Microbiology 2: Yersinia pestis and Plague

Yersinia pestis Overview

• Non-motile, non-spore-forming, gram-negative bacillus exhibiting pleomorphism and bipolar staining.
• Part of the Enterobacteriaceae family, alongside other pathogenic Yersinia species like Y. pseudotuberculosis and Y. enterocolitica.
• Contains virulence plasmids that encode F1 antigen (a glycoprotein capsule) and various enzymes (phospholipase, protease, fibrinolytic activities).
• Has adhesins similar to other Yersinia invaders.

Pathogenesis and Disease Transmission

• Carried via the lymphatic system to regional lymph nodes, where Y. pestis multiplies within phagocytes.
• May spread hematogenously, leading to hemorrhagic lesions in multiple organs.
• Sylvatic plague occurs in wild rodent populations, while urban plague involves domestic rodents.

Disease Cycles

• Sylvatic Plague: No significant rodent mortality (enzootic phase); high mortality and expansion into human areas (epizootic phase).
• Urban Plague: Infected fleas/rodents invade urban settings, resulting in high mortality and disease spread among domestic animals and humans, linked to poverty.

Modes of Transmission

• Transmission through flea bites, contact with infected animal tissues or fluids, and aerosol.
• Human outbreaks predominantly occur from April to November due to flea and host activity.

Flea Vectors

• Fleas can survive off hosts for extended periods; Oropsylla montana is a key vector in the U.S.
• Xenopsylla cheopis is notable for causing epidemics in Asia, Africa, and South America.

Clinical Presentation

• Onset includes fever and painful bubo, commonly found in the groin or axilla.
• Without treatment, serious outcomes include bacteremia leading to septic shock or pneumonic plague, with mortality rates as high as 75%.
• Pneumonic plague also presents rapidly and requires immediate antibiotic intervention.

Laboratory Diagnosis

• Recognized via gram-stained smear of bubo aspirates, typically showing bipolar-staining gram-negative bacilli.
• Culturing on blood agar or MacConkey agar; specimen collection includes bubo aspirate, blood, and sputum.
• Notification of suspicion is critical for prompt diagnosis and hazard prevention.

Treatment

• First-line treatments include gentamicin or streptomycin, often combined with doxycycline for both bubonic and pneumonic plague.
• Alternatives include ciprofloxacin or chloramphenicol when meningitis is present, with timely treatment reducing mortally rates significantly.

Prevention and Control

• Urban plague prevention via rat control and public health measures; difficult to eliminate sylvatic plague due to extensive rodent reservoirs.
• Recommendations include avoiding contact with sick or dead rodents and treating pets for fleas to minimize infection spread.
• Chemoprophylaxis with doxycycline or ciprofloxacin is advised for close contacts of infected individuals.
• The previous formalin-killed plague vaccine for high-risk populations is no longer available, making awareness and proactive measures essential.

This quiz covers the microbiological properties of Yersinia pestis, including its cultural techniques, epidemiology, and pathophysiology. It also addresses clinical presentations, specimen collection for culture, treatment options, and prevention strategies related to this pathogen. Perfect for students in Basic Medical Sciences focusing on the Blood and Lymphatic System.