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Mem Inst Oswaldo Cruz, Rio de Janeiro, VOLUME 121 | 2026

Research Articles

Giardia duodenalis assemblage A: new genotype in non-human primates from the Brazilian Amazon region revealed by high-resolution MLST

Lisiane Lappe dos Reis^1,3,4,+, Lirna Salvioni Silva de Souza¹, Maria Gabriela Rodrigues Antunes¹, Alessandra Ferreira Dales Nava², Ana Carolina Paulo Vicente³

¹Fundação Oswaldo Cruz-Fiocruz, Instituto Leônidas & Maria Deane, Laboratório de Diversidade Microbiana da Amazônia de Importância para a Saúde, Manaus, AM, Brasil
²Fundação Oswaldo Cruz-Fiocruz, Instituto Leônidas & Maria Deane, Laboratório de Ecologia de Doenças Transmissíveis na Amazônia, Manaus, AM, Brasil
³Fundação Oswaldo Cruz-Fiocruz, Instituto Oswaldo Cruz, Laboratório de Genética Molecular de Microrganismos, Rio de Janeiro, RJ, Brasil
⁴Fundação Oswaldo Cruz-Fiocruz, Instituto Oswaldo Cruz, Programa de Pós-Graduação Stricto Sensu em Biologia Parasitária, Rio de Janeiro, RJ, Brasil

DOI: 10.1590/0074-02760250234

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ABSTRACT

BACKGROUND Giardia duodenalis is an intestinal protozoan parasite that infects a wide range of vertebrate hosts, including humans, and is the etiological agent of giardiasis. Within this species, assemblage A is further subdivided into three sub-assemblages: AI, AII, and AIII.
OBJECTIVES To apply the high-resolution multilocus sequence typing (MLST) to perform molecular epidemiology of G. duodenalis assemblage A in humans and animals in the State of Amazonas, Brazil.
METHODS We performed parasitological analyses of faecal samples from animals and collected Giardia-positive samples from humans in the State of Amazonas, Brazil. Giardia genotyping was carried out using an MLST scheme based on six genes (CID1, NEK15411, DIS3, HCMP22547, HCMP6372, RHP26), as well as the three conventional loci (tpi, bg and gdh), followed by phylogenetic analysis.
FINDINGS Using an extended MLST scheme for assemblage A, we identified a new genotype infecting two non-human primate (NHP) species from the Amazon region. Additionally, Giardia from sub-assemblage AII infecting humans in this region shows a close phylogenetic relationship with isolates from other countries. Furthermore, a sub-assemblage AI isolate from an anteater (Tamandua tetradactyla) belongs to a lineage infecting diverse animals and humans, highlighting its zoonotic and cosmopolitan nature.
MAIN CONCLUSIONS These findings reveal a new, genetically distinct lineage within G. duodenalis assemblage A, likely representing a new sub-assemblage (AIV) associated with NHPs in the Amazon region, and reinforce the usefulness of high-resolution MLST for detecting fine-scale genetic diversity and potential zoonotic transmission pathways.

key words: molecular epidemiology multilocus sequence typing zoonoses genetic diversity giardiasis

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