Site segregation of Thelazia skrjabini and Thelazia gulosa (Nematoda: Thelazioidea) in the eyes of cattle.

One thousand three hundred and twenty-two eyes obtained from slaughtered cattle throughout Alberta were examined for eyeworms. Each eye was partitioned into 9 sites and all eyeworms were recorded by site. Seven hundred eyeworms were recovered from 121 infected eyes. The distribution of Thelazia skrjabini across the 9 sites differed significantly (P < 0.001) from that of Thelazia gulosa. The 2 major lacrimal ducts associated with the Harderian gland contained 58% (354/613) of the T. skrjabini present, whereas the large ventral lateral duct of the orbital gland contained 58% (50/87) of the T. gulosa recovered. Eyeworms occurred more often (90%, 631/700) in a duct as a single species than as a mixed species infection (10%, 69/700). The data suggest that T. skrjabini and T. gulosa are more site specific than previously believed.