Thelazia
Encyclopedia
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 "thelaziasis
" (occasionally spelled "thelaziosis"). Adults are usually found in the eyelids, tear glands
, tear ducts
, or the so-called "third eyelid" (nictitating membrane
). 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 cavity of the eyeball. All species of Thelazia for which the life cycle has been studied are transmitted by species of Diptera
(flies) which do not bite, but which feed on tears.
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
worms which parasitize the eyes and associated tissues of various bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
and mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
hosts, including humans. They are often called "eyeworms," and infestation with Thelazia species is referred to as "thelaziasis
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 of various mammal and bird hosts, including humans...
" (occasionally spelled "thelaziosis"). Adults are usually found in the eyelids, tear glands
Lacrimal gland
The lacrimal glands are paired almond-shaped glands, one for each eye, that secrete the aqueous layer of the tear film. They are situated in the upper, outer portion of each orbit, in the lacrimal fossa of the orbit formed by the frontal bone. Inflammation of the lacrimal glands is called...
, tear ducts
Lacrimal canaliculi
The lacrimal canaliculi, also known as the lacrimal canals or lacrimal ducts, are the small channels in each eyelid that commence at minute orifices, termed puncta lacrimalia, on the summits of the papillae lacrimales, seen on the margins of the lids at the lateral extremity of the lacus...
, or the so-called "third eyelid" (nictitating membrane
Nictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...
). Occasionally, they are found in the eyeball itself, either under the conjunctiva
Conjunctiva
The conjunctiva covers the sclera and lines the inside of the eyelids. It is composed of rare stratified columnar epithelium.-Function:...
(the membrane that covers the white part of the eye) or in the vitreous cavity of the eyeball. All species of Thelazia for which the life cycle has been studied are transmitted by species of Diptera
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
(flies) which do not bite, but which feed on tears.
Representative species
- Thelazia anolabiata (Molin, 1860)
- Definitive hosts: Andean Cock-of-the-RockAndean Cock-of-the-rockThe Andean Cock-of-the-rock is a medium-sized passerine bird of the Cotinga family native to Andean cloud forests in South America. The plural is Andean Cocks-of-the-rock...
(Rupicola peruviana) and many other Brazilian birds - Intermediate hosts: Not known
- Distribution: South America
- Definitive hosts: Andean Cock-of-the-Rock
- Thelazia bubalis Ramanujachari and Alwar, 1952
- Definitive hosts: Water buffaloWater buffaloThe water buffalo is a domesticated bovid widely kept in Asia, Europe and South America.Water buffalo can also refer to:*Wild water buffalo , the wild ancestor of the domestic water buffalo...
- Intermediate hosts: Not known
- Distribution: India
- Definitive hosts: Water buffalo
- Thelazia californiensis Price, 1930
- Definitive hosts: DogDogThe domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
(Canis lupus familiaris), CatCatThe cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...
(Felis catus), occasionally HumanHumanHumans are the only living species in the Homo genus...
(Homo sapiens), Domestic sheepDomestic sheepSheep are quadrupedal, ruminant mammals typically kept as livestock. Like all ruminants, sheep are members of the order Artiodactyla, the even-toed ungulates. Although the name "sheep" applies to many species in the genus Ovis, in everyday usage it almost always refers to Ovis aries...
(Ovis aries), Mule deerMule DeerThe mule deer is a deer indigenous to western North America. The Mule Deer gets its name from its large mule-like ears. There are believed to be several subspecies, including the black-tailed deer...
(Odocoileus hemionus), CoyoteCoyoteThe coyote , also known as the American jackal or the prairie wolf, is a species of canine found throughout North and Central America, ranging from Panama in the south, north through Mexico, the United States and Canada...
(Canis latrans) and American Black BearAmerican black bearThe American black bear is a medium-sized bear native to North America. It is the continent's smallest and most common bear species. Black bears are omnivores, with their diets varying greatly depending on season and location. They typically live in largely forested areas, but do leave forests in...
(Ursus americanus). - Intermediate hosts: Lesser house flyLesser house flyThe lesser house fly or little house fly, Fannia canicularis, is somewhat smaller than the common housefly. It is slender, and the median vein in the wing is straight. Larvae feed on all manner of decaying organic matter, including carrion...
