Thelazia callipaeda

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Thelazia callipaeda Railliet and Henry, 1910

ETYMOLOGY: Thelazia for Dr. Thelaz and calli = beautiful + paeda = child referring to the beuatiful larvae within the female worm.


HISTORY: This worm was described by Railliet and Henry (1910) for specimens collected from the nictitating membrane of a dog in Pawal Pindi, Punjab, India.

GEOGRAPHIC LOCATION: Europe, China, India, and Southeast Asia. Di Sacco et al. (1995) described an infection with Thelaziacallipaeda in the eye of a cat in Italy. Morishige et al. (1992) found Thelazia callipaeda in 5 of 11,581 cats in Japan; the cats were examined by the inversion of the eyelid. Shi et al. (1988) reported 2 or 4 cats and 37 of 39 dogs infected in Guang Hua of Hubei Province China; there were also 37 human cases diagnosed during the same five-year period, 1970\ to 1975.

LOCATION IN HOST: These worms are parasites of the orbits of the eye, being found on the conjunctiva and under the lids and nictitating membrane.

PARASITE IDENTIFICATION: These are white to cream colored worms. The males are 9 to 12 mm long with dissimilar spicules, the left being 1.3 to 2.3 mm long and the right being 0.12 to 0.16 mm long. The females are 10 to 18 mm long. The vulva of the female is located anterior to the esophageal intestinal junction and is 0.5 to 0.7 mm from the anterior end. This species differs from Thelaziacaliforniensis in that in the latter, the vulva is located posterior to the junction of the esophagus and intestine.

LIFE CYCLE: Kozlov (1962 and 1963; Wang 1990; Wang and Yang, 1993) reported on the life cycle of this worm. Sheathed larvae were fed to flies of the Drosophila family, Amiota (= Phortica) variegata, where within about three weeks they had become infective third-stage larvae. The larvae present in the flies had genital systems that were much more highly advanced than is typical of third-stage larvae, the testes was already quite extended, and both branches of the uterus in the female were readily apparent). When placed in the eyes of dogs, Kozlov found adult males and females present by three weeks after infection, and a few days latter, the uterus of the female contained larvated eggs. By 55 days after infection, motile larvae were present in the vagina of the female.

CLINICAL PRESENTATION AND PATHOGENESIS: The cat described by Di Sacco et al. (1995) was a castrated 10-year-old male. The cat presented with blepharospasm and epiphora of the left eye. There was a monolateral keratoconjunctivitis with corneal opacities noted on the nasal quadrant of the eye starting at the limbus. The worms were noted on ocular examination and removed. A total of four worms, 3 females and a male, were recovered. The worms were about 8 to 12 mm long.

TREATMENT: Treatment would most typically be by the application of local anesthetic and the careful removal of the worms from the eye.

EPIZOOTIOLOGY: Kozlov (1962) reported that adult worms were found in the eyes of dogs throughout the year. It thus appears possible that there may be various populations of worms infecting the eye throughout the year in areas where the prevalence is high.

HAZARDS TO OTHER ANIMALS: Other known hosts include canids and rabbits. There would not be direct transmission from cats to other hosts, but because the intermediate host is a gnat, it seems possible that it would be highly possible that the gnats could set up a cycle in the vicinity of a cattery and not be initially posed as a threat to the health of the animals.

HAZARD TO HUMANS: Infections of humans with this species of eye worm have been more commonly reported than infections in the United States with Thelaziacaliforniensis. Human infections have been reported from throughout southeastern Asia. Examples of human cases from vairious countries include: China (Lu, 1996; Hsü, 1933); Thailand (Bhaibulaya et al., 1970), Japan (Arizono et al, 1976), Indonesia (Kosin et al., 1989), Korea (Hong et al, 1988).

CONTROL/PREVENTION: Control would be by preventing the flies from feeding around the eyes of cats. There is no information as to whether monthly ivermectin for cats would prevent infections with this worm; however, because of the external site of development, it is likely that this would not be effective.


Arizono N, Yopshida Y, Kondo K, Kuimoto H, Oda K, Shiota T, Shimada Y, Ogino K. 1976. Thelaziacallipaeda from man and dogs in Kyoto and its scanning electron microscopy. [In Japanese] Jap J Parasit 25:402-408.

Bhaibulaya M, Prasetsilpa S, Vajrasthira S. 1970. Thelaziacallipaeda Railliet and Henry, 1910, in a man and dog in Thailand. Am J Trop Med Hyg 19:476-479.

Di Sacco B, Ciocca A, Sirtori G. 1995. Thelaziacallipaeda (Railliet and Henry, 1910) nel sacco congiuntivale di un gatto di Milano. Veterinaria 9:81-84.

Hong ST, Lee SH, Kim SI. 1985. A human case of Thelaziacallipaeda infection with reference to its internal structures. K J Parasitol 26:137-140.

Hsü HF. 1933. On Thelazia callipaeda Railliet and Henry, 1910, infection in man and dog. Arch Schiffs Tropenhyg 37:363-369.

Kosin E, Kosman ML, Depary AA. 1989. First case of human thelaziasis in Indonesia. SE Asian J Trop Med Pub Hlth 20:233-236.

Kozlov DP. 1962. The life cycle of the nematode, Thelaziacallipaeda, parasitic in the eye of man and carnivores. [in Russian]. Doklady Akademii Nauk SSSR 142:732-733.

Kozlov DP. 1963. Biology of Thelaziacallipaeda Railliet and Henry, 1910. [in Russian]. Trudi Gelmintologisscheskoi Laboratorii 13:330-346.

Lu YF. 1996. An infant with Thelaziacallipaeda infection. [In Chinese] Chin J Parasitol & Parasitic Dis 14:138.

Morishige K, Saito T, Maeda S, Tongu Y. 1992. Infection rate of Thelaziacallipaeda in dogs and cats in Bingo District and Okayama City. Jap J Parasitol 41:431-433.

Shi YE, Han JJ, Yang WY, Wei DX. 1988. Thelaziacallipaeda (Nematoda: Spirurida): transmission by flies from dogs to children in Hubei, China. Trans Roy Soc Trop Med Hyg 82:627.

Railliet A, Henry ACL. 1910. Nouvelles observations sur les thélazies nématodes parasites de l’oiel. Compt Rend Soc Biol, Paris 68:783-785.

Wang ZX, Yang ZX. 1993. Studies on the development of Thelaziacallipaeda larva in the intermediate host Amiotavariegata in China. Chin J Zool 28:4-8.

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