Difference between revisions of "Salmonella"

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Salmonella spp. are gram-negative straight rods, usually flagellated, facultative anaerobes.  
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<big><center>[[Enterobacteriaceae|'''BACK TO ENTEROBACTERIACEAE''']]</center></big>
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<big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big>
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<big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big>
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*Some serotypes tend to be more species specific, whereas others can affect a wide range of species. For example:
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* '''''Salmonella enteritidis'''''
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* '''''Salmonella typhimurium'''''
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** Widespread in most species.  
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* '''''Salmonella dublin'''''
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* Cattle
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* '''''Salmonella cholerae suis'''''
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** Pigs
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** Usually speticaemic.
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** A cause of [[Intestines - Ulcerative Enteritis|ulcerative enteritis]] in the pig.
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** Not very common now.
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* '''''Salmonella montevideo '''''
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** Produces outbreaks from contaminated imported meat and bone meal.  
  
===Overview===
 
  
*Important member of the enterobacteria
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* [[Intestines - Fibrinous/ Haemorrhagic Enteritis#Salmonellosis|Salmonellosis]]
*Cause disease in humans and animals worldwide
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* * Can cause haemorrhagic disease by [[General Pathology - Haemostasis#Secondary Thrombocytopenic Disease|secondary thrombocytopenic disease]].
*Reservior of infection in poulty, pigs, rodents, cattle, dogs
 
*Bacteria may be present in water, soil, animal feed, raw meat
 
*Cause enteritis and systemic infection (septicaemia and abortion)
 
*''Salmonella'' may be carried sub-clinically
 
*Some human strains cause enteric fever (''S. Typhi'' causes typhoid), also gastroenteritis, septicaemia or bacteraemia
 
  
 
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*''Salmonella'' in [[Bones - inflammatory#Osteomyelitis|Osteomyelitis]]
===Characteristics===
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* In [[Joints - inflammatory#Infectious arthritis|arthritis]] of horses
 
 
*Gram negative bacilli
 
*Facultative intracellular pathogens
 
*Non-lactose fermentors, oxidase negative
 
*Do not produce urease or indole from tryptophan
 
*Utilise citrate as a carbon source
 
*Reduce nitrates to nitrites
 
*Grow on MacConkey
 
*Red colonies on brilliant green agar indicating alkalinity
 
*Ferment glucose to produce acid and gas
 
*Usually produce hydrogen sulphide - red colinies with black centre on XLD agar
 
*Most motile with flagellae (H antigen)
 
*H antigen can be in phase 1 or phase 2, depending on a genetic switch allowing for one of the H antigen genes to be transcribed at any one time
 
 
 
 
 
===Classification===
 
 
 
*Single species, ''Salmonella enterica''
 
*Over 2400 pathogenic serotypes or serovars identified
 
*Grouped into 9 groups according to Somatic, O antigen (lipopolysaccharide) by the Kauffmann-White scheme - determined by slide agglutination of the bacteria with specific antisera
 
*Categorised into serovars depending on and H (Flagellar) antigen, e.g. ''Salmonella enterica'' subspecies ''enterica'' serovar Tymphimurium; must also determine phase of H antigen (isolates must be in phase 1 to be typed)
 
*Most animal and human isolates in Groups B to E 
 
 
 
 
 
===Pathogenicity===
 
 
 
*Faecal-oral transmission
 
*Infection frequently transmitted from faeces of rodents and birds
 
*Young, immunocompromised animals particularly susceptible
 
*Comparitively large dose required for infection due to gastric acid, normal intestinal flora and local immunity
 
*Enterocolitis:
 
**Acute enteritis
 
**Bacteria adhere to intestinal epithelial cells in the ileum and colon, probably via fimbrae, O antigen and flagellar H antigen
 
**Multiply in and destroy epithelial cells
 
**Cytotoxin may cause epithelial cell damage by inhibiting protein synthesis and causing calcium escape from cells
 
**Enterotoxin may induce fluid secretion into intestinal lumen
 
**Degeneration of microvilli
 
*Systemic disease:
 
**Bacteria invade and replicate in host cells and resist phagocytosis and destruction by complement
 
**Bacteria internalised by intestinal epithelial cells by inducing ruffling of cell membranes and uptake into vesicles
 
**The organisms replicate within the vesicles and are released from the cells
 
**Stimulate immune response on reaching the lamina propria
 
**Acute inflammation, possibly with ulceration; prostaglandin and cytokine production by epithelial cells; enterotoxin production damaging mucosa
 
**Phagocytosis of bacteria by [[Neutrophils|neutrophils]] and macrophages
 
**Bacteria either destroyed by the phagocytic cells or survive and multiply in the cells to cause systemic disease
 
**Resistance to phagocytosis and destruction by complement allows spread within the body - bacteraemia and septicaemia
 
**LPS O antigens prevent damage to bacterial cell wall by complement
 
**LPS also causes endotoxaemia, and may contribute to local inflammatory response damaging intestinal cells to cause diarrhoea
 