(Fannia canicularis) and Fannia benjamini - Distribution: Western North America
- Definitive hosts: Dog
- Thelazia callipaedaThelazia callipaedaThelazia callipaeda is a parasitic nematode, and the most common cause of "thelaziasis" 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 reported in the medical literature.-Hosts:In addition to humans, cats and dogs,...
Railliet & Henry, 1910 (sometimes called "Oriental eyeworm")- Definitive hosts: typically reported from DogDogThe domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
(Canis familiaris), CatCatThe cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...
(Felis catus), and HumanHumanHumans are the only living species in the Homo genus...
(Homo sapiens); occasionally reported from Wolf (Canis lupus), Raccoon dogRaccoon DogThe raccoon dog , also known as the magnut or tanuki, is a canid indigenous to east Asia. It is the only extant species in the genus Nyctereutes...
(Nyctereutes procyonoides), Red FoxRed FoxThe red fox is the largest of the true foxes, as well as being the most geographically spread member of the Carnivora, being distributed across the entire northern hemisphere from the Arctic Circle to North Africa, Central America, and the steppes of Asia...
(Vulpes fulva), European RabbitEuropean RabbitThe European Rabbit or Common Rabbit is a species of rabbit native to south west Europe and north west Africa . It has been widely introduced elsewhere often with devastating effects on local biodiversity...
(Oryctolagus cuniculus). Over 250 cases of T. callipaeda infestation in humans have been reported thus far. - Intermediate hosts: Fruit flies (Amiota (Phortica) variegata in Europe, and Phortica okadai in China)
- Distribution: Asia and Europe
- Definitive hosts: typically reported from Dog
- Thelazia erschowi Oserskaja, 1931
- Definitive hosts: pigPigA pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
(Sus domesticus) - Intermediate host: Not known
- Distribution: Post-Soviet statesPost-Soviet statesThe post-Soviet states, also commonly known as the Former Soviet Union or former Soviet republics, are the 15 independent states that split off from the Union of Soviet Socialist Republics in its dissolution in December 1991...
- Definitive hosts: pig
- Thelazia gulosa (Railliet & Henry, 1910)
- Definitive hosts: YakYakThe yak, Bos grunniens or Bos mutus, is a long-haired bovine found throughout the Himalayan region of south Central Asia, the Tibetan Plateau and as far north as Mongolia and Russia. In addition to a large domestic population, there is a small, vulnerable wild yak population...
(Bos grunniens) and other CattleCattleCattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
(Bos taurus) - Intermediate hosts: Face fly (Musca autumnalisMusca autumnalisMusca autumnalis, the face fly or autumn house-fly, is a pest of cattle and horses- Description :The face fly is similar to the closely related house fly. Slightly larger, averaging about 7 - 8 mm long and Grey in colour with 4 dark stripes on the thorax, with a grey-black patterned abdomen...
) in Europe and North America, Musca larvipara in the Ukraine, Musca vitripennis in CrimeaCrimeaCrimea , or the Autonomous Republic of Crimea , is a sub-national unit, an autonomous republic, of Ukraine. It is located on the northern coast of the Black Sea, occupying a peninsula of the same name...
, and Musca amica in the Far East - Distribution: Asia, Europe, and North America
- Definitive hosts: Yak
- Thelazia lacrymalis (Gurlt, 1831)
- Definitive hosts: HorseHorseThe horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
(Equus caballus) and CattleCattleCattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
(Bos taurus) - Intermediate hosts: Face fly (Musca autumnalisMusca autumnalisMusca autumnalis, the face fly or autumn house-fly, is a pest of cattle and horses- Description :The face fly is similar to the closely related house fly. Slightly larger, averaging about 7 - 8 mm long and Grey in colour with 4 dark stripes on the thorax, with a grey-black patterned abdomen...
