americas, Africa, and the Middle East. These spiders only infrequently bite humans, typically if threatened or pressed against the skin.
- Clinical features:
- Most bites by the brown recluse spider result in only minor injury with edema and erythema, although severe necrosis of the skin and SC tissue and systemic hemolysis may occur.
- Within hours, the site of the bite becomes painful and pruritic, with central induration surrounded by zones of ischemia and erythema.
- Fever and other nonspecific systemic symptoms may develop within 3 days of the bite.
- Lesions typically resolve within a few days, but severe cases can leave a large ulcer and a depressed scar that take months or years to heal.
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Recluse Spider Bites
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Widow Spider Bites
- Epidemiology: Black widow spiders, recognized by a red hourglass marking on a shiny black ventral abdomen, are most abundant in the southeastern United States. Other Latrodectus species are present in other temperate and subtropical parts of the world.
- Pathogenesis: Female widow spiders produce a potent neurotoxin that binds irreversibly to presynaptic nerve terminals and causes release and depletion of acetylcholine and other neurotransmitters.
- Clinical features:
- Within 60 min, painful cramps spread from the bite site to large muscles of the extremities and trunk.
- Extreme abdominal muscular rigidity and pain may mimic peritonitis, but the abdomen is nontender.
- Other features are similar to that of acetylcholine overdose (e.g., excessive salivation, lacrimation, urination, and defecation; GI upset; and emesis).
- Although pain may subside within the first 12 h, it can recur for weeks.
- Respiratory arrest, cerebral hemorrhage, or cardiac failure may occur.
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Widow Spider Bites
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