||This article needs more medical references for verification or relies too heavily on primary sources. (December 2013)|
|Classification and external resources|
The American Black Widow spider (Latrodectus mactans), a cause of latrodectism
|MeSH||bites / diagnosis spider bites / diagnosis|
Latrodectism is the clinical syndrome caused by the neurotoxic venom (see latrotoxin) that can be injected by the bite of spiders in the spider genus Latrodectus, of the family Theridiidae. Pain, muscle rgidity, vomiting, and sweating are the hallmarks of latrodectism. Contrary to popular conception it is not fatal.
The most well known of members in the Latrodectus genus are the Southern black widow spider (L. mactans), the Australian redback spider (L. hasselti), the European black widow (L. tredecimguttatus), 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)
Bite incidents of Latrodectus occur usually because of accidental contact with the spiders. The species are not aggressive to humans naturally, but may bite when trapped. Exposure occurs because the species house in domestic domains, found in shoes or under furniture. As such, bite incidents may be described as accidents. - Several thousand black widow bites are reported to Poison Control in the United States each year. About 800 were reported from heath care facilities. Amongst those 800 bites only a dozen had major complications and none were fatal. - In Australia a report on bite incidents in the period 1979-1988 in a children hospital in Perth. There were 241 bite incidents, mostly in the summer, of which 156 were from red back spiders. Twice as many boys were bitten as girls, with a peak age distribution around the second and third year of age. A third of children developed latrodectism and there were no deaths.
Signs and symptoms
Clinically, a bite of Latrodectus may not inject venom of any significant dose. If there is a substantial dose, a bite can cause latrodectism, a disease consisting of generalized muscle pain, abdominal cramps, nausea and vomiting.
The average duration of the syndrome in humans is 3 to 6 days. Untreated patients have exhibited clinical signs for a period of 7 days, but weakness and some muscle pain and malaise may persist for weeks. About 75% of the intoxicated patients experience local effects and do not develop systemic envenomation. A pinprick or burning sensation can be felt when bitten by widow spiders. Local pain worsens over time, which may combine with sweating and piloerection. The pain may spread to local lymph nodes or become generalized.
- Intense local pain develops 5–10 minutes after the bite and is followed by sweating and piloerection (goosebumps) within an hour. Neither puncture marks nor redness are necessarily seen.
- A few patients go on to have widespread symptoms. Pain typically starts at the bite site travel up then general (e.g. pelvic, back, abdominal, chest or shoulder pain). Other neurotoxic features include severe sweating, which may be regional (e.g. both legs) or generalized, mild increase in blood pressure and heart rate may occur
- Non-specific features of envenoming include headache, nausea, vomiting and feeling ill and weak
- Untreated, symptoms may wax and wane over the next 1–4 days. Rarely, patients may feel unwell for up to 1 week. Very rarely, untreated patients report ongoing bite site pain that last weeks or months.
- During pregnancy the pain and abdominal cramps may be confused with other conditions 
- Early medical reports of latrodectism were described in men using an outhouse. The genitals were often the site of the bite. No direct injury to site is reported 
- Myocarditis (inflammation of the heart muscle) has been associated with the lone death in the last 50 years 
- rhabdomyolysis (rapid skeletal muscle tissue breakdown),
The venom acts on nerves causing the release of the neurotransmitters acetylcholine, norepinephrine, and GABA. The release of these neurotransmitters leads to the clinical manifestations of envenoming.
Many bites do not inject venom (a dry bite), others have minimal venom. If enough venom is injected into a person's body, severe pain in local muscle groups occurs, and eventually to regional muscle groups.
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.
There are no tests required to diagnose widow spider bites, or latrodectism symptoms. The diagnosis is clinical and based on historic evidence of widow spider bites. Pathognomonic symptoms such as localized sweating and piloerection provide evidence of envenomation. Unlike brown recluse, the widow species are easily identified by most people.
Diagnosis is obvious in victims reporting contact with 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, or acute abdomen. Blood values are typically unimportant but may be needed to show myocarditis or dehydration from vomiting.
Symptoms self-resolve in a majority of bites, in hours to days. When the bite incident becomes too painful, anti-venom is administered. Pain resolves in a short time according to most. Anti-venom is made by injecting horses with latrodecuts venom over a period of time. The horse develops antibodies against venom. The horse is bled and the antibodies purified for later injection. Doctors recommend the use of pain relief medicine before anti-venom administration. These medicines are considered because antivenom can induce allergic reactions to the horse proteins. The efficacy of anti-venom has come under scrutiny as patients receiving placebo aslo recovered quickly
People who have been bitten by a venomous spider should seek professional medical assistance for symptoms.
Treatments have varied over the years. Some (calcium gluconate) may have been discovered to be useless  usually involve symptomatic therapy with pain medication, muscle relaxants, and anti-venom. The venom does not typically cause problems at the bite site itself. Since latrodectism is not a lethal condition, treatment is not life-saving. Antivenom is used widely in Australia for Latrodectus bites, however in the United States it is less commonly used. Antivenom made from prior spider bite victims has been used since the 1920s  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.
The vast majority of victims fully recover without significant sequela. Death from latrodectism is reported as 5% However It has been reported as low as 0.2%. That same reference had 2 deaths out of 968 bites.
Despite freguent reference to young and old age being a predisposing factor it has been demonstrated that young children appear to be at lowest risk for a serious bite, perhaps owing to the rapid use of antivenom  In general, bite victims who are very young, old, hypotensive, preganancy or who have existing heart problems are reported the most likely to suffer complications with latrodectism. However due to the low incidence of complications these generalizations simply refer to known complications (see special circumstances).
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