) and Musca osirisMusca osirisMusca 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, according to Willi Hennig.... - Distribution: Asia, Europe, Middle East, North America and South America
- Definitive hosts: Horse
- Thelazia leesei Railliet & Henry, 1910
- Definitive hosts: DromedaryDromedaryThe dromedary or Arabian camel is a large, even-toed ungulate with one hump on its back. Its native range is unclear, but it was probably the Arabian Peninsula. The domesticated form occurs widely in North Africa and the Middle East...
(Camelus dromedarius) and Bactrian CamelBactrian camelThe Bactrian camel is a large, even-toed ungulate native to the steppes of central Asia. It is presently restricted in the wild to remote regions of the Gobi and Taklamakan Deserts of Mongolia and Xinjiang. A small number of wild Bactrian camels still roam the Mangystau Province of southwest...
(Camelus bactrianus) - Intermediate hosts: Flies (Musca lucidulus)
- Distribution: Post-Soviet statesPost-Soviet statesThe post-Soviet states, also commonly known as the Former Soviet Union or former Soviet republics, are the 15 independent states that split off from the Union of Soviet Socialist Republics in its dissolution in December 1991...
and India
- Definitive hosts: Dromedary
- Thelazia rhodesii (Desmarest, 1828)
- Definitive hosts: mainly bovidBovidA bovid is any of almost 140 species of cloven-hoofed ruminant mammal at least the males of which bear characteristic unbranching horns covered in a permanent sheath of keratin....
s, CattleCattleCattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
(Bos taurus), BuffaloWater BuffaloThe water buffalo or domestic Asian water buffalo is a large bovine animal, frequently used as livestock in southern Asia, and also widely in South America, southern Europe, northern Africa, and elsewhere....
(Bubalus bubalis), ZebuZebuZebu , sometimes known as humped cattle, indicus cattle, Cebu or Brahmin cattle are a type of domestic cattle originating in South Asia, particularly the Indian subcontinent. They are characterised by a fatty hump on their shoulders, drooping ears and a large dewlap...
(Bos indicus), BisonBisonMembers of the genus Bison are large, even-toed ungulates within the subfamily Bovinae. Two extant and four extinct species are recognized...
(Bison bonasus), and sometimes HorseHorseThe horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
(Equus caballus), Domestic sheepDomestic sheepSheep are quadrupedal, ruminant mammals typically kept as livestock. Like all ruminants, sheep are members of the order Artiodactyla, the even-toed ungulates. Although the name "sheep" applies to many species in the genus Ovis, in everyday usage it almost always refers to Ovis aries...
(Ovis aries), DromedaryDromedaryThe dromedary or Arabian camel is a large, even-toed ungulate with one hump on its back. Its native range is unclear, but it was probably the Arabian Peninsula. The domesticated form occurs widely in North Africa and the Middle East...
(Camelus dromedarius), and GoatGoatThe domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...
(Capra hircus) - Intermediate hosts: Flies (Face fly (Musca autumnalisMusca autumnalisMusca autumnalis, the face fly or autumn house-fly, is a pest of cattle and horses- Description :The face fly is similar to the closely related house fly. Slightly larger, averaging about 7 - 8 mm long and Grey in colour with 4 dark stripes on the thorax, with a grey-black patterned abdomen...
, Musca larvipara, and Musca sorbens) - Distribution: Africa, Asia, and Europe
- Definitive hosts: mainly bovid
- Thelazia skrjabini Erschow, 1928
- Definitive hosts: CattleCattleCattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
(Bos taurus) and YakYakThe yak, Bos grunniens or Bos mutus, is a long-haired bovine found throughout the Himalayan region of south Central Asia, the Tibetan Plateau and as far north as Mongolia and Russia. In addition to a large domestic population, there is a small, vulnerable wild yak population...
(Bos grunniens) - Intermediate hosts: Face fly (Musca autumnalisMusca autumnalisMusca autumnalis, the face fly or autumn house-fly, is a pest of cattle and horses- Description :The face fly is similar to the closely related house fly. Slightly larger, averaging about 7 - 8 mm long and Grey in colour with 4 dark stripes on the thorax, with a grey-black patterned abdomen...
), Musca vitripennis, and Musca amica - Distribution: Europe and North America
- Definitive hosts: Cattle