Molecular Typing of Giardia lamblia in Humans and Dogs and Evidence for Sexual Recombination

Abstract

Giardia lamblia is a eukaryotic parasite that causes diarrhea in humans worldwide. Diarrheal diseases cause stunting and mental retardation in children in developing nations, therefore it is important to understand the molecular epidemiology of G. lamblia. Compounding this, it is not clear if companion animals such as dogs contribute to infections in humans through zoonotic transmission. The genotypes of G. lamblia that have been found in humans are A1, A2 and B, while those in dogs have been on rare occasions all three human genotypes, but largely C and D, which have only been reported in dogs and appear to be species-specific. The molecular epidemiology of G. lamblia in humans and dogs was assessed in an endemic region of Lima, Peru. With one exception, dogs were found to harbor the C and D dog genotypes of G. lamblia. A single family dog was found to harbor a human genotype of G. lamblia. A2 and B genotypes of G. lamblia, but not A1, were found in humans in the endemic region. Previous literature reported that A2 and B typing within genotype tools were available, however the A2 samples from the endemic region could not be distinguished from one another through nucleotide polymorphism sequence analysis. A molecular typing technique was developed to type A2 samples. The extensive sequence analysis performed on two chromosomes of G. lamblia, yielded different phylogenetic tree groupings for the same samples. This lead to algorithmic analysis, which demonstrated a significantly high probability that meiotic recombination is occurring in the A2 samples of G. lamblia. As G. lamblia is largely believed to be asexual, the conclusion of doctoral research performed in this study yielded controversial, yet significant evidence that sex in G. lamblia A2 genotype samples is indeed occurring.