Molecular Characterisation of Giardia lamblia Assemblages in Children and Domestic Animals in Ogun State

The zoonotic transmission potential of Giardia lamblia is determined by assemblage type, as assemblages A and B infect both humans and animals, while C through H are largely host-specific. Characterising assemblage distribution is therefore critical for understanding transmission pathways in households with shared human-animal contact. This study molecularly characterised G. lamblia assemblages in children and domestic animals in rural communities of Ogun State, Southwest Nigeria. Stool samples from 200 children under ten years and 180 domestic animals including dogs, goats, and cattle were screened by microscopy and confirmed by PCR targeting the triose phosphate isomerase (tpi) gene. Positive samples were sequenced and assemblages assigned by phylogenetic analysis. G. lamblia was confirmed in 19.0 percent of children and 14.4 percent of animals. Assemblage B predominated in children (64.2 percent), while assemblage A was more common in animals. Genetically identical tpi sequences were found in child-animal sample pairs from three households, providing molecular evidence for zoonotic transmission events. Dog ownership without anthelmintic treatment and children's direct contact with livestock were significant risk factors for assemblage A infection. These findings confirm zoonotic Giardia transmission in rural Ogun State and call for integrated one-health interventions addressing human and animal reservoirs simultaneously. Keywords: Giardia lamblia, assemblage typing, zoonosis, molecular characterisation, Ogun State.