Abstract
Virginia opossums (Didelphis virginiana) are the only native marsupials in the United States of America and Canada. Females have a reproductive tract consisting of a complex duplex (bifurcated) reproductive system, with 2 ovaries, 2 uteri and uterine tubes, and a vaginal complex composed of 2 lateral vaginae, vaginal sinuses, and a urogenital sinus. Few conditions of the reproductive tract have been described in these marsupials. A 2-y-old, female Virginia opossum was presented because of hematuria and was found dead shortly after admission. The autopsy revealed left lateral vaginal torsion and pyovagina. Streptococcus didelphis was isolated and identified from the lateral vaginal exudate, blood, and liver using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Histologic examination confirmed suppurative and lymphoplasmacytic vaginitis, endometritis, cystitis, pyelonephritis and interstitial nephritis, portal hepatitis with fibrosis, myocarditis, and adrenalitis with intralesional gram-positive cocci. These results suggest ascending S. didelphis infection of the lateral vagina with subsequent torsion, bacterial translocation, bacteremia, and sepsis as the cause of death.
Virginia opossums (Didelphis virginiana) are the only native species of marsupial present in the United States of America and Canada. These iconic mammals thrive in diverse habitats, from forests to urban areas. Virginia opossums are opportunistic omnivorous and frequent scavengers, contributing to ecosystems by consuming insects and other small animals, fruits, and human refuse.
The 4 main forms of the uterus in mammals are duplex, bipartite, bicornuate, and simplex. Female opossums possess a duplex (bifurcated) reproductive system, with 2 ovaries, 2 uteri and uterine tubes, 2 vaginal complexes (each composed of a lateral vagina and a vaginal sinus or cul-de-sac), and a common urogenital sinus in which the urogenital tract and rectum converge. 8 The morphology of the vaginal complex is consistent among the various opossum species and is intended to receive the bifid penis during copulation. 8 Opossums have a unique reproductive biology; however, reports of the reproductive pathology of these unique mammals are scarce.
An adult, 2-y-old, female Virginia opossum under human care was presented to the Cornell University Hospital for Animals (Ithaca, NY, USA) with a 3-d history of hematuria and a 1-d history of ataxia. The patient was found dead shortly after admission, and the body was submitted to the Cornell Animal Health Diagnostic Center for autopsy. This opossum had been found as a joey and was not releasable from a rehabilitation center because of congenital microphthalmia. The clinical history reported a healed abscess on the right side of the neck.
On gross examination, both eyelids were reduced in size with narrowing of the palpebral fissure, and microphthalmia was confirmed. The left lateral vagina was twisted 360 degrees clockwise (Fig. 1A), markedly dilated, and filled with purulent exudate consistent with unilateral suppurative vaginitis (Fig. 1B). The mucosa of the lateral vagina was petechiated, and the junction between the uterine cervix and the urogenital sinus was congested. The visceral pleura contained dozens of irregular, well-demarcated, 0.5–1.0-cm, yellow, raised, firm plaques. Samples of the vaginal exudate were collected with swabs for bacteriologic culture; blood and liver samples were cultured as well. Representative tissue samples from all organs were fixed in 10% neutral-buffered formalin and processed routinely for histologic examination.
Pyovagina and sepsis due to Streptococcus didelphis in a Virginia opossum.
Bacteriologic culture of the vaginal exudate yielded 3 isolates, which were examined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS; Bruker). From the vagina, the most common isolates were Streptococcus didelphis (MALDI-TOF MS score of 2.19) and Proteus mirabilis (score of 2.44), and less abundant was Enterococcus spp. (score of 1.69). Pure cultures isolated from blood and liver were identified as S. didelphis (score of 2.16).
