Bacteria 8 (gram -ve): Plague Flashcards
Which bacteria causes the plague?
- Yersinia pestis
- Potential for biowarfare
Which organism transmits the plague?
An important factor in transmission is hosts: once rodents in an area become hosts, transmission is much more likely
How many people are affected by the plague and how is it transmitted?
- Zoonotic infection in small mammals, rodents
- Transmitted by flea bite [xenopsylla cheopis]; also by eating raw meat of infected mammals/skinning hides, then can be person-to-person transmission: if pneumonic then respiratory droplet, airborne transmission, direct contact. There are some cases of plague being transmitted by human flea as well.
- 2017: About 3200 cases last year with almost 600 deaths
- Bubonic plague - not P2P
- Pneumonic plague - P2P
What is the life cycle of yersinia pestis?
Plague is often preceded by the death of rats in the area
Hosts:
Y. pestis bacteria are maintained in a complex cycle involving rodents and fleas.
Infected fleas tend to remain in burrows for prolonged periods. Hence, burrowing rodents, their predators and animals that share similar habitats as burrowing rodents will often have high rates of infection when compared to other species.
Spill-over from rodents to other species often results in outbreaks or epizootics.
Rabbits, carnivores, primates and birds are generally not involved in cycles, although they may occasionally aid in spreading infectious fleas or prey.
Transmission:
Transmission of bacteria usually occurs via a flea bite; blood-borne bacteria from the infected animal, remaining in the gastrointestinal tract of the flea, is transferred when the flea begins its blood meal from its next uninfected host.
Less commonly, a predator/scavenger can become infected upon ingestion of tissues of an infected animal. Sharp objects, such as bones, may puncture tissues of the mouth and throat, thereby enabling entry of the bacteria.
Rarely, infection occurs through inhalation of aerosolized bacteria.
What are the clinical features of plague?
- Two main clinical forms:
- Bubonic (swollen LNs)
- Penumonic
How do we diagnose the plague?
- Blood/sputum/bubo pus/lymph node – MC&S for gram-negative bacilli
- Rapid serological antigen tests now available for field use.
Why was the plague called the ‘black death’?
- In septicaemic plague, bacterial endotoxin causes DIC - creates tiny clots through the body, causing ischaemic necrosis (tissue death through lack of circulation/perfusion of tissue)
How do we treat plague patients?
- Antibiotics: Doxycyline / tetracycline / Cipro / Gent / Streptomycin
- Treat any contacts irrepective of clinical picture
What does a bubo look like?
- At an advanced stage, the inflamed lymph node can turn into an open pus-filled sore
Example preventive medicine question - You are working in Madagascar and are alerted to a suspected outbreak of plague. What steps would you take to confirm the outbreak, control the outbreak and manage suspected cases? (20 marks)
Tip: In the rush to answer these questions, try to use the correct vocabulary at least once to show that you know your stuff e.g. “Plague (Yersinia Pestis)…” and “transmission by flea (xenopsylla cheopis)…”.
Confirm outbreak of plague
- Establish outbreak – higher number of cases for a region then expected
- Clinical diagnosis – clinical features (e.g. buboes/RTI) + rapid antigen testing.
- Treat as plague until proven otherwise.
- Confirm diagnosis – reference lab testing i.e. MC&S of Yersinia pestis in pus/lymph/blood/sputum
- Case definition e.g. “buboes or cough/breathless person with suspected RTI”
- Alert local, national and international bodies inc. WHO of plague outbreak
- Recruit political support, funding +/- external/NGO support for outbreak mgmt.
Epidemiology
- Identify source of infection in area where human cases are – often areas with large number of small animal/rodent deaths.
- Expert destruction of flea population with insecticide/pyrethroid
- Expert destruction of mammal/rat population.
- Ongoing surveillance and reporting of new cases, establishing end of outbreak, etc.
Prevention
- Immediate public health campaign on outbreak with a advice on signs/symptoms, seek medical attention, hand hygiene, etc.
- Request cessation to public gatherings e.g. schools, markets, etc. to avoid person to person (P2P) transmission
- Safe burial of bodies.
Treatment
• Hospital preparedness:
o Ensure adequate supply of diagnostic kits, antibiotics (Doxycycline, Gentamycin, etc.), IV fluids, PPE, etc.
o Consider cancelling elective procedures
o Training of staff on infection control
• Triage of cases for inpatient/outpatient management o Manage bubonic cases as OP with PO Doxy and advice
o Manage pneumonic cases/septic cases on IP basis
- Prompt isolation with side/room masks + treatment (abx) of pneumonic cases
- Follow sepsis guidelines for management of septic cases
- Adjust antibiotics to sensitivities when available – empirical gram negative cover
- Prophylactic Doxycycline for 7/7 to householders of pneumonic/bubonic cases
- PPE with masks and barrier nursing for healthcare staff
- Prophylactic Doxy to workers in contact with pneumonic cases for duration of contact
After
• Post-outbreak analysis + information sharing
What are general principle in the management of a disease outbreak?
Disease outbreak management principles 2
Disease outbreak management principles 3
Who should be vaccinated against the plague?
