Thelazia eyeworm: an original endo- and ecto-parasitic nematode.

The genus Thelazia comprises several parasites, commonly named eyeworms, which infect the eyes and associated tissues of mammals, including humans. Transmission of eyeworms occurs via non-biting diptera that feed on the ocular secretions, tears and conjunctiva of animals. The disease, thelaziosis, is characterized by a range of subclinical to clinical signs, such as epiphora, conjunctivitis, keratitis, corneal opacity and ulcers. Human thelaziosis is common in poor socio-economic settings in many Asian countries. The relationship between eyeworms and their hosts are discussed here, together with recent molecular insights that are instrumental in investigating the biology of Thelazia in their definitive and intermediate hosts.