Difference between revisions of "Salmonellosis"

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* '''Stricture of the [[Rectum - Anatomy & Physiology|rectum]]'''.
 
* '''Stricture of the [[Rectum - Anatomy & Physiology|rectum]]'''.
 
** A possible sequel to acute salmonellosis, especially in the piglet.
 
** A possible sequel to acute salmonellosis, especially in the piglet.
** Just a few centimetres in from the [[[[Anus - Anatomy & Physiology|anus]] - Anatomy & Physiology|[[Anus - Anatomy & Physiology|anus]]]].
+
** Just a few centimetres in from the [[Anus - Anatomy & Physiology|anus]].
 
** Gives rise to:
 
** Gives rise to:
 
**# Difficulty in passing faeces.
 
**# Difficulty in passing faeces.

Revision as of 14:18, 7 June 2010

  • There are many different serotypes of Salmonella.
    • All can produce disease BUT only a few commonly produce illness in UK.
    • Salmonella poses a serious risk to man.
    • Some serotypes tend to be more species specific, whereas others can affect a wide range of species. For example:
    • Strains are often named after where they were first isolated.
    • Typing is important for epidemiology.
    • All strains can occur epizootically, enzootically and sporadically.
    • All strains can also produce very similar changes.
  • Salmonellosis is NOT very common in the dog and cat.
  • However, the horse is often a carrier.
    • Stress may precipitate the disease, meaning Salmonellosis is seen often in veterinary hospitals.

Pathogenesis

  • Disease is often seen associated with stress.
  • organisms penetrate enterocytes before crossing the mucosa and entering macrophages.
    • After entering macrophages, organins may then either remain localised to the gut, or are carried round the body to cause disease.
  • There are 2 main types of disease- septicaemic and enteric.
    • Each outbreak causes only one type of disease.
    • Type of disease is linked to serotype- some serotyopres produce septicaemia, whereas others remain localised in the gut.


Septicaemic Salmonellosis

  • Septicaemic salmonellosis is very dramatic and produces death quite suddenly.
  • diarrhoea is often not seen before death.
  • This form of the disease is unusual in the very young.
Pathogenesis
  • The organism colonises bowel epithelium, where it affects the Peyers patches.
    • It then invades macrophages, which enable it to invade across the epithelium to the submucosa. It may then either
      • Remain localised to submucosa, or
      • Spread to the lymph nodes and enter the circulation to become septicaemic.
  • Animals may die at this stage (30%), but this depends on such factors as the infecting dose and strain.
  • Is similar to septicaemic E. Coli.
Clinical
  • Is usually post-weaning (is unusual in the very young animal).
    • 6 to 9 months in calves.
    • 6 to 10 weeks in piglets.
  • Animals suffer from pyrexia, and occasionally a little bit of diarrhoea.
  • Skin is reddened diffusely
    • Bruise-like dark purplish-red blotched may be seen.
Pathology
  • Intestines
    • May show mild catarrhal enteritis, becoming fibrinous lower down.
    • The bowel is generally flaccid, reddened and filled with fluid.
    • Ecchymotic and petechial haemorrhages on serosa and mucosa.
    • Enlarged, haemorrhagic mesenteric lymph nodes.
  • Excessive blood-tinged peritoneal fluid.
  • Lungs are collapsed and frothy.
  • Heart is often dilated with ecchymotic haemorrhages.
  • Viscera have a "half-cooked appearance"
    • Pale in colour.
    • The liver and kidneys are also flabby and may have subcapsular haemorrhages.
    • The liver may contain small white foci of necrosis known as paratyphoid granulomas.
Diagnosis
  • By culture of blood and from mesenteric lymph nodes (which are oedematous and red).


Enteric Salmonellosis

  • Enteric Salmonellosis shows differences in clinical presentation between species.
    • Horse - acute fatal colitis.
    • Cows - lingering febrile diarrhoea with passage of pseudomembranes.
    • Calves - acute diarrhoea like colibacillosis.
    • Dogs - acute bouts of diarrhoea.
    • Cats - febrile enterocolitis.
    • Pigs - septicemia or enterocolitis.
Clinical
  • Affected animals produce acute diarrhoea, which causes many deaths.
    • Watery and yellow.
    • May be tinged with a little blood.
  • Animals may die from dehydration.
  • In some outbreaks, particularly in pigs, chronic low-grade diarrhoea only is seen.
  • Calves usually die in acute stage, but may also recover.
Pathology
  • Enteritis is seen throughout the gut, but is worse further along the gut.
    • Inflammation is catarrhal in the duodenum.
    • By the ileocaecal junction enteritis is often fibrinous, sometimes with formation of diptheric membranes on the mucosal surface.
  • The necrotic and fibrinous changes particularly affect the Peyers patches and the caecal and colonic lymphoid nodules.
    • May lead to "button ulcers" in the terminal ileum and colon.
      • These ulcers rupture very rarely.
  • Focal necrosis may also be seen.
    • Particularly in the liver, but also in the spleen.
    • Histologically, foci show a central zone of necrosis, surrounded by macrophages and lymphocytes- paratyphoid granulomas.
      • Although this indicates the animal has had a systemic incfection, paratyphoid granulomas may be present without showing signs of septicaemia.
      • Enteric cases of salmonella infection nearly always show some evidence of systemic spread.
  • Septicaemic form may relocalise in the gut, resulting in enteric disease.
Sequelae
  • Animals can remain carriers for months/years following recovery from the acute diarrhoea phase.
    • Bacteria is shed from the bile duct and mesenteric lymph nodes.
      • A source of infection for other animals and people.
      • Shed particularly in times of stress.
  • Stricture of the rectum.
    • A possible sequel to acute salmonellosis, especially in the piglet.
    • Just a few centimetres in from the anus.
    • Gives rise to:
      1. Difficulty in passing faeces.
      2. Megacolon
      3. thin watery diarrhoea in small 'pencils'.
      4. blown up abdomen
    • Animals eventually die from the stricture if they are not first destroyed.

Ulcerative Enteritis

        • Salmonella typically produces a broad spectrum of disease.
        • Classically may produce 'button' ulcers, especially in the terminal small intestine and upper large intestine (Ileocaecocolic junction).

Hepatitis

  • Salmonella dublin
  • calves
Clinical
Gross
  • severe, often haemorrhagic, inflammation in the ileum
  • paratyphoid nodules - pale foci of necrosis in the liver
Microscopically
  • foci of hepatocytic necrosis
  • mixed mononuclear inflammatory cell infiltrate

NB: small foci of hepatocytic necrosis are often found as incidental lesions at post mortem examination