''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 Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

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" (occasionally spelled "thelaziosis"). Adults are usually found in the eyelids, tear glands,

tear ducts The nasolacrimal duct (also called the tear duct) carries tears from the lacrimal sac of the Human eye, eye into the nasal cavity. The duct begins in the eye socket between the maxillary and lacrimal bones, from where it passes downwards and backw ...

, 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 conjunctiva is a thin mucous membrane that lines the inside of the eyelids and covers the sclera (the white of the eye). It is composed of non-keratinized, stratified squamous epithelium with goblet cells, stratified columnar epithelium ...

(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'' ( 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'' Ramanujachari and Alwar, 1952 ** Definitive hosts:

Water buffalo The water buffalo (''Bubalus bubalis''), also called the domestic water buffalo or Asian water buffalo, is a large bovid originating in the Indian subcontinent and Southeast Asia. Today, it is also found in Europe, Australia, North America, So ...

** Intermediate hosts: Not known ** Distribution: India *'' Thelazia californiensis'' Price, 1930 ** Definitive hosts:

Dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...

(''Canis familiaris''),

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

(''Felis catus''), occasionally

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

(''Homo sapiens''),

domestic sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in everyday usage it almost always refers to domesticated sh ...

(''Ovis aries''),

mule deer The mule deer (''Odocoileus hemionus'') is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer. Unlike the related whit ...

(''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''

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 The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...

(''Canis familiaris''),

(''Felis catus''), and occasionally reported from

grey wolf The wolf (''Canis lupus''; : wolves), also known as the gray wolf or grey wolf, is a large canine native to Eurasia and North America. More than thirty subspecies of ''Canis lupus'' have been recognized, and gray wolves, as popularly ...

(''Canis lupus''),

raccoon dog The common raccoon dog (''Nyctereutes procyonoides''), also called the Chinese or Asian raccoon dog, is a small, heavy-set, fox-like canid native to East Asia. Named for its raccoon-like face markings, it is most closely related to foxes. Common ...

(''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 The European rabbit (''Oryctolagus cuniculus'') or coney is a species of rabbit native to the Iberian Peninsula (including Spain, Portugal, and southwestern France), western France, and the northern Atlas Mountains in northwest Africa. It has ...

(''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'' Oserskaja, 1931 ** Definitive hosts:

Pig The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus s ...

(''Sus domesticus'') ** Intermediate host: Not known ** Distribution:

Post-Soviet states The post-Soviet states, also known as the former Soviet Union (FSU), the former Soviet Republics and in Russia as the near abroad (russian: links=no, ближнее зарубежье, blizhneye zarubezhye), are the 15 sovereign states that wer ...

*'' Thelazia gulosa'' (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 Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult mal ...

(''Bos taurus''), and rarely

(''Homo sapiens'') ** Intermediate hosts: Face fly ('' Musca autumnalis'') in Europe and North America, ''Musca larvipara'' in the Ukraine, ''Musca vitripennis'' in

Crimea Crimea, crh, Къырым, Qırım, grc, Κιμμερία / Ταυρική, translit=Kimmería / Taurikḗ ( ) is a peninsula in Ukraine, on the northern coast of the Black Sea, that has been occupied by Russia since 2014. It has a pop ...

, and ''Musca amica'' in the Far East ** Distribution: Asia, Europe, and North America *'' Thelazia lacrymalis'' (Gurlt, 1831) ** Definitive hosts:

Horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...

(''Equus caballus'') and

(''Bos taurus'') ** Intermediate hosts: Face fly ('' Musca autumnalis'') and '' Musca osiris'' ** Distribution: Asia, Europe, Middle East, North America and South America *'' Thelazia leesei'' Railliet & Henry, 1910 ** Definitive hosts:

Dromedary The dromedary (''Camelus dromedarius'' or ;), also known as the dromedary camel, Arabian camel, or one-humped camel, is a large even-toed ungulate, of the genus ''Camelus'', with one hump on its back. It is the tallest of the three species of ...

(''Camelus dromedarius'') and

Bactrian camel The Bactrian camel (''Camelus bactrianus''), also known as the Mongolian camel or domestic Bactrian camel, is a large even-toed ungulate native to the steppes of Central Asia. It has two humps on its back, in contrast to the single-humped drom ...

(''Camelus bactrianus'') ** Intermediate hosts: Flies (''Musca lucidulus'') ** Distribution:

and India *'' Thelazia rhodesii'' (Desmarest, 1828) ** Definitive hosts: mainly

bovid The Bovidae comprise the biological family of cloven-hoofed, ruminant mammals that includes cattle, bison, buffalo, antelopes, and caprines. A member of this family is called a bovid. With 143 extant species and 300 known extinct species, the ...

(''Bos taurus''),

water buffalo The water buffalo (''Bubalus bubalis''), also called the domestic water buffalo or Asian water buffalo, is a large bovid originating in the Indian subcontinent and Southeast Asia. Today, it is also found in Europe, Australia, North America, So ...

(''Bubalus bubalis''),

zebu The zebu (; ''Bos indicus'' or ''Bos taurus indicus''), sometimes known in the plural as indicine cattle or humped cattle, is a species or subspecies of domestic cattle originating in the Indian sub-continent. Zebu are characterised by a fatty ...

(''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 The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...

(''Equus caballus''),

(''Ovis aries''),

dromedary The dromedary (''Camelus dromedarius'' or ;), also known as the dromedary camel, Arabian camel, or one-humped camel, is a large even-toed ungulate, of the genus ''Camelus'', with one hump on its back. It is the tallest of the three species of ...

(''Camelus dromedarius''), and

goat The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the a ...

(''Capra hircus'') ** Intermediate hosts: Face fly ('' Musca autumnalis'', ''Musca larvipara'', and ''Musca sorbens'') ** Distribution: Africa, Asia, and Europe *'' Thelazia skrjabini'' Erschow, 1928 ** Definitive hosts:

Cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult mal ...

(''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 autumnalis''), ''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