Pathogenesis and Transmission

Concerning the vector of Thelazia callipaeda it has been hypothesised, based on study results, that only Phortica variegata males may act as an intermediate host under natural conditions (Otranto et al., 2006). It was further speculated that the specificity in the development of T. callipaeda in male P. variegata might have biased the zooophilic behaviour of the fly (Otranto et al., 2006). For details on the developmental cycle see under Pathogens.

A seasonal activity in the reproduction of T. callipaeda, coinciding with the presence/absence of the vector could be observed, with activity of the intermediate host from early spring to early autumn (Otranto et al., 2004).

Clinical symptoms are mainly caused by L3 and/or L4 immature stages and appear to be similar to those of allergic conjunctivitis (Otranto, 2008). Symptoms of thelaziosis are mainly due to the lateral serration of the T. callipaeda cuticle which is responsible for mechanical damage of the conjunctival and corneal epithelium (Otranto et al., 2003b). Clinical manifestations (here for human thelaziosis) are related to the number of nematodes present in the eye, their location, the host-immune response and the occurrence of secondary infection with bacteria (Shen et al., 2006). Tangled worms are mostly localised in the conjunctival sac and the medial or lateral canthus, but have also been detected in the anterior chamber (here in humans) (Shen et al., 2006).

Further information

  • Otranto D: Thelazia callipaeda eyeworm: a”neglected” CVBD of human concern. Proc. 3rd Int. CVBD Symposium, 2008, 94-102
  • Otranto D, Lia RP, Traversa D, et al.: Thelazia callipaeda (Spirurida, Thelaziidae) of carnivores and humans: morphological study by light and scanning electron microscopy. Parassitologia. 2003b, 45, 125-33
  • Otranto D, Lia RP, Buono V, et al.: Biology of Thelazia callipaeda (Spirurida, Thelaziidae) eyeworms in naturally infected definitive hosts. Parasitology. 2004, 129, 627-33
  • Otranto D, Cantacessi C, Testini G, et al.: Phortica variegata intermediate host of Thelazia callipaeda under natural conditions: evidence for pathogen transmission by a male arthropod vector. Int J Parasitol. 2006, 36, 1167-73
  • Shen J, Gasser RB, Chu D, et al.: Human thelaziosis – a neglected parasitic disease of the eye. J Parasitol. 92, 2006, 872-5

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