Abstract
Chryseobacterium meningosepticum (previously Flavobacterium) is an important pathogen in captive frogs and presumably originates from contaminated water sources.1,2,3 The organism is difficult to eradicate and can have a major negative impact on captive populations and research. In spontaneous infections, aquatic species, such as Xenopus laevis, primarily present with severe coelomic and lymph sac effusion (a.k.a. edema syndrome), lethargy, color change and sudden death.1 In large colonies, clinical signs are overlooked easily and infection may manifest as an acute mortality event. In contrast, spontaneous infections of semi-aquatic or terrestrial anuran species, such as Rana castesbeiana, R. pipiens and Hyperolius sp., primarily present as acute or chronic vestibular dysfunction, neurological disease, and/or endophthalmitis.2,3
This study was conducted to compare clinical signs and pathologic lesions between aquatic species, X. laevis, and semi-aquatic species, R. pipiens, of frogs experimentally inoculated with C. meningosepticum. Two groups of R. pipiens and X. laevis were inoculated intracoelomically or into the dorsal lymph sac with phosphate buffered saline (PBS) containing 106 (n = 6 of each species) or 108 (n = 6 of each species) bacteria. Control groups were inoculated with sterile PBS.
At the termination of the study, morbidity and mortality were higher for R. pipiens than X. laevis. In the high dose group, five R. pipiens developed infection of the endolymphatic and/or perilymphatic structures. In two of these frogs, histological lesions closely resembled the otitis interna and meningitis observed in natural infections of R. pipiens. Also in the high dose group, five R. pipiens developed ocular infections, some of which progressed to rupture the globe. In the high dose group, two X. laevis developed infection of the endolymphatic and/or perilymphatic systems and three developed ocular infection similar to those seen in R. pipiens. In both high and low dose groups, frogs of both species developed chronic multisystemic infections, some of which were clinically inapparent, and remained culture positive for up to 50 days post-infection. Finally, mild coelomic effusion developed during the course of infection in some individuals of both species, but not to the severity characteristic of "edema syndrome."
In this study, R. pipiens was more susceptible to experimental infection with high and low dose inoculation of C. meningosepticum; however, when susceptible, R. pipiens and X. laevis demonstrated similar clinical and pathological lesions. High dose groups developed otitis interna, meningitis and severe ocular lesions that resembled spontaneous infections. In some frogs, infection led to chronic, multisystemic disease that affected the endolymphatic and perilymphatic systems, eye, coelomic cavity, pericardium and ovary. Frogs with subclinical, chronic infections have not been described previously and may provide a source of contamination and infection in captive populations.
Acknowledgments
The authors would like to thank Eileen Samitz of the UC Davis Microbiology Laboratory for assistance with bacterial cultures and the UC Davis Histology Laboratory for histology services.
References
1. Green SL, et al. 1999. Identification and management of an outbreak of Flavobacterium meningosepticum infection in a colony of South African clawed frogs (Xenopus laevis). Journal of the Veterinary Medical Association. Vol. 214(12). Pp. 1833-1838.
2. Mauel MJ, DL Miller, KS Frazier, ME Hines. 2002. Bacterial pathogens isolated from cultured bullfrogs (Rana castesbeiana). Journal of Veterinary Diagnostic Investigation. Vol. 14. Pp. 431-433.
3. Taylor FR, RC Simmonds, DG Loeffler. 1993. Isolation of Flavobacterium meningosepticum in a colony of leopard frogs (Rana pipiens) Laboratory Animal Science. Vol. 43(1). Pp. 105.