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)