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| − | Salmonella spp. are gram-negative straight rods, usually flagellated, facultative anaerobes. | + | <big><center>[[Enterobacteriaceae|'''BACK TO ENTEROBACTERIACEAE''']]</center></big> |
| | + | <big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big> |
| | + | <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=== |
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| | *Important member of the enterobacteria | | *Important member of the enterobacteria |
| − | *Cause disease in humans and animals worldwide | + | *Cause disease in humans and animals |
| | + | *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
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| | *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 |
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| | ===Characteristics=== | | ===Characteristics=== |
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| − | *Gram negative bacilli
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| | *Facultative intracellular pathogens | | *Facultative intracellular pathogens |
| − | *Non-lactose fermentors, oxidase negative | + | *Non-lactose fermentor |
| | *Do not produce urease or indole from tryptophan | | *Do not produce urease or indole from tryptophan |
| − | *Utilise citrate as a carbon source | + | *Utlise citrate as a carbon source |
| − | *Reduce nitrates to nitrites
| + | *Usually produce hydrogen sulphide |
| − | *Grow on MacConkey
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| − | *Red colonies on brilliant green agar indicating alkalinity
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| − | *Ferment glucose to produce acid and gas
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| − | *Usually produce hydrogen sulphide - red colinies with black centre on XLD agar | |
| − | *Most motile with flagellae (H antigen)
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| − | *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
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| − | | |
| | | | |
| | ===Classification=== | | ===Classification=== |
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| | *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 Somatic, O antigen (lipopolysaccharide) by the Kauffmann-White scheme - determined by slide agglutination of the bacteria with specific antisera
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| − | *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)
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| − | *Most animal and human isolates in Groups B to E
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| | | | |
| | + | ===Pathogenesis=== |
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| − | ===Pathogenicity===
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| − | *Faecal-oral transmission
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| − | *Infection frequently transmitted from faeces of rodents and birds
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| − | *Young, immunocompromised animals particularly susceptible
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| − | *Comparitively large dose required for infection due to gastric acid, normal intestinal flora and local immunity
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| − | *Enterocolitis:
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| − | **Acute enteritis
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| − | **Bacteria adhere to intestinal epithelial cells in the ileum and colon, probably via fimbrae, O antigen and flagellar H antigen
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| − | **Multiply in and destroy epithelial cells
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| − | **Cytotoxin may cause epithelial cell damage by inhibiting protein synthesis and causing calcium escape from cells
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| − | **Enterotoxin may induce fluid secretion into intestinal lumen
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| − | **Degeneration of microvilli
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| − | *Systemic disease:
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| − | **Bacteria invade and replicate in host cells and resist phagocytosis and destruction by complement
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| − | **Bacteria internalised by intestinal epithelial cells by inducing ruffling of cell membranes and uptake into vesicles
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| − | **The organisms replicate within the vesicles and are released from the cells
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| − | **Stimulate immune response on reaching the lamina propria
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| − | **Acute inflammation, possibly with ulceration; prostaglandin and cytokine production by epithelial cells; enterotoxin production damaging mucosa
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| − | **Phagocytosis of bacteria by [[Neutrophils|neutrophils]] and macrophages
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| − | **Bacteria either destroyed by the phagocytic cells or survive and multiply in the cells to cause systemic disease
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| − | **Resistance to phagocytosis and destruction by complement allows spread within the body - bacteraemia and septicaemia
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| − | **LPS O antigens prevent damage to bacterial cell wall by complement
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| − | **LPS also causes endotoxaemia, and may contribute to local inflammatory response damaging intestinal cells to cause diarrhoea
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| − | **Endotoxic shock during septicaemic [[Salmonellosis|salmonellosis]] due to LPS
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| − | **Septicaemia may cause [[Bacterial skin infections - Pathology#Systemic bacterial infections|cyanosis of extremities]]
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| − | **Intracellular carriage if bacteria no completely removed
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| − | **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
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| − | **''Salmonellae'' are facultative intracellular organisms, allowing them to move from the gut in macrophages and cause a bacteraemia and lesions throughout the body
