Faecal egg counts and expulsion dynamics of the whipworm, Trichuris trichiura following self-infection

Egg excretion patterns of soil-transmitted helminth infections in humans following albendazole-ivermectin and albendazole treatment

BACKGROUND

Control efforts of soil-transmitted helminthiases rely primarily on large scale administration of anthelminthic drugs. The assessment of drug efficacies and understanding of drug behavior is pivotal to the evaluation of treatment successes, both in preventive chemo-therapy programs as well as in research of novel treatment options. The current WHO guidelines recommend an interval of 14-21 days between the treatment and follow-up, yet no in-depth analysis of egg excretion patterns of Trichuris trichiura after treatment has been conducted to date.

METHODS

Within the framework of a multi-country trial to assess the efficacy and safety of albendazole-ivermectin combination therapy vs albendazole monotherapy against T. trichiura infections, we conducted a study collecting daily stool samples over the period of 28 days post-treatment in 87 participants in Pak Khan, Lao PDR. Egg counts were derived by duplicate Kato-Katz on-site for T. trichiura, hookworm and Ascaris lumbricoides and stool sample aliquots were subsequently analyzed by qPCR for the detection of T. trichiura infections. Sensitivity and specificity was calculated for each day separately using data derived by Kato-Katz to determine the optimal timepoint at which to assess drug efficacy.

RESULTS

Egg excretion patterns varied across treatment arms. For T. trichiura, only the albendazole-ivermectin treatment led to a considerable reduction in mean egg counts, whereas both treatments reduced hookworm egg counts and A. lumbricoides were cleared in all participants after day 7. For T. trichiura, we found sensitivity to be highest at days 18 and 22 when using egg counts as outcome and days 19 and 24 when using qPCR. Specificity was high (>0.9) from day 14 onwards. For hookworm, the highest sensitivity and specificity were found at days 17 and 25, respectively.

CONCLUSIONS

Based on our study, the ideal time period to assess drug efficacy for soil-transmitted helminth infections would be between day 18 and 24. The current WHO recommendation of 14 to 21 days is likely to yield acceptable outcome measures for soil-transmitted helminth infections.

TRIAL REGISTRATION

NCT03527732.

Longevity of Trichuris trichiura infection in the human host

In this research, we present evidence-based data for the longevity of Trichuris trichiura on a healthy volunteer who had ingested eggs of T. trichiura. Hence, T. trichiura lives in a human host for at least 6 years and 5 months. Concurrently, this study highlighted consideration for returning travellers and migrants.

Population genomics of ancient and modern Trichuris trichiura

The neglected tropical disease trichuriasis is caused by the whipworm Trichuris trichiura, a soil-transmitted helminth that has infected humans for millennia. Today, T. trichiura infects as many as 500 million people, predominantly in communities with poor sanitary infrastructure enabling sustained faecal-oral transmission. Using whole-genome sequencing of geographically distributed worms collected from human and other primate hosts, together with ancient samples preserved in archaeologically-defined latrines and deposits dated up to one thousand years old, we present the first population genomics study of T. trichiura. We describe the continent-scale genetic structure between whipworms infecting humans and baboons relative to those infecting other primates. Admixture and population demographic analyses support a stepwise distribution of genetic variation that is highest in Uganda, consistent with an African origin and subsequent translocation with human migration. Finally, genome-wide analyses between human samples and between human and non-human primate samples reveal local regions of genetic differentiation between geographically distinct populations. These data provide insight into zoonotic reservoirs of human-infective T. trichiura and will support future efforts toward the implementation of genomic epidemiology of this globally important helminth.

Evidence for mitochondrial pseudogenes (numts) as a source of contamination in the phylogeny of human whipworms

Trichuris trichiura and T. suis are whipworms of humans and pigs, respectively, but it has recently been suggested that humans may be infected with multiple genotypes or species of Trichuris and cross-infection with Trichuris of pig origin has also been reported. In addition, the species status of Trichuris in non-human primates is unsettled and it is unknown how many whipworm species we share with other primates. Herein, we inferred the phylogeny of Trichuris collected from human, baboon and pig based on nuclear (18S and beta-tubulin) and mitochondrial (cox1) genes and evaluated the use of three PCR linked restriction fragment length polymorphism (PCR-RFLP) to identify worms. We found that all baboon worms clustered with human worms and that all these primate worms are different from T. suis. In general, there was an agreement between the phylogeny established based on the nuclear and mtDNA genes. However, we found evidence for non-targeted cox1 gene amplification for a subset of the human worms and suggest the presence of mitochondrial pseudogenes (numts) of pig cox1 gene in the human Trichuris genome. In conclusion, phylogenetic characterization of human whipworm based on the cox1 gene alone may be problematic without suitable preceded measures to avoid the numts amplification.

Mebendazole treatment persistently alters the size profile and morphology of Trichuris trichiura eggs

The soil transmitted whipworm, Trichuris trichiura affects about half a billion people globally. Diagnosis is based on identification of characteristic lemon-shaped eggs in stool samples. Occasionally large Trichuris eggs have been reported and have been ascribed to variation within T. trichiura or zoonotic infection with T. vulpis from dogs. We observed that the egg size profile changed markedly after anthelmintic treatment, and remained so, in a human individual self-infected with T. trichiura. The large eggs were detected with two standard diagnostic methods, Kato-Katz thick smear and salt-flotation (McMaster) method. It is therefore important to bear in mind that the morphology of parasite eggs may vary, e.g. in response to previous drug treatment. Large Trichuris eggs in human stool samples should not be diagnosed as T. vulpis infection without confirmation by other means.

Immune responses and parasitological observations induced during probiotic treatment with medicinal Trichuris suis ova in a healthy volunteer

Ingestion of eggs (ova) of the porcine nematode parasite Trichuris suis (TSO) may reduce the severity of autoimmune disorders, however the development of TSO treatment as a useful therapy for autoimmune diseases is hampered by a lack of knowledge on the development of the parasite and the nature of the local immune responses in humans. Here, we used colonoscopy to investigate the development of T. suis and related mucosal and systemic immune responses during TSO treatment in an intestinally healthy male volunteer. TSO treatment induced T. suis-specific serum antibodies, a transient blood eosinophilia, and increases in IFNγ⁺ and IL4⁺ cells within the circulating CD4⁺ T-cell population. Increased expression of genes encoding cytokines (IL4, IL10, IL17 and TGF-β), and transcription factors (FOXP3, GATA3 and RORC) were apparent in the ascending and transverse colon (the predilection site of the worms), whereas only limited changes in gene expression were observed proximally (ileum) and distally (descending colon) to the infected tissue. We further show that T. suis is able to colonise the human colon, with a number of worms developing to a similar size and morphology observed in the natural pig host, and a small number of unembryonated eggs were passed in the faeces, indicating patent infection. Notably, the volunteer experienced a substantial improvement in psoriasis during the course of TSO treatment. Thus, TSO treatment induced a mixed Th1/Th2/T regulatory response at the local site of infection, which was also reflected to some extent in the peripheral circulation. These results, together with the first definitive observations that T. suis can mature to adult size and reproduce in humans, shed new light on the interaction between the human immune system and probiotic helminth treatment, which should facilitate further development of this novel therapeutic option.