Rhabditoid Ophthalmitis and Meningoencephalitis in Captive Asian Horned Frogs (Megophrys montana)
Ocular and neural nematodiasis in amphibians is sporadic and typically an extension of visceral larval migrans.2,4 Two genera of rhabditoid nematodes, Rhabdias and Strongyloides, are usually involved. These nematodes have a direct life cycle and can be free-living or parasitic. Low numbers cause little impact; however, high numbers can cause considerable morbidity and mortality, particularly in confined captive populations.3
At the San Diego Zoo, an Asian horned frog (Megophrys montana) was necropsied after prolonged treatment for bilateral corneal ulceration and perforation and acute onset of neurologic signs. Histopathologic findings confirmed the corneal perforations and revealed granulomatous ophthalmitis and meningoencephalitis with intralesional nematodes. The small size, thin cuticle, platymyarian musculature and uninucleate intestinal cells identified the nematodes as rhabditoids.1 Samples of frozen, ethanol-preserved and formalin-fixed tissue and samples of the enclosure substrate were submitted for nematode speciation. Comparison of the 28s rRNA and internal transcribed spacer region gene sequence of two nematodes isolated from formalin-fixed tissue resulted in absolute homology to Caenorhabditis elegans. Though much is known about C. elegans as a research model, its potential as a pathogen has not been thoroughly investigated. To this date, there are no reports of C. elegans associated with disease in vertebrates. After this case was documented, three additional confirmed and potential cases from the same exhibit were identified. Heavy environmental contamination with free-living nematodes and subsequent direct corneal invasion was suspected. Management changes included disinfection of the exhibit, increased frequency of substrate changes and anti-helminthic treatment of the remaining frog.
1. Gardiner, C.H., and S.L. Poynton. 1999. An Atlas of Metazoan Parasites in Animal Tissues. Armed Forces Institute of Pathology, Washington, DC. Pp. 14–16.
2. Green, D.E. 2001. Pathology of amphibia. In: Wright, K. M. and B.R. Whitaker (eds.). Amphibian Medicine and Captive Husbandry. Kreigar Publishing Co., Malabar, Florida. Pp. 435–437.
3. Poynton, S.L., and B.R. Whitaker. 2001. Protozoa and metazoa infecting amphibians. In: Wright, K. M. and B.R. Whitaker (eds.). Amphibian Medicine and Captive Husbandry. Kreigar Publishing Co., Malabar, Florida. Pp. 210–211.
4. Whitaker, B.R. 2001. The amphibian eye. In: Wright. K. M. and B.R. Whitaker (eds.). Amphibian Medicine and Captive Husbandry. Kreigar Publishing Co., Malabar, Florida. Pp. 250.