Abstract
Background Giardia duodenalis is prevalent in tropical settings where diverse opportunities exist for transmission between people and animals. We conducted a cross-sectional study of G. duodenalis in people, livestock, and wild primates near Kibale National Park, Uganda, where human-livestock-wildlife interaction is high due to habitat disturbance. Our goal was to infer the cross-species transmission potential of G. duodenalis using molecular methods and to investigate clinical consequences of infection.Methodology/Principal FindingsReal-time PCR on DNA extracted from fecal samples revealed a combined prevalence of G. duodenalis in people from three villages of 44/108 (40.7%), with prevalence reaching 67.5% in one village. Prevalence rates in livestock and primates were 12.4% and 11.1%, respectively. Age was associated with G. duodenalis infection in people (higher prevalence in individuals ≤15 years) and livestock (higher prevalence in subadult versus adult animals), but other potential risk factors in people (gender, contact with domestic animals, working in fields, working in forests, source of drinking water, and medication use) were not. G. duodenalis infection was not associated with gastrointestinal symptoms in people, nor was clinical disease noted in livestock or primates. Sequence analysis of four G. duodenalis genes identified assemblage AII in humans, assemblage BIV in humans and endangered red colobus monkeys, and assemblage E in livestock and red colobus, representing the first documentation of assemblage E in a non-human primate. In addition, genetic relationships within the BIV assemblage revealed sub-clades of identical G. duodenalis sequences from humans and red colobus.Conclusions/SignificanceOur finding of G. duodenalis in people and primates (assemblage BIV) and livestock and primates (assemblage E) underscores that cross-species transmission of multiple G. duodenalis assemblages may occur in locations such as western Uganda where people, livestock, and primates overlap in their use of habitat. Our data also demonstrate a high but locally variable prevalence of G. duodenalis in people from western Uganda, but little evidence of associated clinical disease. Reverse zoonotic G. duodenalis transmission may be particularly frequent in tropical settings where anthropogenic habitat disturbance forces people and livestock to interact at high rates with wildlife, and this could have negative consequences for wildlife conservation.
Highlights
Giardia is a genus of parasitic protozoan that infects the small and large intestines of a broad range of vertebrate hosts [1]
G. duodenalis infection in people was not associated with other factors related to behavior and hygiene, and infected people were no more likely to have reported gastrointestinal symptoms than were uninfected people
These results demonstrate that G. duodenalis transmission from humans and domestic animals to wildlife may occur with ease in locations such as western Uganda, where habitat disturbance causes ecological overlap among people, livestock, and primates
Summary
Giardia is a genus of parasitic protozoan that infects the small and large intestines of a broad range of vertebrate hosts [1]. Considered among the most common human intestinal protozoa, especially in the tropics [2], G. duodenalis ranges in clinical severity from asymptomatic to highly pathogenic [3]. Both host factors (e.g. nutrition, immunity, co-infection with other agents) and pathogen factors (e.g. strain, infectious dose) are thought to contribute to the clinical severity of giardiasis [2]. Most studies that have applied molecular methods to G. duodenalis in wild mammals have found that samples fall into assemblages A or B, which characteristically infect people, concluding that the animal hosts involved may represent reservoirs of infection for humans (e.g [7,9,10,11,12,13]). Our goal was to infer the cross-species transmission potential of G. duodenalis using molecular methods and to investigate clinical consequences of infection
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