7 - Plague

Question 1

which bacteria causes plague?

Answer 1

Yersinia pestis

• gram-negative
• facultative anaerobes

Question 2

what are the 2 habitats of yersinia pestis

Answer 2

1. gut of a flea ( ambient temp)

2. blood/tissues of mammalian host (body temp)

Question 3

which animals are the natural hosts for plague

Answer 3

rats and other rodents

Question 4

which animal is the natural host for plague

Answer 4

the rat flea - Xenopsylla cheopis

Question 5

why are fleas effective vectors

Answer 5

• insect immunity- antimicrobial peptides
• midgut digestive enzymes- pathogen must evade these
• frequency of feeding and defecation - pathogen must avoid being removed
• flea lifespan after infection- pathogen mustn’t kill vector (too quickly)

Question 6

transmission by the flea

Answer 6

• vectors become infected following a blood meal uptake, pathogen replicates
• Y.pestis is confined to the digestive tract and is transmitted by regurgitation
• y.pestis does not invade the midgut epithelium so is susceptible to elimination via faeces
• forms biofilm which fills lumen, impeding blood flow to midgut
• blocks the proventricular valve, enhancing regurgitative transmission

Question 7

what does Y.pestis persistence in the flea depend on?

Answer 7

1. forming muticellular aggregates too large to be passed in faeces
2. ability to form a biofilm and create blockage in the PV

Question 8

Y.pestis effect on humans

Answer 8

• induces lesions
• endothelial damage

+ necrosis= haemorrhaging

Question 9

3 major plague pandemics

Answer 9

1. 541 - the Justinianic plague
2. 1347 - the Black death
3. 1894 - modern plague

Question 10

541- the Justinianic plague

Answer 10

began in 541 AD and was followed by frequent outbreaks over the next two hundred years – estimated to have killed over 25 million people around the Mediterranean basin

Question 11

1347 Black Death

Answer 11

originated in China in 1334 and spread along great trade routes to Constantinople (now Istanbul) and then on to Europe – estimated to have killed 30-50% of the European population

Question 12

1894 - modern plague

Answer 12

began in China in the 1860s and appeared in Hong Kong by 1894. Over the next 20 years, it spread to port cities around the world – estimated to have caused approximately 10 million deaths

Question 13

plague + biological warfare

Answer 13

1. Widespread availability around the world
2. Capacity for mass production and aerosol dissemination
3. High fatality rate of pneumonic plague
4. Potential for rapid secondary spread
5. In 1970, WHO published a report that estimated the deliberate release of 50 kg of Yersinia pestis in an aerosolised form over a city of 5 million could result in pneumonic plague in up to 150,000 people and 36,000 deaths

Question 14

symptoms

Answer 14

• incubation: 2-4 days

- flu like symptoms

Question 15

what are the 3 different forms of plague

Answer 15

bubonic, septicemic, pneumonic

Question 16

Bubonic Plague

Answer 16

• initiated by flea bite
• bacteria enter body and spreads to lymphatic system
• lymph nodes become enlarged
• mortality rate (untreated) = 50-60%

Question 17

Septicaemic plague

Answer 17

• occurs when infection spreadsd to bloodstream
• results from flea bite or direct contact with infective materia;
• bloodstream infection, DIC
• mortality (untreated) = 100%

Question 18

Disseminated Intravascular Coagulation (DIC)

Answer 18

systemic activation of blood coagulation leads to gangrene of the extremities (Black Death) and multi-organ failure

Question 19

pneumonic plague

Answer 19

• caused by infection spreading to lungs
• acute pulmonary insufficiency, sepsis and toxic shock as a result of infection spreading to the lungs in advanced bubonic plague
• very rapid development
• 100% case fatality

Question 20

What are the three ways that the plague can be transmitted and which types of plague can be transmitted this way?

Answer 20

• Flea bites from an infected flea (bubonic and septicaemic)
• contact with contaminated fluid or tissue (bubonic and specticaemic)
• infectious droplets expelled when someone with pneumonic plague coughs (only pneumonic)

Question 21

How is the plague identified in a patient?

Answer 21

• Visualisation of bipolar-staining, ovoid, gram negative organisms
• PCR or antigen detection may be used when live organisms are unculturable

Question 22

How is the plague treated?

Answer 22

Immediate large doses of antibiotics along with supportive therapy such as hydration

Question 23

Where can specimens be obtained from in a patient with suspected plague?

Answer 23

• lymph nodes (buboes in bubonic plague)
• blood (if the patient is specticeamic)
• Sputum (in severe cases of pneumonic plague, but blood is usually culture positive at this time)
• bronchial/ tracheal washing (not ideal since other bacteria can mask the presence of Y. Pestis)

Question 24

What are some preventative measures used for the plague?

Answer 24

• avoidance of direct contact with infected fluids and tissues
• rodent control (particularly at airports and ports)
• precautions against flea bites and avoiding handling animal carcasses
• vaccination for people working directly with the pathogen

Question 25

What are the three main processes that lead to bacterial evolution?

Answer 25

Horizontal gene transfer (add), intra-genomic changes (stir) and gene deletions (reduce)

Question 26

Which bacteria did Y. pestis evolve from?

Answer 26

Y. pseudotuberculosis