Working on a plague shot

Recent cases of the plague in Oregon have raised concerns about the return of the Black Death.

The WHO has declared the disease re-emergent and researchers are working on a vaccine. Christian Demeure at the Pasteur Institute in Paris is one of them. He and his colleagues recently discovered a hopeful candidate.   

ResearchGate: Why do we still need a vaccine against the plague? How and how often do people get infected with the plague today?  

Christian Demeure: We still need a vaccine because, in countries where the plague exists, it kills more than 10% of the people who contract it in spite of existing treatments. This is mostly because patients start the treatment late, for instance when they can’t get to the hospital in time. Vaccination is the only way to lower mortality. Unfortunately, no plague vaccine is currently available.

Plague exists in many areas of the world, usually hosted by rodents and transmitted by fleas, and occasionally the disease spreads from animals to humans. The disease is considered re-emergent by the World Health Organization (WHO). Some human cases have been observed in recent years in countries where the disease had disappeared for decades like in Algeria, Lybia, Jordan, Zambia, Botswana, India, Saudi Arabia and Russia. From 1983-2003 the WHO recorded more than 38000 human cases in 25 countries.

RG: You’re working on a vaccine against the plague. How far are you?

Demeure: We have developed a strategy to vaccinate using a live, genetically modified bacterium, via the oral route. The strain we use is not Yersinia pestis, but its much less virulent ancestor Yersinia pseudotuberculosis. " We added a surface antigen from the original pathogen to teach the immune system to recognize the plague. With this vaccine, we want to provide protection (for the moment in mice) against both the bubonic and pneumonic forms of plague, even if they are caused by high doses of the pathogen. A single dose of vaccine is required, and protection is long-lasting. 

RG: There’ve been reports of an unusually high number of cases of the plague in Oregon. How dangerous is an outbreak like this?

Demeure: As observed in Oregon, human plague generally starts with a person contracting it through a flea bite from infected wild animals. The Oregon cases were detected and treated, but that’s not always the case. Left untreated, bubonic plague occasionally turns into the very contagious pneumonic form, which allows human-to-human transmission through the air. You can imagine the damage that a coughing pneumonic plague patient could cause in a crowded place. The disease would rapidly spread far from the original patient, transported by secondary patients, and eased by panic.

RG: How do you treat the plague?

Demeure: The plague agent Yersinia pestis is a bacterium and is susceptible to a series of antibiotics. The treatment is very efficient if started early enough. It is less easy to treat pneumonic plague, because this form of the disease evolves quickly and has a high mortality rate if it’s not treated almost immediately after contamination. Eliminating infected fleas is also an efficient way to control outbreaks at the source.

RG: Could the plague be used as a bio weapon and how dangerous would that be?

Demeure: The plague has been used as a bio weapon several times in history. In the 14th century, Mongols used the plague against the Genoese defending the Crimean city of Caffa. Some historians believe that this may have allowed the plague to enter Europe, which caused the famous Black Death of the Middle Ages. More recently, the Japanese army used the plague against the Chinese and their allies during World War II. The plague is considered a potential bioterrorist threat by governments and is listed as a Tier 1 agent in the United States.

RG: What could be done in that case?

Demeure: After September 11, many governments increased the means devoted to preparedness against bioterrorism, including the plague but also anthrax, tularemia, and more. Measures include the training of medical personnel and emergency services, as well as the development and stockpiling of vaccines and antibiotics.

The recent Ebola outbreak has highlighted the need for preparedness against highly fatal endemic diseases that are silent most of the time and then suddenly cause large outbreaks. Preparedness includes vaccine development, and we hope that the plague vaccine project will receive support before the next large plague outbreak.