Mutant Y. pestis May Hold the Key to Potential Vaccine for Plague

The bacteria Yersinia pestis is responsible for bubonic, septicemic, and pneumonic plague. Without prompt treatment, infections are 100% fatal. Humans can become infected by handling an infected animal or by being bitten by fleas carrying the bacteria. It is responsible for killing millions of people in Europe during the Middle Ages but, human plague infections still occur today.

The World Health Organization (WHO) has classified Y. pestis as a re-emerging pathogen because of an increase in human infections globally. The Centers for Disease Control and Prevention (CDC) has classified Y. pestis as a tier-1 select agent—materials that have been identified by the federal government as agents that can be used as bioweapons. Antibiotic resistant strains of the bacteria can be isolated from patients with plague and used in biological terrorism.

However, a potential vaccine may have been discovered by researchers from the University of Texas Medical Branch at Galveston (UTMB) that provides animals with long-term protection from the plague. In a press release from UTMB, Ashok Chopra, UTMB professor of microbiology and immunology said, “The optimal strategy for protecting people and animals against this deadly disease would be through vaccination, but there are no FDA-licensed plague vaccines available in the US. We've been working to develop a vaccine that will generate long-term immunity and protection against the plague."

Published in NPJ Vaccines, the researchers constructed new versions of the Y. pestis bacteria, by deleting and modifying certain genes. This “mutant bacteria” was designed to provide immunity from the plague without making the animals in the study ill. The researchers also tested the longevity of the immune response after vaccination and found the animals were protected for up to five months.

Chopra emphasized, “In addition to how well a vaccine works to protect against disease, safety is another important aspect for vaccine development. We have shown that our mutants (versions of the bacteria) are safe vaccine candidates as our detailed analyses showed no sign of damage to bodily tissues in the vaccinated animals.”

The study authors plan to request the CDC exclude their “mutants” from the select agent list in order to be able to safely produce and test the potential vaccines. Further research will continue to evaluate the safety and efficacy in non-human primates.