**Endotoxic shock during septicaemic [[Salmonellosis|salmonellosis]] due to LPS
 
**Septicaemia may cause [[Bacterial skin infections - Pathology#Systemic bacterial infections|cyanosis of extremities]]
 
**Intracellular carriage if bacteria no completely removed
 
**Invasive potential of certain strains e.g. ''Salmonella'' Dublin associated with carriage of a large plasmid, encoding genes to allow intracellular survival in macrophages and also to allow iron acquisition
 
**''Salmonellae'' are facultative intracellular organisms, allowing them to move from the gut in macrophages and cause a bacteraemia and lesions throughout the body
 
**Possession of Pathogenicity Islands associated with virulence
 
*Carriage:
 
**''Salmonellae'' can persist in the gut or gall bladder
 
**Excreted in faeces after clinical signs disappeared - active carriage
 
**Bacteria can survive intracellularly, avoiding the immune system and antimicrobials
 
**May have latent carriage and intermittent excretion in faeces
 
**Stresses e.g. transportation, illness, parturition, overcrowding promote excretion in carrier animals and may cause clinical signs to be shown
 
**Tortoises, terrapins, snakes and other reptiles ofter carry ''Salmonellae''
 
**Asymptomatic carriage allows faecal spread of infection
 
 
 
===Clinical infections===
 
 
 
*Zoonotic
 
*Most human infections contracted from animals, especially poulty and cattle
 
*Some serotypes are host-specific, some infect a wide range of species
 
*Healthy adult carnivores are resistant to [[Salmonellosis|salmonellosis]]
 
*Clinical outcome depends on number of bacteria ingested, virulence of serotype, susceptibility of host
 
*Young and debilitated animals susceptible
 
*''Salmonella'' serotypes:
 
**''S.'' Typhimurium infects many species; causes severe diarrhoea; non-invasive; causes of food poisoning in humans, e.g. from infected poultry
 
**''S. enteritidis'': non species-specific; losses in young birds; causes food poisoning in humans
 
**''S.'' Dublin: invasive serovar; infects cattle
 
**''S.'' Cholerae-Suis: primarily infects pigs; also causes severe human disease
 
**''S.'' Pullorum: infects poultry; egg-transmitted; causes bacillary white diarrhoea, known as pullorum disease
 
**''S.'' Gallinarum: infectes older birds; known as fowl typhoid
 
**''S.'' Abortis-ovis: infects sheep
 
**''S.'' Abortus-equi: infects horses outside of the UK
 
**''S.'' Typhi, ''S.'' Paratyphi: infect humans
 
**''S.'' Montevideo produces outbreaks from contaminated imported meat and bone meal
 
*Enteric [[Salmonellosis|salmonellosis]]:
 
**Enterocolitis occurs in most farm animal species affecting all ages
 
**[[:Category:Enteritis, Ulcerative|Ulcerative enteritis]]
 
**Fever, depression, anorexia, foul-smelling diarrhoea containing blood, mucus and epithelial casts
 
**Dehydration and weight loss
 
**Abortion
 
**Fatal within days in severely young animals
 
**Milder syndrome where endemic on farms, possibly due to acquired immunity
 
**Chronic enterocolitis can occur in surviving pigs, cattle, horses, causing intermittent fever, soft faeces and gradual weight loss
 
*Septicaemic [[Salmonellosis|salmonellosis]]:
 
**Most common in calves, neonatal foals, pigs under one month
 
**Sudden onset fever, depression, recumbency
 
**Die within 48 hours if not treated
 
**Persistent diarrhoea, meningitis, arthritis or pneumonia may occur in surviving animals
 
**Found in [[Infectious Arthritis#In Horses|arthritis of horses]]
 
**Can cause haemorrhagic disease by [[Platelet Abnormalities|secondary thrombocytopenic disease]]
 
**''S.'' Cholerae-Suis in pigs causes blue discoloration of ears and snout; co-infection with viruses causes severe clinical forms of disease
 
*Bovine [[Salmonellosis|salmonellosis]]:
 
**Syndrome of fever and diarrhoea (with dysentery), often fatal, in calves and adult cattle
 
**Abdominal pain in adult cattle due to necrotic bowel
 
**Recumbency and depression, with death after 7-10 days during severe infection - mortality up to 75% in untreated adult animals
 
**Antibiotic treatment reduces mortality to 10%
 
**Diarrhoea lasts for up to 2 weeks, and complete recovery may take months
 
**May cause abortion of pregnant cattle in absence of other signs
 
**Septicaemia in neonates; accute enteritis in older calves
 
**Calves are dull, lethargic, inappetent, pyrexic, with profuse, fowl-smelling diarrhoea
 
**Death in calves can occur after 2-3 days
 
**Diarrhoea in survivors may last 2 weeks
 
**Caused by infection with various ''Salmonella'' serotypes, e.g. ''S.'' Dublin and ''S.'' Typhimurium
 
**An important zoonosis and reportable
 
**Carrier animals important for spread
 
**''Salmonella'' Dublin:
 
***Causes enterocolitis with blood-stained, foul-smelling diarrhoea containing mucus and epithelial cells
 
***Can cause fatal septicaemia - fever, depression, drop in milk yield; calves may develope arthritis, meningitis, pneumonia
 
