Survey of numbers and types of lesions detectable in pig heads and the implications for human and animal health
subclinical sheep scab in bighorn sheep when mite numbers have been very low (Boyce and others 1991). More important, however, is how early in the progression of the disease a diagnosis can be made by serological methods. ELISAs are one of the most frequently used methods for this but there is a wide variation in the time at which ELISA seropositivity occurs, usually coinciding with the onset of clinical signs, an increase in the number of mites and lesion spread. While diagnosis of scab can be made by ELISA as early as seven days after infestation in experimentally infested cattle (Lonneux and others 1998), this does not appear to be the case in sheep in which circulating antibodies detectable by ELISA appear only after about four weeks, coinciding with the onset of the rapid growth phase of the disease (Bates 1997). The present observations would appear to confirm this. In a separate experiment (not reported here), two sheep were experimentally infested with P ovis and serum taken from them at weekly intervals was assayed by immunoblotting and ELISA. The sheep were positive by immunoblotting two and three weeks after infestation whereas they were unequivocally ELISA positive only five and six weeks after infestation (one was just positive after four weeks) (Fig 1). In the serological investigations of the second outbreak on the affected farm, the two methods were compared. The most significant finding was that immunoblotting was superior to ELISA not only in early diagnosis, but also in differential diagnosis of sheep scab in cases where the ELISA results were negative. The reason for this is not clear, but it is worth noting that native antigens were used in ELISA, while denatured antigens were used in immunoblotting.
Food safety on the slaughterline: inspection of pig heads
This paper summarises information on the current inspection procedures for pig heads on the slaughterline and their impact on food safety, and considers the implications for food safety of certain lesions. It is argued that although a modified slaughter and inspection technique would decrease the contamination of the carcase with pathogenic microorganisms, leaving lesions in the head undiscovered would be of little or no importance either for human health or for the overall supervision of animal health.
Influence of pork consumption on human infection with Mycobacterium avian-intracellulare
The hypothesis that eating pork from animals infected with organisms of the Mycobacterium avium-intracellular complex is a significant cause of human mycobacteriosis was examined by skin testing students with purified protein derivative from M. intracellulare to determine their sensitivity to M. avium-intracellulare. No significant differences in sensitivity could be demonstrated between those individuals who had never eaten pork and those who ate pork routinely. It was concluded that sensitivity to purified protein derivative from M. intracellulare in this population did not involve eating pork.