Clinical and pathological findings of Rhodococcus equi infection in foals

Abstract

Infection by Rhodococcus equi is considered one of the major health concerns for foals worldwide. In order to better understand the disease’s clinical and pathological features, we studied twenty cases of natural infection by R. equi in foals. These cases are characterized according to their clinical and pathological findings and immunohistochemical aspects. Necropsy, histologic examination, bacterial culture, R. equi and Pneumocystis spp. immunohistochemistry were performed. The foals had a mean age of 60 days and presented respiratory signs (11/20), hyperthermia (10/20), articular swelling (6/20), prostration (4/20), locomotor impairment (3/20) and diarrhea (3/20), among others. The main lesions were of pyogranulomatous pneumonia, seen in 19 foals, accompanied or not by pyogranulomatous lymphadenitis (10/20) and pyogranulomatous and ulcerative enterocolitis (5/20). Pyogranulomatous osteomyelitis was seen in 3 foals, one of which did not have pulmonary involvement. There was lymphoplasmacytic (4/20), lymphoplasmacytic and neutrophilic (1/20) or pyogranulomatous arthritis (1/20), affecting multiple or singular joints. Immunohistochemistry revealed to be a valuable tool for the detection of R. equi, confirming the diagnosis in all cases. Furthermore, pulmonary immunostaining for Pneumocystis spp. demonstrates that a coinfection with R. equi and this fungal agent is a common event in foals, seen in 13 cases.

Pathologic characteristics of infectious diseases in macaque monkeys used in biomedical and toxicologic studies

“…Macrophages occasionally contain myriad coccobacillary basophilic gram-positive bacteria. Lung lesions may also include multinucleated giant cells, multifocal thrombosis, interstitial and alveolar edema, and tissue necrosis 140 . In humans treated with immunosuppressants for organ transplantation, R. equi- related lung lesions include inflammation of the lung parenchyma, with foamy histiocytic infiltration.…”

“…Diagnosis. In addition to the characteristic histopathologic findings of pyogranulomatous pneumonia with intracytoplasmic bacteria in the macrophages infiltrating the lesions, positive staining for R. equi in intralesional macrophages is a potential tool for definitive diagnosis 140 . However, obtaining an appropriate antibody for IHC analysis is sometimes difficult.…”

Bacterial and viral enterocolitis in horses: a review

“…Histologically, the mucosa and submucosa are expanded by pyogranulomas with variable numbers of intrahistiocytic and free gram-positive coccobacilli 100,146 (Fig.17). A similar pyogranulomatous infiltrate is noted within the regional lymph nodes.…”

“…A similar pyogranulomatous infiltrate is noted within the regional lymph nodes. 100 Diagnosis. Antemortem diagnosis may be challenging, and it is based on clinical signs, coupled with imaging and detection of virulent strains of R. equi in feces.…”

“…Microscopic pathology. Histologically, the mucosa and submucosa are expanded by pyogranulomas with variable numbers of intrahistiocytic and free gram-positive coccobacilli 100,146 (Fig. 17).…”