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Spider venom reveals new secret.

The genus Loxosceles, which contains about 100 spider species, includes the brown recluse (or fiddler spider), whose venom, it turns out, produces a different chemical product in the human body than scientists believed. The finding has implications for understanding how these spider bites affect humans and for the development of possible treatments.

One of few common spiders whose bites can have a seriously harmful effect on humans, the brown recluse has venom that contains a rare protein that can cause a blackened lesion at the site of a bite, or a much less common, but more dangerous, systemic reaction in humans. "This is not a protein that is usually found in the venom of poisonous animals," points out chemist Matthew Cordes, who led the study, published in the journal PLOS ONE.

The research team discovered that the venom protein causes lipids to bend into a ring structure, generating a cyclical chemical product that is very different than the linear molecule it was assumed to produce. "The very first step of this whole process that leads to skin and tissue damage or systemic effects is not what we all thought it was," Cordes notes.

The lipid knocks off its own head by making a ring within itself, prompted by the protein from the spider venom. The cyclical shape of the headless molecule means that it has different chemical properties than the linear headless lipid previously believed to be generated by the protein.

For those who do have a reaction to the venom, the most common response is inflammation that, after one to two days, can develop into a dark lesion surrounding the bite site. The blackening, or necrosis, of the skin is dead skin cells, evidence of the immune system's efforts to prevent spread of the toxin by stopping blood flow to the affected area.

"Our bodies are basically committing tissue suicide," explains biologist Greta Binford, a member of the research team. "That can be very minor to pretty major, like losing a big chunk of skin. The only treatment in that case is usually to have a skin graft done by a plastic surgeon."

About once every five years, someone develops a serious systemic reaction to a brown recluse bite, which can be fatal. "If it goes systemic, then it can cause destruction of blood cells and various other effects that can, in extreme cases, lead to death by kidney failure or renal failure," Cordes relates.

However, it is believed that the vast majority of brown recluse bites are so minor that they go unnoticed by those who were bitten. It is not known what determines the type or severity of reaction a person is likely to get when bitten by a brown recluse, "but what is known is that this protein is the main cause of it," states Cordes.

For the spider biologists and chemists, the work has just begun. "These spiders have been around with this toxin for over 120,000,000 years," Binford marvels. "I want to understand the full set of variation present in a single spider and across the entire genus and the activity of this compound.

"People think about the brown recluse with fear. When I think about a brown recluse or any other spider, I think about how a single spider can have 1,000 chemicals in its venom and there are about 44,000 species, so there are tens of millions of unique compounds in spider venom that we're in the process of discovering. We have a lot to learn about how these venom toxins work and potential for understanding new chemistry and developing new drugs or treatments."
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Title Annotation:Poisoning
Publication:USA Today (Magazine)
Geographic Code:1USA
Date:Oct 1, 2013
Words:606
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