Snake bite treatments have been all the rage of late here at Nature Medicine. This month, we have a podcast interview with the author of a recent paper who found that applying an off-the-shelf ointment can slow the spread of snake venom. Last summer, we reported how drug companies aren’t developing new antivenom therapies despite the medical need. And dipping into the archive, five years ago we published a commentary on the role that the immune system’s mast cells play in inactivating snake toxins.
But snakes aren’t the only vermin with a venom-filled bite. Each year hundreds of thousands of people around the world are bitten by venomous spiders. Some of these, such as the redback spider of Australia, cause neurotoxic effects, leading to cramps, nausea, paralysis and even death. Others, including North America’s brown recluse spider (pictured at right), have cytotoxic venom that kills cells and tissue leading to nasty, ulcerated wounds.
As such, one might think that spider antivenoms, which have been on the market for over half a century, could go a long way to treating the effects of these eight-legged onslaughts. But in practice, antivenoms are largely ineffective because spider bite victims often don’t know for many hours that they’ve been nipped. This means that bite victims generally fail to seek medical help fast enough for these treatments to make a difference, two spider bite experts argue in a report out this week in The Lancet.
“Antivenom is never going to be of any practical value because you can’t administer in a way that’s going to work,” says study coauthor Geoff Isbister, a clinical toxicologist at the University of Newcastle in Australia. “If this was a drug developed in the last 20 years it would never have got through” regulatory scrutiny, he adds.
Three years ago, Isbister and his colleagues published the results of a 126-person randomized trial conducted at 11 Australian hospitals that tested two different routes of antivenom administration to treat redback widow bites. Reporting in the journal QJM, they found little added benefit of antivenom over placebo.
Others have had better outcomes. In a smaller, placebo-controlled trial involving an experimental antivenom called Analatro, Richard Dart, director of the Rocky Mountain Poison and Drug Center in Denver, and his colleagues showed that the drug, developed by Mexico’s Bioclon Institute, effectively combat black widow bites even though the subjects in the trial only received the treatment 10 hours, on average, after being bitten. “We didn’t get them that early,” says Dart. Nonetheless, “our results in just 24 patients were quite promising.” They are now conducting a larger phase 3 follow-up.
A tangled web
Medicine’s problem with treating spider bites is not just restricted to effective antivenom. As Isbister and Hui Wen Fan of the Butantan Institute in São Paulo, Brazil note in their new Lancet paper, physicians often mistakenly ascribe necrotic skin lesions to the arachnid attackers instead of the true culprits, such as chemical burns, bacterial infections and Lyme disease. “‘Spider bite’ is a sexy diagnosis,” says entomologist and brown recluse spider expert Rick Vetter of the University of California-Riverside. “It’s really kind of amazing how sloppy the medical literature is in this area.”
To explore this problem, Jeffrey Suchard, a professor of clinical emergency medicine at the University of California–Irvine Medical Center, tracked 182 people who came into his hospital over a two-year period complaining of spider bites. Reporting in the Journal of Emergency Medicine, he found that seven were diagnosed with actual spider bites, nine with bites from other animals and the vast majority with infections, mostly from methicillin-resistant Staphylococcus aureus.
Suchard allows that many of these seven spider bite diagnoses could be incorrect as spider bites are uncommon in Southern California. But, he notes, since doctors often incorrectly prescribe antibiotics for spider bites, in all likelihood “they turned out to have done the correct treatment despite themselves.”
Not all misdiagnoses turn out so well, though. Many people incorrectly identified with spider bites fail to receive proper treatment for their true ailment in a timely fashion. What’s more, these people often unnecessarily receive antivenom drugs, which can cause allergic reactions. Around 20 years ago, one person even died of severe lung spasms after receiving antivenom.
The solution to all these problems, according to Laura James, a pediatrician at the University of Arkansas for Medical Sciences in Little Rock, who, in May, reported on the complications seen from brown recluse spider bites in children: “We just need better research to be able to recognize these lesions.”
Image of brown recluse spider via the CDC / Ohio State University