Effect of Echinostoma caproni on Presumptive Lactic Acid Bacteria Abundance and Salmonella enterica Serovar Typhimurium Colonization in the Mouse Gut

Co-infections of mammalian hosts with intestinal helminths and bacterial pathogens are common, especially in areas with inadequate sanitation. Interactions between co-infecting species and host microbiota can cause significant changes in host immunity, disease severity, and pathogen transmission, requiring unique treatment for each case. A greater understanding of the influences of parasite-bacteria co-infections will improve diagnosis and therapeutic approaches to control infectious diseases. To study the influence of the trematode parasite Echinostoma caproni on commensal and pathogenic bacteria in the mouse gut, we examined the abundance of intestinal lactic acid bacteria and Salmonella enterica serovar Typhimurium in control mice not exposed to E. caproni (P-) or S. Typhimurium (S-), E. caproni-infected (P+S-), S. Typhimurium-infected (P-S+), and E. caproni-S. Typhimurium co-infected (P+S+) mice, and determined bacterial burdens in the livers and spleens of the P-S+ and P+S+ mice. We also examined a subset of P+S- and P+S+ mice for survival and the relative location of E. caproni in the small intestine. The numbers of presumptive lactic acid bacteria were significantly higher in the P+S+ and P-S+ mice compared to the uninfected mice, and S. Typhimurium colonization in the liver and spleen was significantly reduced in the P+S+ mice compared to the P-S+ mice. Echinostoma caproni were located anteriorly in the intestine of P+S- mice, while in the P+S+ mice, the parasites were distributed more posteriorly. Survival of E. caproni was unaffected in either group. The results of our study suggest that E. caproni facilitates a higher abundance of presumptive lactic acid bacteria in the mouse intestine and reduces colonization of S. Typhimurium in the liver and spleen of the co-infected host.

Effects of Echinostoma caproni infection on the neutral and polar lipids of intestinal and non-intestinal organs in the BALB/c mouse as determined by high-performance thin-layer chromatography

The goal of this study was to characterize and quantify the various neutral and polar lipid classes in the BALB/c mouse that are associated with Echinostoma caproni infection. Ten infected mice and 10 uninfected control mice were used for this study (five infected and five uninfected were used for each of the neutral lipid and polar lipid studies). After 3 weeks postinfection, the mice were necropsied and various organs were removed and prepared for lipid class analysis. The organs used were liver, kidney, spleen, colon, cecum, anterior portion of the small intestine (SI), middle portion of the SI, and posterior portion of the SI. Lipids were determined by high-performance thin-layer chromatography (HPTLC) with Analtech 10 x 20 cm HPTLC-HLF silica gel plates. For neutral lipids, petroleum ether-diethyl ether-glacial acetic acid (80:20:1) mobile phase and 5% ethanolic phosphomolybdic acid detection reagent were used to determine the neutral lipids in each organ. Chloroform-methanol-deionized water (65:25:4) mobile phase and 10% cupric sulfate in 8% phosphoric acid detection reagent were used to determine the polar lipids in each organ. The analyzed polar lipids in all organs were phosphatidylcholine (PC), phosphatidylethanolamine (PE), and sphingomyelin (SM). Using HPTLC-densitometry for quantification, PC was found in the greatest amount and SM the smallest of all organs analyzed. The PE in the anterior portion of the SI was determined to be significantly greater (using the Student's t test with P < 0.05), with about twice the amount of PE in mice infected with E. caproni relative to the uninfected mice. No significant differences in any of the neutral lipid classes were found between infected and uninfected samples.

The selection of experimental doses and their importance for parasite success in metacercarial infection studies

Experimental studies of parasite transmission are essential for advances in basic and applied parasitology. A survey of the results of published experiments can identify the determinants of both variation among studies in experimental design and of parasite infection success. Here, analyses are conducted on data compiled from a total of 106 metacercarial infection experiments (35 on Echinostomatidae, 37 on Fasciolidae, 34 on other trematodes) obtained from 83 studies. All of these involved experimental oral infection of individual definitive hosts by a single known dose of metacercariae under controlled conditions. Across these studies, the metacercarial dose used (i) was typically about 10 times higher than the average natural dose that could be acquired by feeding on intermediate hosts (for taxa other than Fasciolidae), and (ii) showed a positive relationship with the body mass of the definitive host, although this relationship was only significant for Fasciolidae. Although the chosen dose was rarely justified, the larger the definitive host, the more metacercariae it received. Among Echinostomatidae and Fasciolidae, there was also a significant dose-dependent effect on infection success: the higher the dose used in an experiment, the smaller the proportion of metacercariae recovered from the host. This effect was mitigated by definitive host body mass, with infection success being generally lower in larger definitive hosts. For Echinostomatidae, the taxonomic identity of the definitive host also mattered, with metacercariae achieving higher infection success in mammals than in birds. The present findings suggest that the design of experimental infection studies requires greater consideration if their results are to yield useful biological insights.

In vitro and in vivo trematode models for chemotherapeutic studies

Schistosomiasis and food-borne trematodiases are chronic parasitic diseases affecting millions of people mostly in the developing world. Additional drugs should be developed as only few drugs are available for treatment and drug resistance might emerge. In vitro and in vivo whole parasite screens represent essential components of the trematodicidal drug discovery cascade. This review describes the current state-of-the-art of in vitro and in vivo screening systems of the blood fluke Schistosoma mansoni, the liver fluke Fasciola hepatica and the intestinal fluke Echinostoma caproni. Examples of in vitro and in vivo evaluation of compounds for activity are presented. To boost the discovery pipeline for these diseases there is a need to develop validated, robust high-throughput in vitro systems with simple readouts.