Red Meat Pathology 1

What are the 6 most common lung conditions you will see in sheep upon PMI?

1) Enzootic pneumonia

2) Fibrinous pneumonia

3) Ovine pulmonary adenocarcinoma

4) Muellarius infection

5) Dictyocaulus infection

6) Abscesses

Describe the classic gross features of an enzootic pneumonia (suppurative pneumonia)…

• Cranioventral distibution; consolidated to those fields

• Usually bilateral

• Causes range from:

  • Mycoplasmas

  • Pasteurella multocida

Partial rejection (just the lungs)

Describe the classic gross features of a fibrinous pneumonia…

• Cranioventral distribution

• Pleura covered by fibrinous exudate

• Can be bilateral or unilateral

• Most common cause:

  • Mannheimia haemolytica

Partial rejection

Describe the classic gross features of an OPA…

• Large, consolidated pink areas of the lungs

• Usually in the center, firm and raised

Will also see abundant, frothy fluid in the trachea

Partial rejection

Describe the classic gross features of a muellarius infection…

A type of “verminous pneumonia”

• Multifocal “lead shot” lesions found on the dorsal aspects of the lungs

More chronic cases can have larger spots along the dorsal aspect of the lungs that seem to coalesce

• Can see worms and eggs in alveoli upon histology

Partial rejection

Really quickly review the life cycle of Muellerius capillaris…

Adults produce eggs in the lungs of sheep… eggs hatch in lungs

• Arrested development

Once L1, are shed in feces

Snail eats them; L1→ L3 in snail, temperature dependent development

• Faster in warmer temps

• May overwinter in snail

Once L3, leave snail and onto grass

L3 ingested by sheep, migrate from GI to lungs via mesenteric lymph nodes, thoracic duct, heart, and pulmonary arteries

Describe the classic gross features of a dictyocaulus infection…

Consolidation of the CAUDAL part of the lungs

Adults will live in bronchi, can be seen

Partial rejection

Really quickly review the life cycle of Dictyocaulus filaria…

Lamb eats L3 in pasture

L3 penetrate SI mucosa; L3 → L4 in mucosa

L4 travel to lungs via blood and lymph; penetrate capillaries and enter alveoli

L4 migrate to bronchioles

L4 → Adult in bronchi

Eggs hatch in lung and migrate up trachea

• Coughed up

• Swallowed

• Released in feces

L1 → L2 → L3 in grass

• Pilobilus fungi help to distribute to clean grass, which sheep then eats

Dictyocaulus filaria is the sheep one… D. viviparus is the cow one

Describe the classic gross features of an abscess…

Hard to miss

Often happen due to secondary opportunistic bacteria

• Trueperella pyogenes

• Staphylococcus aureus

Partial rejection if only lung abscess

What are 3 less common lung lesions you could see?

1) Hydatidosis

2) Caseous Lymphadenitis → TB

3) Maedi visna viral infection

Describe the classic gross features of hydatidosis…

Intermediate stage of Echinococcus granulosus

• Definitive host is dog; intermediate is sheep

Will see cysts usually in the lungs; may find them in the liver

• Focal lesion

• Fluid filled with a thick capsule

IS ZOONOTIC; check farmer and family

Partial rejection

Describe the classic gross features of caseous lymphadenitis…

Caused by inhalation of bacteria or bloodstream/lymphatic spread from an existing infection elsewhere in the body

• Usually caused by knicking when shearing with dirty equipment

• Corynebacterium pseudotuberculosis specifically

Need to check the rest of the carcass in this case for other infected lymph nodes

FULL REJECTION

Describe the classic gross features of the Maedi visna virus…

INTERSTITIAL PNEUMONIA

• Lung thick and rubbery, unable to deflate normally

• No exudate whatsoever

Partial rejection

What is a common lesion you may see in the sheep lungs / heart that ISN’T pathological, but instead is caused perimortem by improper electrical stunning technique?

Blood splashing

• Caused by the sudden blood pressure increase due to electrical stunning

  • Ecchymotic or petechial hemorrhages on the lungs, heart, and skeletal muscle

• If happening to lots of sheep, need to check stunning procedure; amperage may be too high (must be at least 1.0A to ensure proper stun)

HEART, MUSCLE, and BONES

What are 2 major cardiac lesions you could see upon PM in a sheep?

1) Pericarditis

Characterized by:

• Surrounding exudate around the pericardium

  • fibrous / constrictive mostly, signs of chronic pericarditis; acute (fibrinous) much less common to see in abattoir (see images)

2) Cysticercosis

• Cysticercus ovis COMES FROM dog tapeworm, Taenia ovis

  • Sheep are intermediate hosts… ingest infected dog feces, larvae migrate into muscle and heart and encyst there (C. ovis)

    • C. ovis is essentially the intermediate stage of Taenia ovis

• Found in SKELETAL MUSCLE, CARDIAC MUSCLE, and the DIAPHRAGM

  • So if you’re doing a PM and see cysts in the heart, need to check entire carcass… sheep may have generalized cysticercosis, and will need to be totally rejected

What is osteomyelitis, and how does it present in sheep in a PMI?

