High Frequency of Nitroimidazole-Resistant Trichomonas gallinae in Competition Pigeons: Risk Factors and Therapeutic Implications

Trichomonas gallinae is a protozoan parasite of major concern in avian medicine, particularly in domestic pigeons (Columba livia). This study investigated the risk factors associated with the frequency of nitroimidazole resistance and T. gallinae prevalence in domesticated pigeons from Eastern Spain, kept for different competitions. A total of 220 pigeons from 11 lofts were sampled and examined by microscopy and culture, revealing a 63.6% infection prevalence. Genotyping identified genotype C as predominant, with occasional detection of genotype A, mixed A/C infections, and one isolate of Lineage III. In vitro susceptibility testing of 42 isolates showed a high prevalence (81%) of metronidazole resistance (MIC values [≥] 20 {micro}g/ml), with minimum inhibitory concentrations (MICs) ranging from 5 to >100 {micro}g/mL in 9/11 pigeon lofts examined. Resistance was significantly associated with the use of metronidazole and was more frequent in young and non-reproductive birds. Biannual treatments and the combination of ronidazole and dimetridazole at higher doses were associated with lower infection rates than monotherapies or annual treatments. No significant associations were found between resistance and environmental or loft management parameters, although poor hygiene and high bird density were common in lofts with resistant strains. These findings highlight the urgent need for regulated treatment protocols, improved biosecurity, and the development of alternative trichomonacidal agents to combat the emergence of drug-resistant T. gallinae in pigeon populations.