||Most infectious agents have been investigated in experimental studies with only one pathogen, but concurrent infections with more pathogenic agents in the mammalian host are common. Concomitant infections may affect the course, and the resulting disease outcome, of each pathogen. As the vast majority of gastrointestinal parasitic and bacterial infections in man and pig are subclinical, our primary aim was to establish and investigate the interaction between two such infections, using primarily an Oesophagostomum-Salmonella pig model. Ascaris suum and Trichuris suis were furthermore included in one experiment. Salmonella Oesophagostomum, Ascaris and Trichuris coexist naturally in pig herds in Denmark and possible interactions were therefore relevant to investigate. Parts of the experiments were designed to examine the influence of an initial helminth infection on the outcome of a challenge S. Typhimurium infection. In these experiments, it was also possible to study the effect of the superimposed S. Typhimurium infection on the further development of the primary helminth infection. In other experiments, we measured the effect of a challenge helminth infection on a primary natural or experimental Salmonella infection. We measured the size of infections on the basis of egg, bacterial and worm counts, supplemented by clinico-pathological and pathological assessments. Immunological responses, apart from blood cell counts, were examined in some experiments using intracellular staining and flow cytometry.
Increased S. Typhimurium excretion in pigs could be induced by infection with large doses of Oesophagostomum, but no clear interactions were found between the other frequently occurring helminths and S, Typhimurium as well as with lower doses of Oesophagostomum. It may be concluded that helminth-S. Typhimurium interactions are not of significant importance on herd level for fluctuations in and persistence of S. Typhimurium infections.
A cross sectional study was furthermore performed in Guinea-Bissau, West Africa, with the objective to demonstrate possible associations between intestinal WDWDS and other enteropathogens in children aged four to 12 years and mostly harbouring subclinical infections. No overall interaction between helminths and bacteria were found, but Entamoeba histolytica appeared to be linked with helminth infections. Risk of infection with helminths was furthermore increased with increasing age, male sex, and presence of chickens in the neighbouring family. Maternal school attendance, belonging to a Muslim family, or having electricity decreased the risk of helminth infection. The study was carried out in the dry season in a population with hookworms as the dominant helminth infection. Had the study been carried out in a different season and in an area with other pathogenic helminths, the picture may have been different.