Plague

Question 1

Where is Y. pestis (the plague) found?

Answer 1

All continents except Australia

Question 2

Why can the plague not be eradicated?

Answer 2

Because it is widespread in wildlife rodent reservoirs

Question 3

Where is the plague endemic?

Answer 3

Madagascar

Question 4

How man cases in US, Canada and globally

Answer 4

US: 10-15 cases/year
Canada: none since 1939
Globally: 1500 cases/year since 1965

Question 5

How long does the plague take to infect someone?

Answer 5

Incubation: 2-6 days
Death: 2-4 days

Question 6

What are the symptoms?

Answer 6

1. Fevers, chills, headaches, muscle pain, weakness
2. painful swellings (buboes) of the lymph nodes in armpits, legs neck or groin
3. High fever, delirium, mental deterioration, large blackish pustules that burst, vomiting of blood, bleeding in lungs

Question 7

When was the first pandemic?

Answer 7

Plague of Justinian, started 541-542 AD, caused by Y. pestis
~ 50% of pop. died
Continued in clucles for 200 years and disappeared for ~800 years
- killed 100 million people by the end

Question 8

What are the 3 species of Yersinia?

Answer 8

Gram-, rods, facultative anaerobes
- Y. enterocolitica - causes yersiniosis - rare cause of diarrhea and abdominal pain
- Y. pseudotuberculosis - animal pathogen, causes tuberculosis-esque sympotoms in animals, enteritis in humans
Y. pestis - causes plague

Question 9

Who discovered Y. pestis?

Answer 9

Alexandre Yersin and Shibasaburo Kitasato in 1894

Question 10

Is Y. pestis an efficient colonizer of humans?

Answer 10

No, it is extremely virulent, causes death within 2-4 days by sepsis and overwhelming pneumonia

Question 11

When was the second pandemic?

Answer 11

“Black Death”, medieval apndemic caused by Y. pestis
Started in Asia and reached Europe in 1340
Reduced the global pop. from 450 million to 350 million
Killed 25 milion europeans, destroyed the feudal system (many jobs needed to be filled)

Question 12

When was the 3rd pandemic?

Answer 12

Started in China in 1850s and spread to all continents (active til 1959)

• 12 million deaths in China and Indea alone
• Reached sanfranscisco in 1900 - infected rats exchanged fleas with local wildlife (Y. pestis is now established in SW US)

Question 13

How is Y. pestis transmitted?

Answer 13

• Live in rodents, transmitted by fleas (bites)
• zoonotic pathogen
• Y. pestis causes “blocking” in the flea (Biofilm formation in proventriculus)
• Handling infected animals (sin contact, scratch, bite)
• inhalation from humans (pneumonic) or animals
• Ingested infected meat

Question 14

What is the infective dose?

Answer 14

~ 10 cells

Question 15

Where does Y. pestis survive and grow?

Answer 15

Initially it survives and grows in macrophages

• then is transported to lymph nodes causing major swelling
• Y. pestis continues to grow extracellularly

Question 16

When does host blood contains high [bacterial cells]?

Answer 16

At the terminal stage, this is essential for transmission as fleas take a blood meal

Question 17

What did Y. pestis evolve from? What is different about it?

Answer 17

Y. pseudotuberculosis within the last 20,000 years

• has new virulence plasmids
• does not survive well in animal intestines, but can infect flea and is hypervirulen in humans

Question 18

Virulence factors of Y. pestis include:

Answer 18

Type 3 secretion (intracellular pathogen)
Phospholipase (survival in flea)
LPS (septicemia)
Plasminogen activator -> clot buster (dissemination)
- CAN OVERCOME MANY IMMUNE DEFENSE MECHANISMS RESULTING IN MASSIVE GROWTH

Question 19

What is Bubonic plague?

Answer 19

• Transmitted by flea bites
• Can develop into the other types, 40-60% mortality if untreated
• Painfully swollen lymph nodes

Question 20

What is Septicemic plague?

Answer 20

• Presence of Y. pestis is systemic (in blood) an overwhelming and progressive bacteremia
• Can be transmitted to new host
• Gangrene and disseminated intravascular coagulation (no blood clots)
• 50-90% mortality if untreated

Question 21

What is Pneumonic plague?

Answer 21

• Most dangerous
• Transmission via aerosols directly into the lung, or spread from septicemic plague
• Short incubation
• Can be transmitted directly from person-person by coughing
• 95-100% mortality if untreated, but only treatable within 1st 24 hours

Question 22

Diagnosis, treatment and prevention

Answer 22

Rapid = essential
Endemic regions - stains, antigen tests
Isolation of pneumonic plague patients
Outbreaks - insecticides for fleas, treat humans with antibiotics, prophylaxis to exposed individuals

Question 23

What Bioterrorism potential is there?

Answer 23

Category A organism (easily disseminated/transmitted from person to person)

• potential for major public health impact
• easy to grow (2 days)

Question 24

Worst case scenario:

Answer 24

50kg Y. pestis over city of 5 million people (150,000 infected, 36,000 deaths)