CAHFS Connection - December 2024

Avian:

Highly pathogenic avian influenza (HPAI) in several turkey and chicken submissions has resulted in only mild gross lesions, including air-sacculitis, pulmonary congestion, and splenomegaly. However, severe typical microscopic lesions including vasculitis and pancreatic necrosis are seen. The gross lesions seen at necropsy or during field necropsies can mimic other diseases and mortality rates in these cases have only been slightly elevated at the time of submission. The commonly seen HPAI lesions of head, comb, wattle, and snood edema, and red/purple discoloration and hemorrhage of feet and shanks have been absent. Proventricular and cecal tonsil hemorrhage has also been rare in these recent cases. 

West Nile virus (WNV) infection was diagnosed in a  4-year-old pet Ancona duck that was found dead in a pond. A postmortem evaluation revealed varying degrees of lymphoplasmacytic infiltration and necrosis in the brain, spleen, and liver. Immunohistochemistry was strongly positive for WNV. This is a mosquito-borne pathogen primarily maintained in nature through transmission cycles between birds and mosquitoes. Dead-end hosts for this virus include horses, humans, and other mammalian species. Infections in these hosts are frequently fatal.

Bovine

Fusobacterium necrophorum hepatic abscesses were diagnosed in tissues submitted from a high-producing Holstein cow that had been off-feed before being found dead. The liver had multifocal, 2-2.5cm dry abscesses with peripheral fibrosis. Histologically, filamentous bacilli typical of Fusobacterium sp. were seen in the chronic abscesses, and F. necrophorum was isolated on anaerobic culture of the liver. This organism usually gains entrance to the liver following bouts of ruminal acidosis. 

Blackleg was diagnosed in a 4-month-old Jersey heifer that had been dehorned and vaccinated against brucellosis six days prior to death. Necropsy revealed black, dry, and emphysematous skeletal muscles in the fore and hind legs (see photo). A fluorescent antibody (FA) test for Clostridium chauvoei was positive, confirming a diagnosis of blackleg. Clostridium septicum was isolated from the affected muscles. However, the FA test for this organism was negative, and thus post-mortem overgrowth and invasion of the affected muscles was considered likely. 

Bovine (cont.)

Ureaplasma diversum was the cause of chronic pneumonia in a crossbred beef calf found dead. The source herd of 73 cows housed on dryland pasture recently had four abortions or stillbirths. The calf submitted had been born alive and died soon after birth. Histology revealed lymphoplasmatic perivascular and interstitial pneumonia suggestive of Ureaplasma diversum which was detected by PCR on lung. Ureaplasma spp.  usually causes placental lesions; unfortunately, the placenta was not available for evaluation in this case.

Actinomyces bovis osteomyelitis and jejunal hematoma were diagnosed in a Holstein cow that was three months in lactation had an overnight marked drop in milk production, accompanied by drooling, pale mucous membranes, bloating, tacky manure with bloody mucus, shivering, and recumbency.  Necropsy revealed a 30cm intramural jejunal hematoma with clotted blood in the lumen. An incidental finding was a 21cm diameter yellow caseous mass expanding the right mandible with smaller, yellow firm nodules in the surrounding skeletal muscle. Actinomyces bovis was isolated from the mass and histologic lesions of osteomyelitis and rhabdomyositis were found.

Equine:

Pyrrolizidine alkaloid (PA)-induced chronic hepatopathy was diagnosed in an 18-year-old Quarter horse that was euthanized. The submitted horse had a one-week history of illness and elevated liver enzymes. Necropsy findings included an enlarged, firm, discolored liver with enhanced lobular pattern, generalized icterus, and hemorrhage in the cecum and colon. Histology had typical liver lesions of widespread fibrosis with megalocytes present. The farm reported two other deaths due to the same cause. PA toxicosis causes chronic and progressive liver lesions. Often the inciting plant in the Crotalaria or Senecio genera is no longer present in the feed by the time animals show clinical signs.

Porcine:

Discospondylitis and vertebral body osteomyelitis resulted in a 2-year-old Yorkshire sow becoming acutely paralyzed in the hind legs leading to euthanasia. Necropsy revealed light green pus in the T11-T12 disc space and extending into the adjacent vertebral bodies. The abscess material also compressed the spinal cord in the area and resulted in meningitis and myelitis. Trueperella pyogenes was isolated from the lesions.

Small Ruminants:

Caprine arthritis and encephalitis virus (CAEV) interstitial pneumonia was the cause of death in a 3.5-year-old Alpine goat doe with a 22-day history of rapid respiratory rate and agitation which failed to respond to antibiotics. Necropsy revealed red-brown atelectatic lungs with multiple gray firm infiltrates in all lobes. Histology confirmed chronic pneumonia with alveolar protein fluid in all lobes and lungworms in the caudal lobes. The goat also had lymphocytic interstitial mastitis, a lesion seen with CAEV infection. CAEV was detected in the lung by immunohistochemistry, and serology for this virus was positive.