6-year-old Charlotte is carried into your emergency department by her father. She had been helping him tidy up the garage, and she thought she had scratched herself on an old box of toys. An hour later, she was inconsolable and refusing to walk. She thinks a spider bit her.
Bottom line
Redback spider bites, though painful, don’t kill you.
They typically present with delayed-onset, intense pain associated with local autonomic symptoms and signs.
Redback spider antivenom may resolve symptoms within a day in 85% of cases, but this should be weighed against the risk of an acute hypersensitivity reaction.
Funnel-web spider bites, however, can be deadly.
Australia is a dangerous place to live.
How do children with a Redback spider bite present?
Redbacks (Latrodectus hasselti) are found throughout Australia, whereas their kissing cousins, the Katipo (Latrodectus katipo), are more common in New Zealand. They thrive in urban environments and are one of the reasons this author refuses to use outdoor toilets.
Their bites are not immediately painful and can often be mistaken for a scratch, but within about 30 minutes, there is intense regional pain accompanied by sweating and piloerection.
Their venom contains alpha-latrotoxin, which causes neurotransmitter release at nerve terminals in the sympathetic nervous system. Whilst children are often bitten on the leg, the pain can radiate to the leg that has not been chomped on. This triad of intense pain, sweating and piloerection is the classic presentation of lactrodectism.
Systemic envenomation occurs in approximately a third of cases and is characterised by autonomic features (e.g., sweating) and more general features such as nausea, vomiting, and headache.
Be aware that Redback bites have been known to present atypically. They have been confused with appendicitis, intussusception and meningitis, so they should be on the differential for any inconsolable child with irritability and diaphoresis.
The autonomic effects have even been known to cause priapism in young boys.
How do you treat Redback bites?
If the bite is left untreated, symptoms should resolve in three to four days.
You can apply simple first-aid measures at home, including applying ice packs to the bite and using simple analgesics to relieve pain. There is no evidence that pressure immobilisation bandages are effective in treating Redback bites.
Once in the hospital, the child should be reassured and given appropriate analgesia. Often, they need titrated doses of opiates. They may also be offered antivenom.
If there is an antivenom, shouldn’t we give it?
CSL Redback Spider antivenom is indicated for severe local pain that does not respond to simple analgesics. The standard dose is two undiluted vials IM or two vials diluted in 100 mL of normal saline IV over 30 minutes.
Interestingly, the RAVE trial found detectable antivenom levels only in patients who received intravenous treatment, with no appreciable clinical difference between the IV and IM groups at two hours. Doubt has now been cast on its usefulness.
When one considers that up to 5% of patients undergo an immediate hypersensitivity reaction and 16% of antivenom recipients develop serum sickness within two weeks, there needs to be a shared decision with the patient/parents as to whether or not to give it. Because of these risks, it should be given in a monitored environment.
Redback antivenom can also be used to treat a Cupboard spider bite.
How about funnel-web spiders? Are they more dangerous?
Funnel-web spiders belong to the famous BBS, or Big Black Spider, group of Australian nasties. They can be found around a 120km radius of Sydney.
Their venom, a potent neurotoxin, can be lethal if untreated. Because of the rapid onset of venom action, pain is immediate, with systemic symptoms occurring within half an hour of envenomation. Effects are felt within two hours of the bite.
General features of funnel-web envenomation include headache, listlessness and nausea, but this rapidly progresses to life-threatening cardiovascular, respiratory and neurological compromise. In the late stages of envenomation, the child may become bradycardic and hypotensive (or hypertensive due to autonomic overactivity) and develop acute pulmonary oedema. They may complain of perioral paraesthesia and may have visible muscle fasciculations. These all herald impending doom and potential cardiorespiratory arrest.
How should they be treated?
The spider is big enough to be seen and leaves visible fang marks, so there is often no doubt about what has happened. The victim must be transported to a centre capable of dealing with such an envenomation as quickly as possible. In cases of funnel-web envenomation, proper application of a pressure immobilisation bandage may be life-saving.
Once in the hospital, the ABCs should be managed in the usual fashion, with priority given to the provision of antivenom. Two vials should be given immediately, though there are case reports of four vials being given peri-arrest. Funnel-web anti-venom can also be used to treat the bite of the mouse spider.
Any other scary spiders I should know about?
Australia has a lot of scary-looking creepy crawlies. One common reason for ED visits is the White Tail.
These spiders can be found throughout Australia. Like most arachnids, they can cause painful bites for a few hours, but they rarely cause systemic envenomation. Unlike their North American cousins, the Brown Recluse spider, they have not been shown to cause necrotic skin ulcers. Generally, they cause local pain and may leave a red mark for a day or two, but there is no evidence of skin breakdown. There is no role for prophylactic antibiotics.
Charlotte is treated initially with intranasal fentanyl and oral adjunctive therapy. After discussion with her father, you elect not to give Redback anti-venom on the proviso that they return should the pain be uncontrollable.
References
Isbister, G. K., et al. “A randomised controlled trial of intramuscular vs. intravenous antivenom for latrodectism—the RAVE study.” QJM 101.7 (2008): 557-565
Isbister, Geoffrey K. “Antivenom efficacy or effectiveness: the Australian experience.” Toxicology 268.3 (2010): 148-154.
Isbister, Geoffrey K., and Hui Wen Fan. “Spider bite.” The Lancet 378.9808 (2011): 2039-2047.
Isbister, GK. Safety of IV administration of redback spider antivenom. Internal Medicine Journal 37 (2007) 820-822
Daly, Frank, Mike Cadogan, and Mark Little. Toxicology handbook. Elsevier Australia, 2011.