Emma Bellinger
Emergency Registrar

Alfred Health

Redback spiders

Good ol’ Australia

Creepy crawlers galore

Spiders and snakes

And plenty more

The red-back spider

is one to know about

As her bites you will see

In Emergency no doubt

When someone presents

With a bite on their skin

How can you tell

That a red-back did the sin?

Ouch! They may scream

As It hurts like hell

Their hairs will stand up

And they won’t feel well

The sweat starts to pour

Their heart starts to race

If their blood pressure rises

 

They’ll go red in the face

They might get a surprise

If they are a gent

To find that they have

“Pitched the tent!!”

Despite all this

The news isn’t all bad

For the venom won’t kill

Which is pretty rad

The main stay of treatment

Is to manage the pain

Consider anti venom

But be aware the risk versus gain

So next time you see

A red-back spider bite

Don’t run away

Everything will be alright

By Emma Bellenger (The ED poet)

The BLUF
  • Red-back spider envenomation hurts, but won’t kill you
  • Keep red-back spider bites in the back of your mind for non-specific presentations
  • To anti-venom or not to anti-venom? Weigh up the risks vs benefits
  • Female red-backs are boss ladies, but spiders in general are gross

I am terrified of spiders. Last week a patient presented to ED with a spider in a jar, asking for a doctor to identify it. NO, THANKS!

Thankfully, managing spider bites is much less scary. In fact, in Australia only one spider can actually kill you – the funnel web. But that’s for another day. Today we are going to delve in to red-back spider bites.

The red-back spider is an Australian Icon. Many young Aussies grew up checking under their toilet seats religiously for red-backs, thanks to the Aussie song hit “There’s a red-back on the toilet seat” (or was that just me?). It’s probably worth the look because red-back spider bites are frequent, particularly in summer months, where they thrive in dry, sheltered areas. Only the female red-back is dangerous, and she can be identified by her characteristic red stripe on her round pea-sized black body.

A redback spider (Latrodectus hasseltii) female, found in suburban Sydney, NSW, Australia. By Toby Hudson – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=18357388

The red-back spider is worthy of it’s own song, and although not deadly, is certainly worthy of knowing how to identify the symptoms and management of this boss lady’s bite.

First thing’s first – Do thousands of baby spiders really ever hatch out from a bite??

Literally my worst fear. Fortunately, this is a MYTH.

The red-back spider venom contains alpha-latrotoxin which causes activation of the sympathetic nervous system. It does NOT cause thousands of eggs to hatch and baby spiders to emerge from the skin.

PHEW!

Now that we’ve cleared that up…

How does a red-back spider bite present?

The envenomation syndrome caused by red-back spiders is called ‘latrodectism’. The classic triad of symptoms is:

  1. Intense pain at the bite site – usually radiating proximally
  2. Sweating – sometimes only on the affected limb
  3. Piloerection

Systemic envenomation may occur and cause further autonomic symptoms such as hypertension and tachycardia.

Priapism may also occur in young males, so with any presentation of priapism red-back spider bites should always be a differential.

But did you die?

Contrary to common belief, red-back spider envenomation is not life threatening.

Tricks for young players

Like most things in medicine, the textbook presentation of syndromes is rarely as straight forward as it seems. Red-back spider bites can present with non-specific features such as generalised pain, headache, nausea and vomiting. In young children the only symptom may be inconsolable crying.

So, keep red-back spider bites in the back of your mind at all times (get ready for the impending nightmares).

smile [Ed – in my (limited) experience of having seen a few of these, the systemic symptoms of envenomation didn’t occur until 12 hours or so after the bite, which could make it harder to think of the diagnosis.]

How to fix it

The mainstay of treatment is pain relief. Apply ice to the area and give simple analgesia to begin with. If pain is non-remitting then opiates may be necessary.

Symptoms will usually reside within 3-5 days.

Anti-venom is a debated topic in the management of red-back spider bites. It should be considered when pain is severe and not responding to analgesia.

