Caprine abscess model of tulathromycin concentrations in interstitial fluid from tissue chambers inoculated with Corynebacterium pseudotuberculosis following subcutaneous or intrachamber administration.

Corynebacterium pseudotuberculosis causes chronic, suppurative, abscessing conditions in livestock and humans. We used an in vivo model to evaluate antimicrobial efficacy for focal abscesses caused by C. pseudotuberculosis. Tissue chambers were surgically implanted in the subcutaneous tissues of the right and left paralumbar fossa of 12 goats to serve as a model for isolated, focal abscesses. For each goat, one tissue chamber was inoculated with C. pseudotuberculosis, while the contralateral chamber served as an uninoculated control. Six goats were administered a single dose of tulathromycin at 2.5 mg/kg of body weight subcutaneously, while the other six received the same dose by injection directly into the inoculated chambers. Our objective was to compare the effects and tulathromycin concentrations in interstitial fluid (IF) samples collected from C. pseudotuberculosis-infected and control chambers following subcutaneous or intrachamber injection of tulathromycin. In addition, the effects of tulathromycin on the quantity of C. pseudotuberculosis reisolated from inoculated chambers were assessed over time. Tulathromycin IF concentrations from C. pseudotuberculosis-infected and control tissue chambers were similar to those in plasma following subcutaneous administration. Following intrachamber administration, tulathromycin IF concentrations in infected chambers were continuously above the MIC for the C. pseudotuberculosis isolate for 15 days. There were no significant differences for plasma area under the curve and elimination half-lives between subcutaneous and intrachamber administration. Six of the 12 infected chambers had no growth of C. pseudotuberculosis 15 days postadministration. Results of this study indicate that tulathromycin may be beneficial in the treatment of focal infections such as those caused by C. pseudotuberculosis.

Neurological disease in lambs associated with exposure to high environmental temperature and humidity.

BACKGROUND: We detected a pattern of lambs presenting with hyperthermia and neurological signs during the summer. OBJECTIVES: The main objectives of this study were to compare clinical findings and results of diagnostic testing and to identify a potential etiology. ANIMALS: Fifteen clinical cases of lambs less than 12 months of age presenting with neurological signs, tachypnea, and hyperthermia over 4 summers. METHODS: Retrospective case series. Medical records were searched for lambs less than 12 months of age that presented with neurological signs including the following: kyphosis, pelvic limb hyperextension, treading of feet, muscle tremors and recumbency, and hyperthermia of greater than 104°F. A grading system was established to describe severity of presenting neurological signs. Weather data were collected from weather stations near the farm of origin for 3 days prior to presentation. RESULTS: The lambs were from 7 flocks in central Texas. All cases occurred between July and September, with a median heat index of 90.5 for the 3 days before presentation. Complete blood count, serum chemistry, necropsy examination, rumen content, virology, brain MRI, liver copper, selenium, and vitamin E failed to identify a consistent etiology for the signs presented. The only common factor was high heat and humidity. Histopathological examination identified axonal degeneration and skeletal muscle necrosis in some lambs. CONCLUSIONS AND CLINICAL IMPORTANCE: These clinical cases appeared similar to the Australian disease humpyback and indicate that lambs exposed to high environmental temperatures and humidity might be at risk of developing the described clinical presentation.