The different pandemics
The pests of antiquity like the plague of Athens in 430 BC, the plague of Antonin in 165 AD and the plague of Cyprian in 251 AD were not really epidemics of plague stricto sensu, but diseases which clinical signs make we think about typhoid, smallpox or typhus.
The first pandemic, also called Justinian’s plague, was well described by Procope of Caesarea and remained on the European continent from 541 to 767.
The second pandemic, also known as the "Black Death", started in the steppes of Central Asia and spread troughout Europe from 1347. Around 75 million people perished, the half of the population. It was followed by numerous resurgences until 1828. (It returned to Lyon in 1628 and to Marseille in 1720).
The third pandemic began in 1894: it reached Paris in 1920 (plague of ragpickers) and it contiuues in Africa, Asia and several countries in South America. Between 1895 and 1930 it caused approximately 12 million deaths, mostly in India.
All three pandemics were caused by Yersinia pestis. It is a Gram-negative bacillus characterized by Yersin in Hong Kong in 1894 (at the beginning of the 3rd pandemic). It belongs to the Enterobacteriaceae family but is distinguished from other genera because it develops at lower temperatures (30 ° C instead of 37 ° C) and gives a visible culture only after 48 hours of incubation instead of 24 hours.
It is phylogenically derived from Y. Pseudotuberculosis which does not have the same pathogenic power.
Plague is an animal disease that affects rodents (rats, squirrels ...). Transmission occurs by the rat flea. Sometimes, this "wild" plague comes near the villages to give the "urban" plague in domestic rodents. When an imbalance occurs the rats die in excessive quantities and fleas bite the man for food : so, the first cases of human plague appear.
It may be noted that plague representations often show dead rats, the first signs of the disease (one can also refer to the novel by Albert Camus: the plague).
The plague presents 3 more common and distinct clinical forms
The "bubonic" plague: it is characterized by the presence of inflammatory lymph nodes most often on the inguinal-crural region. They are called "buboes". Death occurs in 60% of cases without treatment.
The "septicemic" plague is characterized by the passage of the bacteria in the blood. It is generally the result of the evolution of bubonic plague, but in some cases no buboes appears. The lethality is 100%. Death occurs within 24 to 48 hours and, in most cases, the patient dies before the diagnosis is made. The "pneumonic" plague follows the contamination, not by fleas but by pulmonary droplets contaminated by the bacilli. It is the only form that allows the passage from man to man without the intermediary of the flea. Death occurs very quickly and without treatment the lethality is greater than 95%.
The best treatment is streptomycin by injection. Out of 392 clinical strains of Y. Pestis from 17 countries, none showed resistance to any of the 8 antibiotics known to be active.
Several plague vaccines have already been developed, but they have serious side effects. Moreover, they don’t have effect on pneumonic plague, which is the most serious form of the disease.
A re-emerging disease
Plague has completely disappeared from Europe, but it still persists in some countries and has caused epidemics during the 20th century in Africa, Asia and America. It is found in Madagascar, Democratic Republic of Congo and Peru. Over the past 15 years, nearly 40,000 cases have been reported in 24 countries. In 2013, 783 human cases were registered worldwide, of which 126 deaths.
Plague is considered a re-emerging disease. The number of cases continues to increase. It reappeared in Algeria in 2003 and 2008. New epidemic outbreaks have also been described in Russia or the USA in Oregon and Colorado.
The strains of Y. Pestis are genetically studied closely because they evolve regularly. For example some molecular sequences are similar to sequences found in Mycobacterium leprae responsible for leprosy. Travels are fast and easy, population movements are often accompanied by lack of hygiene, ecological upheavals affect the fauna : these are some factors that can cause epidemics.
Plague and bioterrorism
In recent history, the temptations to use plague as a biological weapon were frequent: after the Second World War, the Japanese army dropped clay pots containing contaminated fleas in Chinese regions causing localized epidemics of Plague on at least 3 of them. It is known that during the Cold War, the United States and the USSR developed weapons based on aerosolized Y. Pestis.
Currently plague is still classified in group A of the CDC:
1- easily disseminated or transmitted from person to person;
2- large lethality that can be responsible for a significant health impact;
3- that may result in a major panic, disturbing social structures;
4- requires substantial preparation by the public authorities.
According to the WHO calculations, 50 kg of Y. Pestis culture aerosolized on a city of 5 million could make ill 150 000 people and cause the death of 36 000 of them. Depending on the wind, bacteria could be spread over a distance of 10 km.
However, the final mathematical calculations show that the risk of secondary contamination is negligible. Moreover, since the bacillus does not form spore, its survival in the environment is relatively limited. Therefore, to date, no aerosolization test of Y. Pestis has been fruitful.
In the case of a terrorist act, unfortunately, non-specific pneumopathies would appear which would quickly lead to death. Antibiotic preventive treatments for doxycycline are effective.
T Sandle. Could the "black death" become a re-emerging infectious disease ? J. Anc. Dis. Prev. Rem. 2013, 1, 3
LA Santana, SS Santos, JLD Gazineo, AP Gomes, PSB Miguel, M Geller, R Siqueira-Batista. Plague : a new old disease. J. Epidemiol. Public Health Rev. 2016, 1(4):doi http://dx.doi.org/10.16966/2471-8211.128
N Peiffer-Smadja, M Thomas. La peste, une maladie qui hante encore notre mémoire collective. Rev. Med. Interne, 2017, http://dx.doi.org/10.1016/j.revmed.2017.03.008