Mosquitoes are such dicks. Not content with just sucking your blood, these spindly flying syringes will also pump their saliva into your body as a way to stop your blood clotting and keep it flowing. It’s your body's reaction to the saliva, not the blood sucking, that causes the unbearable itchiness.
New research has found out how mosquito saliva produces an extremely “unexpected” and complex immune response in the body, hinting at why mosquito bites can remain itchy for days, if not weeks, at a time. Even more importantly, this discovery could explain how their saliva makes our bodies more at risk of mosquito-borne diseases such as yellow fever, Zika, and Dengue fever.
To simulate a human immune system, the researchers injected baby mice with human stem cells. They then let virus-less mosquitoes go to town on the mice, allowing them to suck blood and inject saliva to their hearts' content. Over the following week, the researchers took a number of blood and tissue samples from the mice to see how their immune systems responded.
As reported in the journal PLOS Neglected Tropical Diseases, the mice had an unusually long-lasting and complicated immune response to the mozzie saliva. Despite no infectious agent being administered, the immune response appeared to go into hyperdrive.
"We found that mosquito-delivered saliva induced a varied and complex immune response we were not anticipating," co-author Dr Silke Paust, assistant professor of pediatrics at Baylor and Texas Children's Hospital, said in a statement.
"For instance, both the immune cell responses and the cytokine levels were affected. We saw activation of T helper cells 1, which generally contribute to antiviral immunity, as well as activation of T helper cells 2, which have been linked to allergic responses."
If there is a virus or parasite present in the mosquito's saliva, the immune system is also busy responding to the saliva with a complex allergic response, giving an infectious agent more of a chance to get a foot in the door.
“The virus present in that mosquito’s saliva, it’s like a Trojan horse,” Jessica Manning, an infectious diseases physician, neatly explained to Popular Science. “Your body is distracted by the saliva [and] having an allergic reaction when really it should be having an antiviral reaction and fighting against the virus. Your body is unwittingly helping the virus establish infection because your immune system is sending in new waves of cells that this virus is able to infect.”
The researchers are going to pick apart the 100-plus proteins in mosquito saliva to see how and why it has this effect on the immune system. In turn, the research could also help scientists work out how to prevent the spread of these nasty mosquito-transmitted tropical diseases.