Clinical history and questions
Abattoir specimens from a couple of 40kg pigs, which had appeared clinically normal at pre-slaughter inspection. The animals came from an intensive 200-sow piggery near Mundubbera (on the Burnett River) in Queensland. The water supply was drawn from dams on the property.
- Describe the abnormalities
- What basic disease processes might be present?
- Pathological diagnosis (give other possibilities in order of preference)?
- Differential aetiological diagnoses, in order of preference?
- On the basis of you preferred diagnosis, what action and advice might be appropriate before laboratory diagnosis has been made?
An interpretation of Diagnostic Exercise No. 13 – Roger Kelly
The image is of the ventral two-thirds of one spleen and dorsal two-thirds of another with some portions of what is presumably omentum, some of which is adherent to the parietal surface of one spleen at one point. Both spleens have pale, spheroidal, fairly sharply demarcated nodules, up to about 20mm diameter, partially embedded in and protruding from the splenic parenchyma. Some nodules are incised to reveal opaque pale homogenous material surrounded by a dense fibrous capsule (inset).
Both chronic inflammation and neoplasia are possible, but the capsular adhesions and the apparently caseous centres to some of the nodules strongly suggest chronic inflammation.
chronic multifocal splenitis (multifocal splenic abscessation).
Randomly distributed multiple splenic abscesses implicate a systemic bacterial infection as cause. Systemic bacterial infections in swine include erysipelas; systemic streptococcal infections; haemophilosis (Glassers disease); salmonellosis; swine brucellosis; coliform septicaemias and septicaemic pasteurellosis. None of these infections are noted for producing subclinical splenic abscessation in this class of pig. Porcine melioidosis caused by infection by Burkholderia pseudomallei (formerlyPseudomonas pseudomallei) can produce abscesses in lung, thoracic lymph nodes and liver in pigs, often without causing clinical illness. It was diagnosed in this case by culture of the splenic foci.
The significance of the condition in these circumstances is the zoonotic potential of the infection, which means that affected carcases must be condemned for human consumption and appropriate disinfection has to be carried in the processing plant. The organism lives in soil and surface waters in certain areas of the world. The disease is recognised in wet tropical areas of Queensland and in other tropical areas of Northern Territory and South East Asia. Most of the cases occur in pigs raised in wet muddy conditions; however outbreaks can occur in intensive piggeries if drinking water is sourced from a creek that is contaminated with the bacterium. During the early 1980s the disease was diagnosed in the sub-tropical Central Burnett region in several intensive piggeries. All the affected piggeries pumped water from the Burnett River into dams to supply the animals. Accordingly, piggery owners using this water were advised to chlorinate it in an effort to prevent infection.
(reference: QDPIF note)
Thus it would have been appropriate to institute appropriate disinfection procedures in the abattoir before receipt of laboratory result in this case.
(NOTE: since this exercise was posted, it has emerged from QDPIF records that, of 14 cases of porcine splenic abscessation diagnoses in abattoir specimens since 2000, only one was due to B. pseudomallei; 2 to Arcanobacter pyogenes; the cause of one was unidentified, while 10 were due to Pasteurella multocida)
(NOTE: if any of you experienced a twinge of déjà vu on viewing the inset to this image, it might be explained by comparing it to Fig. 2.94 on p.238 of vol.3 of the 4th edn. of Jubb, Kennedy & Palmer, where the same specimen was mis-labeled as being from a goat. In the previous edition, the same image was labelled as being caseous lymphadenitis. Will it be correctly captioned in the next edition?)