Lamb mortality in an outbreak of Yersinia pseudotuberculosis mastitis, as a collateral effect of colostrum feeding for Lentivirus-control

Abstract

Yersinia pseudotuberculosis infections have been reported in a wide range of wild and domestic hosts, as well as humans. There have been some reports on involvement of this pathogen in the aetiology of mastitis in cows and goats, but apparently not in sheep. We report here a case where subclinical mastitis in a Latxa dairy sheep flock appeared to cause an outbreak of perinatal mortality, as a consequence of unknowingly feeding infected colostrum for preventing vertical transmission of Small Ruminant Lentivirus. The flock was composed of 188 ewes that had lambed in late-January 2008. Deaths of 3–5-day-old lambs reached 50% mortality of lambs born on the 20th and the 21st day of the outbreak and then decreased, averaging 34% out of 105 lambs born during a 6-day period. Affected lambs appeared inactive and ceased eating and growing. Two lambs submitted for post mortem examination showed necrosuppurative enterocolitis, mesenteric lymphadenitis, necrotizing hepatitis, splenitis and pneumonia. Bacterial culture yielded Y. pseudotuberculosis. It was noticed that all sick lambs had been fed with colostrum from a single ewe that had three lambs on the 20th January. All that colostrum had been consumed, but the milk of all animals in the flock was immediately submitted to the California Mastitis Test (CMT). Several ewes resulted positive, but only two yielded any significant isolation, which was in both cases of Y. pseudotuberculosis. One was also a colostrum donor. Treatment with enrofloxacin was immediately given to the surviving lambs and these showed a quick recovery. All the contaminated bulk milk was destroyed after the first Y. pseudotuberculosis isolation from milk samples; the two infected ewes were separated and dried-off on a treatment with enrofloxacin immediately and at the end of lactation, respectively. On the 71st day, the donor ewe was killed after showing an acute mastitis, from which Y. pseudotuberculosis was recovered. The surviving ewe, that carried two foetuses, suffered pregnancy toxaemia 1 week after being transferred to new facilities nine months later. Stenotrophomonas maltophilia was isolated from placenta, right mammary gland and faeces and Escherichia coli from the intestine and lung, but no Y. pseudotuberculosis was recovered from any sample. Regarding use of colostrum, it was concluded that it is necessary to always check it with the CMT before using it for lambs on artificial lactation.