Bovine thelaziasis: a re-emerging parasitic disease of cattle and buffaloes

Thelaziasis, also known as thelaziosis, is a neglected vector-borne disease caused by parasitic nematodes from the genus Thelazia, belonging to the family Thelaziidae. The disease is transmitted biologically by various fly species, including the genus Musca (family Muscidae), Phortica (family Drosophilidae), and Fannia (family Fanniidae). These flies act as intermediate hosts (IHs) by depositing infective third-stage larvae (L3) during their tear feeding. Thelazia spp., such as T. gulosa, T. skrjabini, and T. rhodesi, inhabit the ocular regions of various animals, including humans and birds. Adult Thelazia worms are slender and creamy-white, measuring between 8-12 mm in males and 12-21 mm in females, with females releasing live larvae into the host's tear secretions. The presence of these parasites can lead to serious ocular conditions such as keratitis, conjunctivitis, and even blindness. Diagnosis typically involves identifying the adult nematodes in the conjunctival sac, where they appear as active, slender, creamy-white organisms. Management of the infection can include the physical removal of the parasites and the use of effective anthelmintics like Eprinomectin, Doramectin, Ivermectin and Levamisole, administered either subcutaneously or intramuscularly. Regular deworming and treatment of infected animals are essential practices in areas where the disease is endemic, and effective prevention and control strategies are necessary to mitigate its impact. Hence, this comprehensive review has provided updated information about the oldest known but neglected and re-emerging parasitic disease in bovines worldwide.