title: Multilocus genotyping of human Giardia isolates suggests limited zoonotic transmission and association between assemblage B and flatulence in children.
abstract: BACKGROUND
  Giardia intestinalis is one of the most common diarrhea-related parasites in humans, where infection ranges from asymptomatic to acute or chronic disease. G. intestinalis consists of eight genetically distinct genotypes or assemblages, designated A-H, and assemblages A and B can infect humans. Giardiasis has been classified as a possible zoonotic disease but the role of animals in human disease transmission still needs to be proven. We tried to link different assemblages and sub-assemblages of G. intestinalis isolates from Swedish human patients to clinical symptoms and zoonotic transmission.
  
  
  RESULTS
  Multilocus sequence-based genotyping of 207 human Giardia isolates using three gene loci: ß-giardin, glutamate dehydrogenase (gdh), and triose phosphate isomerase (tpi) was combined with assemblage-specific tpi PCRs. This analysis identified 73 patients infected with assemblage A, 128 with assemblage B, and six with mixed assemblages A+B. Multilocus genotypes (MLGs) were easily determined for the assemblage A isolates, and most patients with this genotype had apparently been infected through anthroponotic transmission. However, we also found evidence of limited zoonotic transmission of Giardia in Sweden, since a few domestic human infections involved the same assemblage A MLGs previously reported in Swedish cats and ruminants. Assemblage B was detected more frequently than assemblage A and it was also more common in patients with suspected treatment failure. However, a large genetic variability made determination of assemblage B MLGs problematic. Correlation between symptoms and assemblages was found only for flatulence, which was significantly more common in children less than six years of age infected with assemblage B.
  
  
  CONCLUSIONS
  This study shows that certain assemblage A subtypes are potentially zoonotic and that flatulence is connected to assemblage B infections in young children. Determination of MLGs from assemblages A and B can be a valuable tool in outbreak situations and to help identify possible zoonotic transmission.
authors.affiliation: Department of Diagnostics and Vaccinology, Swedish Institute for Communicable Disease Control, Solna, Sweden.
authors.forename: Marianne
authors.initials: M
authors.lastname: Lebbad
authors.forename: Ingvor
authors.initials: I
authors.lastname: Petersson
authors.forename: Lillemor
authors.initials: L
authors.lastname: Karlsson
authors.forename: Silvia
authors.initials: S
authors.lastname: Botero-Kleiven
authors.forename: Jan O
authors.initials: JO
authors.lastname: Andersson
authors.forename: Bo
authors.initials: B
authors.lastname: Svenungsson
authors.forename: Staffan G
authors.initials: SG
authors.lastname: Svärd
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000483:Alleles; D000818:Animals; D000981:Antiprotozoal Agents / Q000627:therapeutic use; D016009:Chi-Square Distribution; D002648:Child; D002675:Child, Preschool; D003598:Cytoskeletal Proteins / Q000235:genetics; D016054:DNA, Protozoan / Q000032:analysis; D004587:Electrophoresis, Agar Gel; D005260:Female; D005414:Flatulence / Q000453:epidemiology / Q000469:parasitology*; D016829:Giardia lamblia / Q000145:classification* / Q000235:genetics; D005873:Giardiasis / Q000453:epidemiology / Q000235:genetics / Q000469:parasitology* / Q000635:transmission; D005969:Glutamate Dehydrogenase / Q000235:genetics; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D058885:Multilocus Sequence Typing; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D015800:Protozoan Proteins / Q000235:genetics; D013548:Sweden / Q000453:epidemiology; D014305:Triose-Phosphate Isomerase / Q000235:genetics; D015047:Zoonoses / Q000469:parasitology*
chemical_list: D000981:Antiprotozoal Agents; D003598:Cytoskeletal Proteins; D016054:DNA, Protozoan; D015800:Protozoan Proteins; C038207:giardin protein, Giardia lamblia; D005969:Glutamate Dehydrogenase; D014305:Triose-Phosphate Isomerase