JOHNE’S DISEASE IN SHEEP Association between lymph node size and histologic characteristics

Abstract

AIM: To describe if there is a relationship between mesenteric lymph node (MLN) size and histologic characteristics of Mycobacterium avium subsp. Paratuberculosis (MAP). Hunnam et al. (2010 submitted) found that in deer 94% of the enlarged lymph nodes were MAP positive. The aim of this study is to determine if there is a same relationship in sheep.

METHODS: 750 MLN were sampled from 250 slaughter lambs from 25 different farms (10 sheep/farm). Mycobacterium avium subsp. Paratuberculosis status of the farms was unknown. The LN were sampled at 25%, 50% and 75% of the MLN chain, where the 25% section was taken at the beginning of the ileum and the 75% section from the ileocecal LN. The circumference of the MLN was measured and abnormal coloration described. The samples were stored in 60 ml containers with formalin. At the 75% sample location an additional two samples were taken and stored fresh frozen at -80oC for PCR and culture. Fixed sections were stained with Haematoxyline and Eosin and if necessary with Ziehl Neelsen. The slides were examined for lesions typical for Johne’s disease using an Olympus BX51 and XC50 microscope. RESULTS: No LN were found histologically positive for Johne’s disease. In one LN typical lesions for Johne’s were found, but on the Ziehl Neelsen no acid fast organisms (AFO) were found. This LN was categorized as highly suspicious for Johne’s disease. Most LN showed some hyperplasia and some worms and coccidia were found accompanied by eosinophils. LN size was not affected by abnormal coloration, but appeared to be significant affected (P<0,001) by sample location (25, 50 or 75%). The smallest circumferences were measured at the 75% sample location at the largest at the 50% sample location.

CONCLUSION: To determine if there is a relationship between LN size and histologic characteristics more LN will have to be examined preferable of older sheep from the same farms where the lambs for this study were sampled. This will provide useful information about LN characteristics and the relationship with age in MAP infected sheep. A culture and/or PCR must be done on the sampled lamb LN to determine if these lambs were MAP infected or not, even though no histological lesions were found.