By Sandy Hemphill, Contributing Writer, BabyMed
Summertime is mosquito time, pretty much wherever you are. A certain mosquito – the Aedes aegypti– has become infamous in recent months because it spreads the Zika virus associated with severe birth defects that can occur when a pregnant woman is exposed to the virus. The A. aegypti isn’t the only mosquito that bites, though, and Zika isn’t the only disease spread by mosquitoes. This mosquito has, however, generated a great deal of interest in the field of medical research.
One recent study of mosquitos and their bites indicates the itchier a mosquito bite is, the more likely it will lead to viral infection. Clive McKimmie, senior author of the study’s paper and research fellow at the University of Leeds in England, said, "Before we did this study, little was known about the events and processes that occur at mosquito bite sites."
Until this study, McKimmie said viruses were not thought to infect the cells of the immune system but that’s exactly what he and his research team discovered. He describes the discovery as “a big surprise we didn’t expect.”
The Battle Begins with the Bite
The researchers injected mice with the Semliki Forest virus, a virus similar to the chikungunya virus and spread by the same mosquito. Some of the mice were bitten by virus-free mosquitoes and the virus was manually injected at the site of the bite. Others were not bitten by mosquitos; the virus was injected into smooth, unblemished skin.
When any mosquito bites, it injects saliva into the person or animal it is biting. Any disease-causing virus the mosquito carries is transferred via the saliva from mosquito to victim. The mosquito saliva, with or without viral contamination, creates inflammation (redness, heat, swelling, pain, and itch) that sets off an immune-system alarm that calls white blood cells to the bite site. Typically, white blood cells attack and destroy foreign invaders such as a virus.
That isn’t what happened with mosquito bites, though. McKimmie and his researchers discovered that when the virus was injected into the mosquito bite, the virus fought back. It invaded the white blood cells and used them to produce even more virus cells that increased the chance of illness.
There was a minor immune-system response when the virus was injected into the clear skin of the mice not bitten by mosquitos. Only a few white blood cells appeared at the injection site but their number was too few to generate much replication of the virus. The risk for disease was very small compared to the risk created by the mosquito bite.
And the risk increased the more itchy the bite. The worse the inflammation, the more white blood cells were called in to stop it. The more white blood cells at the bite site, the more the virus could replicate and cause disease.
"We think the bite itself is affecting the systemic course and clinical outcome of the infection," McKimmie said. He suggests topical creams that minimize inflammation at the bite site may reduce the risk of viral infection but further research is needed to prove this theory.
Bite Prevention
Since the bite itself seems to be important in disease development, it seems bite prevention is the best way to avoid getting sick from mosquito-borne illnesses. A team of researchers from Minnesota tested various methods of protection and found repellants that contain DEET, IR3535, picardin, and PMD work best in most cases. IR3535 did not provide adequate protection against mosquitos that cause malaria so it should not be used in malaria-prone areas.
Other preventive measures include wearing protective clothing that covers as much of the skin as possible and using bed nets treated with insecticides when sleeping in open or outdoor areas. Clothing treated with insecticides are also recommended.
The Minnesota researchers found spatial repellants (area-wide products that include coils, candles, and such) may reduce the risk of getting bit but they don’t protect against disease if bitten.
Do What the Pros Do
Most people willingly avoid marshes and swampy areas where mosquitos thrive but there’s no avoiding these mosquito-rich environments if you are a mosquito researcher. Susan Brink, investigating for NPR, asked a number of mosquito researchers what they do to protect themselves when knowingly and willingly entering a mosquito-infested environment.
As with the Minnesota study, covering the skin from head to foot was important. DEET was the favorite chemical repellant but picardin was recommended, too, as was a particular perfume sold under the Victoria’s Secret label.
Sources:
McKimmie, Clive S, et al. "Host Inflammatory Response to Mosquito Bites Enhances the Severity of Arbovirus Infection."Immunity / Elsevier Inc. 44.6 (2016): 1455-69. Web. 30 June 2016.
Alpern, JD, et al. "Personal Protection Measures Against Mosquitoes, Ticks, and Other Arthropods."PubMed. Medical Clinics of North America / Elsevier, Inc., Mar. 2016. US National Library of Medicine / National Institutes of Health. Web. 30 June 2016.
Brink, Susan. "What's The Best Way To Keep Mosquitoes From Biting?"NPR / Goats and Soda. NPR, 30 Jan. 2016. Web. 30 June 2016.