UPPER RESPIRATORY-TRACT DISEASE AND MYCOPLASMOSIS IN DESERT TORTOISESFROM NEVADA

A population of desert tortoises (Gopherus agassizii) at Yucca Mountai n (Nevada, USA) was monitored during four sampling periods using enzym e-linked immunosorbent assays (ELISA) to determine the percentage of i ndividuals that had been exposed to Mycoplasma agassizii, a causative agent of upper respiratory tract disease. Respiratory tract disease ha s been considered a significant factor in the decline of desert tortoi se populations in the Mojave Desert (USA). Few differences between sex es in ELISA values or percentages testing positive were noted. From 15 to 23% of samples per period tested positive for exposure to the myco plasma. However, we noted few clinical signs of upper respiratory trac t disease. This is in contrast to an earlier study which reported a si milar proportion of seropositive tortoises as well as a high percentag e of tortoises with clinical signs. However, our results are consisten t with that study's conclusion that seropositivity for M. agassizii wa s a poor predictor of the likelihood to exhibit clinical signs of uppe r respiratory tract disease. Earlier reported epizootics of mycoplasma -associated respiratory disease occurred mainly during times of drough t. Our samples were collected during a period of average to above-aver age rainfall, suggesting that manifestation of clinical signs of the d isease may depend upon the physiological condition of tortoises which, in turn, is related to environmental conditions.