Spider bites

Spiders are a class of ancient animals widely distributed in almost all terrestrial ecosystems, and are the most diverse terrestrial invertebrates except insects. Spider bites are one of the most common animal injuries in emergency medicine, and the incidence has been on the rise in recent years. Some patients with spider bites are seriously ill, which is a predisposing factor for a variety of emergencies.


Causes

Spider venoms are a mixture of small molecular substances, such as organic bases containing inorganic salts, polyamines, and neurotransmitters, polypeptides rich in disulfide bonds, and enzymic proteins secreted by spider venom glands. According to the composition and biological effect, the venom can be decomposed into neurotoxin, necrotoxin, and mix toxin. Neurotoxins mainly act on neuromuscular synapses, causing the release of acetylcholine from synaptic vesicles, resulting in excessive muscle depolarization and autonomic nervous hyperarousal. Necrotoxin can cause hemolysis through sphingomyelinase in the toxin, and its own hyaluronidase and proteolytic enzymes can depolymerize hyaluronic acid, dissolve intercellular substance, increase tissue permeability, and release vasoactive substances, leading to local swelling and pain. Mix toxin has properties of neurotoxin and necrotoxin.

Figure 1 spider


Signs and Symptoms

Severe pinprick sensation may occur at the bitten site. There may be a small bruised area with peripheral redness, possibly with 2 punctate tooth marks. Skin rash and mild edema are common, and bleb or necrosis can occur at the bitten site in some patients.

Video 1 skin lesions caused by spider bites

Systemic manifestations include fever, headache, dizziness, irritability, anxiety, nausea, vomiting, abdominal pain, abdominal distention, jaundice, weakness of limbs, profuse sweating, and cold and clammy skin. In severe cases, acute respiratory failure, renal failure, myocarditis, and anaphylactic shock may be complicated.


Diagnosis

If there are a history of exposure to spiders and clinical presentations, the condition can be diagnosed.


Treatment

The bitten site should be rinsed with clear water or normal saline immediately and fully disinfected with iodophor. Local blocking with 0.5% lidocaine may be considered.
If there is obvious swelling, the affected limb can be elevated, and local cold compresses may be needed within 24 - 48 hours. If there are one or more large blebs (>2cm in diameter), incision and drainage can be performed early. If the wound surface is necrotic and ulcerated, full debridement should be given. For local contact allergies not caused by bites, the eyes and skin should be cleaned in time and carefully inspected, and foreign bodies such as suspected spider stinging hair should be removed, and glucocorticoid-containing eye drops or skin topical drugs should be used.

Early administration of antihistamines and glucocorticoids can reduce inflammation and allergic reactions caused by spider venom. Cholinergic receptor blockers, such as atropine and scopolamine, can be used for toxin-induced cholinergic nerve excitation and crisis, such as bradycardia, miosis, increased glandular secretion, and skeletal muscle excitation.

If severe or fatal poisoning occurs, epinephrine hydrochloride 0.5 mg should be administered intramuscularly immediately. For severe patients with acute respiratory failure, tracheal intubation and mechanical ventilation should be performed as soon as possible. Routine blood purification therapy is not recommended. In severe patients, if acute renal failure occurs, blood purification therapy can be considered.