Case 170519-2

One-year-old male red-flanked duiker (Cephalophus rufilatus).

Limited clinical history is available. The patient was anorectic and dull, and died.

The patient was an 8.8 kg red-flanked duiker in thin body condition, with scant fat. Ocular and gingival mucosae were red. Palpable lymph nodes were slightly enlarged and red. The trachea and bronchi contained moderate amounts of white to yellow stable foam. The visceral pleura had a few fibrin strands. The lungs had numerous, 0.3- to 0.5-cm-diameter, coalescing red areas, which sometimes contained a white spot in the middle. The right apical lobe was red and firm. Mediastinal lymph nodes are moderately enlarged and red. The pericardial sac contained 5 ml of yellow fluid.

The abdomen contained approximately 20 ml of yellow fluid, which was partially clotted, plus a few fibrin strands. The perirenal tissue had multifocal hemorrhages. The liver was markedly enlarged, with rounded margins and numerous pin-point foci dispersed throughout the parenchyma. The spleen was mildly enlarged. The kidneys were enlarged and had numerous irregular white areas along the surface. The cut surface displayed prominent cortical radiations and an orange color of the medulla. The urinary bladder mucosa was diffusely red with numerous petechial hemorrhages. Urinalysis provided the following values: protein (+++), pH 7.5, blood (++++), ketones (-), bilirubin (++) and glucose (-).

No significant findings were identified in the gastrointestinal tract. Mesenteric lymph nodes were moderately enlarged and red.

The brain was slightly swollen, with mild coning of the cerebellum.

This slide includes four sections of testicle and epididymis in which the interstitium is markedly expanded by a dense cellular infiltrate of mixed cells dominated by round cells resembling lymphoblasts, that pack and separate seminiferous tubules and efferent epidydimal ducts. The lymphoblast-like cells have fairly distinct cell borders, scant to small amounts of, pale-eosinophilic, slightly granular cytoplasm, and a single round to ovoid, central nucleus with coarsely-clumped chromatin and indistinct nucleolus. Anisocytosis in this population is mild, anisokaryosis is mild to moderate, and there are three mitotic figures in ten 400x fields. Moderate numbers of small lymphocytes and fewer macrophages are admixed with this population. Small- to medium-sized vessels are partially filled by the same cell population. Scattered plasma cells and macrophages are admixed with the blastic cell population.

Approximately 80% of the seminiferous tubules and efferent ducts are at various stages of degeneration with moderate to marked reduction in spermatogenesis. Affected seminiferous tubules are characterized by marked depletion of mature spermatids, reduction germinal cells and Sertoli cells, and frequent proliferation of immature multinucleated spermatids admixed with individual apoptotic and necrotic cells within the tubular lumina. Degenerate efferent ductules are moderately to markedly depleted of spermatozoa and lined by fragmented/necrotic columnar principal cells and a variably thickened and undulating basal cell layer.

Polymerase chain reaction (PCR) assays for known gammaherpesviruses in the malignant catarrhal fever group were negative. A PCR using degenerate primers amplified a ~1kb region of a novel viral genome (see comment).

Aerobic cultures of liver, lung, and urine were negative. Aerobic cultures of kidney and mesenteric lymph nodes grew small numbers of Streptococcus lutetiensis.

A fluorescent antibody assay for Leptospira was performed on a kidney impression smear, but it was negative.

A PCR for bovine leucosis virus was negative.

PCR for Mycobacterium avium ssp. paratuberculosis was negative.

Salmonella PCR and cultures (liver, mesenteric lymph node, small intestine) were negative.

Fecal flotation did not demonstrate parasite eggs.

A heavy metal screen was interpreted as within normal limits, although reference ranges for this species were not available.

Immunohistochemistry on a section of kidney demonstrated CD3+ immunoreactivity in approximately 80% of the proliferative round cells. Admixed CD79a+ cells comprised 10-20% of the round cells. They were negative for CD204.

Virus isolation from pooled tissues and electron microscopy of cell cultures did not identify any viruses.

Testis and epididymis: Marked interstitial lymphoproliferative infiltration

Testis and epididymis: Moderate to severe tubular and ductular degeneration with testicular atrophy

The lesions in this case were strikingly lymphoproliferative, so much so that a neoplastic process was suspected initially. A second case was also submitted from the same collection, with more prominent vasculitis and less lymphoid proliferation. Given the findings of a lymphoproliferative process with vasculitis, malignant catarrhal fever was considered. The PCRs for known viral causes of malignant catarrhal fever (Alcelaphine herpesvirus-1, Ovine herpesvirus-2, Caprine herpesvirus-2) were negative (Hong Li, Pullman, WA). However, a PCR using degenerate primers yielded a segment of the genome from a novel gammaherpesvirus, most closely phylogenetically related to a strain of Caprine herpesvirus-2. This represents a novel isolate associated with malignant catarrhal fever (MCF), which has not previously been reported in this species. The source or reservoir of the infection is not known at present.

Conference participants discussed the difficulty in distinguishing a neoplastic from an inflammatory process in these sections. Some pointed out the distribution and pleocellular character of the infiltrating population as being most suggestive of inflammation. Others suggested that the morphology of the cells in question would support a neoplastic process. This conversation recapitulates the research that has been completed to date on MCF, which is considered a lymphoproliferative disease, with a transformative associated gammaherpesvirus.

There was brief discussion of Marek’s disease virus, a lymphotropic herpesvirus that can produce lymphoproliferative or neoplastic lesions, in addition to vasculitis. One participant pointed out the difficulty in distinguishing between lymphoid proliferation and an overt neoplastic process. It was generally agreed that assays for clonality would be critical in making the final determination, although these are not available in this species.

This case was contributed by Dr Patti Pesavento of the UC Davis, School of Veterinary Medicine, and Dr. Francisco Carvallo of the California Animal Health & Food Safety System.

References