Issues and special features of animal health research.

In the rapidly changing context of research on animal health, INRA launched a collective discussion on the challenges facing the field, its distinguishing features, and synergies with biomedical research. As has been declared forcibly by the heads of WHO, FAO and OIE, the challenges facing animal health, beyond diseases transmissible to humans, are critically important and involve food security, agriculture economics, and the ensemble of economic activities associated with agriculture. There are in addition issues related to public health (zoonoses, xenobiotics, antimicrobial resistance), the environment, and animal welfare.Animal health research is distinguished by particular methodologies and scientific questions that stem from the specific biological features of domestic species and from animal husbandry practices. It generally does not explore the same scientific questions as research on human biology, even when the same pathogens are being studied, and the discipline is rooted in a very specific agricultural and economic context.Generic and methodological synergies nevertheless exist with biomedical research, particularly with regard to tools and biological models. Certain domestic species furthermore present more functional similarities with humans than laboratory rodents.The singularity of animal health research in relation to biomedical research should be taken into account in the organization, evaluation, and funding of the field through a policy that clearly recognizes the specific issues at stake. At the same time, the One Health approach should facilitate closer collaboration between biomedical and animal health research at the level of research teams and programmes.

Listeria monocytogenes translocates throughout the digestive tract in asymptomatic sheep.

Ruminants are fed forage which is often contaminated with Listeria, and frequently shed Listeria monocytogenes with their faeces. The present study was designed to localize the sites of infection in the digestive tract concomitant with Listeria faecal excretion in a sheep model. Ten Listeria-free sheep were inoculated per os with a dose of 10(10) c.f.u. of a pathogenic L. monocytogenes strain. Listeria received by two of the ten animals were radiolabelled with (111)indium oxine. The dissemination of the Listeria was assessed by in vivo imaging, by culture of bacteria in the faeces, organs and digesta samples taken at slaughter on days 1, 2, 6, 10 and 14 post-inoculation, and by measuring gamma radioactivity of samples on day 6. It was shown that Listeria spread through the entire volume of the forestomachs within 4 h, and through the whole gastrointestinal tract (GIT) within 24 h. Faecal shedding of Listeria lasted 10 days. Rumen, duodenum, jejunum, ileum, caecum and colon walls and digesta, mesenteric lymph nodes, liver and spleen were temporarily infected. However, Listeria persisted for at least 14 days in rumen digesta and retropharyngeal lymph nodes, and at a relatively high level (1 x 10(4) c.f.u. g(-1)) in palatine tonsils. These findings suggest that L. monocytogenes can translocate from all parts of the GIT, with the rumen digesta, but not the gallbladder, serving as a reservoir. The results indicate that brief and low-level faecal excretion of L. monocytogenes is concomitant with a transitory asymptomatic infection in sheep.

Avirulence of viable but non-culturable Listeria monocytogenes cells demonstrated by in vitro and in vivo models.

The virulence of Viable But Non-Culturable (VBNC) cells of 4 strains of Listeria monocytogenes was investigated in both a human adenocarcinoma cell line (HT-29) and a mouse model. LO 28, ATCC 19115 and CNL 895807 strains of Listeria monocytogenes became VBNC when incubated in microcosm water at 20 degrees C and Scott A strain at 4 degrees C. No culturable bacteria were detected in the VBNC state, although 104 active cells/mL were found by the Direct Viable Count (DVC) and CTC-DAPI double staining methods. A comparison of virulence in both human adenocarcinoma cell line HT-29 and the mouse model showed that culturable controls were more virulent than VBNC cells, which appeared to be avirulent regardless of the virulence methods applied. Pathogenicity was tested in each model and was lost concomitantly with culturability, whereas some cells were still metabolically active (determined by CTC and DVC). Moreover, amplification of a 388 bp fragment with Immunocapture-PCR revealed the presence of Listeria monocytogenes DNA in all mixed spleen samples after intravenous injection of VBNC cells. These results demonstrate that VBNC cells were present in the mouse spleens. The results of the study suggest that Listeria monocytogenes strains might remain in the aquatic environment for prolonged periods in the VBNC state but these cells were not pathogenic in the conditions tested. These findings demonstrate the value of VBNC studies and show the need to investigate the role of VBNC cells in environmental transmission of Listeria monocytogenes. Further studies are needed in order to investigate the virulence of VBNC cells of Listeria monocytogenes after recovery of a culturable state.