''Thelazia'' is a genus of

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 ...

worms which parasitize the eyes and associated tissues of various bird and

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

hosts, including humans. They are often called "eyeworms", and infestation with ''Thelazia'' species is referred to as "

thelaziasis Thelaziasis is the term for infestation with parasitic nematodes of the genus ''Thelazia''. The adults of all ''Thelazia'' species discovered so far inhabit the eyes and associated tissues (such as eyelids, tear ducts, etc.) of various mammal an ...

" (occasionally spelled "thelaziosis"). Adults are usually found in the eyelids, tear glands, tear ducts, or the so-called "third eyelid" (

nictitating membrane The nictitating membrane (from Latin '' nictare'', to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision. All ...

). Occasionally, they are found in the eyeball itself, either under the conjunctiva (the membrane that covers the white part of the eye) or in the

vitreous Vitreous may refer to: Materials * Glass, an amorphous solid material ** Vitreous enamel, a material made by fusing powdered glass to a substrate by firing * Vitreous lustre, a glassy luster or sheen on a mineral surface Biology * Vitreous body, ...

cavity of the eyeball. All species of ''Thelazia'' for which the life cycle has been studied are transmitted by species of

Diptera Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...

(flies) which do not bite, but which feed on tears.

Representative species

*''

Thelazia anolabiata ''Thelazia'' is a genus of nematode worms which parasitize the eyes and associated tissues of various bird and mammal hosts, including humans. They are often called "eyeworms", and infestation with ''Thelazia'' species is referred to as " thela ...

'' ( Molin, 1860) ** Definitive hosts:

Andean cock-of-the-rock The Andean cock-of-the-rock (''Rupicola peruvianus''), also known as ''tunki'' (Quechua), is a large passerine bird of the cotinga family native to Andean cloud forests in South America. It is widely regarded as the national bird of Peru. It has ...

(''Rupicola peruviana'') and many other Brazilian birds ** Intermediate hosts: Not known ** Distribution: South America *''

Thelazia bubalis ''Thelazia'' is a genus of nematode worms which parasitize the eyes and associated tissues of various bird and mammal hosts, including humans. They are often called "eyeworms", and infestation with ''Thelazia'' species is referred to as " thela ...

'' Ramanujachari and Alwar, 1952 ** Definitive hosts: Water buffalo ** Intermediate hosts: Not known ** Distribution: India *''

Thelazia californiensis ''Thelazia californiensis'' is a nematode 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 ...

'' Price, 1930 ** Definitive hosts: Dog (''Canis familiaris''), cat (''Felis catus''), occasionally human (''Homo sapiens''), domestic sheep (''Ovis aries''), mule deer (''Odocoileus hemionus''),

coyote The coyote (''Canis latrans'') is a species of canis, canine native to North America. It is smaller than its close relative, the wolf, and slightly smaller than the closely related eastern wolf and red wolf. It fills much of the same ecologica ...

(''Canis latrans'') and

American black bear The American black bear (''Ursus americanus''), also called simply a black bear or sometimes a baribal, is a medium-sized bear endemic to North America. It is the continent's smallest and most widely distributed bear species. American black bear ...

(''Ursus americanus''). ** Intermediate hosts:

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'') and ''Fannia benjamini'' ** Distribution: Western North America *''

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 ...

Railliet Louis-Joseph Alcide Railliet (also known as Alcide Railliet, born 11 March 1852 at La Neuville-lès-Wasigny in the Ardennes – died 25 December 1930) was a French veterinarian and helminthologist. Professor at the Veterinary School of Alfort, ...

& Henry, 1910 (sometimes called "Oriental eyeworm") ** Definitive hosts: Typically reported from dog (''Canis familiaris''), cat (''Felis catus''), and occasionally reported from grey wolf (''Canis lupus''), raccoon dog (''Nyctereutes procyonoides''),

red fox The red fox (''Vulpes vulpes'') is the largest of the true foxes and one of the most widely distributed members of the Order (biology), order Carnivora, being present across the entire Northern Hemisphere including most of North America, Europe ...

(''Vulpes vulpes''), European rabbit (''Oryctolagus cuniculus''). Over 250 cases of ''T. callipaeda'' infestation in humans have been reported thus far.Koyama, Y., A. Ohira, T. Kono, T. Yoneyama, and K. Shiwaku (2000)
Five cases of thelaziasis
" ''British Journal of Ophthalmology'' 84(4):441-442. (Note: This pdf includes pp. 439-440 in addition to the cited article.) ** Intermediate hosts: Fruit flies (''Amiota (Phortica) variegata'' in Europe, and ''Phortica okadai'' in China) ** Distribution: Asia and Europe *''

Thelazia erschowi ''Thelazia'' is a genus of nematode worms which parasitize the eyes and associated tissues of various bird and mammal hosts, including humans. They are often called "eyeworms", and infestation with ''Thelazia'' species is referred to as " thela ...

