''Thelazia californiensis'' is a
nematode
The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...
that originates in the genus ''Thelazia'', which comes from phylum Nematoda. This worm has been known to cause
Thelaziasis in hosts.
Morphology
As with most ''Thelazia'' worms, they are small parasites that average about 12-13 mm long.
To differentiate between other members of this genus, ''T. californiensis'' has a vulva that opens mid-ventrally, while ''T. callipaeda'' has an anterior vulva.
Hosts
Similar to
Thelazia callipaeda
''Thelazia callipaeda'' is a parasitic nematode, and the most common cause of thelaziasis (or eyeworm infestation) in humans, dogs and cats. It was first discovered in the eyes of a dog in China in 1910. By 2000, over 250 human cases had been r ...
, the worm has definitive hosts in dogs, cats, sheep, and occasionally humans. They also use intermediate hosts to move around, specifically using the
lesser house fly
The lesser house fly or little house fly, ''Fannia canicularis'', is somewhat smaller () than the common housefly. It is best known for its habit of entering buildings and flying in jagged patterns in the middle of a room. It is slender, and the ...
(''Fannia canicularis'').
Life cycle
The worm starts its life cycle by laying eggs in the tears and
tear duct
The nasolacrimal duct (also called the tear duct) carries tears from the lacrimal sac of the eye into the nasal cavity. The duct begins in the eye socket between the maxillary and lacrimal bones, from where it passes downwards and backwards. The ...
s of the host and the eggs are picked up by the flies. Because the eggs develop into
larvae
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
inside the fly, it is a parenthetic host. After developing in the fly, the larvae move so they can easily escape the fly's mouth when it feeds again, starting the cycle over.
=Symptoms
=
Both the adult and larval stages cause disease in the eye, which can have different levels of pain and discomfort. Some of the problems include
keratitis
Keratitis is a condition in which the eye's cornea, the clear dome on the front surface of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves any of the following symptoms: pain, impaired e ...
, ulcers,
conjunctivitis
Conjunctivitis, also known as pink eye, is inflammation of the conjunctiva, outermost layer of the white part of the eye and the inner surface of the eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness, or itchiness may ...
, and other afflictions.
Diagnosis and treatment
As with other eyeworms, the course of diagnosis is to exam the eye and spot any worms that are moving around. In some cases, microscopes can be used to look at tear fluid to see eggs or larvae. Treatment consists of pulling the worms out with forceps in humans. Some cases of infection have shown promising results by using ivermectin.
References
{{Taxonbar, from=Q96356151
Nematodes
Parasites