Watch Out for Wasps: Insect Sting Causes Man's Stroke

People's reactions to getting stung by a bee or wasp can range from a feeling bit of pain to a suffering a deadly allergy reaction — and now a recent report of one man's case highlights a particularly rare complication of a sting: having a stroke.

The 44-year-old Ohio man was working at a construction site when he was stung by a wasp on his leg, according to the report. Initially, the man developed a rash and hives. But about an hour later, the man displayed several telltale signs of a stroke — difficulty speaking, paralysis on one side of his body and a facial "droop" — and was rushed to the hospital.

A stroke occurs when a part of a person's brain is starved of blood, typically because of a blood clot or a leaky blood vessel. [7 Things That May Raise Your Risk of Stroke]

Dr. Michael DeGeorgia, who treated the man, told Live Science that he had never before seen a case where a stroke was caused by a wasp sting. DeGeorgia is the director of the Neurocritical Care Center at University Hospitals Case Medical Center in Ohio.

There are several other reports, however, of patients who had strokes after being stung by a bee or a wasp, said DeGeorgia, who was the senior author of the case report, published in August in the Journal of Emergency Medicine. (Bees and wasps are both part of an category of insects called hymenopterans, which also includes ants and sawflies.) In most of the cases where a bee sting led to a stroke, however, the patients received multiple stings, the researchers wrote in their report.

There are several mechanisms through which a wasp sting could lead to a stroke, according to the report.

First, because wasp venom contains a number of compounds that cause a person's blood vessels to constrict, it's possible that a sting could cause blood vessels in the brain to constrict enough that a stroke occurs. In addition, some of the compounds in wasp venom are "prothrombotic," meaning they can cause blood to clot, which could also trigger a stroke, according to the report.

Wasp stings may also lead to a type of irregular heart beat called atrial fibrillation, according to the report. People with atrial fibrillation are at increased risk of stroke because the condition causes blood to pool in the heart. This makes clots more likely to form, which travel up to the brain and cause a stroke.

Finally, severe allergic reactions can cause a person's blood pressure to drop, according to the report. When a person has very low blood pressure, also called hypotension, not enough blood flows to the blood vessels in the brain and this can lead to a stroke, DeGeorgia said. To picture what's going on, DeGeorgia said, imagine a sprinkler in the front yard. If you turn off the water, the flow slows to a trickle and then nothing, he said. That's how low blood pressure causes a stroke, he said.

(High blood pressure also increases a person's risk for stroke, because it can cause a person's arteries to narrow and makes blood clots more likely, DeGeorgia added.)

In the man's case, the doctors believe that the first mechanism — the blood vessel-constricting compounds in the wasp venom — is what lead to his stroke.

When the doctors did brain scans on the man, they found that blood vessels in his brain were constricted, DeGeorgia said. They didn't find a blood clot, but that could be because the clot broke up before they were able to do the brain scans, he added.

It's possible that the man also had an irregular heart beat that could've contributing to the clotting, but the doctors didn't catch it, DeGeorgia said. Irregular heart beats can come and go, he said.

Still, it isn't clear why a single wasp sting caused the man's stroke, DeGeorgia said. It seems that in most cases, a person needs to get a lot of wasp venom for a stroke to occur, he said. The man may have just been especially sensitive to the venom, he said. [Here's a Giant List of the Strangest Medical Cases We've Covered]

And although there aren't any specific risk factors that would make a stroke more likely after a wasp sting, in people who already have risk factors for stroke, such as high blood pressure or high cholesterol, perhaps an insect sting could tip them over the edge, DeGeorgia said. In the man's case, however, he didn't have any of the obvious risk factors, he noted.  

Strokes aren't caused by just one thing, DeGeorgia told Live Science. "It's a confluence of things," he said. On a certain day, a person's blood may clot just a little more, and his or her arteries are just a little more narrowed, for example, he said.

The man was treated with the "standard stroke treatment," a drug called tissue plasminogen activator, or tPA, DeGeorgia said. The drug works by dissolving blood clots and improving blood flow.

The patient recovered and is doing well, DeGeorgia said. However, he now carries an EpiPen in case he gets stung again, he said. EpiPens deliver a dose of epinephrine to the body, which can raise a person's blood pressure if it drops too low.

Originally published on Live Science.