Latrodectism

Latrodectism
The Southern Black Widow spider (Latrodectus mactans), a cause of latrodectism
Classification and external resources
Specialty	emergency medicine
ICD-10	T63.3
ICD-9-CM	989.5
eMedicine	derm/599
MeSH	bites / diagnosis spider bites / diagnosis
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Latrodectism is the illness caused by the bite of Latrodectus spiders (the black widow spider and related species). Pain, muscle rigidity, vomiting, and sweating are the hallmarks of latrodectism. Contrary to popular conception, latrodectism is very rarely fatal to people. Domestic cats have been known to die with convulsion and paralysis.

There are several spider species all named black widow: southern black widow spider (L. mactans), the European black widow (L. tredecimguttatus), Western black widow spider (L. hesperus), Northern black widow spider (L. variolus). Other Latrodectus that cause latrodectism are the Australian redback spider (L. hasselti), and the katipo spider (L. katipo). Several other members of Latrodectus genus are not commonly associated with latrodectism including the cosmopolitan brown widow (L. geometricus).

A bite of Latrodectus may not inject any venom (known as a dry bite) and so no illness occurs. About 75% of "wet" bites will have localized pain and nothing more. If, however, there is a substantial dose, a bite can cause latrodectism. The main symptoms are generalized muscle pain, stomach cramps, nausea and vomiting. Initially a pinprick or burning sensation can be felt when bitten by widow spiders. If there was enough venom injected, pain worsens over the next hour. The area will develop localized sweating and gooseflesh piloerection. The pain may spread and become generalized. The typical duration is three to six days. Some people who do not receive antivenom may feel under the weather, be weak, and have muscle pain for weeks.

Spider venoms are a complex collection of toxic agents. Unique to the widows is Latrotoxin. The venom acts on nerves causing the massive release of the neurotransmitters acetylcholine, norepinephrine, and GABA. The release of these neurotransmitters leads to pain, cramps, sweating and fast pulse. Latrotoxin acts on presynaptic nerve membranes (See Chemical synapse) and through the cell's signalling protein (calcium-independent receptor of alpha-latrotoxin CIRL). Thus initial pain is often followed by severe muscle cramps. Contraction of musculature may extend throughout the body, though cramping in the abdomen is frequently the most severe. Latrotoxin may act on muscles directly preventing relaxation, promoting tetany — constant, strong, and painful muscle contractions.

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