First Plague Pandemic: Justinian Plague
When was the second wave of plague
AD 1347-1722 (in Western Europe); the first two waves (1347-1353 and 1360-1361)= the Black Death
When was the Justinian Plague
AD 541-750
Three ways humans can get infected via enzootic/epizootic cycle
All three ways start with wild rats being infected by fleas carrying bacillus and bacillus becomes enzootic in wild rats. 1) When these wild rats die, the fleas can migrate temporarily to humans who can then get infected directly through a flea bite or a human flea can bite an infected wild rat and then bite a human but these are very rare. 2) when these infected wild rats come into contact with other wild animals, rat fleas can infect them and human fleas can bite these infected animals and then bite a human. 3) Infected wild rats can transmit disease to commensal rats making the bacillus epizootic. Human fleas can then bite the commensal rodents and then bite humans (primary mode of transmission)
. Pneumonic
Average incubation of 4 days. Once symptomatic, death occurs within 2-4 days. Case fatality rates close to 100%
Bacillus life cycle in fleas
Bacillus proliferates for two weeks before the fleas proventriculus becomes blocked, allowing it to pass the infection to a rat or human
Spread of Justinian Plague
Begins in Pelusium( eastern end of the Nile Delta). Spreads east to Persia, north into Europe. Arrives in Ireland, then England, then again in Ireland. Continues in waves every 6-20 years(918 waves over 2 centuries)
Septicemic
Death within a few hours, without any symptoms. Case fatality rates of 90-100%
When was the third wave of plague
Modern Pandemic; AD 1850-1918 (or 1930). Famous outbreaks in Hong Kong in 1894, in Hawaii and San Fran in 1899
How is Plague introduced into human populations
Pandemics are caused by humans carrying wild rats and infected fleas with bacilli over long distances. Once the fleas/rats enter a new area, they infect humans through a enzootic cycle or epizootic cycle. Epizootic is the primary form of transmission
Skeletal involvement
Plague kills too quickly to leave any skeletal lesions but can recover the DNA of Y. pestis from dental pulp
Plagues character as a zoonosis
Plague mainly affects rodents and is transmitted by fleas from rodents to other animals and to humans. It is a animal disease meaning the disease has to transmit from an animal to us
proximate cause of Justinian Plague
Proximate cause: dust veil of year 536 that covered the old world.
geographic distribution of modern plague
Started in China, spread to the Ancient Mediterranean, then Europe and then the new world
Initial impact of Justinian Plague
The Ancient Mediterranean(Constantinople, Jerusalem, Alexandria, Gaza)
Origin of Plague
Yersinia Pestis evolved from closely related Yersinia psuedotuberculosis in China within the past 20,000 years. It belongs to a family that includes e. coli and other enteric pathogens typically transmitted through contaminated food and water
Three manifestations in humans
bubonic, pneumonic, and Septicemic
Plague Pathogen
caused by the bacterium Yersinia Pestis. Zoonosis: endemic to rodent populations. Primary vector is the rat flea. Plague is incidental but often fatal
Epizootic
disease occurs in a general animal population. Not just wild rats, but all rats.
What does the Bacillus life cycle mostly take place in
fleas
Evidence of Plague
from silence: communication networks go dead, cities are abandoned. Historical texts and writings. Hearsay references to what might have been plague in mid 1st century AD: all report a disease with buboes. Range of documented cases
Bubonic
lesion at site of flea bite with tissue death. Drainage into lymph system creates buboes which occur in 80% of cases. Buboes are pathognomonic. Transmission occurs during warm periods. Incubation period of 2-5 days. Case fatality rates range from 60-70% in cases not treated by antibiotics
What does it mean that the bacillus is enzootic
the Bacillus is endemic (regularly found) in certain wild rodent populations that have developed tolerance; tarbagans, marmots, ground squirrels, and gerbils
Three modes of transmission
transmission via infected flies(bubonic), human to human transmission via inhaled aerosol droplets,(pneumonic) and blood to blood transmission via human flea or iatrogenic/lancing buboes(septicemic)