An outbreak of Mycoplasma mycoides subspecies capri arthritis in young goats: a case study

Abstract

Mycoplasmosis is a well-known cause of morbidity and mortality in small ruminants. Previously recognized outbreaks have involved arthritis, and pneumonia or pleuropneumonia. Modern bacteriology procedures rely less on isolation techniques that require special media for mollicutes given that these species are notoriously difficult to isolate, and rely more on PCR tests. We report an outbreak of arthritis, pleuropneumonia, and mild meningitis affecting dairy goat kids, spanning a period of 3 y, which had unusual epidemiologic characteristics related to husbandry practices. Lesions were characterized by polyarthritis of the appendicular joints, with copious joint fluid and extension of arthritic exudate beyond the joint itself. The cause remained unknown until serendipitous isolation of a mycoplasma on blood agar. Mycoplasmosis was not detected from synovial samples by a general mycoplasma PCR, despite multiple attempts. Isolated colonies were also negative by this general PCR assay. The isolate was identified as Mycoplasma mycoides subspecies capri, using universal 16S primers and amplicon sequencing. Testing of additional isolates from other diseased goats in the herd confirmed that this was the cause of illness. A failure to recognize the distinct nature of organisms of the M. mycoides group of mycoplasmas meant that a PCR test that cannot detect this group of organisms was utilized at first, and the etiology of the illness was overlooked for a period of time. Veterinary pathologists and microbiologists must be aware of the limitations of some PCR assays when confronted with joint disease and pleuropneumonia in small ruminants.

Keywords: PCR; arthritis; goats; mycoplasmosis; neonate; pleuritis.

Figure 1.

Histologic lesions in goat kids with Mycoplasma mycoides subsp. capri infection. A. Characteristic synovial inflammation extends from the synovial lumen (L) deeply to involve remaining synovium and joint capsule (JC). Adherent fibrin in the joint space (arrow). Dense, basophilic foci of degenerate neutrophils (N) are evident among more dispersed leukocytes. H&E. Bar = 500 μm. B. A higher magnification from another goat’s synovium contains a mixture of degenerate and viable neutrophils near the joint lumen (upper left). H&E. Bar = 100 μm. C. A thick layer of fibrin and degenerate neutrophils covers the pleural surface (P), with only mild inflammation extending into the lung (L). H&E. Bar = 500 μm. D. Mild leptomeningitis. H&E. Bar = 100 μm.