Venezuelan equine encephalitis virus is a deadly disease for infected donkeys, horses, and zebras, and has a mortality rate that can reach 80 percent in affected animals. Symptoms include catastrophic and rapid brain swelling that has serious neurological effects. It can even cause sudden death. Infected humans experience similar symptoms. The VEEV virus was weaponized by both the United States and the Soviet Union, and as such has been classified as a category B pathogen – an agent that is in the second highest risk group when assessing dangers to national security and public safety.
VEEV is an RNA virus, which means that instead of DNA as genetic material, it has RNA. Many dangerous viruses that are serious threats to public health are also RNA viruses with similar weaknesses in their codes. Research into the development of therapeutics for such viruses like Zika and HIV may benefit greatly from this work.
"RNA viruses tend to cause acute infections," explained senior author of the study Jonathan Dinman, Professor and Chair of the UMD Department of Cell Biology and Molecular Genetics. "You either fight them off quickly, like the common cold, or they overwhelm you, like Ebola."
The researchers used a mechanism that enables RNA viruses to put a lot of genetic information into a bit of RNA; it’s called programmed ribosomal frameshifting (PRF) – animation seen below. PRF makes an infected cell read the same RNA sequence in two different phases, so a virus can thus create two different proteins rather than one from the same genetic information.
The researchers disrupted PRF by mutating the genetic code of VEEV and disrupted the mechanism that makes a second protein from one piece of RNA. Cells grown in culture did not show much change how fast the virus was produced. After testing the mutant virus in lab mice, they observed a significant increase in ability of infected mice to survive the disease.
"With some simple mutations, we compromised VEEV's ability to be a virulent virus," commented the lead author, Joe Kendra, a biological sciences graduate student at UMD. "This result shows that PRF might be a therapeutic target for other viruses. If we can confirm that the mutant virus confers immunity, opening the door to a vaccine, that will be very exciting."
Not only was there a higher survival rate in mice carrying mutant VEEV, less of the virus was seen accumulating in tissues of the brain. The researchers suggest mutant virus lacks a protein that enables it to cross the blood-brain barrier - a precursor to brain swelling.
"It's interesting that the virus uses PRF to survive, but we can also manipulate that mechanism to work against it," said study co-author Yousuf Khan, a Goldwater Scholar at UMD. "This is a new way to target viruses and make vaccines. It opens up a lot of new research questions."
According to Dinman, this data is especially interesting because as the threat of climate change looms, such viral threats may begin to reach areas further north.
"So many of these diseases are borne by mosquitoes. Chikungunya is now established in the Caribbean, and Zika has been found in two counties in Florida," said Dinman. "These viruses are on our doorstep. But these results give us hope. Developing a vaccine takes a long time, but with a concerted effort across government and academic labs, we have a good chance."
If you’d like to know more about diseases of equine encephalitis, watch the short video.
Sources: AAAS/Eurekalert via University of Maryland, NIAID, Journal of Virology