1. Yersinia Non lactose fermenting Gram negative rods
Motile (except Y. pestis)
10 species, only Y. pestis (plague), Y. enterocolitica, Y. pseudotuberculosis (enteric disease, septicaemia) pathogenic for animals and man
Demonstrate bipolar staining in Giemsa stained smears from animal tissues
Serotyping and biotyping used to discriminate between strains
10 serotypes of Y. pseudotuberculosis, serotypes I, II and III contain majority of pathogenic isolates
5 biotypes and more than 50 serotypes of Y. enterocolitica

2. Diagnosis Histological examination of intestinal lesions
Giemsa stained smears of pus reveal large numbers of bipolar rods
Culture of Y. enterocolitica and Y. pseudotuberculosis from faeces, pus or tissue
Plated on MacConkey agar for growth at 37 or room temperature
DFA tests (direct fluorescent
antibody)
API 20E
Cold enrichment
Serotyping

6. Yersinia species
Y. pseudotuberculosis and Y. enterocolitica in intestinal tract of wild mammals, birds and domestic animals
All may be reservoirs of infection
Many avian species may act as amplifier hosts and may transfer the organisms mechanically
Both organisms grow in a wide temperature range (5-42 degrees)
In endemic areas wild rodents are important reservoirs of Y. pestis. Fleas, especially the Oriental rat flea transmit the infection to man and other animals

7. Pathogenesis of enteric disease
Pathogenic enteric Yersinia invade some cells (M cells) and prevent uptake by other cells (phagocytes)
Virulence factors maintain survival and inhibit phagocytosis by PMN’s and macrophages
Enteric Yersinia infection (Y. enterocolitica and Y. pseudotuberculosis) gain access to intestinal mucosa via M cells of Peyers patches
Adhesion too and invasion of these cells facilitated by adhesion and invasion proteins which bind to receptors on host cells (invasin binds host integrins)
In GI mucosa, bacteria prevent phagocytosis, replicate in mesenteric lymph nodes with the development of necrotic lesions and neutrophil infiltration

8. Pathogenesis
Survival of Y. enterocolitica and Y. pseudotuberculosis is enhanced by anti-phagocytic proteins secreted by the organism (via a type III secretion system) which interfere with the normal functioning of neutrophils and macrophages in the host
Plasmid encodes the Yop virulon
This is a system allowing extracellular bacteria adhering on the surface of eukaryotic cells to secrete and inject bacterial effector proteins called Yops into the cytosol of the target cell in order to disable or alter their function

9. Plague!

10. Plague Caused by Yersinia pestis (3 biotypes)
Black death in 1300’s killed a quarter of Europe’s population
Zoonotic infection in rodents, transferred by fleas
Organism in blood of rodents, blood (+ organism) taken up by fleas and flea bites humans (or cats)
Humans infected by flea bites
Endemic in Africa, Asia, USA - southwest and pacific coast plague foci (and others) (prairie dogs, ground squirrels, antelope ground squirrels, chipmunks, wood rats and deer mice)
Potential bioterrorist weapon (pneumonic plague – person-person spread by airborne route)

11. Yersinia pestis

13. Clinical infection
Y. pestis can infect both dogs and cats in endemic areas
Cats are particularly susceptible, may be a source of infection for owners and attending vets
Usually acquired by ingesting infected rodents
Bubonic, septicaemic, pneumonic
Cats with pneumonic plague are a source of human infection through aerosol generation and should be euthanized
Human infection acquired through cat scratches and bites and fleas from infected cats
Care required when handling any infected animals!

14. Plague syndromes in man
Bubonic - fever painful lymphadenopathy – (bubo)
Septicaemic – fever, hypotension w/wo bubo
Pneumonic – cough, haemoptysis, w/wo bubo
Meningitis – fever, nuchal rigidity usually with bubo

15. Pneumonic
Bubonic
Septicaemic

16. Virulence factors specific to Y. pestis
phospholipase D required for survival in flea midgut.
HPI for iron acquisition (also Ye and Yp)
Fraction 1 (F1) antigen associated with capsule around the bacteria. F1 prevents opsonisation
Pla is essential for Y. pestis to disseminate from a subcutaneous site of inoculation to lymph nodes or the bloodstream.

17. Treatment and control Cats with suspected plague kept in isolation
IV tetracycline or chloramphenicol for bubonic plague
Endemic areas dogs, cats routinely treated for fleas
Rodent control
Effective human and animal based surveillance
Incidence in animal population
Avoid sick/dead animals
Avoid endemic areas or outbreak areas
Vaccination
Insect repellents
Isolate human cases (and contacts)
Treat human cases with antibiotics