'' Oserskaja, 1931 ** Definitive hosts: Pig (''Sus domesticus'') ** Intermediate host: Not known ** Distribution: Post-Soviet states *''

Thelazia gulosa ''Thelazia'' is a genus of nematode worms which parasitize the eyes and associated tissues of various bird and mammal hosts, including humans. They are often called "eyeworms", and infestation with ''Thelazia'' species is referred to as " thela ...

'' (Railliet & Henry, 1910) ** Definitive hosts:

Yak The domestic yak (''Bos grunniens''), also known as the Tartary ox, grunting ox or hairy cattle, is a species of long-haired domesticated cattle found throughout the Himalayan region of the Indian subcontinent, the Tibetan Plateau, Kachin Sta ...

(''Bos grunniens'') and other cattle (''Bos taurus''), and rarely human (''Homo sapiens'') ** Intermediate hosts: Face fly (''

Musca autumnalis ''Musca autumnalis'', the face fly or autumn housefly, is a pest of cattle and horses. Description The face fly is similar to the closely related housefly but is slightly larger, averaging about 7–8 mm long and grey in colour with four ...

'') in Europe and North America, ''Musca larvipara'' in the Ukraine, ''Musca vitripennis'' in Crimea, and ''Musca amica'' in the Far East ** Distribution: Asia, Europe, and North America *'' Thelazia lacrymalis'' (Gurlt, 1831) ** Definitive hosts: Horse (''Equus caballus'') and cattle (''Bos taurus'') ** Intermediate hosts: Face fly (''

'') and ''

Musca osiris ''Musca osiris'' is a species of fly in the genus ''Musca''. It and ''Musca vitripennis'' are the only two species of ''Musca'' native to the Palearctic realm, according to Willi Hennig Emil Hans Willi Hennig (20 April 1913 – 5 November 197 ...

'' ** Distribution: Asia, Europe, Middle East, North America and South America *''

Thelazia leesei ''Thelazia'' is a genus of nematode worms which parasitize the eyes and associated tissues of various bird and mammal hosts, including humans. They are often called "eyeworms", and infestation with ''Thelazia'' species is referred to as " thela ...

'' Railliet & Henry, 1910 ** Definitive hosts: Dromedary (''Camelus dromedarius'') and Bactrian camel (''Camelus bactrianus'') ** Intermediate hosts: Flies (''Musca lucidulus'') ** Distribution: Post-Soviet states and India *''

Thelazia rhodesii ''Thelazia'' is a genus of nematode worms which parasitize the eyes and associated tissues of various bird and mammal hosts, including humans. They are often called "eyeworms", and infestation with ''Thelazia'' species is referred to as " thela ...

'' (Desmarest, 1828) ** Definitive hosts: mainly bovids, cattle (''Bos taurus''), water buffalo (''Bubalus bubalis''), zebu (''Bos indicus''),

bison Bison are large bovines in the genus ''Bison'' (Greek: "wild ox" (bison)) within the tribe Bovini. Two extant and numerous extinct species are recognised. Of the two surviving species, the American bison, ''B. bison'', found only in North Ame ...

(''Bison bonasus''), and sometimes horse (''Equus caballus''), domestic sheep (''Ovis aries''), dromedary (''Camelus dromedarius''), and goat (''Capra hircus'') ** Intermediate hosts: Face fly (''

'', ''Musca larvipara'', and ''Musca sorbens'') ** Distribution: Africa, Asia, and Europe *''

Thelazia skrjabini ''Thelazia'' is a genus of nematode worms which parasitize the eyes and associated tissues of various bird and mammal hosts, including humans. They are often called "eyeworms", and infestation with ''Thelazia'' species is referred to as "thela ...

'' Erschow, 1928 ** Definitive hosts: Cattle (''Bos taurus'') and

yak The domestic yak (''Bos grunniens''), also known as the Tartary ox, grunting ox or hairy cattle, is a species of long-haired domesticated cattle found throughout the Himalayan region of the Indian subcontinent, the Tibetan Plateau, Kachin Sta ...

(''Bos grunniens'') ** Intermediate hosts: Face fly (''

''), ''Musca vitripennis'', and ''Musca amica'' ** Distribution: Europe and North America

References

{{Taxonbar, from=Q3656383 Spirurida Secernentea genera Parasitic nematodes of vertebrates Veterinary helminthology

Representative species

See also

References