Diseases in farmed american bull frog (Rana catesbeiana shaw, 1802) in Uruguay.
Rolando Mazzoni
Director Frog Farming Project, INAPE/IIP, Uruguay.
E-mail: rolo@pes.fvet.edu.uy
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The goal of this paper is to communicate the importance of frog diseases as a limiting factor for frog farming. It also wants to be a useful information for other researchers who work with amphibian diseases either in captivity or in natural environments. Frog husbandry is a new activity in South America. It has less than twenty years, and most of the effort has been done by private farmers induced by excellent market prices and a high demand. A small number of pathologist are working directly over the problems, and there is a lack of specialized personnel and laboratories. High densities, management, feeding practices and environmental conditions are important factors that usually contribute to reduce natural defensive mechanisms and immune response, and as a result frogs suddenly get sick and die. As a result, common saprophyte organisms like Aeromonas hydrophila are frequently isolated. Streptococcus spp. has been also commonly isolated from heart blood, liver and kidneys. The "red leg syndrome" is always present with exactly the five patterns illustrated by Cunningham et al. (1996). There is also common a neurological syndrome, where frogs show convulsions or remain in abnormal positions like a significant scoliosis or remain upside down moving around but not been able to recover the normal position. The experience says that these bacteria only attack frogs when they are stressed or affected with bad management practices, or after the action of a primary pathogen. Their presence may also mask the action of other "real" pathogens that will be the main responsible of the disease.
However, in some farms with good management practices and technical supervision, severe diseases outbreaks and high mortality occurred. In some cases, tadpoles showed symptoms of TEV (Wolf et al, 1968). Frogs in most cases showed unspecific symptoms. Groups of sick frogs located into the same tank may show simultaneously all the different patterns mentioned above. The viral etiology has been suspected but not confirmed already. High and sudden mortalities in newly metamorphosed frogs with accumulations of sloughed skin were observed many times. According to the recent findings in wild frogs (Berger et al. 1998, Berger & Spare, 1998, Longcore et al. 1998, Pessier et al. 1999), a chytrid like organism was found and Chytridiomycosis was probably the cause of the disease. The presence of chytrid infection was confirmed in histology sections (Cunningham, 1999 pers.com.) and from TEM (Daszak, 1999 pers.com.). The species of chytrid is now being studied to determine if it is or is not Batrachochytrium dendrobatidis, the one that affected frogs in Central America, USA and Australia, and the paper about the specific outbreak is in preparation. This is the most southerly finding of chytridiomycosis so far reported in South America. The disease has economically damaged the frog industry and has also the potential to affect wild populations.
It will be concluded that farmed frogs are being critically affected by diseases as it is also happening with wild populations (Daszak et al. 1999) around the world.
BIBLIOGRAPHY
Berger, L.; Speare, R.; Daszak, P.; Green. D.; Cunningham, A.; Goggin, L.; Slocombe, R.; Ragan, M.; Hyatt, A.; McDonald, K.; Hines, H.; Lips, K.; Marantelli, G.; Parkes, H. Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America. Proceedings of the National Acadamy of Science.1998;95:9031-9036.
Berger,L.; & Speare,R. (1998) Chytridiomycosis: a new disease of wild and captive amphibians. ANZCCART Newsletter 1998; 11(4):1-3.
Cunningham, A. A.; Langton, T. E. S.; Bennett, P. M.; Lewin, J. F.; Drury, S. E. N.; Gough, R. E.; Macgregor, S. K. (1996) Pathological and microbiological findings from incidents of unusual mortality of the common frog (Rana temporaria). Philosophical Transactions of the Royal Society of London. 1996; 351:1539-1557.
Daszak,P.; Berger,L.; Cunningham,A.; Hyatt,A.; Green,D. and Speare,R. (1999) Emerging infectious diseases and amphibian population declines. CDC Journal Vol.5, Nš6 21pp.
Longcore, J.E., Pessier, A.P. and Nichols, D.K. (1999) Batrachochytrium dendrobatidis gen. et sp. nov., a chytrid pathogenic to amphibians. Mycologia 91: 219-227.
Pessier, A.P., Nichols, D.K., Longcore, J.E., and Fuller, M.S. (1999). Cutaneous chytridiomycosis in poison dart frogs (Dendrobates spp.) and White's tree frogs (Litoria caerulea). Journal of Veterinary Diagnostic Investigation 11: 194-199.