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| − | **Possession of Pathogenicity Islands associated with virulence
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| − | *Carriage:
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| − | **''Salmonellae'' can persist in the gut or gall bladder
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| − | **Excreted in faeces after clinical signs disappeared - active carriage
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| − | **Bacteria can survive intracellularly, avoiding the immune system and antimicrobials
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| − | **May have latent carriage and intermittent excretion in faeces
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| − | **Stresses e.g. transportation, illness, parturition, overcrowding promote excretion in carrier animals and may cause clinical signs to be shown
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| − | **Tortoises, terrapins, snakes and other reptiles ofter carry ''Salmonellae''
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| − | **Asymptomatic carriage allows faecal spread of infection
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| | | | |
| | ===Clinical infections=== | | ===Clinical infections=== |
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| − | *Zoonotic
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| − | *Most human infections contracted from animals, especially poulty and cattle
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| − | *Some serotypes are host-specific, some infect a wide range of species
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| − | *Healthy adult carnivores are resistant to [[Salmonellosis|salmonellosis]]
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| − | *Clinical outcome depends on number of bacteria ingested, virulence of serotype, susceptibility of host
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| − | *Young and debilitated animals susceptible
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| − | *''Salmonella'' serotypes:
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| − | **''S.'' Typhimurium infects many species; causes severe diarrhoea; non-invasive; causes of food poisoning in humans, e.g. from infected poultry
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| − | **''S. enteritidis'': non species-specific; losses in young birds; causes food poisoning in humans
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| − | **''S.'' Dublin: invasive serovar; infects cattle
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| − | **''S.'' Cholerae-Suis: primarily infects pigs; also causes severe human disease
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| − | **''S.'' Pullorum: infects poultry; egg-transmitted; causes bacillary white diarrhoea, known as pullorum disease
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| − | **''S.'' Gallinarum: infectes older birds; known as fowl typhoid
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| − | **''S.'' Abortis-ovis: infects sheep
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| − | **''S.'' Abortus-equi: infects horses outside of the UK
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| − | **''S.'' Typhi, ''S.'' Paratyphi: infect humans
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| − | **''S.'' Montevideo produces outbreaks from contaminated imported meat and bone meal
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| − | *Enteric [[Salmonellosis|salmonellosis]]:
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| − | **Enterocolitis occurs in most farm animal species affecting all ages
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| − | **[[:Category:Enteritis, Ulcerative|Ulcerative enteritis]]
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| − | **Fever, depression, anorexia, foul-smelling diarrhoea containing blood, mucus and epithelial casts
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| − | **Dehydration and weight loss
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| − | **Abortion
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| − | **Fatal within days in severely young animals
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| − | **Milder syndrome where endemic on farms, possibly due to acquired immunity
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| − | **Chronic enterocolitis can occur in surviving pigs, cattle, horses, causing intermittent fever, soft faeces and gradual weight loss
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| − | *Septicaemic [[Salmonellosis|salmonellosis]]:
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| − | **Most common in calves, neonatal foals, pigs under one month
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| − | **Sudden onset fever, depression, recumbency
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| − | **Die within 48 hours if not treated
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| − | **Persistent diarrhoea, meningitis, arthritis or pneumonia may occur in surviving animals
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| − | **Found in [[Infectious Arthritis#In Horses|arthritis of horses]]
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| − | **Can cause haemorrhagic disease by [[Platelet Abnormalities|secondary thrombocytopenic disease]]
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| − | **''S.'' Cholerae-Suis in pigs causes blue discoloration of ears and snout; co-infection with viruses causes severe clinical forms of disease
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| − | *Bovine [[Salmonellosis|salmonellosis]]:
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| − | **Syndrome of fever and diarrhoea (with dysentery), often fatal, in calves and adult cattle
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| − | **Abdominal pain in adult cattle due to necrotic bowel
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| − | **Recumbency and depression, with death after 7-10 days during severe infection - mortality up to 75% in untreated adult animals
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| − | **Antibiotic treatment reduces mortality to 10%
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| − | **Diarrhoea lasts for up to 2 weeks, and complete recovery may take months
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| − | **May cause abortion of pregnant cattle in absence of other signs
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| − | **Septicaemia in neonates; accute enteritis in older calves