***Abortion with no other clinical signs
 
***Chronic infections with ''S.'' Dublin in calves cause dry gangrene of extremities due to disseminated intravascular coagulation; tips of ears, tail and limbs may slough
 
***Can cause [[Osteomyelitis|Osteomyelitis]] in young animals
 
***Most survivors become subclinical excretors
 
***May become latent carriers with no excretion
 
*<div id="Spleen">[[Salmonellosis|Salmonellosis]] in poultry:
 
**''S.'' Pullorum and ''S.'' Gallinarum now rare in UK due to eradication programs including the Pullorum test (whole blood slide agglutination to detect antibody to both ''S.'' Pullorum and ''S'' Gallinarum)
 
**These ''Salmonellae'' can infect the ovaries of hens and be transmitted via eggs
 
**Pullorum disease infects young chickens and turkeys (under 3 weeks); high mortality rates; anorexia, depression, white diarrhoea; white nodules throughout lungs; focal necrosis of liver and [[Spleen - Anatomy & Physiology|spleen]]</div>
 
**Fowl typhoid causes similar lesions to pullorum disease in young birds; septicaemic condition in adult birds with sudden death (enlarged, friable, bole-stained liver and enlarged [[Spleen - Anatomy & Physiology|spleen]]). On post mortem inspection bronzing of the organs is notable.
 
**Paratyphoid caused by non host-specific ''Salmonella'' serotypes, e.g. ''S.'' Enteritidis and ''S.'' Typhimurium; often subclinical infections
 
 
 
===Diagnosis===
 
 
 
*History of previous outbreaks; clinical signs
 
*Post mortem: enterocolitis; blood-stained intestinal contents; enlarged mesenteric lymph nodes
 
*Laboratory confirmation by detection in faeces and blood from live animals; intestinal contents and tissue samples from dead animals
 
*Isolation from blood or tissues confirms septicaemic salmonellosis
 
*Heavy growth on plates innoculated with faeces or intestinal contents from infected animals suggests ''Salmonella'' as cause
 
*Light growth may suggest carrier state
 
*Culture specimens on BG and XLD agar; also add to enrichment broth such as selinite or tetrathionate broth; incubate plates and broth under aerobic conditions at 37 degrees centigrade for 48 hours; subculture from enrichment broth at 24 and 48 hours
 
*Suspicious colonies should be identified biochemically by reactions in TSI agar and lysine decarboxylase
 
*Slide agglutination using antisera for O and H antigens confirm the serotype
 
*The antigens in both phases of the H antigen must be identified
 
*Phage typing is used for epidemiological studies of isolates
 
*A rising antibody titre using paired serum samples in ELISA indicates active infection
 
 
 
 
 
===Treatment===
 
 
 
*Intravenous antibiotics used to treat septicaemic salmonellosis
 
*Effective antimicrobials include tetracyclines, chloramphenicol, trimethoprim-sulphonamides, ampicillin, amoxicillin, 3rd generation cephalosporins, fluoroquinolones, but depend on the susceptiblity of individual isolate
 
*Fluid and electrolyte replacent to prevent dehydration and shock
 
 
 
 
 
===Control===
 
 
 
*Reduce exposure of young animals from fomites, food, water, infected animals
 
*Avoid stresses e.g. overcrowding
 
*Purchase animals from reliable sources and isolate incoming animals
 
*Separate animals according to age
 
*Rodent control, good hygiene, pasture rotation
 
*Avoid grazing animals on pasture fertilised by slurry for at least 2 months after spreading
 
*Attenuated live ''S.'' Typhimurium and ''S.'' Dublin vaccines used in cattle
 
*Avoid oral prophylactic antimicrobials
 
 
 
 
 
==In Reptiles==
 
 
 
It is estimated that between 36 and 77% lizards harbour Salmonella - the most recognized reptilian zoonosis. Owners must be educated regarding the public health hazard (especially for the very young, the old and the immune compromised).
 
 
 
[[Category:Lizard_and_Snake_Glossary]]
 
 
 
[[Category:Enterobacteriaceae]]
 
[[Category:Zoonoses]]
 
[[Category:To_Do_-_Bacteria]]
 

Revision as of 15:18, 5 October 2007

BACK TO ENTEROBACTERIACEAE
BACK TO BACTERIA
BACK TO INFECTIOUS AGENTS AND PARASITES
  • Some serotypes tend to be more species specific, whereas others can affect a wide range of species. For example:
  • Salmonella enteritidis
  • Salmonella typhimurium
    • Widespread in most species.
  • Salmonella dublin
  • Cattle
  • Salmonella cholerae suis
  • Salmonella montevideo
    • Produces outbreaks from contaminated imported meat and bone meal.