Ability of the Probiotic Vivomixx to Improve Environmental Enteropathy in Pregnant Women: a Proof of Concept Trial in Bangladesh, Pakistan, Senegal and Zambia

Stunting in young children refers to attenuated linear growth. In the year 2020, 149.2 million children under the age of 5 years of age were stunted, accounting for 22% of stunting globally. Stunting has short- and long-term consequences of increased morbidity and mortality, impairment of neurocognitive development, impaired responses to oral vaccines, and increased risk of noncommunicable diseases. Stunting is partly driven by Environmental Enteric Dysfunction (EED), an enteropathic condition characterised by altered gut permeability, infiltration of immune cells and changes in villous architecture and cell differentiation. EED may help explain why nutritional supplementation either during pregnancy or early childhood has minimal value in correcting childhood stunting. Indeed, EED is believed to be responsible for 40% of childhood stunting.

Disruption in intestinal barrier function affects gut immune homeostasis, nutrient flows, and consequently dysbiosis in the gut microbiome. The gut microbiota consists of 100 trillion bacteria which interact with epithelial cells, the mucus layer and the mucosal immune system that balances tolerance and effector functions. Thus, the gut microbiome has an important role in shaping the responsiveness of the gut immune system. The mucus barrier and the normal gut microbiota limit enteropathogen colonisation. Influx of bacteria from the lumen to the systemic circulation represents microbial translocation and initiation of systemic of inflammatory process through recognition of pathogenassociated molecular patterns (PAMPs) by Pattern Recognition Receptors (PRRs) present on Antigen Presenting Cells (APCs). Three fundamental processes drive the epithelial damage which is so important in EED: infection, undernutrition, and immune dysfunction. Multiple clinical trials show that efforts to correct malnutrition through conventional therapies and improving hygiene and sanitation do not overcome growth deficits by more than about 10%. There is increasing interest in the use of probiotics which may allow pathogen decolonization, improve barrier function and restore overall gut homeostasis. Such therapies are at early stage of trials but may have potential in addressing the global burden of EED, by improving barrier function and gut pathophysiology.

Colonization of gut by enteropathogens is common in children with EED. These include ETEC, Campylobacter, Shigella and Salmonella species. Consistent data from Bangladesh and Zambia show that children with refractory stunting carry over four pathogens on average, whilst controls carry less than two. There is also clear evidence of altered composition of the microbiota in children with EED.

Probiotics may serve to overcome the problem of EED through all mechanisms of pathogenicity, by providing additional bacteria that may help in intestinal decolonization of pathogenic microorganisms (changing the microbiological niche), promoting epithelial healing, improving nutrient absorption, and restoration of an appropriate immune balance between tolerance and responsiveness.

To date the focus of research on childhood stunting has been on the young child. It is increasingly appreciated, however, that stunting often begins in utero and the focus has shifted to women's health and pregnancy. For example, the Lancet 2021 Series on maternal and child undernutrition states that "Investments to reduce undernutrition in women are important not only for women's own health but also for the health and nutrition of their children". Results from rural Bangladesh reveal poor gestational weight gain that ultimately leads to intrauterine growth restriction, low birth weight and ultimately stunting and wasting. Furthermore, another study recently completed in slum settlements of Dhaka, Bangladesh demonstrated a high prevalence of EED among undernourished women. Intestinal histopathology was abnormal in more than 80% of women. We postulate that growth retardation in utero is a consequence of EED in the mother during pregnancy and lactation. This leads to systemic inflammation, which leads to disadvantageous partitioning of nutrients, and reduced nutrient availability.