Feared spider bites may be misdiagnosis
Spider researchers are encouraging people to keep the offending hobo spider after receiving a bite, said Rod Crawford, curator of arachnids at the Burke Museum at the University of Washington.
Equally important is that people see a doctor as a result of a suspected spider bite, and tell the doctor whether they actually saw a spider, Crawford said.
“Misdiagnosing a spider bite is no trivial thing,” Crawford said. He said people have died as a result of being diagnosed with a spider bite, when the illness was actually something else.
More research needs to be done on Hobo spider bites to help medical doctors make correct diagnoses of lesions, said Richard S. Vetter of the department of entomology at UC-Riverside.
This conclusion is based on a study published in the “Annals of Emergency Medicine, December 2004,” which Vetter co-authored.
“Hobo spiders live in northern Utah,” Vetter said. A distributional chart of Hobo spider territoy across the United States can be viewed on the Burke Museum’s website through the University of Washington.
Vetter said the medical community is supportive of the efforts he and Isbister have made.
“Most doctors are incredibly supportive,” Vetter said. “The general public thinks that doctors know everything, but the misdiagnosis rate by doctors is 15 percent. This means doctors make three misdiagnoses a day.”
This could jeopardize a person’s health, said Ryan Davis, an anthropod diagnostician with the Utah Plant Pest Diagnostic Lab. The Lab is part of USU’s biology and natural resources department. The lab at Utah State identifies pest problems for the entire state of Utah, Davis said.
“Doctors may be incorrectly diagnosing health issues as spider bites, and a person’s health issue could be more serious, such as a staph infection,” Davis said.
Vetter said there is a psychological component to the problem, too. People want a diagnosis from a doctor in some cases. Also, “people want to blame the spider,” he said.
The research in the “Annals of Emergency Medicine” says a researcher implicated the Hobo spider in necrotic lesions in 1987, after pushing the spider into the shaved flesh of a rabbit. Since that time the Hobo spider has been listed in medical texts along with the Brown Recluse as medically dangerous, according to the article.
This research was “sufficiently valid circumstantial evidence,” the article says, “to elevate the spider to that of medical significance.”
The problem, Crawford said, is scientists have now learned that animal models are not necessarily good models to test the effect of something on humans.
An example is the effect of black widow spiders on rats.
“The black widow has very little effect on rats,” Crawford said.
Since the research by Vetter and Isbister, Utah State’s extension service has changed its fact sheets on the hobo spider, Davis said. The change has downgraded the medical significance of the hobo spider.
“There are two reasons why people may be able to be less concerned about hobo spider bites,” Davis said. “One, the sample used in the rabbit study was small. Two, there are few verified hobo spider bites.”
This doesn’t mean that hobo spider bites aren’t dangerous, Davis said, but researchers need more verified bites to study effects further.
“We want the proof,” Vetter said.
Vetter said the only verified bite causing a lesion was on a woman who had a disease that also causes necrotic lesions, Vetter said. This is the only bite in 80 years.
Doctors now say they will have to look more closely at their diagnoses, Vetter said.
The reason bites need to be verified is that people will identify the Hobo spider by a pattern on its back, but lots of spiders have the same pattern. In this situation, the spider has to be identified by a professional, Vetter said.
Davis encourages people who think they have been bitten to find the spider, put the spider in a container, and bring it to the lab. This way it can be identified.
According to the journal article by Vetter and Isbister, the hobo spider cannot be accurately identified by visual inspection.
“One must examine the microscopic structures (of the spider) for accurate species identification,” the article reads.
“The jury is still out,” Vetter said.
– keith.burbank@aggiemail.usu.edu