Difference between revisions of "Salmonella"

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<big><center>[[Enterobacteriaceae|'''BACK TO ENTEROBACTERIACEAE''']]</center></big>
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Salmonella spp. are gram-negative straight rods, usually flagellated, facultative anaerobes.  
−
<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>
 
−
*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'''''
 
−
** Pigs
 
−
** Usually speticaemic.
 
−
** A cause of [[Intestines - Ulcerative Enteritis|ulcerative enteritis]] in the pig.
 
−
** Not very common now.
 
−
* '''''Salmonella montevideo '''''
 
−
** Produces outbreaks from contaminated imported meat and bone meal.
 
−
 
 
−
 
 
−
* [[Intestines - Fibrinous/ Haemorrhagic Enteritis#Salmonellosis|Salmonellosis]]
 
−
* * Can cause haemorrhagic disease by [[General Pathology - Haemostasis#Secondary Thrombocytopenic Disease|secondary thrombocytopenic disease]].
 
−
 
 
−
*''Salmonella'' in [[Bones - inflammatory#Osteomyelitis|Osteomyelitis]]
 
−
* In [[Joints - inflammatory#In Horses|arthritis of horses]]
 
  
 
===Overview===
 
===Overview===
  
 
*Important member of the enterobacteria
 
*Important member of the enterobacteria
−
*Cause disease in humans and animals  
+
*Cause disease in humans and animals worldwide
−
*Oral transmission
 
 
*Reservior of infection in poulty, pigs, rodents, cattle, dogs
 
*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)
 
*Cause enteritis and systemic infection (septicaemia and abortion)
 
*''Salmonella'' may be carried sub-clinically
 
*''Salmonella'' may be carried sub-clinically
 
*Some human strains cause enteric fever (''S. Typhi'' causes typhoid), also gastroenteritis, septicaemia or bacteraemia
 
*Some human strains cause enteric fever (''S. Typhi'' causes typhoid), also gastroenteritis, septicaemia or bacteraemia
 +
  
 
===Characteristics===
 
===Characteristics===
  
 +
*Gram negative bacilli
 
*Facultative intracellular pathogens
 
*Facultative intracellular pathogens
−
*Non-lactose fermentor
+
*Non-lactose fermentors, oxidase negative
 
*Do not produce urease or indole from tryptophan
 
*Do not produce urease or indole from tryptophan
−
*Utlise citrate as a carbon source
+
*Utilise citrate as a carbon source
−
*Usually produce hydrogen sulphide
+
*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)
 
*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
+
*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===
 
===Classification===
Line 47: Line 32:
 
*Single species, ''Salmonella enterica''
 
*Single species, ''Salmonella enterica''
 
*Over 2400 pathogenic serotypes or serovars identified
 
*Over 2400 pathogenic serotypes or serovars identified
−
*Grouped into 9 groups according to O antigen (lipopolysaccharide) by the Kauffmann-White scheme - determined by slide agglutination of the bacteria with specific antisera
+
*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  
+
*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 
  
−
===Pathogenesis===
 
  
 +
===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===
 
===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===
 
===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===
 
===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===
 
===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]]

Latest revision as of 15:45, 15 March 2015

Salmonella spp. are gram-negative straight rods, usually flagellated, facultative anaerobes.

Overview

  • Important member of the enterobacteria
  • Cause disease in humans and animals worldwide
  • 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


Characteristics

  • 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 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 due to LPS
    • Septicaemia may cause 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
  • 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:
    • Enterocolitis occurs in most farm animal species affecting all ages
    • 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:
    • 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 arthritis of horses
    • Can cause haemorrhagic disease by 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:
    • 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 in young animals
      • Most survivors become subclinical excretors
      • May become latent carriers with no excretion
  • 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
  • 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). 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).

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