These US cases usually occur in rural northern New Mexico, northern Arizona, southern Colorado, California, southern Oregon, and far western Nevada.In November 2017, the Madagascar Ministry of Health reported an outbreak to the WHO (World Health Organization) with more cases and deaths than any recent outbreak in the country. Unusually, most of the cases were pneumonic rather than bubonic.In June 2018, a child was confirmed to be the first person in Idaho to be infected by bubonic plague in nearly 30 years.A couple died in May 2019, in Mongolia, while hunting marmots. Another two people in the province of Inner Mongolia, China were treated in November 2019 for the disease. In July 2020, in Bayannur, Inner Mongolia of China, a human case of bubonic plague was reported. Officials responded by activating a city-wide plague-prevention system for the remainder of the year. Also in July 2020, in Mongolia, a teenager died from bubonic plague after consuming infected marmot meat. History
Yersinia pestis has been discovered in archaeological finds from the Late Bronze Age (~3800 BP). The bacteria is identified by ancient DNA in human teeth from Asia and Europe dating from 2,800 to 5,000 years ago. First pandemic
The first recorded epidemic affected the Sasanian Empire and their arch-rivals, the Eastern Roman Empire (Byzantine Empire) and was named the Plague of Justinian after emperor Justinian I, who was infected but survived through extensive treatment. The pandemic resulted in the deaths of an estimated 25 million (6th century outbreak) to 50 million people (two centuries of recurrence).
The flea is parasitic on house and field rats and seeks out other prey when its rodent hosts die. Rats were an amplifying factor to bubonic plague due to their common association with humans as well as the nature of their blood. The rats blood allowed the rat to withstand a major concentration of the plague. The bacteria form aggregates in the gut of infected fleas and this results in the flea regurgitating ingested blood, which is now infected, into the bite site of a rodent or human host. Once established, bacteria rapidly spread to the lymph nodes and multiply. The fleas that transmit the disease only directly infect humans when the rat population in the area is wiped out from a mass infection. Furthermore, in areas of a large population of rats, the animals can harbor low levels of the plague infection without causing human outbreaks. With no new rat inputs being added to the population from other areas, the infection would only spread to humans in very rare cases of overcrowding. Signs and symptoms
After being transmitted via the bite of an infected flea, the Y. pestis bacteria become localized in an inflamed lymph node, where they begin to colonize and reproduce. Infected lymph nodes develop hemorrhages, which result in the death of tissue.Y. pestis bacilli can resist phagocytosis and even reproduce inside phagocytes and kill them. As the disease progresses, the lymph nodes can hemorrhage and become swollen and necrotic. Bubonic plague can progress to lethal septicemic plague in some cases.