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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