Lecture 5 Plague Flashcards
(27 cards)
Name the bacterium that causes the plague
Yersinia pestis
What bacteria shape is Yersinia pestis ?
Rod-shaped bacteria
What family does Yersinia pestis come from?
Enterobacteriaceae
Is Yersinia pestis a gram-positive or gram-negative bacteria ?
Gram-negative
Yesrsinia pestis is capable of surviving in both aerobic and anaerobic environments. What do you call bacteria that can do this?
Facultative anaerobes
What is there oriental rat flea called?
Xenopsylla cheopis
What are the 2 main habitats of Yersinia pestis ?
- The gut of a flea, at ambient temperature
- Blood or tissues of a mammalian host, at body temperature
Rats and other rodents are the natural hosts for plague. The host species varies in different parts of the world. What are the host species for plague in the flowing places :
- Mongolia
- Africa
- North America
- South America
- Mongolia - marmots
- Africa - gerbils
- North America - ground squirrels, chipmunks and prairie dogs
- South America - wild guinea pigs
What is the link between wild and domestic rodents?
Brown rat (Rattus norvegicus)
What rodent is usually the source of human infection and is very susceptible to plague?
The black rat (Rattus rattus)
What are the chief reservoirs for plague?
Wild and domestic rodents
What is the disease usually transmitted by and what is the most important vector?
- Transmitted by fleas
- the rat flea - Xenopsylla cheopis
What is the estimated number of flea species and subspecies ?
2,500
Approximately how many species of fleas have found to be infected with Y.pestis ?
80
How do vectors become infected with Y.pestis?
Become infected following uptake of an infected blood meal
Where is Y.pestis confined to in a flea and how is it transmitted ?
Y. pestis remains confined to the flea digestive tract and is transmitted by regurgitation
Why is Y.pestis potentially susceptible to elimination in flea faeces ?
Y.pestis does not adhere to, or invade, the midgut epithelium
What does Y.pestis persistence in flea depend on? (2)
- Formation of multicellular aggregates (too large to be passed out of faeces)
- Their ability to form a biofilm and which creates a blockage in the proventriculus - a valve that connects to he oesophagus and midgut
What happens as biofilm grows?
It fills the lumen and when the flea tries to feed it impedes blood flow into midgut
Blocking proventricular valve enhances regurgitative transmission of the bacterium
What produced by Yersinia causes most of the harm to humans and how does it do this? (3)
The toxins cause most of the harm
- cause endothelial damage and necrosis
- leading to vascular destruction and local haemorrhaging
- can also destroy macrophages and other phagocytes cells
Why is Yersinia pestis highly pathogenic in humans?
Pathogenicity results from the ability of Y.pestis to overcome host defences and multiply within the body -mainly extracellularly (multiplies outside cells)
What does infection with Y.pestis result in?
-Accumulation of neutrophils - early in infection Y.pestis may be killed by neutrophils
- however as Y.pestis is surrounded by the F1 capsule protein, phagocytosis by neutrophils is prevented
- later in infection Yp injects effector proteins (Yops) into neutrophils killing/disabling them
Macrophages role in Y.pestis infection?
They can phagocytose Y.pestis but cannot kill it
Why is the potential use of plague as a biological weapon of great concern ? (5)
- Widespread availability around the world
- Capacity for mass production and aerosol dissemination
- High fatality rate of pneumonic plague
- Potential for rapid secondary spread
- 1970 WHO published report estimated deliberate release of 50kg Y.pestis in aerosolised form over city of 5 million could result in pneumonic plague in up to 150,000 people