Time to RAVE on about anti venom

To give or not to given anti-venom? Spoiler alert – there’s no correct answer.

Why would you give it?

Anti-venom should be considered when pain is severe and non-remitting.

Why wouldn’t you give it?

There are considerable side effects to giving anti-venom, the main two being anaphylaxis and serum sickness, experienced in approximately 5% and 16% of patients respectively.

RAVE 2(1) concluded there is no significant clinical benefit of anti-venom above standard analgesia for pain management in red-back spider bites.

Want more on RAVE-II?
  • Multicentre randomised placebo controlled trial
  • P: 224 patients ≥ 7 years with RBS bite & severe pain (+/- systemic effects)
  • I: RBS antivenom
  • C: Placebo (saline)
  • O: Clinically significant reduction in pain at 2 hours
    • 2nd 1* outcome: subgroup with systemic features resolution of systemic symptoms at 2 hours
      • 🤔 two primary outcomes
  • Conclusion: The addition of antivenom to standardised analgesia in patients with latrodectism did no significantly improve pain or systemic effects
  • Editor’s thoughts: Sample size was for difference of 20% in pain improvement and 30% in systemic effects
    • 30% seems high for reduction in systemic symptoms
    • Didn’t reach their sample size (short by 16 patients – 7% of their target of 240)
    • The trend in the results is toward benefit from anti-venom (CI -1.1-22.6%), so while the effect probably isn’t as much as the 20% they were looking for, there probably is benefit and they were underpowered to find it. Though as they discuss, even if the difference is 10% (a NNT of 10 for pain relief), that would be an unacceptable efficacy in the context of the potential risk of hypersensitivity reaction (4% or NNH 25)
    • Much the same for their second primary endpoint. Underpowered to show that benefit.
  • Clinical bottom line:
    • As with everything, this paper doesn’t give a definitive answer for the treatment of ‘all-comers’, but it does suggest there is no benefit (vs the harm) for the routine treatment of latrodectism.
    • I have used it in the past (on tox advice and a shared decision with the patient) for a patient with significant systemic symptoms. They felt great within about an hour. In that study of n=1 it was great.

Why won’t you just tell me what to do?!

Unfortunately, there’s no one case fits all answer, which usually means it’s time to float some buzz words:

“shared decision making”

“patient centred care”

“risk vs benefit”

You also have your local poisons hotline for advice and wisdom!

Go! Check under your toilet seat

So there you have it. Red-back spider bites. Ouchies! Definitely wouldn’t want a bite on my bottom, so I hope you’ll all join me in checking under the toilet seat forever onwards.

There was a red-back on the toilet seat When I was there last night, I didn’t see him in the dark, But boy! I felt his bite! And now I’m here in hospital, A sad and sorry plight, And I curse that red-back spider On the toilet seat last night.” –

  • Not by Emma the ED poet, but by Slim Newton, “The Red-back on the Toilet Seat”

References

  1. Isbister GK, Page CB, Buckley NA, Fatovich DM, Pascu O, MacDonald SPJ, et al. Randomized controlled trial of intravenous antivenom versus placebo for latrodectism: the second Redback Antivenom Evaluation (RAVE-II) study. Ann Emerg Med. 2014 Dec;64(6):620-628.e2
  2. Austin Clinical Toxicology Service. Redback Spider (RBS) bite – Latrodectus hasselti. Version 2. Austin Health. August 2020.
  3. Austin Clinical Toxicology Service. Redback Spider Antivenom (RBS AV). Version 1. Austin Health. January 2019.
  4. Piloerection image by Ildar Sagdejev (Specious) – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4277167
Emma Bellenger

Emma Bellenger

Emergency Registrar, Alfred Health

Emma’s self-declared strengths are energy and efficiency and a keenness to learn. She likes cats in hats, running, poetry and Nutella. She does not like chronic pain, people who waffle (not to be confused with waffles themselves which belong in the ‘likes’ column) and coffee.