Soil-borne helminth infections (STH) are among the most common and widespread infections. It is currently estimated that more than 1.5 billion people are infected with helminths worldwide, and more than a quarter of the world’s population is expected to be at risk of infection.

The four main groups of nematodes responsible for STH infections in humans include the giant roundworm (Ascaris lumbricoides), Whipworm (Trichuris trichiura), Roundworm (Strongyloides stercoralis) and hookworms (Ancylostoma duodenale and Necator americanus).

Life cycle of Trichuris trichiura inside and outside the human body. Source: CDC, public domain – https://www.cdc.gov/dpdx/trichuriasis/index.html

These parasitic nematodes enter the host through ingestion of soil contaminated with embryonated eggs. In case of Trichuris trichuiraOnce the eggs are hatched, juvenile worms grow and mature and then migrate to the host’s cecum where they invade the intestinal lining to feed on the host’s blood and tissues. Penetrating worms destroy parts of the intestinal epithelium and disrupt normal intestinal homeostasis.

Chronic STH infections can lead to blood loss-induced anemia, abdominal pain, diarrhea and malnutrition and cause almost 5 million years of life for people with disabilities (DALYs) worldwide.

Infection with STHs, such as Trichuris trichiuraThe resulting disruption of the intestinal epithelium has been reported to disrupt the host’s gut microbiome and increase the incidence of potentially pathogenic gut bacteria.

The disruption of a healthy gut microbiome by infection with GH opens an interesting avenue of research, as the microbial community in the human gut has been shown to play a crucial role in nutrient uptake and metabolic modulation. It also supports immune system development and is heavily involved in maintaining the host’s health.

Studying the interactions between helminths and the human gut microbiota could therefore lead to the development of alternative GH infection treatments, a better understanding of infectious pathology, and possibly even novel treatments for autoimmune and chronic inflammatory diseases.

Hong-liang Chen and colleagues decided to study this interaction and characterize the differences in intestinal bacterial communities between helminth-infected and uninfected individuals.

Your investigation
The researchers recruited 32 mother-child pairs from the island of Pemba off the coast of Tanzania and monitored the differences in gut microbiota from uninfected and Trichuris trichiura-infected mothers and children.

At the beginning, stool samples were taken from each participant and examined for the presence of T. trichiura. The parasitological diagnosis indicated that seventeen samples (11 mothers and 6 children) were positive T. trichiura Infection.

Next, to evaluate differences in the composition of gut microbes between T. trichiura For helminth infected and uninfected participants, DNA was extracted from all feces of the participants. From this extracted DNA, the 16S ribosomal RNA (a genetic marker useful in identifying bacteria) was amplified and sequenced to identify the presence of intestinal bacterial species from each participant. The frequency of identified bacteria between helminth infected and uninfected mothers and children was then analyzed at the phylum and genus level.

Microbiome differences between T. trichiura-infected and uninfected participants
The researchers found that there were significant differences between the entire gut microbial community in both helminth-infected mothers and children compared to uninfected mothers, which shows T. trichiura Infection is associated with changes in the composition of the intestinal microbiome. Interestingly, infection with T. trichiura actually appeared to increase gut microbial biodiversity in both mothers and children.

For example, Succinivibrio (Phylum Proteobacteria) was a genus of anaerobic bacteria that was less abundant in helminth-infected mothers and children, while those in the Ruminococcaceae family (Phylum Firmicutes) were more abundant.

Animals infected with helminths show an increase in microbial diversity in the intestine in mothers (a) and children (b), which is carried out with three different measures. Observed OTUs, Shannon Index, and Faith’s Phylogenetic Diversity Index (from left to right). MN = uninfected mothers, MP = mothers infected with helminths. CN = uninfected children, CP = children infected with helminths.

Source: Chen et al., Parasites & Vectors 2021. CC BY 4.0.

T. trichiura Infection affects the intestinal bacterial communities of mothers and children differently
The team also showed similarities and differences in the microbial composition of the gut between helminth-infected mothers and children. For example reciprocal bacteria from the Akkermansia and Lactobacillus Genera were more enriched in mothers infected with helminths than in non-infected mothers. However, the frequency of these normal intestinal bacteria was significantly reduced in children infected with helminths compared to uninfected children. Children infected with helminths, microbiota, also saw an increase in the incidence of opportunistic bacteria Enteroccocus.

The genus Campylobacter, known to contain several disease-causing bacteria, also showed different trends between helminth-infected mothers and children (increased in mothers compared to children).

Clear differences in the intestinal microbe community can be seen between uninfected and helminth-infected mothers (a) and children (b). Others represent all genera with a relative frequency <0.5%.

Source: Chen et al., Parasites & Vectors, 2021.

Effects of altered intestinal microbial community on the host
Although helminth-infected participants showed an increase in gut microbial biodiversity, the incidence of beneficial, beneficial bacteria was lower in those infected with helminths, while opportunistic and possibly pathogenic bacteria were much higher in incidence (dysbiosis).

The lesser amount of Succinivibrio For example, it has been suggested that helminth-infected children may have disrupted normal digestion of carbohydrates because these bacteria are involved in breaking down starch and hemicellulose. Also of interest is the significantly lower incidence of Lactobacillus in children infected with helminths Lactobacillus is a beneficial bacterium that supports the digestive process, protects against pathogenic bacteria and promotes / modulates normal immunological responses to infections.

Likewise the reduced frequency of Akkermansia spp. Of particular concern in children infected with helminths compared to uninfected children is that these types of bacteria are beneficial and protect the gut by converting mucins to short chain fatty acids (SCFA), which are believed to mediate anti-inflammatory effects in the gut. In addition, other SCFA-producing intestinal bacteria, such as Blautia (in children infected with helminths) and Prevotella 2 (in helminth-infected mothers) showed lower incidence and potentially delivered a double blow to SCFA-induced anti-inflammatory protection, a process particularly required in infections with intestinal wall-digging helminths such as T. trichiura.

Finally, the significantly higher frequency of Campylobacter In helminth-infected mothers, an increasing number of mothers is particularly alarming Campylobacter spp. Substances found in humans have been shown to be resistant to a range of antibiotics and, as such, a global campylobacteriosis surveillance network has been proposed.

Possible advances in therapies and control measures
The knowledge gained about the effects of helminth colonization on the human intestinal microbiome as well as the possible roles and contributions of important intestinal bacteria to the human host have led to a better understanding of the interactions between helminths and microbiota and could support the development of new measures and strategies to disrupt the Control transmission Trichuris trichiuraand possibly other STH in the future.

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