Plague

Plague

Disease caused by Yersinia pestis.

Causative agent of plague

Yersinia pestis.

Gram stain of Y. pestis

Gram-negative.

Shape of Y. pestis

Coccobacillus.

Motility of Y. pestis

Non-motile.

Oxygen requirement of Y. pestis

Facultative anaerobe.

Does Y. pestis form spores?

No.

Main vector

Fleas.

Primary hosts

Humans and other mammals.

Most common natural infection

Bitten by infected flea.

Major virulence factors

Three plasmids.

Function of plasmids

Encode proteins that increase virulence and evade immunity.

Low Calcium Response (LCR) genes

Express Yersinia outer proteins (Yops).

Yops function

Block immune defenses.

Yop H

Inhibits phagocytosis.

Yop E

Disrupts host cell cytoskeleton.

Yop M

Interferes with immune response.

Plasmid encoding capsule

Plasmid 3.

Capsule function

Antiphagocytic.

Plasminogen activator (Pla)

Helps bacteria spread through tissues.

Murine toxin (Ymt)

Allows survival inside fleas.

First plague pandemic

Justinian Plague.

Justinian Plague began

541 AD.

Deaths in Justinian Plague

About 25 million.

Second plague pandemic

Black Death.

Black Death began

1334.

Black Death started

China.

Population killed in Europe

About 60%.

Third plague pandemic

Modern Plague.

Modern plague occurred

1860s–1900s.

Spread by

Ships.

Deaths during third pandemic

About 10 million.

Worldwide plague cases each year

1,000–2,000.

Most plague cases today

Sub-Saharan Africa and Madagascar.

US plague cases each year

About 7.

States with most US cases

New Mexico, Arizona, Colorado, California, Oregon, Nevada.

Last US urban plague epidemic

Los Angeles (1924–1925).

Main vector of plague

Flea.

Major rodent reservoirs

Rats, prairie dogs, squirrels.

How do humans become infected?

Flea bites, infected tissue, respiratory droplets.

Most common transmission

Flea bite.

Direct contact transmission

Handling infected animal tissue or fluids.

Only person-to-person transmission

Pneumonic plague by respiratory droplets.

What happens during plague epizootics?

Rodents die and infected fleas seek new hosts.

Dogs and cats can bring

Infected fleas into homes.

Proventriculus

Flea valve between esophagus and stomach.

Blocked flea consequence

Flea repeatedly feeds and regurgitates bacteria.

Blocked fleas eventually die

Starvation and dehydration.

Warm temperatures effect

Fewer blocked fleas develop.

Three major forms of plague

Bubonic, Septicemic, Pneumonic.

Average incubation period

2–6 days.

Primary site of infection

Lymph nodes.

Most common plague

Bubonic plague.

Percent of plague cases that are bubonic

About 80%.

Main transmission of bubonic

Flea bite.

Characteristic lesion

Bubo.

Bubo

Swollen, painful lymph node.

Size of bubo

Up to the size of a chicken egg.

Untreated mortality of bubonic plague

About 50%.

Complications of bubonic plague

Bacteremia, septic shock, multi-organ failure.

Disseminated intravascular coagulation (DIC)

Widespread blood clotting followed by bleeding.

Septicemic plague

Bacteria multiply directly in bloodstream.

Percent of cases that are septicemic

About 10%.

Most susceptible group

Children.

Symptoms of septicemic plague

High fever, chills, GI symptoms.

Cause of Black Death appearance

DIC causing black skin lesions.

Untreated mortality of septicemic plague

Nearly 100%.

Pneumonic plague

Plague infection of the lungs.

Percent of cases that are pneumonic

About 10%.

Transmission of pneumonic plague

Inhalation of infectious droplets.

Maximum droplet distance

About 4 feet.

Person-to-person transmission

Occurs only with pneumonic plague.

Most common cause of secondary pneumonic plague

Spread from untreated bubonic or septicemic plague.

Early pneumonic sputum

Little or no blood.

Late pneumonic sputum

Bloody with many bacteria.

Untreated pneumonic mortality

Nearly 100%.

Treatment must begin

Within 18–24 hours.

Symptoms of pneumonic plague

Dry cough, fever, bloody sputum, respiratory failure.

Why is plague a bioweapon concern

High mortality and aerosol spread.

Most likely bioterrorism form

Aerosolized pneumonic plague.

50 kg aerosol over city could cause

150,000 cases.

Estimated deaths in attack

About 36,000.

Viability of aerosolized plague

Up to 1 hour.

Distance aerosol can travel

Up to 10 km (6 miles).