Even a Mosquito's Spit May Help Make You Sick

News Picture: Even a Mosquito's Spit May Help Make You Sick

MONDAY, May 21, 2018 (HealthDay News) -- When a pesky mosquito bites you, even its saliva triggers an immune response, new animal research suggests.

The study, conducted in mice, suggests the illnesses that come from mosquito bites -- diseases such as malaria, dengue fever or Zika, for example -- might be exacerbated by mosquito saliva.

The new research delivered the dengue fever virus to mice either via a needle or mosquito bites. The mice were genetically engineered to mimic at least some parts of the human immune system.

"When the mosquitoes delivered the virus, the mice had more of a rash, more fever and other characteristics that mimic the disease presentation in humans," said study lead researcher Rebecca Rico-Hesse, a professor of molecular virology and microbiology at Baylor College of Medicine in Houston.

The new study was funded by the U.S. National Institutes of Health. Rico-Hesse's team used a mouse model of the human immune system to examine the effects of just the saliva of mosquitoes on the immune system.

"Billions of people worldwide are exposed to diseases transmitted by mosquitoes, and many of these conditions do not have effective treatments," Rico-Hesse said in a university news release. "One of the interests of my lab is to study the development of dengue fever, which is caused by the dengue virus transmitted by mosquito Aedes aegypti."

The researchers noted, however, that studying dengue fever is challenging because the virus only causes disease in people. "No other animals can be used as models of the condition to develop preventive and therapeutic measures," Rico-Hesse said. "To overcome this challenge, we have been working with a mouse model of the human immune system."

The mice involved in the study were born without an immune system of their own. The animals were given human stem cells, enabling them to develop parts of the human immune system.

The Baylor team found that mosquito-bite delivery of the virus that causes dengue fever resulted in a more human-like disease than when the mice were injected with the virus using a needle.

The study concluded that mosquitoes are not acting like needles, delivering viruses. Instead, their saliva plays an active role in how the disease progresses.

Next, the team investigated how mosquito saliva could affect the immune system. They allowed a group of four mosquitoes to bite the footpads of anesthetized humanized mice. Blood and tissue samples were collected from the mice six hours, 24 hours and seven days later. The researchers compared these samples to those taken from mice not bitten by mosquitoes.

"We found that mosquito-delivered saliva induced a varied and complex immune response we were not anticipating," said study co-author Silke Paust, assistant professor of pediatrics at Baylor and Texas Children's Hospital.

Overall, the study showed that mosquito saliva alone can trigger prolonged immune responses up to seven days after a bite.

"The diversity of the immune response was most striking to me. This is surprising given that no actual infection with any type of infectious agent occurred," Paust said.

The study was published May 17 in PLOS Neglected Tropical Diseases.

-- Mary Elizabeth Dallas

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SOURCE: Baylor College of Medicine, news release, May 17, 2018