By Drs. David Niesel and Norbert Herzog
While we are all aware of the Zika virus, scientists are only in the early stages of understanding how this virus actually causes disease. The real headline grabber has been the condition called microcephaly in some babies born to infected mothers. Zika is one of many tropical viruses spread by mosquitoes. While we focus on the consequences of infection by Zika, we tend to overlook the contributions of its essential accomplice, the mosquito. In addition to providing an efficient transportation system and effective injection system, mosquito saliva or "spit" helps the virus spread through the body. We also know that saliva contributes to the severity of this viral disease.
When you get bitten by a female mosquito, your blood is required to produce eggs. The mosquito's mouth parts penetrate the skin using a flexible tube that can be manipulated to reach a blood vessel. Think about this. Mosquitoes drink for an average of four minutes and they can suck so hard, scientists have actually observed the collapse of the blood vessels they are feeding from! As the mosquito probes the surface of your skin, it begins to salivate. In this saliva is a cocktail of substances that prevent blood vessel contraction and blood clotting that would inhibit the blood from flowing. Mosquito spit also contains substances that numb the pain of the bite and prevents irritation and inflammation at the bite site. This means you might not notice the bite until it is too late. Pretty sneaky! Overall, it is generally agreed that microbes delivered by mosquitoes are likely to cause serious disease.
Scientists using a milder disease causing relative of Zika virus have shown that infection triggers an accumulation of our white blood cells called neutrophils. These are our body's first responders to most infections. These first responders release substances that recruit other immune cells including macrophages. These cells help orchestrate the rest of how our body responds to these infections. But rather than cleaning up the infection, these macrophages become part of it. The virus infects these macrophages, which then helps to spread the infection throughout the body.
Here's the real interesting part. Without mosquito spit, much less virus was made or spread and in experimental models the infection was less lethal. So not only are itchy mosquito bites annoying, they help to make virus infections worse.
What is evident is that humans develop enough Zika virus in the blood to infect other uninfected mosquitoes that can spread the virus to other humans. Think of the Miami neighborhoods. The clever Zika virus has evolved to take advantage of both its mosquito and human hosts.
This will not be the last mosquito-borne virus that will affect humans. There are hundreds of others waiting in nature for the ideal circumstance to emerge and cause human misery. Our advice - use bug repellent or other strategies to avoid being bitten by a mosquito that could be carrying Zika or other disease causing microbes. If you are considering pregnancy, be sure to follow the CDC guidelines and talk to your physician about the precautions you should take.
Medical Discovery News is hosted by professors Norbert Herzog at Quinnipiac University, and David Niesel of the University of Texas Medical Branch. Learn more at www.medicaldiscoverynews.com.