Lecture 8: Yersinia pestis and plague

Yersinia pestis

• Gram-negative coccobacillus bacteria

• Agent of the plague

• Pathogen of humans, rodents, and arthropods (fleas)

What hosts are Yersinia pestis a pathogen of?

Humans, rodents, and arthropods (fleas)

Three main human forms of the plague

• Bubonic

• Septicemic

• Pneumonic plague.

Bubonic plague

hemorrhaging, inflamed lymph nodes → large bumps

• Spread via bites of infected fleas

Septicemic plague

Disseminated infection in bloodstream originating from infected lymph nodes

• Causes skin hemorrhages - “Black Death”

Pneumonic plague

Infection of the lungs, derived from bubonic and septic plagues

• Highly transmissible via aerosol and sputum

What was the deadliest pandemic in human history to date?

The Black Death (200 million people killed)

Does multi-drug resistance exist for Y. pestis strains?

Yes

Treatment for Plague

Antibiotics (must be given quickly)

• No vaccines available in the US

Yersinia pestis is a zoonotic pathogen. What does this mean?

An infectious disease can be transmitted from animals to humans

What are two ways that Y. pestis can be transmitted to humans?

1. Rodent bites → saliva with bacteria enters body

2. Flea bites → bacteria enters body

What animal is a reservoir for Y. pestis?

Rodents

How does transmission of the plague differ depending on the hosts?

• Direct contact is involved for transmission between fleas, rodents, and humans.

• Transmission between humans occurs by respiratory droplets.

Sylvatic (wild) Cycle of Plague

• Reservoir (foci) = wild rodents

• Vector = wild rodent flea

Urban (domestic) Cycle of Plague

• Reservoir = domestic (urban) black rat

• Vector = oriental rat flea

Human Cycle of Plague

Bubonic plague occurs when humans become infected through flea bites or contact with infected animals (sylvatic or urban reservoirs). It can further spread through respiratory droplets from infected individuals as pneumonic plague.

What system in Y.pestis enhances its ability to transmit to another host from fleas?

Biofilm formation in a flea’s gut blocks blood meal entry → makes fleas starve and want to bite more animals/ humans → transmission of bacteria

Typhus

A disease caused by infection with one or more rickettsial bacteria

• Killed Napoleon’s army