Histologically, the mucosae of the left vagina (Fig. 1C), left uterine horn, urinary bladder, and ureter had erosions and were diffusely infiltrated by moderate numbers of viable and degenerate neutrophils, lymphocytes, and plasma cells; cocci were observed in the lumina. Other histologic findings included multifocal suppurative and/or lymphoplasmacytic myocarditis (Fig. 1D), portal hepatitis with mild portal fibrosis, adrenalitis with intralesional bacteria, renal tubulitis (Fig. 1D) and pyelonephritis with intraluminal bacteria and nephrocalcinosis, and interstitial nephritis. Intravascular gram-positive cocci were seen in the heart, lungs, liver, spleen, adrenal glands, and kidneys (Fig. 1E, inset). In addition, the lungs had multifocal, histiocytic pneumonia with intramacrophage lipid consistent with endogenous lipid pneumonia.
Histologically, bilateral congenital microphthalmia consisted of a 4 × 3-mm, rounded structure surrounded by a collagenous sclera-like rim; irregularly folded, melanin-laden uvea-like tissue, occasionally lined by a single lining of epithelial cells; a single lining of cuboidal cells with abundant cytoplasmic melanin granules reminiscent of retinal pigment epithelium; and retina-like capillaries. The posterior cavity was filled with wispy, pale eosinophilic, vitreous-like material. The conjunctival epithelium was moderately hyperplastic.
Short-tailed opossums (Didelphis albiventris), which are used as laboratory animals, and Virginia opossums have been reported to have endometritis 5 ; however, we did not retrieve any reports of vaginitis or pyovagina in any opossum species in a search of Google, PubMed, CAB Direct, Web of Science, and Scopus. Pyovagina is rare in marsupials and has been reported in 2 koalas (Phascolarctos cinereus) with concurrent pyometra and cystitis. 3 Our case had no gross evidence of pyometra despite having mild suppurative and lymphoplasmacytic endometritis and cystitis. The urogenital sinus in marsupials serves as the common junction for the vagina, urethra, and rectum, and may facilitate ascending infections leading to vaginitis, metritis, and pyelonephritis, as seen in our case and in koalas with pyovagina.3,5 The ureters are contained within the vaginal canals in marsupials, unlike in placental mammals, which may also facilitate ascending infection.
Bacteria associated with pyometra or pyovagina in marsupials include Actinomyces spp., Bacteroides spp., Escherichia coli, Proteus ssp., Staphylococcus aureus, and Streptococcus spp.3,5 We isolated S. didelphis from the torsed left lateral vagina, blood, and liver in our case, indicative of bacteremia. S. didelphis has been isolated from white-eared opossums with suppurative, necrotizing, or ulcerative dermatitis, cellulitis, and myositis,2,7 and cutaneous lesions have led to systemic spread to the lungs, liver, spleen, or kidneys in Virginia and white-eared opossums.2,4,7 Histologically, white-eared opossums had pneumonia, hepatitis with hepatic fibrosis, splenitis, and nephritis; and less often, tracheitis, myocarditis, adrenalitis, meningitis, salivary adenitis, gastritis, and enteritis.2,4,7
Genitourinary tract infection, unilateral pyovagina, vaginal torsion, and translocation of bacteria led to bacteremia and sepsis in our case. S. didelphis has a variety of genes involved in proteolytic activity, phagocytosis evasion, cellular adherence, biofilm production, and toxin–antitoxin systems, among other virulence factors, 2 which may have facilitated infection of the lower genitourinary tract and systemic spread in our case. Myocarditis, hepatitis, adrenalitis, nephritis, and gram-positive cocci in multiple organs support bacteremia in our case.
We also isolated P. mirabilis in moderate numbers and Enterococcus spp. in low numbers from the vaginal exudate. P. mirabilis is a gram-negative bacillus regarded as a part of the vaginal microbiome in healthy mammals including dogs, rats, and giant pandas (Ailuropoda melanoleuca).6,7,9,10 P. mirabilis has been associated with cases of urinary tract infection in animals; however, its potential to cause severe infections and bacteremia alone is limited in the absence of other pathogenic bacteria. 1 Also, the absence of gram-negative bacilli based on the Gram stain of tissues in our case does not support a substantial contribution by P. mirabilis. The isolation of Streptococcus spp. in pure culture from blood and liver, and further identification as S. didelphis, matches the gram-positive cocci observed histologically in multiple tissues and rules out a pathogenic role for Enterococcus spp.
Footnotes
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
