Evidence of heterozygosity and recombinant alleles in single cysts of Giardia duodenalis.

Giardia duodenalis is divided into eight assemblages (named A to H). Isolates of assemblage A are divided into four sub-assemblages (AI, AII, AIII and AIV). While isolates of sub-assemblage AII are almost exclusively detected in human hosts, isolates of assemblage B are encountered in a multitude of animal hosts and humans. Here, we isolated single cysts of G. duodenalis from a human stool sample and found that one of them had overlaps of assemblage AII and B alleles and an unexpectedly high number of variants of the beta-giardin (Bg) and GLORF-C4 (OrfC4) alleles. In addition, one of the Bg alleles of that cyst had a fragment of sub-assemblage AII interspersed with fragments of assemblage B, thus indicating that this allele may be a recombinant between sequences A and B. Our results are unprecedented and put a check on the statement that different assemblages of G. duodenalis represent species with different host specificities.