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| − | **Calves are dull, lethargic, inappetent, pyrexic, with profuse, fowl-smelling diarrhoea
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| − | **Death in calves can occur after 2-3 days
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| − | **Diarrhoea in survivors may last 2 weeks
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| − | **Caused by infection with various ''Salmonella'' serotypes, e.g. ''S.'' Dublin and ''S.'' Typhimurium
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| − | **An important zoonosis and reportable
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| − | **Carrier animals important for spread
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| − | **''Salmonella'' Dublin:
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| − | ***Causes enterocolitis with blood-stained, foul-smelling diarrhoea containing mucus and epithelial cells
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| − | ***Can cause fatal septicaemia - fever, depression, drop in milk yield; calves may develope arthritis, meningitis, pneumonia
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| − | ***Abortion with no other clinical signs
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| − | ***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
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| − | ***Can cause [[Osteomyelitis|Osteomyelitis]] in young animals
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| − | ***Most survivors become subclinical excretors
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| − | ***May become latent carriers with no excretion
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| − | *<div id="Spleen">[[Salmonellosis|Salmonellosis]] in poultry:
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| − | **''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)
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| − | **These ''Salmonellae'' can infect the ovaries of hens and be transmitted via eggs
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| − | **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>
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| − | **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.
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| − | **Paratyphoid caused by non host-specific ''Salmonella'' serotypes, e.g. ''S.'' Enteritidis and ''S.'' Typhimurium; often subclinical infections
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| | ===Diagnosis=== | | ===Diagnosis=== |
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| − | *History of previous outbreaks; clinical signs
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| − | *Post mortem: enterocolitis; blood-stained intestinal contents; enlarged mesenteric lymph nodes
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| − | *Laboratory confirmation by detection in faeces and blood from live animals; intestinal contents and tissue samples from dead animals
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| − | *Isolation from blood or tissues confirms septicaemic salmonellosis
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| − | *Heavy growth on plates innoculated with faeces or intestinal contents from infected animals suggests ''Salmonella'' as cause
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| − | *Light growth may suggest carrier state
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| − | *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
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| − | *Suspicious colonies should be identified biochemically by reactions in TSI agar and lysine decarboxylase
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| − | *Slide agglutination using antisera for O and H antigens confirm the serotype
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| − | *The antigens in both phases of the H antigen must be identified
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| − | *Phage typing is used for epidemiological studies of isolates
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| − | *A rising antibody titre using paired serum samples in ELISA indicates active infection
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| | ===Treatment=== | | ===Treatment=== |
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| − | *Intravenous antibiotics used to treat septicaemic salmonellosis
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| − | *Effective antimicrobials include tetracyclines, chloramphenicol, trimethoprim-sulphonamides, ampicillin, amoxicillin, 3rd generation cephalosporins, fluoroquinolones, but depend on the susceptiblity of individual isolate
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| − | *Fluid and electrolyte replacent to prevent dehydration and shock
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| | ===Control=== | | ===Control=== |
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| − | *Reduce exposure of young animals from fomites, food, water, infected animals
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| − | *Avoid stresses e.g. overcrowding
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| − | *Purchase animals from reliable sources and isolate incoming animals
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| − | *Separate animals according to age
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| − | *Rodent control, good hygiene, pasture rotation
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| − | *Avoid grazing animals on pasture fertilised by slurry for at least 2 months after spreading
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| − | *Attenuated live ''S.'' Typhimurium and ''S.'' Dublin vaccines used in cattle
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| − | *Avoid oral prophylactic antimicrobials
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| − | ==In Reptiles==
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| − | 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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| − | [[Category:Lizard_and_Snake_Glossary]]
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| − | [[Category:Enterobacteriaceae]]
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| − | [[Category:Zoonoses]]
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| − | [[Category:To_Do_-_Bacteria]]
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