Yersinia and Others - Detailed Notes on Yersinia Pestis and Related Species

Yersinia pestis: Plague

  • Introduction

    • Yersinia pestis is a small, gram-negative coccobacilli and a non-lactose fermenter.

  • Reservoir and Transmission

    • Rodents are the natural reservoir for Yersinia pestis.
    • Transmission occurs primarily through flea bites.
    • Over 200 mammalian species can carry the bacteria, including:
    • Squirrels
    • Rabbits
    • Prairie dogs
    • Cats
    • Disease may have originated in the Himalayas before spreading to China, India, the Middle East, and Europe.

  • Historical Pandemics

    • The plague has caused three major pandemics:
    • 541 - 544 AD: First recorded pandemic.
    • 1330 - 1480 AD: Second pandemic (Black Death).
      • Resulted in at least 25% of the European population dying.
    • 1855: Third pandemic.
    • Notable outbreaks in the 1990s occurred in:
    • Tanzania
    • Zaire
    • Peru
    • India
    • Madagascar
    • Fatality rates in recent outbreaks have been as high as 20%.

  • Symptoms and Disease Progression

    • Incubation period: 2-6 days post-flea bite.
    • Initial symptoms include:
    • Sudden onset headache
    • Malaise
    • Myalgia (muscle pain)
    • Fever
    • Tender lymph nodes
    • An intense inflammatory response can lead to lymph node swelling, forming a "bubo" (bubonic plague).
    • Potential progression to:
    • Septicemia
    • Meningitis
    • Pneumonia
    • Pneumonic plague can spread via aerosols, leading to near-fatal outcomes without early diagnosis (nearly 100% fatal within 3 days).

  • Mortality Rates

    • If contracted through flea bite, mortality is high at:
    • 50 - 75% fatality rate, often within one week.
    • The term "Black Death" refers to necrotic lesions in peripheral blood vessels causing skin discoloration.

  • Recovery and Immunity

    • Survivors develop long-lasting immunity.
    • Available vaccines:
    • Three types exist but are ineffective against pneumonic plague.
    • Generally administered only to researchers or military in endemic areas.
    • Treatment options:
    • Streptomycin is the drug of choice.
    • Alternatives include tetracycline, gentamycin, or chloramphenicol.

Other Yersinia Species

Yersinia enterocolitica and Yersinia pseudotuberculosis

  • Cause gastroenteritis (yersiniosis) 24-48 hours post-ingestion.
  • Symptoms include:
    • Bloody diarrhea
    • Fever
    • Severe abdominal pain (may be misdiagnosed as appendicitis).
  • Associated with:
    • Undercooked pork
    • Non-pasteurized milk.
  • Bacteria can multiply at refrigerator temperatures and may contaminate transfused blood.

Klebsiella pneumoniae

  • Associated with multiple infections:
    • Pneumonia
    • Bacteremia
    • Meningitis
    • Wound infections and urinary tract infections (UTIs).

Serratia marcescens

  • Opportunistic infections, particularly in immunocompromised individuals:
    • UTIs
    • Respiratory infections.

Enterobacter Species

  • Associated mainly with wound infections.

Proteus mirabilis

  • Commonly linked to UTIs.

Enterobacter sakazakii

  • Linked to serious infections, particularly in premature infants:
    • Meningitis
    • Septicemia
    • Necrotizing enterocolitis.
  • Outbreaks in newborn nurseries associated with powdered milk formula as the bacteria can survive in dried milk for years.