Thelazia species (eyeworms) infection in cattle: Prevalence, species diversity, seasonal dynamics and its ocular effects in South Gondar zone, Northwest Ethiopia

Thelaziasis is a neglected vector-borne disease widely distributed throughout the world and is responsible for severe economic losses in cattle. The disease is caused by parasitic nematodes of the genus Thelazia (Spirurida, Thelaziidae). So far, limited attention has been given to ungulate-associated Thelazia species though it is a highly prevalent disease that raises concerns for animal welfare and potential economic impacts. A cross sectional study was carried out between August 2023 to July 2024 in the South Gondar Zone of Northwest Ethiopia, aiming to estimate the prevalence, investigate the seasonal dynamics, identify the species involved, demonstrate the ocular effects, and to assess the potential risk factors associated with the occurrence of thelaziasis in cattle. A multistage sampling technique was employed to select study animals. Data analysis was performed with logistic regression using SPSS software version 27.0. A total of 690 cattle were examined, of which 165 tested positive for Thelazia, resulting in an overall prevalence of 23.9 % (95 % CI: 20.7–27.2). Thelazia rhodesi and Thelazia gulosa were the identified species infecting cattle. Sex, body condition score and district of cattle were not associated with the occurrence of thelaziasis (p > 0.05). However, age, breed, management and season had influenced the occurrence of parasitosis (p < 0.05). Adult cattle (30.6 %), local breed (26.9 %), and extensive management system (29.8 %) categories have demonstrated higher infection rates than young (15.3 %), crossbreed (16.5 %), and semi-intensive management system (10.5 %). The occurrence of infection showed apparent seasonality (p < 0.001) with the maximum prevalence appeared in autumn (39.7 %). Ocular lesions such as lacrimation, conjunctivitis and ulceration were detected in 142 (20.6 %) of examined cattle, and the occurrence of ocular lesions exhibited significant association with the prevalence of parasitosis (p < 0.001). The occurrence of Thelazia species with high prevalence in the study area alarms the significance of incorporating this parasite in the differential diagnosis of eye diseases in cattle, especially when adults affected in areas with free grazing management system.