Ajakaye, O. G. | bioRxiv Science

bioRxiv2024

Genomic data reveal a north-south split and introgression history of blood fluke (Schistosoma haematobium) populations from across Africa

The human parasitic fluke, Schistosoma haematobium hybridizes with the livestock parasite S. bovis in the laboratory, but the frequency of hybridization in nature is unclear. We analyzed 34.6 million single nucleotide variants in 162 samples from 18 African countries, revealing a sharp genetic discontinuity between northern and southern S. haematobium. We found no evidence for recent hybridization. Instead the data reveal admixture events that occurred 257-879 generations ago in northern S. haematobium populations. Fifteen introgressed S. bovis genes are approaching fixation in northern S. haematobium with four genes potentially driving adaptation. We identified 19 regions that were resistant to introgression; these were enriched on the sex chromosomes. These results (i) suggest strong barriers to gene flow between these species, (ii) indicate that hybridization may be less common than currently envisaged, but (iii) reveal profound genomic consequences of rare interspecific hybridization between schistosomes of medical and veterinary importance.

evolutionary biology↗

bioRxiv2024

Giardia intestinalis reshapes mucosal immunity toward a Type 2 response that attenuates inflammatory bowel-like diseases

Diarrheal diseases are the second leading cause of death in children worldwide. Epidemiological studies show that co-infection with Giardia intestinalis decreases the severity of diarrhea. Here, we show that Giardia is highly prevalent in the stools of asymptomatic school-aged children. It orchestrates a Th2 mucosal immune response, characterized by increased antigen-specific Th2 cells, IL-25, Type 2-associated cytokines, and goblet cell hyperplasia. Giardia infection expanded IL-10-producing Th2 and GATA3+ Treg cells that promoted chronic carriage, parasite transmission, and conferred protection against Toxoplasma gondii-induced lethal ileitis and DSS-driven colitis by downregulating proinflammatory cytokines, decreasing Th1/Th17 cell frequency, and preventing collateral tissue damage. Protection was dependent on STAT6 signaling, as Giardia-infected STAT6-/- mice no longer regulated intestinal bystander inflammation. Our findings demonstrate that Giardia infection reshapes mucosal immunity toward a Type 2 response, which confers a mutualistic protection against inflammatory disease processes and identifies a critical role for protists in regulating mucosal defenses.

immunology↗

bioRxiv2023

Extant interspecific hybridization among trematodes within the Schistosoma haematobium species complex in Nigeria

BackgroundNatural interspecific hybridization between the human parasite (Schistosoma haematobium [Sh]) and bovine parasites (S. bovis [Sb], S. curassoni [Sc]) is increasingly reported in Africa. We developed a multi-locus PCR DNA-Seq strategy that amplifies two unlinked nuclear (transITS, BF) and two linked organellar genome markers (CO1, NAD5) to genotype S. haematobium eggs collected from infected people in Ile Oluji/Oke Igbo, Ondo State (an agrarian community) and Kachi, Jigawa State (a pastoral community) in Southwestern and Northern Nigeria, respectively. Principal FindingsWe applied this methodology against 57 isolates collected from a total of 219 participants. All patients from Jigawa state were infected with just one of two haplotypes of an S. haematobium x S. bovis hybrid based on sequences obtained at CO1, NAD5, transITS and BF markers. Whereas samples collected from Ondo state were varied. Mitonuclear discordance was observed in all 17 patients, worms possessed an Sb mitochondrial genome but one of four different haplotypes at the nuclear markers, either admixed (heterozygous between Sh x Sc or Sh x Sb) at both markers (n=10), Sh at BF and admixed at transITS (Sh x Sc) (n=5), admixed (Sh x Sc) at BF and homozygous Sc at transITS (n=1) or homozygous Sh at BF and homozygous Sc at transITS (n=1). SignificancePrevious work suggested that zoonotic transmission of S. bovis in pastoral communities, where humans and animals share a common water source, is a driving factor facilitating interspecific hybridization. However, our data showed that all isolates were hybrids, with greater diversity identified in Southwestern Nigeria, a non-pastoral site. Further, one patient possessed an S. bovis mitochondrial genome but was homozygous for S. haematobium at BF and homozygous for S. curassoni at transITS supporting at least two separate backcrosses in its origin, suggesting that interspecific hybridization may be an ongoing process. Author SummaryInterspecific hybridization between trematode parasites poses serious health risks to humans. Many systems have shown possible hybridization between different schistosome species. As evidence of natural hybridization between human S. haematobium and animal S. bovis or S. curassoni has grown in recent years, epidemiological surveys across potential hybrid zones are required, particularly in endemic African regions. According to several reports, indiscriminate human-animal water contact is a major factor contributing to hybridization of human and animal schistosomes. We collected and genotyped 57 parasite isolates from pastoral and non-pastoral communities in Kachi, Jigawa state, and Ile Oluji/Oke Igbo, Ondo state, Nigeria to screen for hybrids. In both sites, we found Schistosoma hybrids with mitonuclear discordance and repeated backcrossing between S. haematobium, S. bovis, and S. curassoni. Contrary to previous reports, Schistosoma hybrids appear to be widespread and not solely dependent on human-animal water interactions.

microbiology↗