Dynamics of parrot bornavirus infection in traded psittacine birds across El Niño–Southern Oscillation phases in Thailand, 2022–2025

Parrot Bornavirus (PaBV) is the causative agent of proventricular dilatation disease (PDD), a severe and potentially fatal disease in psittacine birds. However, the influence of climatic variability on PaBV epidemiology remains poorly understood. This study evaluated temporal patterns of PaBV infection during representative El Niño, La Niña, and neutral periods in traded psittacine birds in Thailand from 2022 to 2025. The overall PaBV infection rate was highest during the representative El Niño period (12.09%; 95% CI: 10.50–13.82), followed by the La Niña (8.42%; 95% CI: 7.10–9.88) and neutral (8.17%; 95% CI: 6.68–9.86) periods. Infection rates differed significantly among the representative climatic periods ( p < 0.001), with pairwise comparisons indicating higher rates during the El Niño period. Monthly infection rates also exhibited distinct temporal patterns among the representative periods. At the family level, significantly higher infection rates during the El Niño period were observed in Psittacidae ( p = 0.005) and Cacatuidae ( p = 0.025), whereas no significant differences were detected in Psittaculidae. Multivariable logistic regression identified significant differences among the representative climatic periods, with the El Niño period showing higher odds of PaBV detection than the reference period (neutral). February and March were associated with higher odds of infection, whereas May and September showed lower odds. A significant interaction between month and climatic period ( p < 0.001) indicated that temporal patterns differed among the representative periods. Relative humidity was negatively associated with monthly infection rates overall, whereas evaporation showed a positive association during the representative La Niña period. These findings describe temporal variation in PaBV infection among representative climatic periods and provide baseline information for future studies investigating environmental and ecological factors associated with PaBV occurrence.