Thelazia species are thread-like tissue nematodes that primarily affect animals but which occasionally may affect humans.
Species: Thelazias californiensis, Thelazias callipaeda
Vector: flies (genus Fannia, Amioto, others)
Size: up to 1.5 cm
Lifecycle:
(1) A fly ingests embryonated eggs from the ocular tissue of an infected host.
(2) The eggs hatch and release larvae in the flies.
(3) The flies deposit the larvae into the ocular tissue of a new host.
Geographic distribution: China, Japan, Korea, India, Thailand, California
Sites where the worms can be seen:
(1) conjunctiva
(2) over the cornea
(3) lacrimal glands
Signs and symptoms:
(1) excessive lacrimation
(2) ocular itching
(3) foreign body sensation in the eye
(4) ocular pain
(5) conjunctival congestion
