title: Bovine thelaziasis in Iowa.
abstract: The prevalence of developing Thelazia nematodes in face flies (Musca autumnalis) was studied for 7 yr at a beef farm in central Iowa. Juvenile nematodes were not found among flies in reproductive diapause in autumn, nor among nulliparous, overwintered flies in spring, but only among actively reproducing insects. Thus Thelazia probably do not overwinter in face flies. A mean prevalence of 2.0% infected was recorded among flies in 7 fly breeding seasons. No heterogeneity in Thelazia prevalence was detected within fly breeding seasons. The frequency distribution of Thelazia among face flies by year of occurrence was homogeneous, with a mean of 2.75 larval nematodes per infected fly. Thelazia gulosa and T. skrjabini were recovered in necropsy from the eyes of bovines from central Iowa. Prevalence among fat cattle 18-27 mo old was 15%; among cows 3-15 yr old, prevalence was only 3%. Thelazia skrjabini was found in 29 eyes and T. gulosa in 4 eyes. Infections were randomly distributed among the eyes of subject cattle. The mean worm burden was 2.3 T. skrjabini and 12 T. gulosa per infected eye. Thelaziasis is clearly enzootic in Iowa.
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000469:parasitology; D004175:Diptera / Q000469:parasitology*; D005123:Eye / Q000469:parasitology; D005128:Eye Diseases / Q000453:epidemiology / Q000469:parasitology / Q000662:veterinary*; D005260:Female; D007484:Iowa; D008297:Male; D009349:Nematode Infections / Q000453:epidemiology / Q000469:parasitology / Q000662:veterinary*; D012621:Seasons; D013151:Spiruroidea / Q000254:growth & development*; D013802:Thelazioidea / Q000254:growth & development*