The Plague (insert screaming now) Vaughn and Tess February 4, 2008
4 Flavours of The Plague • Bubonic – Fever, buboes (very swollen, painful lymph nodes that can form abscesses), 50-60% mortality • *Pneumonic – coughing, sputum, crackling, dyspnea; near 100% mortality within 2-4 days • *Septicaemic – Fever, GI symptoms (vomitting, diarrhea, pain), purpura, petechiae in late stages; 75% mortality within a few days, quite rare • Meningeal – Fever, same as meningitis; Very rare *Can be primary or secondary plague infection
Clinical Signs of Bubonic Plague • Buboes – Painful, swollen lymph nodes (axillary, inguinal, femoral or cervical) - Can supparate. Bacteria migrate to lymph nodes, resist destruction by phagocytes and multiply rapidly leading to necrosis and hemorrhage
Disease course • Incubation of 1-7 days • Usually starts as bubonic plague, then bacteria spread via lymph nodes through blood (sepsis) • Patients die of pneumonic plague, or septicaemic plague (multi-organ failure) • Necrosis and petechiae characteristic of late stage disease.
Disease Source • Yersinia pestis – rod shaped, gram neg. bacteria • Most are killed by neutrophils, but a few are taken up by histiocytes which can not kill them. Re-synthesize their capsule resist phagocytosismultiply rapidly
Vectors • Main vector – Oriental Rat Flea (Xenopsylla cheopsis) • Stomach becomes blocked from abundance of bacteria. When the flea bites it’s next victim, the bacteria are regurgitated into the blood.
Reservoirs • Many wild rodents • Black rat (Rattus rattus) is the main culprit • Lives in close proximity to humans (homes) • “Rat-fall” is common omen of an epidemic • Domesticated rodents and pets
Transmission • Fleas live in nests of wild rodents • Disturbance (war, flood etc) cause wild rodents to migrate to urban areas. • Infected fleas jump from wild rodents to domesticated rodents, pets Humans • Direct infection from animals possible • Human-to-human transmission via respiratory droplet (pneumonic plague)
Diagnosis • Y. pestis is easily recovered from: blood (septicaemic plague), aspirates of bulboes (bubonic plague), sputum (pneumatic plague) and differentiated in the lab • Capsular fraction 1 antigen basis of serological tests • Note: Can be confused with Y. psuedotuberculosis in labs with little or no experience in dealing with it.
Management • Requires prompt antibiotic treatment. With pneumonic or septicemic plague, must be administered within 1 day of symptoms. • Treatment: Use 1 antibiotic; Streptomycin preferred; gentamicin and tetracycline group also effective • Course of treatment: at least 7-10 days • Resistance: Only 1 case of multi-drug resistance found in Madagascar. • When given early, reduces mortality to 5-14%
Prevention • Formol-killed vaccine once available for health care workers that conferred some immunity against bubonic plague, but not pneumonic plague • Mass immunization not in place • Not practical as immunity too slow to develop in the case of an outbreak • Promise in new vaccines that are under development
Y. pestis Epidemics • Recorded since biblical times, many epidemics throughout history • Examples: • 1st epidemic (Antiqua) – 541 AD; Mediterranean region, 50-60% of pop. • 2nd epidemic (Medievalis) – 1346-1351; 1/3 of the pop. of Europe died (20-30 million) • 3rd epidemic (Orientalis) – 1855-1890; started in China, spread through Asia; 10 million died in India alone
The Modern Day Situation • Roughly 2000 cases and 200 deaths per year (WHO) • Vast majority in Africa • About 13 cases a year in the US
Plague Control • Isolation of patients with pneumonic plague • Flea and rodent control • Start therapy if plague is suspected – can take too long to confirm.
Plague as a Weapon • Aerosolized bacteria Pneumonic plague • Takes 48-72 hours to confirm diagnosis • 50kg of Y. pestis could infect 150,000 and kill 36,000 in a city of 5 million in a worst-case scenario. • Bacteria would remain viable in an aerosol for 1 hour for a distance of 10 km.
Discussion • Would we be better off putting money toward vaccines or emergency response with regards to a bio-terrorist attack? Why?