New genetic fingerprinting tool could transform giardia outbreak investigations
Researchers have developed the first high-resolution genetic typing system for Giardia assemblage B, the parasite responsible for a significant portion of human giardiasis cases worldwide. The discovery enables health authorities and water utilities to rapidly identify outbreak sources and track transmission patterns—critical for protecting public water supplies and controlling a disease affecting hundreds of millions annually.
Originaltitel: High resolution multi-locus sequence typing scheme for Giardia duodenalis assemblage B outbreak and population analysis.
**Ny typningsmetod förbättrar utbrottskontroll för Giardia duodenalis** Giardia duodenalis orsakar omfattande gastroenteritutbrott globalt, men dagens diagnostiska verktyg saknar precision för att spåra smittkedjor inom huvudgruppen assemblage B. Forskare vid Robert Koch-institutet har utvecklat ett MLST-schema (multi-locus sequence typing) baserat på sju genetiska markörer som möjliggör tillförlitlig isolatkategorisering. Metoden testades på 146 provsamlingar och fungerade i 75 procent av fallen. Schemat kunde särskilja ett vattenbundet utbrott (16 fall) från sporadiska infektioner och identifierade två distinkta populationsstrukturer beroende på allelisk sekvensvariabilitet. Detta är särskilt relevant eftersom assemblage B karakteriseras av högt genetiskt innehåll av denna variabilitet. Resultat från italienska, schweiziska och brittiska laboratoria validerar metodens tillämplighet för epidemiologisk övervakning och källattribuering, vilket underlättar snabbare utbredningsbekämpning och riskbedömning för vattenförsörjning och livsmedelskedjor.
Giardia duodenalis represents a species complex of tetraploid protozoan parasites that infect the small intestine of mammals. Human giardiasis is a widespread gastrointestinal disease predominantly caused by two of eight genetically distinct G. duodenalis groups, termed assemblages A and B. These two assemblages differ in their host preferences, grade of genome identity as well as frequency of allelic sequence heterogeneity (ASH), therefore assemblage-specific typing schemes are needed for epidemiological purposes such as outbreak investigations and source attribution. Here, we used whole genome datasets of assemblage B parasites derived from 18 axenically cultured patient isolates to identify genomic markers for molecular typing. Of the 42 identified genomic loci, 20 were selected to design primer sets for a nested PCR and sequencing approach, and a final set of seven markers was included in a new multi locus sequence typing (MLST) scheme. The MLST scheme was successfully applied to 109 (75%) out of 146 tested assemblage B samples. As assemblage B is characterized by high ASH, the analysis included calling of ASH positions as part of the genotyping approach to distinguish isolates. In epidemiologically unrelated samples (n = 80), the MLST scheme revealed a bipartite population structure comprised of organisms with low or high ASH. On the other hand, samples from a waterborne outbreak (n = 16) and samples from six out of eight separate epidemiologically linked cases formed separate clusters that were distinct from unrelated sporadic cases. These results indicate that the new typing scheme is informative and could assist future epidemiological studies of G. duodenalis assemblage B.