Is INFECTION of the bone… can happen anywhere in sheep (legs, vertebrae) but most commonly is seen in the jaw

Common pathogens:

• Trueperella pyogenes, 

• Fusobacterium necrophorum, 

• Staphylococcus aureus, 

• Streptococcus spp, 

• Pseudomonas aeruginosa

If infection is localized to the mandible alone, then can remove the jaw and use the rest of the carcass

• Unfortunately, because of this, sheep don’t eat very well in the first place… if body is also emaciated in addition to this, total rejection of the carcass

LIVER

Which 2 diseases account for 90% of the liver damage detected in sheep in the abattoir?

Fasciolosis

Cysticercosis

Describe fasciolosis… how does it present on the liver in the migratory phase? Mature phase? Chronic phase?

Fasciola hepatica can infect both lambs and adults

• Causes death in acute infections

• Emaciation in chronic infections

Migratory phase

• Damage looks traumatic / inflammatory

  • Multiple hemorrhagic tunnels

    • Burrowing metacercaria = hemorrhagic tracts

  • Fibrin or fibrous, hard tags on the surface of the liver that look like mineralization

• LESIONS CONCENTRATED TO LEFT LOBE

Mature phase

• Adult reaches bile duct; bile duct is swollen and visible on the liver, full of flukes that will be seen grossly

Chronic phase

• Will see more clinical signs:

  • Anemia, hypoproteinemia

  • Loss of metabolic process (emaciated)

  • Atrophy of left lobe, and hypertrophy of right lobe

  • Liver looks distorted and mottled

Partial rejection

Describe how cysticercosis affects the liver… which parasite is the one that targets the liver directly in its intermediate stage? What does the migratory phase look like?

Caused by the intermediate stage of Taenia hydatigena

Migratory stage

• Cysticerci migrate from liver to peritonium… gives you characteristic, serpentine-shaped tracts along the edges of the left lobe

  • Filled with fibrous material after healing; are thickened and pale, making them stand out

Will later develop a bladder cyst when it gets to the peritoneum… thin walled cyst, where you can see the scolex

• May have just one or multiple… if multiple, whole carcass is rejected

**** can arrest in development in the liver; tiny little cysts

Partial rejection if only a few cysts

What is one parasitic condition in sheep that can affect the BRAIN?

Coenurosis / Coenurus cerebralis

• AKA Gid

• AKA parasitic induced cerebral cysts

Is caused by the LARVAL form of the dog tapeworm, Taenia multiceps

• Enters the CNS hematogenously from SI tract (doesn’t target it, just gets there by mistake)

• Coenurus cerebralis = immature stage of Taenia multiceps

Clinical signs: neurologic

• Blindness, nystagmus, deviation of the head and eyes, ataxia, and collapse

What are some control measures you could take to minimize the incidence of Taenia spp. infections in sheep?

• don`t feed farm dogs with uncooked meat /raw diet

• remove carcasses of dead sheep as soon as possible 

• dispose of sheep carcasses as ABP category 2

• regular dosing of dogs with anthelmintic (praziquantel)

  • at least every three months

• farmer to put notes in public footpaths running through sheep fields explaining the disease risks and encouraging dog walkers to worm their dogs regularly

KIDNEYS and GI

What are the 3 main kidney conditions you may see on PMI?

1) Polycystic kidney

• Congenital defect; either one or both effected

• Seen only in young sheep

2) Renal neoplasia

• Only in older animals

• If cancer is localized to just the kidneys, then partial rejection

3) Embolic nephritis

• COULD BE CAUSED BY TB

• Check other areas of the body to confirm ^

** For these, LOCAL REJECTION ALWAYS unless you suscpect uremia or septicemia

What is Johne’s disease?

Disease of the ILEUM

• Caused by Mycobacterium avium (subspecies paratuberculosis)

• Ileum will appear thickened and yellow, looks like a brain

• Need to check mesenteric lymph nodes; can spread through lymph and blood to other parts of the GI tract

Rejection of gut

What disease of the SI might you find as an incidental finding in a sheep over 5 years of age?

Small Intestinal Adenocarcinoma

• Starts in the ileum, may spread to other organs (spreads via contact)

• Occassional weight loss and ascites, but otherwise no clinical signs

What is one big reason an entire sheep carcass may be rejected?

EMACIATION

• Lack of fat on body

• Lack of omental fat around the GI tract

What is one pathological reason an entire sheep carcass may be rejected just by looking at the color of its skin alone?

PALLOR due to ANEMIA, because this indicates…

Parasites

• Haemonchus contortus

• Fasciola hepatica 

• Tick-Borne haemoparasites (Babesia, Theileria)

Nutritional Element Imbalances

• Iron Deficiency

• Copper Deficiency

• 
  

Anaemia of Inflammatory/Chronic Disease

Haemorrhagic Conditions (Bleeding abomasal ulcers, organ rupture, trauma)

What is one AESTHETIC reason an entire sheep carcass may be rejected?

Carotenoid pigmentation

• Accumulation in the adipose tissue

• Rejected on aesthetics 

• But safe for consumption

• Causes

  • Ingestion of feeds rich in carotenoids, such as fresh green pasture, lucerne (alfalfa), and other green plants

  • Breed predisposition

  • Nonsense mutation in the beta-carotene oxygenase 2 (BCO2) gene (Våge and Boman 2010.)

• Should be differentiated from jaundice (icterus)