Abstract
A group of eight unidentified frogs were imported to a herpetological distributor in December 1996. The frogs were apparently normal. No information was supplied by the importer as to the animal’s identification or care. The frogs were placed into a 29-gallon glass aquarium (24×13×30 inches) filled with approximately 10 gallons of chlorinated water. Approximately 15 pounds of river rock were added as substrate (0.5-inch pebble). Two concrete bricks were placed in the aquarium to provide an area for basking/drying. The water was not aerated. No external heat or ultraviolet light sources were provided. The frogs were offered a diet of crickets and common shiners (Notropis cornutus).
After one week, several frogs developed opaque lesions on the eyes. Five frogs were evaluated at Louisiana State University School of Veterinary Medicine. The frogs were identified as helmeted water toads (Caudiverbera caudiverbera). A water sample was collected, and the following parameters were measured: temperature 65–68°F, total hardness 120 ppm, alkalinity 80 ppm, pH 7.6, nitrate 100 ppm, and nitrite 0.5 ppm. On physical examination, the frogs were found to have varying degrees of ocular lesions. Lesions were mostly bilateral and included diffuse corneal edema, keratoconus, central corneal thinning and ulceration, aqueous flare, and hyphema. Corneal edema preceded the formation of corneal ulcers and keratoconus in all five cases. A bacteriologic culture and cytologic examination of the corneas were performed. Standard aerobic cultures were evaluated at room temperature and at 37°C. Mixed populations of organisms were isolated including Alcaligenes spp., Alpha-Streptococcus spp., and Pseudomonas maltophilia. Corneal cytology revealed a mixed population of inflammatory cells, predominantly heterophils and macrophages, and bacteria. Blood samples were collected from the ventral abdominal vein. Packed cell volumes were performed on all five frogs and ranged from 12–29%. White blood cell estimates ranged from 9.8–22.6×103/µl. Enemas were performed on the frogs to collect fecal material for parasite examination. Direct saline smears and fecal flotations were performed. Fecal evaluation revealed moderate numbers of ciliated and flagellated protozoa.
Treatment was started by correcting husbandry methods and instituting systemic and topical antimicrobials. Enrofloxacin was given at 7.5 mg/kg IM in the front limb SID. Topical triple antibiotic ointment was instilled in each eye TID to lubricate and protect the eyes from drying. The frogs did not respond to treatment after 10 days resulting in the need for euthanasia.
Necropsies were performed on all five animals. Gross necropsy findings were unremarkable except for the ocular lesions. Globes and multiple tissues were collected for histopathologic examination. Ocular lesions were mostly bilateral with variable severity and included central corneal thinning, diffuse corneal edema with central corneal ulceration, and a mixed population of inflammatory cells in the corneal stroma. Blood intermixed with inflammatory cells and cellular debris was present in the anterior chamber and was adhered to the inner corneal stroma in areas devoid of corneal endothelial cells. Uniform septate fungal hyphae, approximately 1–2 microns in diameter, were present in some corneas. A mixed population of inflammatory cells were present within the anterior uvea and vitreous body. Sensory retinal detachment was present within some globes.
Cultures of the liver, kidney, spleen, and small intestines were performed. Small numbers of Providencia spp. were isolated from the liver and spleen of two of the frogs. Large numbers of Enterobacter cloacae were isolated from the intestines of three of the frogs and small numbers of Escherichia coli were isolated from the intestines of another frog.
Keratitis in anurans has been associated with bacterial infections and possible ultraviolet light exposure.1,2 Severe vascularizing keratitis associated with a syndrome of corneal melting is less common and often reveals no pathogens, although gram-negative bacteria have been isolated on occasion.2 The finding of fungal elements in the corneas of these anurans has not been previously described. Although the source of the fungi was not determined, the prey items (fish) and poor water conditions may have introduced and maintained the fungi within the environment. Stress associated with transport and the inadequate husbandry methods could have also played a role in pathogenesis by compromising the immune response. This case illustrates the importance of fungi as opportunistic pathogens in captive anurans.
Literature Cited
1. Brooks DE, Jacobson ER, Wolf ED, Clubb S, Gaskin JM. Panopthalmitis and otitis interna in fire-bellied toads. JAVMA. 1983;183(11):1198–1201.
2. Williams D, Whitaker BR. The amphibian eye—a clinical review. J Zoo Wildl Med. 1994;25(1):18–28.