Black Death
Originating in the 1300s, the Black Death or the plague was one of the most devastating global epidemics ever. According to historical records, the plague struck in China, India, Persia, Syria, and Egypt around 1340 but there has been recent research citing that the Black Death may have existed in Europe around 3000 BC. It continued to wreak havoc across trade routes of the Near and Far East. Although there were rumors about how the plague spread, namely that the Mongols catapulted dead plague infected bodies on to European enemies, the most likely spread of the disease was through trading ships. The first set of ships that could have started the reign of Black Death in the 1300s arrived at Sicilians port of Messina in October 1347. The sailors on the ships were either dead or very ill with huge black boils that ooze pus and blood. Although authorities banned the ships for docking too long, the damage had been done. The people in the area were already infected and the Black Death would spread across Europe for the next five years killing twenty million people. Nowadays, the risk of developing the plague is very low. Only a few thousand people develop the plague every year and that is due to overcrowded residences, travel, poor sanitation, and high rodent populations. The greatest number of infections for the plague occur in Africa, Asia, and South America according to recent reports. In the United States, the plague is most commonly identified in rural and semi-rural areas such as New Mexico, Arizona, and Colorado.
The plague is an infectious disease that affects rodents, fleas, humans, and other animals. It is caused by a bacteria called Yersinia pestis, which was discovered by Alexandre Yersin at the end of the 19th century. Typically in the 1300s, the basic transmission cycle of the plague was that people became infected with the plague when a flea that bit a rodent infected with the Y. pestis ended up biting a human too. The plague bacteria could survive for a few days on the blood of the rodents and for an even longer period in fleas. People also became infected through direct contact with infected people, infected tissues or fluids, or inhalation of respiratory droplets of those affected. Due to the sheer abundance of rats and fleas aboard ships as well as lack of biological knowledge of the disease, the spread of the plague was imminent through port cities. Yersinia pestis is primarily a rodent pathogen, with humans being an accidental host when bitten by an infected rat flea. The flea draws viable Y. pestis organisms into its intestinal tract. These organisms multiply in the flea and block the flea's proventriculus.
The Y. pestis is regurgitated everytime a flea has a blood meal, meaning that it is transferring the disease to a new host. When Y. pestis is growing in the flea, it loses its capsular layer and either is killed or taken up by tissue macrophages. Being taken up by macrophages allows bacteria to have a protected environment to make virulence factors. These factors are released into the extracellular environment and resist phagocytosis. Y. pestis spreads to lymph nodes which become hot, tender, swollen, and gives rise to black buboes. Within hours of the initial flea bite, the infection makes its way into the bloodstream of the liver, spleen, and lungs or the patient has inhaled a large number of organisms during a coughing fit.
The plague is diagnosed through several methods by a health care worker such as matching of known symptoms, chest x-rays, samples of patient’s blood, sputum, or lymph node aspiration that all can be sent to a testing laboratory. Confirmation may take up to 48 hours. Although cases of the plague can occur during any season, most cases in the United States have been identified to be around late spring to early fall. Some symptoms of the plague include feeling weak, fever, chills, and headaches. Usually, a person is infected 1-6 days before they start showing symptoms, thus leading to one of the reasons that Black Death spread through Europe rather quickly. Other symptoms depend on the three kinds of plague. For the bubonic plague, a patient can have buboes, which are swollen and painful lymph nodes under the arms, in the groin, or in the neck. The bacteria can quickly spread to other parts of the body if not treated. For septicemic plague, which is more dangerous than bubonic plague and one would want this to be diagnosed early, some symptoms include bleeding under the skin or from the mouth or nose, blackened skin on the nose, fingers, or toes, diaherra, stomach pain, vomiting, and shock. For pneumonic plague, the bacteria is usually in the lungs and it is the rarest kind of the disease. It is very contagious as a result. Some symptoms include dry cough, coughing with blood, nausea, and vomiting.
There is no vaccine for the plague but there are developments of vaccines occuring in labs around the world. However, the plague is treatable through antibiotics. Once there is a positive diagnosis of the plague in a patient, the patient is hospitalized. If the patient has pneumonic plague, they are isolated in the hospital. Laboratory tests such as blood cultures for plague bacteria as well as microscopic examination of lymph nodes, blood, and sputum samples are done for the patient. After collection of these tests, the patient is prescribed antibiotics, preferably 24 hours from the occurrence of first symptoms. Antibiotics that are typically prescribed are streptomycin, gentamicin, doxycycline, or ciprofloxacin. If needed, oxygen, intravenous fluids, and respiratory support are provided. Without treatment, about 50% of plague patients will die but with treatment, the survival increases.
References:
https://www.atsu.edu/faculty/chamberlain/website/lectures/lecture/plague.htm
https://www.ncbi.nlm.nih.gov/pubmed/30940874
