Diagnosis, Surveillance and Management of Streptococcus equi subspecies zooepidemicus Infections in Chinchillas (Chinchilla lanigera)

Abstract

During a 6-mo period, two 5-6 mo old female chinchillas (Chinchilla lanigera) were examined at the University of Colorado Anschutz Medical Campus after the discovery of firm, nonmobile masses in the left ventral cervical and left axillary region. Other than these findings and mild weight loss, both chinchillas' physical exams were normal. Bloodwork revealed an inflammatory leukogram characterized by leukocytosis, toxic neutrophils, lymphopenia, and monocytosis with mild, nonregenerative anemia. At necropsy, both masses were identified as abscesses. Streptococcus equi, subspecies zooepidemicus (S. zooepidemicus) was isolated in pure culture. Histology of the lungs, liver, spleen, and kidneys showed a marked increase in the numbers of both polymorphonuclear leukocytes and lymphocytes. Both animals were deemed unsuitable for research and were euthanized under isoflurane anesthesia by an intracardiac injection of pentobarbital sodium solution. S. zooepidemicus is an opportunistic, commensal organism found in the upper respiratory tract of horses. This organism has been documented to cause disease in other species and is zoonotic. Infections in humans have been reported, resulting in glomerulonephritis, endocarditis, septic arthritis, osteomyelitis, meningitis, and death. To aid in diagnosis and prospective surveillance of this bacteria, oral and nasal swabs were collected from the remaining cohort of chinchillas, and a qPCR screening assay was implemented. Within 12 mo, 4 of 41 additional females tested positive by culture or qPCR, resulting in a disease prevalence of 14% (6 of 43). However, only 2 of the additional 4 S. zooepidemicus positive animals developed clinical signs. The potential for the spread of infection, zoonosis, and adverse effects on research demonstrate that surveillance for S. zooepidemicus should be considered in a biomedical research environment.

Figure 1.

Antemortem and postmortem picture of clinical case 1. (A) The gray gradients of dense and lanate hair coat of the chinchilla effectively obscured the development of the abscess (between arrows) from identification by routine visual evaluation. (B) In dorsal recumbency, alopecia of the dependent aspect of the mass, without noticeable skin inflammation, irritation, or abrasion was a common finding for abscesses of similar size. (C) Necropsy image, in dorsal recumbency with skin removed and encapsulated abscess exposed. The arrow denotes the lack of a deep pectoral muscle in the left axilla. (D) Removal of the mandible and in block removal of the well encapsulated abscess noted atrophy to the left masseter and digastricus muscles (arrow). The dental arcade was within normal limits.

Figure 2.

Cut section of the left submandibular abscess from clinical case 1 containing 9.0 mL of pearl white caseous exudate. The white color of the purulent material within the abscess was consistent with all other clinical cases.

Figure 3.

Histological section of the thick, fibrous, eosinophilic capsule wall of the submandibular abscess from clinical case 1, with a marginated portion of the basophilic, parotid salivary gland.