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|Classification and external resources|
Latrodectism is the clinical syndrome caused by the neurotoxic venom (see latrotoxin) that can be injected by the bite of any spider that is a member of the spider genus Latrodectus, in the family Theridiidae.
The most well known of members in the Latrodectus genus are the black widow spider (L. mactans), the Australian redback spider (L. hasselti), the brown widow (L. geometricus), the European black widow (L. tredecimguttatus), and the katipo spider (L. katipo).
Venom method 
The venom spreads rapidly throughout the body and acts by causing the release of the neurotransmitters acetylcholine, norepinephrine, and GABA. The release of these neurotransmitters leads to the clinical manifestations of envenoming.
If enough venom is injected into a person's body, severe pain in local muscle groups occurs, and eventually to regional muscle groups. The spread relates to the toxin initially being carried by the lymphatic system until it reaches the blood stream. Once in the blood, the venom is moved by circulation, causing its toxins to be deposited in the ends of the nerves that are inserted into the muscle.
The venom acts at nerve endings to prevent relaxation of muscles, causing tetany — constant, strong, and painful muscle contractions. 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. Back and leg muscles can often be affected as well.
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Symptoms occur in three main phases: an exacerbation phase, a dissipation phase and a residual phase.
Exacerbation phase 
During the first 24 hours after a bite:
- Severe pain in muscle groups local to the bite.
- Muscle cramping, primarily in the abdomen, back and thighs.
- Headache, dizziness, tremors, salivation, diaphoresis (excessive sweating), nausea and vomiting.
- Anxiety, fatigue, insomnia.
- Lacrimation (tearing of the eyes).
- Migratory arthralgia (joint pain).
- Tachycardia (rapid heart beat), bradycardia (very slow heart beat), restlessness, hypertension (elevated blood pressure), Tachypnea (hyperventilation).
In some rare and extreme cases, severe complications can arise:
- Spontaneous abortion, preterm labor
- Acute renal failure (failing of kidney function).
- Myocarditis (inflammation of the heart muscle), rhabdomyolysis (rapid skeletal muscle tissue breakdown), paralysis.
- Shock, coma, and death.
Symptoms that may be present at or near the wound:
- Rash, slight erythema (redness of skin), Piloerection (goose bumps).
- Mild edema (swelling due to excess fluid).
- Lesion or mild infection (rare).
Dissipation phase 
During the first 1 to 3 days after the bite:
- Symptoms start to decline.
Residual phase 
During the following weeks or months:
- Muscle spasm, tingling, nervousness and weakness. There is a potential risk of paralysis.
Diagnosis is obvious in victims reporting contact with any Latrodectus spider. However, the absence of such a report, either through inability to communicate or unawareness, greatly complicates diagnosis as symptoms overlap with a variety of other serious clinical syndromes such as tetanus, acute abdomen, and myocardial infarction. Laboratory workups are of limited value.
People who have been bitten by a venomous spider should always seek professional medical assistance immediately. Though complications are rare, and death is even more rare, negative developments can proceed at a quick pace. Changes in heartbeat, breathing or blood pressure should be considered especially ominous.
Standard treatments usually involve symptomatic therapy with pain medication, muscle relaxants, and antivenom. The venom does not typically cause problems at the bite site itself, unless a secondary skin infection occurs.
Antivenom is used widely in Australia for Latrodectus bites, however in the United States it is generally reserved for use only when absolutely necessary. Due to the low mortality rate, the risk of major injuries or death due to anaphylaxis or serum sickness are greater than the risk of death due to the venom itself. In past years, injections of calcium gluconate were used to replace calcium rendered unusable by the neurotoxins, but hospitals have been switching to the use of prescription painkillers — especially opiates such as morphine — to reduce symptoms, as the calcium injections do very little for the pain and do not significantly reduce the recovery time.
Risk indications for complications 
In general, bite victims who are very young, old, hypotensive, pregnant, or who have existing heart problems are the most likely to suffer complications with latrodectism.
Although severe symptoms such as shock and coma are known to have happened, death due to latrodectism is rare. Young children appear to be at highest risk for a lethal bite, probably owing to their smaller body mass.
The vast majority of victims fully recover without significant sequela.
See also