Spider Envenomation

Header Image: Black Widow by © peter_waters; Brown Recluse by © panor156; Funnel Web Spider by © Nattawut / Adobe Stock

Spider bites! Don’t be afraid, we have a new CPG from the JTS on how to treat them. Most spiders don’t have fangs big/strong enough to penetrate human skin but the ones below can cause some problems.

General approach: Tetanus for bites if patients’ tetanus is out of date/unknown. Anaphylaxis is a concern so be prepared to treat it. In general, prophylactic antibiotics are not indicated but may be used if secondary infection occurs. Oh, and STOP blaming every abscess on a spider bite.

Widow Spiders (North America, Asia, Europe, Africa, Australia) — Neurotoxin, symptoms start 15-60 min after bite. Painful muscle cramping in waves at location of bite and then travel towards center of body (can mimic acute abdomen with rigid abdominal muscle cramping). Can have hypertension, tachycardia, vomiting, diaphoresis. Very rarely fatal, mostly supportive care (acetaminophen, benzos) for treatment.

Antivenom (indication = refractory pain/symptoms) is not readily available and can cause anaphylaxis.

Violin Spiders/Brown Recluse (worldwide)- Cytotoxic venom, symptoms start within hours as pain, itching and swelling with blister or purple discoloration at the bite enlarging for 1-2 weeks. Or it may start days after bite as a necrotizing lesion. Systemic envenomation is not correlated to the size/extent of the lesion. Systemic Symptoms start 1-3 days after bite- fever, weakness, vomiting, joint pain, rhabdo, DIC.

Treatment - No antivenom. Admit for systemic symptoms and symptomatic treatment.

Funnel Web Spiders (Australia)- Neurotoxic venom (may “attack” bite and not let go so they have to be physically removed. Symptoms: Biphasic, First phase is pain, perioral tingling and fasciculations to spasms with nausea, vomiting, tachycardia, hypertension, dysrhythmias and acute lung injury. The second phase is refractory hypotension, apnea and death.

Treatment - Local pressure dressing for flow restriction (this is one of the very few times to do this as the venom is locally inactivated). Antivenom is available in Australia and indicated for signs of envenomation (2 vials repeated every 15 min until clinical improvement).

But what about Tarantulas? These are found worldwide. In general it is a painful but not life threatening bite. Some American Tarantulas have barbed hair that can get into the skin and cause pain, irritation and itching. Remove the hairs with tape.