Prevalence, morphology, and molecular characterization of trypanosomes in bulbuls from Thailand

Birds represent the second most species-rich class of vertebrates, comprising more than 10,000 extant species worldwide, including wild and domesticated forms, as well as migratory and resident species. Bulbuls (Family Pycnonotidae) are important seed dispersers, and keeping them in cages is a long-standing tradition in Thai culture. Health assessments of these birds are therefore essential for sustaining cage-bird keeping, supporting local livelihoods, while also supporting biodiversity conservation. This study aimed to investigate the prevalence, morphology, and molecular characteristics of trypanosomes in Olive-winged bulbuls (Pycnonotus plumosus, OWB), Streak-eared bulbuls (Pycnonotus conradi, SEB), and Yellow-vent bulbuls (Pycnonotus goiavier, YVB) captured in Thailand. Blood samples were collected from 121 bulbuls (26 OWBs, 79 SEBs, and 16 YVBs). Three Giemsa-stained blood smears were prepared per sample, and genomic DNA was extracted. Additionally, nested-PCR and sequence analysis of the small subunit ribosomal ribonucleic acid gene (SSU rRNA) were performed. As a result, microscopic examination revealed Trypanosoma spp. infections in seven SEBs and ten YVBs, and up to nine putative morphotypes of Trypanosoma spp. were identified. Nested-PCR revealed a higher prevalence (11.39% in SEBs and 75.00% in YVBs) compared to microscopic examination (8.86% in SEBs and 62.50% in YVBs). Sequence analysis of all 21 nested-PCR positive samples further revealed multiple trypanosome strain/species infections. Collectively, these findings provide baseline data to support veterinary diagnostic laboratories and inform future epidemiologic and molecular investigations of avian trypanosomes in Thailand.