Chapter 36 Plague and Other Bacterial Zoonotic Diseases




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CHAPTER 36
Plague and Other Bacterial Zoonotic Diseases


Many bacterial, rickettsial, and viral diseases are classified as zoonoses, because they are acquired by humans either directly or indirectly from animals. This chapter considers bacteria causing four zoonotic infections that are not discussed in other chapters. All four species, Brucella, Yersinia pestis, Francisella tularensis, and Pasteurella multocida, are Gram-negative bacilli that are primarily animal pathogens. The diseases they cause, brucellosis, plague, tularemia, and pasteurellosis, are now rare in humans and develop only after unique animal contact.

Brucella

I. BACTERIOLOGY


1. Coccobacilli resemble Haemophilus

2. Although long assigned to multiple species the three most common in humans (B. abortus, B. melitensis, B. suis) are now considered variants of Brucella abortus

3. Growth is slow, requiring at least 2 to 3 days of aerobic incubation

II. BRUCELLOSIS

A. EPIDEMIOLOGY


  1. Brucellosis, a chronic infection that persists for life in animals

  2. Causes abortion in cattle, goats, pigs

  3. Humans acquire brucellosis by occupational exposure or consumption of unpasteurized dairy products

  4. Occupational disease for veterinarians

  5. Unpasteurized dairy products and "health" foods are a risk

B. PATHOGENESIS


1. Brucella are facultative intracellular parasites of epithelial cells and professional phagocytes

2. Inhibits myeloperoxidase, lysosome fusion and apoptosis

3. Multiplies in endoplasmic reticulum vesicles

4. Animal placental erythritol stimulates growth

5. Human infection forms granulomas in the reticuloendothelial sites with release of bacteria into the blood

C. IMMUNITY


1. Macrophage killing requires Th 1-type responses

III. BRUCELLOSIS: CLINICAL ASPECTS

A. MANIFESTATIONS


  1. Brucellosis starts with malaise, chills, and fever 7 to 21 days after infection

  2. Pattern of periodic nocturnal fever (undulant fever) typically continues for weeks, months, or even 1 to 2 years

  3. Recurrent bacteremia comes from reticuloendothelial sites

  4. Night sweats and periodic fever continue without obvious organ focus

B. DIAGNOSIS


1. Blood culture is primary method

2. Serologic tests may be useful


C. TREATMENT AND PREVENTION


1. Doxycycline plus aminoglycoside is effective

2. Pasteurization of dairy products is primary prevention



Yersinia Pestis

I. BACTERIOLOGY


  1. Member of the Enterobacteriaceae and shares features of the other Yersinia pathogenic for humans (Y. pseudotuberculosis, Y. enterocolitica)

  2. Virulence plasmids, which code for a glycoprotein capsular antigen called F1 and enzymes with phospholipase, protease, fibrinolytic and plasminogen activating activity

  3. Yersinia outer membrane proteins (Yops), protein capsule, and enzymes are present

II. PLAGUE

A. EPIDEMIOLOGY


1. Y. pestis was the cause of the most virulent epidemic plague of recorded human history, the Black Death of the Middle Ages

2. Plague is a disease of rodents transmitted by the bite of rat fleas (Xenopsylla cheopis) that colonize them

3. Sylvatic transmission among wild rodents is primary reservoir

4. Rat migration to cities increases human risk

5. When infected rodents enter a city, circumstances for a cycle involving urban rats are created

6. Fleas regurgitate into bite wounds

7. The bite of the flea is the first event in the development of a case of bubonic plague

8. Some patients with bubonic plague develop a secondary pneumonia by bacteremic spread to the lungs causing pneumonic plague

9. Pneumonic plague is contagious

10. Nonepidemic disease is linked to direct animal contact

11. Most US cases are in arid western states

B. PATHOGENESIS


1. Of the more than 20 known virulence factors some are deployed primarily in the flea while others are produced only in the rodent or human victim

2. Y. pestis has regulatory systems which sense temperature, calcium, and surely other environmental triggers in order to turn the production of appropriate virulence factors on or off

3. Multiplication in flea foregut is aided by low temperature virulence factors

4. In a warm-blooded host F1 protein, Pla, Yops produced at 37oC

5. F1 is antiphagocytic

6. Yops destroy and disrupt host cells

7. Bubo progresses to bacteremia

8. LPS and other products produce shock


C. IMMUNITY


1. Anticapsular antibody may be protective

III. PLAGUE: CLINICAL ASPECTS

A. MANIFESTATIONS


  1. Onset is marked by fever and the painful bubo, usually in the groin or, less often, in the axilla

  2. Pneumonic plague begins with fever, malaise. Cough, production of sputum, dyspnea, and cyanosis develop in a few days

  3. Bubonic plague mortality is 50–75% in untreated cases

  4. Pneumonic plague is fatal if untreated

  5. Terminal cyanosis = Black Death

B. DIAGNOSIS


1. Immunofluorescent staining is rapid

2. Cultures grow on routine media


C. TREATMENT


1. Streptomycin or gentamicin primary treatment

D. PREVENTION


1. Avoid sick or dead wild rodents

2. Chemoprophylaxis with doxycycline or ciprofloxacin for respiratory exposure



Francisella

I. BACTERIOLOGY


1. Gram-negative coccobacilli have growth requirement for –SH compounds

II. TULAREMIA

A. EPIDEMIOLOGY


1. Infecting dose is low

2. Acquired by tick bites or directly from wild mammal

3. Distributed throughout Northern Hemisphere

B. PATHOGENESIS


1. Intracellular multiplication is key to virulence

2. Escapes phagosome to cytosol


C. IMMUNITY


1. Cell-mediated immunity is dominant

III. TULAREMIA: CLINICAL ASPECTS

A. MANIFESTATIONS


1. Ulceroglandular, oculoglandular, typhoidal, and pneumonic forms exist

2. Ulceroglandular has lowest mortality


B. DIAGNOSIS


1. Special media are needed for culture

2. Serodiagnosis is most common


C. TREATMENT AND PREVENTION


1. Aminoglycosides are effective

Pasteurella multocida

  1. P. multocida, one of many species of Pasteurella in the respiratory flora of animals Infections are treated with penicillin.

  2. Penicillin-sensitive, Gram-negative rods

  3. Most common cause of infected domestic animal bites or scratches


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