An outbreak of compressive myelopathy due to pyogranulomatous reaction to the oily adjuvant of the foot-and-mouth disease vaccine - case report

Abstract

Cases of compressive myelopathy syndrome associated with post vaccinal pyogranulomas were diagnosed post mortem in three cows from a farm in Minas Gerais state, Brazil. These cows presented ataxia and bilateral paresis of the pelvic limbs, which evolved to paralysis, and sternal recumbence. On necropsy, locally extensive areas of the longissimus dorsi muscle were replaced by pyogranulomas supported by moderate amounts of fibrous connective tissue. On the cut surface, some nodules contained yellowish and viscous fluid (purulent exudate) or whitish fluid (interpreted as the oily adjuvant of a vaccine). In the spinal canal of the subjacent vertebrae, compressing the spinal cord, were pyogranulomas identical to those described in the skeletal muscle. Histologically, the pyogranulomas were composed of a central clear vacuole (consistent with the space left by the oil adjuvant droplets), surrounded by neutrophils and, more externally, by large numbers of epithelioid macrophages and fewer multinucleated giant cells. In the white matter of the spinal cord were numerous well-defined, clear vacuoles (Wallerian degeneration). The association of the clinical history and pathological findings allowed the diagnosis of compressive myelopathy associated with pyogranulomatous reaction to the oily adjuvant of the foot-and-mouth disease vaccine, in this case, due to its inadequate application.

Postvaccinal pyogranulomas in cattle

“…Despite the atypical location of some pyogranulomas, the gross and microscopic lesions were highly compatible with other outbreaks involving postvaccinal reactions in beef cattle (4,9), where animals from a same farm had identical lesions in the absence of intralesional microorganisms.…”

“…However, the route is associated with a higher local reaction. Improperly trained personnel frequently contribute to the development of postinjection pyogranulomas (4,9).…”

“…Due to the proximity of the vaccine application site to the spinal cord, post-vaccinal granulomas are sporadically found inside the vertebral canal, compressing the spinal cord (4,9). In these cases, compressive granulomas may result in severe spinal cord syndromes (4, 9); however, postvaccinal granulomas per se may result in significant economic losses for beef cattle industry due to costs involving the removal of affected parts in slaughterhouses (6,7).…”

“…During microscopic examination, intralesional microorganisms were ruled out based on thorough examination of routine (hematoxylin & eosin) and histochemical stains (Grocott-Gomori's Methanamine Silver, Periodic acid-Schiff, Goodpasture, and Ziehl-Neelsen). In the absence of intralesional microorganisms, the clear vacuoles located within most pyogranulomas should not be interpreted as artifacts, considering that the clear spaces were well delimited and surrounded by an exuberant chronic inflammatory infiltrate, which is characteristic of reaction to oily agents (4,9).…”