Dr. Matt Cordes, associate professor emeritus in the University of Arizona Department of Chemistry and Biochemistry, recently led a study about the brown recluse spider venom’s molecular mechanism of action. He says these spiders have their common name (and the dominant U.S. species’ scientific name, Loxosceles reclusa) for a reason.
“They like to hide in wood piles, sheds, things like that,” Dr. Cordes said in a news release. “They prefer dark, covered spaces. Recluse spiders are actually quite common and easy to find if you look for them.”
Related recluse species occur in in west Texas, New Mexico and Arizona, where the Arizona recluse (L. arizonica) is the most common. The news release rounds up five things that the average person might not know about brown recluses specifically. As a professional, how will you score?
1. They only bite when trapped
“There is this myth that they’re aggressive spiders, but they really are not,” Dr. Cordes said. “They generally have a worse reputation than they deserve.”
The spiders typically only bite when they are trapped, between clothing and skin, for example.
2. About 80 percent of people don’t realize they’ve been bitten
Dr. Cordes said most people who get bitten never know it: “Your average bite either has no effect or causes some kind of fairly mild irritation. It’s the maybe 10 percent or 20 percent of cases where you get something that’s necrotic, and then some even smaller fraction of those develop into something that’s really a spreading necrotic lesion.”
When that happens, however, the tissue damage can get extensive, requiring skin grafts and leaving lasting scars.
3. Bites are often misdiagnosed
According to Dr. Cordes, bacterial skin infections such as methicillin-resistant Staphylococcus aureus (MRSA) are prone to being misdiagnosed as recluse bites.
“MRSA produces a sore that presents somewhat like a recluse spider lesion,” he said. “One of the differences is that the recluse lesions don’t really ooze pus the same way MRSA does. Doctors who are familiar with these types of lesions are more likely to make a correct diagnosis, but sometimes it’s hard to tell.”
Dr. Cordes said a correct diagnosis is more likely if following a perceived bite, a spider is found. Location is an important tip-off as well.
“If someone believes they were bitten, and they live outside the range where recluses occur, it’s a red flag,” he explained. “You almost certainly have a misdiagnosis.”
4. Unique venom works like a ‘molecular lawnmower’
Unlike the venom in most spider species, which primarily acts as a neurotoxin that interferes with nerve function, the venom of spiders in the recluse family, known as Sicariids, is very effective at destroying tissue.
While bites from other spiders may cause necrotic lesions, too, the potential of severe, widespread tissue damage is the recluse’s “calling card,” according to Dr. Cordes. Scientist have known for a while that recluse venom contains toxins that disrupt cell membranes, but the precise mechanisms of action have not been well understood. In their recent paper, Dr. Cordes and his research team reported their success catching the toxin “in the act.” Using a technique called X-ray crystallography, the researchers resolved the atomic structure of the molecule, an enzyme known as Phospholipase D, and its active site interacting with the lipid molecules that form the building blocks of cell membranes.
“We believe a likely mode of operation for this thing is to attach itself to a cell and chew up its lipid molecules,” Dr. Cordes said. “These enzymes are what we call processive: They don’t just bite off one molecule’s head and then go away again. More likely, they move from molecule to molecule, mowing them all down, in a lawnmower-like fashion.”
The recluse’s “lawnmower” toxin can account for as much as half the dry weight of the spider’s venom, according to Dr. Cordes. Add the fact it acts a catalyst, unaffected by its destructive activity, and that means each toxin molecule can do a lot of damage. This may help explain the sometimes-extensive tissue defects that result from a bite. During this process, the toxin turns the cell’s lipids into a product that, until this study, was not known to be found in nature, the researchers report.
“It makes a highly unusual, ring-shaped product called cyclic ceramide phosphate,” Dr. Cordes said. “The interesting thing about that is that almost nothing is known about it, other than the fact it’s unique to the venom of recluse spiders.”
While all spiders carry genes encoding for the same enzyme family, they don’t use them in their venom, but for some other unknown purpose in their bodies. Only recluses express these genes in their venom glands, where they make up the bulk of the venom, Dr. Cordes said.
“It appears they kind of took it and ran with it,” he said. “In an interesting evolutionary twist, these phospholipases are also found in the venom of a scorpion species found in the deserts of Iran, and getting stung can cause a medically dangerous reaction, resulting in a necrotic wound similar to that of a recluse bite.”
5. Don’t rely on the ‘fiddle’ alone for identification
Another common name for brown recluse is the fiddleback spider, but the telltale sign of a violin shape on its cephalothorax (the combined head and middle portion of its body) is not as cut-and-dry as it seems. According to Dr. Greta Binford, an arachnologist and professor of biology at Lewis & Clark College in Portland, Ore., who is the paper’s second author, the violin shape can be less prominent depending on the spider’s sex or life stage. In addition, there are other spider species that have a violin-like pattern.
“Brown recluses are often confused with a whole range of other spiders,” she said in the news release. “To identify a brown recluse beyond doubt, two things need to be present: the violin shape and three pairs of eyes. Most other spiders have eight eyes. Sicariids are the only family whose members have six.”
<p>The post 5 things you might not know about the brown recluse first appeared on Pest Management Professional.</p>
from Pest Management Professional https://www.mypmp.net/5-things-you-might-not-know-about-the-brown-recluse/
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