The rabies virus can cause a huge change in the behavior of its host, and now researchers from the University of Alaska Fairbanks say they understand more about how this devastating disease goes about its nefarious ways.
While we know that animals who get rabies become more aggressive, scientists have been unable to figure out specifically how the virus induces such behavior in its host. Lead researcher Karsten Hueffer notes in a statement that the "study provides, for the first time, a detailed molecular mechanism for how an infectious agent induces specific behaviors."
The World Health Organization shared that practically all rabies infections are passed to humans through dogs, with up to 59,000 deaths each year. Around 95 percent of deaths from the virus occur in continents like Africa or Asia, as they don't have the correct resources to help keep the virus away.
Heuffer notes that the rabies virus has only five genes, whilst dogs have 20,000. He says that even though the virus holds “very little information” and dogs have “sophisticated immune and central nervous systems,” the disease can change a dog’s behavior, causing it to attack others and allowing the virus to spread via saliva. The study is published in Scientific Reports.
Prior research showed that a molecule called a glycoprotein on the surface of the virus clings to certain muscle receptors and "hijacks" the muscle and nerve cells, whereby it eventually infects the brain.
Other studies have shown that various amino acids within the rabies glycoprotein are quite similar to amino acids in snake venom, which “has the ability to alter behavior in animals through inhibition of nicotinic acetylcholine receptors present in the central nervous system.”
"We knew that nicotinic acetylcholine receptors, which bind to the virus in muscles, are also found in the brain, and we presumed that virus could also bind to such receptors," Hueffer said. "If snake venom has a similar structure to parts of the virus, and inhibits these receptors, we thought maybe the virus could also inhibit these receptors in the brain. Furthermore, we thought that this interaction could influence behavior.”
Hueffer and co-author Dr Michael Harris set up an experiment to see if this was the case. As Harris explained, they found that "the viruses collect in the spaces between the brain cells during the early stages of infection. These spaces are where brain cells communicate. We thought that if viruses could bind to receptors in these spaces and change how brain cells normally communicate, the virus could change behavior of the infected animal."
The team then injected the brains of mice with a small amount of the rabies virus to see if a specific molecule on the surface induced the frenzied behavior.
"When we injected this small piece of the virus glycoprotein into the brain of mice, the mice started running around much more than mice that got a control injection," he said. "Such a behavior can be seen in rabies infected animals as well."
Rabies is currently rare in the US and can be prevented through a vaccination, however there isn’t a cure once signs of the disease begin to show.