Yersinia pestis
Plague
Yersinia pestis is a Gram negative bacillus which causes plague. Plague is a sometimes severe disease which has caused great epidemics in the past. Rat fleas are one mode of transmission and play a significant role as a reservoir1.
Because of its great mortality, the plague was even used as a weapon of “bioterrorism” in the Middle Ages, a period in which the archers who besieged a castle sent over the ramparts arrows that they had previously dipped in bodies of people who died from the plague.
Favored by global warming
This disease is still current in different countries of the world. Thus, a large epidemic was documented in Madagascar in 2015. The epidemic in Madagascar was probably favored by global warming and the displacement of rodent vectors from the coastal regions to the capital Antananarivo, where several cases of bubonic plague2 were initially documented before person-to-person transmission by aerosols3 causing pulmonary forms.
Bubonic plague and pulmonary plague
The so-called bubonic form is characterized by an extremely swollen lymph node (bubo4) which struggles to contain the infection and which can follow by sepsis (circulation of the bacteria in the blood) and blood clotting disorders, for example. The pulmonary form (pneumonia caused by the plague bacillus) is more contagious and more severe.
Discovered by Alexandre Yersin
The plague bacillus was discovered during the investigation of an epidemic in Southeast Asia by Alexandre Yersin, a Swiss microbiologist. This discovery was helped by the fact that his team did not have, unlike Robert Koch’s team (Berlin), incubators generally used to cultivate bacteria at 37 ° C. It was Yersin’s luck since Yersinia pestis is grown at lower temperatures than most other Enterobacteriaceae.