Difference between revisions of "Yersinia"

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===Overview===
 
*Cause [[Intestine Pathogens - Pathology|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 - Anatomy & Physiology|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''
 

Latest revision as of 13:41, 12 May 2010