If the above photo makes you cringe, you’re not alone. The fear of these beasts, called arachnophobia, is surprisingly common. Somewhere between 15 and 55 percent of people get anxious around spiders or even pictures of spiders. Even many who can stomach the sight of these eight-legged animals would be hesitant to perform the a brazen act of actually holding one—after all, everyone knows spider bites fester into giant, gaping sores which leave hideous scars.
At least, that’s what we grow up believing. In reality, though, there are some 40,000 species of spiders, only a dozen or so are actually dangerous to humans. And of those, only the venom of recluse spiders can cause the kind of tissue death (called necrosis) that we so often attribute to spider bites. Recent studies have shown that, instead, people assume the worst of innocent spiders when much more sinister species, such as methicillin-resistant Staphylococcus aureus (MRSA) are to blame for their wounds.
We would hope that doctors would be more discerning—that they would be able to properly identify spider bites when they (very rarely) occur. But a new paper suggests that our trusted physicians may not be better than the rest of us. A review of clinical literature found that a whopping 78% of “spider bite” cases may be misattributed.
In a paper published online ahead of print this past week in Toxicon, Marielle Stuber and Wolfgang Nentwig from the University of Bern in Switzerland examined 134 cases of “spider bites” published in medical journals from 1939 to 2014. They discovered that the overall quality of the information in these case reports is low, and rarely is a spider bite properly verified. Thus, the authors conclude, “their scientific value is negligible.”
Stuber and Nentwig even go as far as to say these reports aren’t just useless—they’re possibly harmful. “Moreover,” they write, “such publications are even dangerous because they suggest incorrect conclusions.”
Of the 134 reported bites, only 6 of the 64 attributed to recluse spiders (Loxosceles) and 3 of the 35 alleged widow spider bites (Latrodectus) were verified. A “spider” was observed biting in only 45% of cases, and of those, the actual species involved was appropriately vetted less than half of the time. For a proper ID to occur, the spider specimen must be caught and examined by an expert, the authors write, because relying on the patient or even a nurse or doctor to determine the spider’s species is fraught with difficulty. Mistaken identities are disturbingly common; the authors note that “most people, including physicians” can’t tell a spider from a tick or other insects, let alone the dangerous and deadly species from harmless ones.
Such mistakes and the presumption of a spider’s guilt can have dire consequences. In one of the three fatal cases reviewed, for example, a 30-year-old woman in Guatemala presented with a wound on her thigh. She and her doctors assumed she had a recluse spider bite (though there was no evidence presented in the article that any bite actually occurred). As the lesion worsened and ate away at tissues of her leg, tests confirmed a different culprit: Apophysomyces elegans, a fungus known to cause severe infections. Twenty-two days after the necrosis started, the patient was started on an antifungal treatment. Eight days after that, her leg was amputated, but by then, it was too late—the woman died shortly after surgery. The doctors who wrote up the case report say that the fatal result was “partly a result of the delay in diagnosis because of the initial reaction caused by the spider bite”—a bite that may never have occurred in the first place, let alone contributed to the lesion. The wrong diagnosis may have cost the patient her life.
“From the point of scientific integrity or ethical standards, it is astonishing that manuscripts of case studies concerning spider bites are acceptable for publication even if the spider bites are not verified,” the authors write. “One could even argue that published information wrongly attributed to a spider bite could be dangerous when others follow the reported and apparently successful therapies.”
But the authors also note that even when the bite and species are confirmed, published bite records often lack sufficient detail to aid in the treatment of future cases. They propose that all case reports be required to include a well-defined set of detsils which will allow doctors to evaluate which treatments are most effective.
The main goal of publishing case studies is to provide physicians with information; by cross-referencing a possible bite with reported symptoms, attempted treatments, and recovery successes of previous cases, doctors can best determine an optimal clinical course. “Such a well-sorted and growing documentation could help physicians to select the best therapy for the patient in the case of a spider bite or a given follow-up symptom,” the authors write. “The reality, however, is much different, so that this goal cannot be reached.”
Citation: Stuber, M & W. Nentwig, 2016. How informative are case studies of spider bites in the medical literature? Toxicon. doi: 10.1016/j.toxicon.2016.02.023