Passive immunotherpay and probiotic agents in enteric infections in children

Abstract

Diarrhoeal disease remains one of the leading causes of global childhood morbidity and mortality. Rotavirus and pathogenic Escherichia coli are the most common causes of acute diarrheal illness in children. Oral rehydration therapy (ORT), although effective in management or prevention of dehydration, does not reduce the duration or severity of illness. Hence, there is a need for new interventions to further improve therapy for gastrointestinal (GI) tract infections.

We hypothesized that neutralizing antibodies from immunized animal can be used to modulate infections due to diarrhoeal pathogens. The growing understanding of the host-microbe interactions and the role of the indigenous flora on competence of the immune system allowed us to also hypothesize that probiotic agents (health promoting bacteria) could be useful adjunct in the management of infectious diarrhea.

Helicobacter pylori infection is another common infection and affects 50% of world population, and is associated with peptic ulcer disease, gastritis and gastric cancer. Current antibiotic therapy is complex, expensive, is associated with adverse events and often induces resistance. Therefore, alternative approaches for treating such infections are highly desirable.

The objectives of this thesis were to evaluate the potential of oral administration of pathogen-specific antibodies derived from different animal sources, notably immunoglobulin from immunized bovine colostrum (HBC) in rotavirus-induced diarrhea (paper I), from milk concentrate (BIC) in E coli-induced diarrhea (paper II) and H. pylori infections (paper III), and hyperimmune chicken egg yolk (HEY) in rotavirus (RV) induced diarrhea (paper IV) in children. We also evaluated the therapeutic efficacy of a probiotic agent, Lactobacillus paracsei (ST 11) in children with diarrhea (paper V). In order to find a stable form of antibodies and determine potential for cost-effective, large-scale production needed for use in the developing countries, we evaluated if fragments derived from llama produced in yeast, are capable of reducing diarrhea morbidity in mice (paper VI). Finally, to see the therapeutic potentials and to optimize the dose a separate study with lgY was conducted in an infant mouse model of rotavirus-induced diarrhoea (paper VII).

We found impressive results with HBC in ameliorating rotavirus diarrhoea in children (Paper I), but it did not see any effect on the course of E. coli-induced diarrhea or H. pylori infection (Paper II and III) in children. We observed a modest beneficial effect of IgY treatment in reducing morbidity in children with rotavirus diarrhea (Paper IV). In the probiotics study, we failed to observe any beneficial effect of ST11 treatment in the management of rotavirus diarrhoea, however, the probiotic treatment significantly ameliorated morbidity in children with non-rotavirus diarrhoea (Paper V). In paper VI, we demonstrated that monovalent llama-derived antibody fragments produced in yeast. were able to bind to rotavirus G3 strains in vitro. In vivo, these fragments reduced morbidity from rotavirus-induced diarrhoea in mice (Paper VI) demonstrating a potential for its therapeutic use in humans. The use of a mouse model of rotavirus diarrhoea allowed us to evaluate therapy with higher doses of IgY, and the results suggested that an improved therapeutic effect could be achieved (paper VII).

Conclusion: Administration of specific antibodies showed an impressive clinical efficiency against rotavirus diarrhea but had no impact on E. coli-induced diarrhea or H. pylori infection. Feeding of Lactobacillus paracesi ST11 did not produce any clinical benefit in rotavirus diarrhoea; however, the bacteria produced clinical benefits to patients with diarrhoea not due to rotavirus (possibly induced by E. coli or other un-identified bacteria). The divergent effects observed are interesting; our results suggest efficacy of orally administered antibodies against viral pathogens, and a possible effect of orally administered probiotic bacteria on bacterially induced diarrhea. From these findings, it seems likely that a combination therapy using antibodies and probiotic agents could elicit therapeutic benefit in settings where diarrhoea in a majority of children are caused by rotavirus or E. coli.