Ligated ileal loops of calves were inoculated with live and heat-killed Mycobacterium paratuberculosis and were examined by light and electron microscopy. At 5 hours after inoculation, acid-fast bacilli were in subepithelial macrophages, but not in M cells covering domes. At 20 hours, more than 50 acid-fast bacilli per cross section were in subepithelial macrophages in domes. Both living and heat-killed bacilli passed into domes. Addition of anti-M. paratuberculosis bovine serum to the inoculum enhanced entry of bacteria into domes. By electron microscopy, intact bacilli with electron-transparent zones (peribacillary spaces) were in the supranuclear cytoplasm of M cells at 20 hours. M cells also contained vacuoles, including electron-dense material interpreted as degraded bacilli. Subepithelial and intraepithelial macrophages contained bacilli and degraded bacterial material in phagosomes. These results suggest that calf ileal M cells take up bacilli, and that subepithelial and intraepithelial macrophages secondarily accept bacilli or bacterial debris which are expelled from M cells.

Laboratory raised wild Norway rat males (Rattus norvegicus) were injected with leptospires of two serovars: icterohaemorrhagiae and grippotyphosa. The development of a carrier state was monitored serologically, culturally and histologically. Rats infected with icterohaemorrhagiae developed rapidly into a chronic carrier state and shed leptospires in the urine for the duration of the experiment (220 days). At the time of necropsy, histopathologic studies showed evidence of leptospiral infections in the lumen of proximal convoluted tubules of some kidneys. Rats infected with grippotyphosa shed organisms for 40 days after inoculation; thereafter, they apparently cleared the infection. No organisms were detected histologically nor by culture at the end of the experiment (220 days). There appears to be a specific host-parasite relationship in the Norway rat towards becoming chronic carriers when infected with serotype icterohaemorrhagiae but not with grippotyphosa.

The One Health paradigm for global health recognizes that most new human infectious diseases will emerge from animal reservoirs. Little consideration has been given to the known and potential zoonotic infectious diseases of small companion animals. Cats and dogs closely share the domestic environment with humans and have the potential to act as sources and sentinels of a wide spectrum of zoonotic infections. This report highlights the lack of a coordinated global surveillance scheme that monitors disease in these species and makes a case for the necessity of developing a strategy to implement such surveillance.

The genomes of leptospiral field isolates belonging to serogroup Pomona were analyzed and compared with those of type strains by cleavage with restriction endonucleases. This new classification method shows differences among these organisms not indicated by the conventional serological typing method. No differences were observed among isolates from the United States, Canada, and New Zealand. Although all isolates selected for this study had been serologically typed as belonging to serovar pomona, the restriction endonuclease analysis indicates that they belong to serovar kennewicki. kennewicki, a serovar of North American origin, has recently been eliminated from the official serovar list because it was found to be indistinguishable from serovar pomona by the serological method.