Difference between revisions of "Salmonella"
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− | + | Salmonella spp. are gram-negative straight rods, usually flagellated, facultative anaerobes. | |
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===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 |
*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=== | ||
Line 36: | Line 16: | ||
*Gram negative bacilli | *Gram negative bacilli | ||
*Facultative intracellular pathogens | *Facultative intracellular pathogens | ||
− | *Non-lactose | + | *Non-lactose fermentors, oxidase negative |
*Do not produce urease or indole from tryptophan | *Do not produce urease or indole from tryptophan | ||
*Utilise citrate as a carbon source | *Utilise citrate as a carbon source | ||
*Reduce nitrates to nitrites | *Reduce nitrates to nitrites | ||
*Grow on MacConkey | *Grow on MacConkey | ||
+ | *Red colonies on brilliant green agar indicating alkalinity | ||
*Ferment glucose to produce acid and gas | *Ferment glucose to produce acid and gas | ||
− | *Usually produce hydrogen sulphide | + | *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 at any one time | *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 50: | 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 ( | + | *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 | *Comparitively large dose required for infection due to gastric acid, normal intestinal flora and local immunity | ||
*Enterocolitis: | *Enterocolitis: | ||
**Acute enteritis | **Acute enteritis | ||
− | **Bacteria | + | **Bacteria adhere to intestinal epithelial cells in the ileum and colon, probably via fimbrae, O antigen and flagellar H antigen |
− | **Cytotoxin may cause epithelial cell damage | + | **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 | **Enterotoxin may induce fluid secretion into intestinal lumen | ||
**Degeneration of microvilli | **Degeneration of microvilli | ||
*Systemic disease: | *Systemic disease: | ||
− | **Bacteria invade | + | **Bacteria invade and replicate in host cells and resist phagocytosis and destruction by complement |
− | **Bacteria internalised by intestinal epithelial cells | + | **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 | **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 | **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 | **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).