Yersinia


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BACTERIA



Overview

  • Cause intestinal disease in animals and are important zoonoses
  • 10 species of which Y. pestis, Y. pseudotuberculosis and Y. enterocolitica are pathogenic to animals and humans; Y. pestis is the most pathogenic
  • Rodents provide a reservoir of Y. pestis, which is the cause of human plague; fleas transmit the infection to other animals and humans
  • Y. pseudotuberculosis and Y. enterocolitica reside in the intestine of domestic and wild animals and birds
  • Birds may cause mechanical transfer of the organisms

Characteristics

  • Enterobacteria, but grow more slowly and at lower temperatures than other enterobacteria
  • Gram negative, non-spore forming, facultative anaerobes - rods or colibacilli
  • Non-lactose fermentors
  • Facultative intracellular pathogens
  • Show bipolar staining in Giemsa-stained smears from animal tissue
  • Pathogenic strains identified by serotyping and biotyping

Pathogenesis

  • Y. enterocolitica and Y. pseudotuberculosis enter the intestinal mucosa via M cells of the Peyer's patches
  • Engulfed by macrphages in the mucosa
  • All three invasive species are facultative intracellular organisms and grow inside macrophages
  • Plasmid and chromosomal-encoded virulence factors required for survival and multiplication in macrophages
  • Survive in phagolysosomes and do not interfere with degranulation or lysosomal fusion
  • Resistant to macrophage killing mechanisms
  • Antiphagocytic proteins secreted by the organisms interfere with host neutrophils
  • Y. pestis is more invasive than the other species and also possesses and antiphagocytic capsule and a plasminogen activator which aids systemic spread; endotoxin also contributes to its pathogenicity
  • Transport within macrophages to mesenteric lymph nodes
  • Replication in lymph nodes and development of necrotic lesions, with neutrophil invasion
  • The bacteria destroy the macrophages causing septicaemia

Clinical infections

  • Yersinia pestis
    • Cause of bubonic plague in humans, transmitted via fleas from infected rats
    • Not a significant veterinary disease
    • Disease in rats and other rodents similar to the disease in humans
    • Bubonic form can lead to the pneumonic form, which is highly contagious and usually fatal
    • Humans and domestic and wild animals incidental hosts
    • Plague has rarely been reported in dogs, cats, camels, elephants, deer
    • Cats can acquire the disease from ingesting dead rodents, and show lymphadenopathy and abscesses
    • Fever, lethargy, swelling and abscessation of lymph nodes particularly in head and neck region
    • 50% mortality if not treated
    • Possesses 3 plasmids, 2 of which are unique to this species; these encode an endotoxin, and coagulase and fibrinolytic activity
  • Yersinia pseudotuberculosis
    • Less virulent than Y. pestis but closely related
    • Mainly infect animals
    • One plasmid, required for virulence
    • Sporadic cases of pseudotuberculosis in animals and man
    • Wild birds and rodents provide a reservoir of infection by harbouring the the pathogen in their intestinal tract
    • Sources include food and water contaminated by faeces
    • Pseudotuberculosis (caseous abscesses) in rodents, guinea pigs, cats, turkeys
    • Epidymo-orchitis in rams
    • Abortion in goats
    • Occasional infections in pigs, cattle, sheep
    • Multiplication in macrophages leads to granuloma formation
    • Granulomas occur in the gut wall and mesenteric lymph nodes
    • Occasional spread from the mesenteric lymph nodes to the liver and spleen
  • Yersinia enterocolitica
    • Pathogen of animals and humans
    • Found in intestinal tract and oral cavity of animals, eg. pigs, leading to infection of humans via contaminated carcasses
    • Enterocolitis in man which lasts 2-3 weeks or develops into a chronic form
    • Enteric disease in farmed deer
    • Ileitis, gastroenteritis, mesenteric adenitis
    • Pathogenicity related to a heat stable enterotoxin

Diagnosis

    • Yersinia species grow on blood agar and MacConkey agar at room temperature.
    • Y. pseudotuberculosis and Y. enerocolica are motile, unlike Y. pestis
    • Biochemical tests to identify particular species
    • Specific fluorescent antibody staining of lymph node aspirates to identify Y. pestis

Control

    • Control Y. pestis by controlling rodent population and flea control of cats
    • Control of other Yersinia species difficult due to their ubiquity

Treatment

    • Euthanase or isolate animals suspected of Y. pestis infection; Streptomycin, doxycycline, gentamicin or chloramphinol
    • Long-acting tetracyclines, trimethoprim-sulphonamides, aminoglycosides and chloramphicol effective against Y. pseudotuberculosis and Y. enterocolica