The Plague and Leprosy

The Plague primarily affects rodents rather than humans.
Historical plagues are often biological accidents due to interactions involving:
- Bacterium - Yersinia pestis
- Rodent - Rattus rattus (black rat)
- Flea - A vector for the bacterium.

Type: Gram-negative, bipolar-staining bacillus.
Survivability: Quickly destroyed by direct sunlight; can survive in dried sputum for weeks or months.
Infective Dose: Only one (1) bacterium particle is sufficient to cause infection and death.

Fleas can jump 150 times their body length vertically or horizontally.
Acceleration during a jump is approximately 140 times that of gravity.
Fleas can survive for months without food or can endure freezing temperatures for up to one year, reviving afterwards.

Infected Rat: Terminally ill rats have a density of ~10^8 bacteria/ml in their blood.
Flea Feeding: Fleas ingest ~1,000 bacteria during feeding.
Bacterial Growth: The bacterium multiplies in the flea's digestive tract.
Transmission to New Host: When a flea jumps to a new rat host after the original rat dies, it regurgitates between 11,000 and 24,000 bacteria into the new host.
Survival of Fleas: The infected flea serves as a reservoir for The Plague across seasons.

Incubation Period: Ranges from 1 to 6 days with sudden high fever onset and body aches.
Symptoms: Formation of plague pustules at the flea bite site leading to swollen lymph nodes (called buboes).
Progression: Bacteria can spread beyond the lymph nodes into the bloodstream leading to widespread hemorrhage, rashes, and possible death within 3 to 5 days of symptom onset.
Mortality Rate: Ranges from 60% to 90% without treatment.

Transmission: Primarily via respiratory routes and poses the highest risk for human-to-human transmission.
Symptoms: Characterized by rapid onset of high fever, severe headaches, skin flushing; cough and pulmonary congestion follows shortly after.
Progression: Patients may cough up bloody sputum and experience severe respiratory distress.
Mortality Rate: Approaches 100% without treatment, typically leading to death within 3 days post-symptom onset.

Thought to have originated among burrowing rodents of Central Africa or Central Asia.
Earliest recorded outbreak potentially referenced as the Scourge of God striking the Philistines in the 12th Century B.C.
The Old Testament refers to it as “mice that mar the land”.

First Pandemic (541 A.D.): Affected the Mediterranean, lasting ~200 years, leading to approximately 40 million deaths.
Second Pandemic (1347-1352): Marked by mass deaths during ‘The Black Death’ where ~25 million Europeans perished.
Third Pandemic (1855): Originating in Yunnan Province, continued to affect regions globally, with significant epidemics manifesting in various countries.

The arrival of ships in Sicily with infected crews led to heightened global fear.
Early containment included quarantine measures and corpse collection.

Dr. Alexander Yersin identified the bacterium responsible during the Hong Kong epidemic.
Understanding of the disease transmission via fleas and rats created public stigma impacting government actions regarding outbreaks.

Considered highly contagious for many centuries; however, it now is understood that only a few individuals are highly infectious.
Historical context highlights leprosy as a major unmanageable infectious disease until recent decades.

Etiologic Agent: Mycobacterium leprae.
Transmission occurs via respiratory routes and skin contact; the bacterium thrives in cooler areas of the body and can live outside the body for ten days.

There are around 50 to 100 cases in the U.S. annually, usually in warmer climates like Florida.
Treatment involves three antimicrobial agents: Dapsone, Rifampicin, and Clofazimine, requiring a 3 to 5-year regimen.
Multidrug treatment programs have effectively reduced the prevalence of leprosy globally, though it remains significant.