Belonging to the family Thelaziidae, order Spirurida, two out of 16 species of Thelazia have been detected in dogs and humans (Skrjabin et al., 1967): Thelazia callipaeda and Thelazia californiensis. The former has also been detected in cats, rabbits, foxes and wolves (Kozlov, 1961; Otranto et al., 2007; Skrjabin et al., 1967). Apart from dogs and humans, the latter spirurid has also been described in sheep, deer, coyotes and bears (Anderson, 2000).
The nematodes possess a size of approximately 7.5 to 19 mm. The intermediate hosts of T. callipaeda are fruitflies of the genus Phortica.
The parasites live in the orbital cavity and associated tissues. Adult females are viviparous and release first stage larvae (L1) into the lachrymal secretions of the host. Secretophagous non-biting flies feed on these secretions and become infected with the L1. In the arthropod vector, the larvae undergo their development from L1 to L3, the third stage infective larva, while remaining encapsulated in different parts of the vector’s body. This is depending upon the different species of Thelazia. Finally, they migrate through the arthropods’ coeloma to the labella. The infective L3 emerge from the labella of the infected flies as soon as those feed on the lachrymal secretions of receptive animals. In the definite host the L3 develops into the adult stage in the ocular cavity within 3-6 weeks.
- Anderson RC: Nematode parasites of vertebrates. Their development and transmission. 2nd edn., 2000, CAB International, Wallingford, Oxon, UK
- Kozlov DP: [The life cycle of nematode, Thelazia callipaeda, parasitic in the eye of the man and carnivores.] Doklady Akademii Nauk SSSR. 1961, 142, 732-3 [in Russian]
- Otranto D, Cantacessi C, Mallia E, et al.: First report of Thelazia callipaeda (Spirurida, Thelaziidae) in wolves in Italy. J Wildl Dis. 2007, 43, 508-11
- Skrjabin KI, Sobolev AA, Ivashkin VM: Spirurata of animals and man and the disease caused by them (Part 4): Thelazioidea. In: Skrjabin KI (ed.): Principles of Nematology. Vol. IX, 1967, Izdatel’sto Akademii Nauk SSSR, Moscow; English translation published by Israel Program for Scientific Translations, Jerusalem, 1971