CAHFS Connection - May 2025

Avian

Avian mycobacteriosis and coccidiosis was diagnosed in one of two, one-year-old, pigeons submitted for necropsy. The birds had a history of feather loss and appearing cold; the submitter suspected a respiratory infection. On gross examination, the bird had multifocal, tan nodules (Fig.1) in all liver lobes, 50% of the spleen was replaced by a 2cm diameter, firm tan nodule, and similar, smaller nodules were noted in the pancreas and mesentery. Microscopically, multifocal granulomas with large numbers of acid-fast bacilli were present in the spleen and liver. Moderate enteritis with modest numbers of coccidian stages was also seen. The other submitted pigeon was unremarkable except for moderate infestation by chewing lice.

Avian mycobacteriosis is a chronic disease caused by Mycobacterium spp., including Mycobacterium avium, Mycobacterium genavense and Mycobacterium fortuitum. All species of birds can be infected and the disease occurs worldwide. The most common route of infection is ingestion, and bacteria are shed in feces from infected birds. This disease is zoonotic and immunocompromised individuals are at higher risk. Coccidiosis in pigeons often manifests as loose greenish droppings, weight loss, lethargy, fluffed feathers and increased mortality.

Figure 1: The spleen is replaced by a firm tan nodule. Inset: large number of acid-fast bacilli are seen microscopically.

Diphtheritic (wet) fowl pox was diagnosed in two chickens from a flock of approximately 100 birds, in which six birds had died over a 5-day period. The birds had respiratory distress including dyspnea on inhalation with increased respiratory effort. On postmortem examination, the birds had extensive yellow diphtheritic plaques in the choana, larynx, and esophagus, and caseous exudate in the infraorbital sinuses. Histologically, these lesions were typical of fowlpox. Fowlpox virus was also detected by PCR on esophageal tissue. The birds were also positive for infectious coryza (Avibacterium paragallinarum) and Mycoplasma gallisepticum by PCR.

Bovine

Pneumonia was diagnosed in six, 4–6-month-old dairy calves with respiratory signs that were refractory to treatment. Necropsy confirmed pneumonia, and Histophilus somni (four calves), Bibersteinia trehalosi (five calves), and Mycoplasma bovis (four calves) in various combinations were detected. The B. trehalosi isolate was resistant to many of the antimicrobials used to treat bovine respiratory disease. Five of the six calves also had moderate to severe vitamin E deficiency, which can result in reduced immunity, poor growth rate, infertility and myodegeneration.

Pine needle abortion was diagnosed in a 7-month gestation Angus fetus from a 100-head-herd in which four heifers had aborted during a 2-3-week period after a possible exposure to pine needles. The fetus had hemorrhages over the thymus but no other lesions. Testing for epizootic bovine abortion and other bacterial and viral agents was negative. Tetrahydroagathic acid, a biomarker for isocupressic acid (the toxin in pine needles), was detected in fetal fluid confirming thus the diagnosis of pine needle abortion.

Equine

Aortic rupture resulted in the sudden death of three unrelated horses. A seven-year-old Friesian gelding that collapsed had a thoracic aortic rupture and surrounding massive hematoma. A 15-year-old Thoroughbred gelding found dead in the stall had an abdominal aortic rupture and hemoabdomen.  A 10-month-old Warmblood colt found dead in the stall after recovering from a recent colic episode, had an aortic root rupture with hemopericardium. Aortic rupture in horses is a rare event and the cause is usually undetermined.

A luteinized ovarian cyst/anovulatory hemorrhagic cyst was the cause of acute colic in a 5-year-old Thoroughbred mare with a history of an enlarged left ovary. The left mesovarium was strangulating a segment of the small colon. A large, thick-walled cystic structure containing abundant dark-red, coagulated, friable material was identified in the left ovary. Histologically, the cyst wall was composed of luteinized cells, which was also confirmed by electron microscopy. No significant bacterial pathogens or parasites were found in the intestinal tract. Luteinized ovarian cyst and mesovarium intestinal strangulation is a rare but important differential diagnosis in mares presenting with acute colic.

Small Ruminants

Yersinia pseudotuberculosis enteritis was diagnosed in two goats from two separate premises. This included a 1.5-year-old Boer buck with diarrhea of one week duration from a herd of 20 goats, and a yearling Nigerian dwarf buck from a herd with multiple deaths. On post-mortem exam, both goats had atrophy of fat, a common finding with yersiniosis. Histology revealed intestinal lesions consistent with yersiniosis. Y. pseudotuberculosis was isolated from liver of the Boer goat, mesenteric lymph node of the dwarf goat, and from intestine of both animals. Yersiniosis is most common in cold weather and results in multifocal intestinal lesions that may be missed on necropsy. Weight loss is a common finding.

Wildlife

Sarcocystis sp.-associated encephalitis was diagnosed in a free-ranging river otter that exhibited neurological signs including ataxia. Microscopically, multifocal encephalitis was observed with a few merozoites that were positive for Sarcocystis sp. by immunohistochemistry. There is not much information about Sarcocystis encephalitis in river otters, but in related species such as sea otters, Sarcocystis neurona causes fatal neurologic disease.