| Thelaziasis | |
|---|---|
| Other names | Thelaziosis |
 | |
| Thelazia callipaeda infestation in a dog [1] | |
| Specialty | Infectious disease |
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 and bird hosts, including humans. [2] Thelazia nematodes are often referred to as "eyeworms".
In animal and human hosts, infestation by Thelazia may be asymptomatic, though it frequently causes watery eyes (epiphora), conjunctivitis, corneal opacity, or corneal ulcers (ulcerative keratitis). [1] Infested humans have also reported "foreign body sensation" –the feeling that something is in the eye.
In the uterus of the adult female, the embryos develop into first-stage larvae (L1), which remain in the eggshell (sheath). [3] The female deposits these sheathed larvae in the tears of the mammal or bird definitive host, and the larvae are ingested by tear-feeding flies. In the fly, the larvae "hatch" (exsheath), penetrate the gut wall, and migrate to either the fat body, testes or egg follicles (depending on the species). There they develop into third-stage larvae (L3), which migrate to the head of the fly. The infective L3 larvae wiggle out of the straw-like feeding apparatus of the fly when it feeds on the tears of another mammal or bird host. The L3 larvae develop into adults in the eye or surrounding tissues of the host, where they may live for over one year.
In the definitive host, Thelazia have been found in various tissues of the orbit (or socket) of the eye, including within the eyelids, in the tear glands, tear ducts, or the so-called "third eyelid" (nictitating membrane) or in the eyeball itself. [4]
While a few dozen species of Thelazia have been described in the literature, only three have been reported to infest humans, and only seven are commonly reported in veterinary contexts. The remaining species are occasionally found in birds or wild mammals.
In humans, dogs and cats, thelaziasis cases due to Thelazia callipaeda (Asia, Europe), and occasionally T. californiensis and T. gulosa (western North America), have been reported. [5]
Horses are infested by T. lacrymalis (worldwide) and, less frequently, by T. rhodesii (Africa, Asia, Europe).
In cattle, T. gulosa (Asia, Europe, North America), T. rhodesii (Africa, Asia, Europe) and T. skrjabini (Europe, North America) are the primary species of concern.
In camels, T. leesei infestations have been reported from the Post-Soviet states and India.
The intermediate hosts of several Thelazia species are known, and in each case they are tear-feeding flies of the genera Musca (family Muscidae), Phortica (family Drosophilidae), or Fannia (family Fanniidae).
Diagnosis involves simply examining the eyes and nearby tissues for the worms. Adult Thelazia are very active, one author described T. californiensis as a "short lively piece of nylon fishing line about 10 mm long." [6]
Because they live so close to the outside of the body, Thelazia is one of the few nematode infections which can be treated topically.
Topical treatment of livestock, [7] dogs and cats [8] with organophosphates (such as ecothiopate iodide or isofluorophate) and systemic treatment with anthelmintics (such as ivermectin, levamisole, and doramectin) are recommended by the Merck Veterinary Manual. Other sources have reported positive results treating dogs with moxidectin, imidacloprid, or milbemycin oxime.
For the treatment of human cases, removal of the worm is suggested. Topical treatment with cocaine or thiabendazole have also been reported to kill the worms in human cases. [6] Because most, if not all, species of Thelazia are spread by flies, sanitary practices which reduce the presence of flies will also reduce the spread of thelaziasis.
In canines, prevention against canine thelaziosis by monthly administrations of a combination of milbemycin oxime and afoxolaner (NexGard Spectra) has been found effective. [9]
By one author's count, 257 human cases of Thelazia callipaeda had been reported worldwide by the year 2000, [10] though thelaziasis is still considered to be a rare disease.
Various livestock and wildlife surveys suggest that thelaziasis is quite common among animals.
Strongyloides stercoralis is a human pathogenic parasitic roundworm causing the disease strongyloidiasis. Its common name in the US is threadworm. In the UK and Australia, however, the term threadworm can also refer to nematodes of the genus Enterobius, otherwise known as pinworms.
Mange is a type of skin disease caused by parasitic mites. Because various species of mites also infect plants, birds and reptiles, the term "mange", or colloquially "the mange", suggesting poor condition of the skin and fur due to the infection, is sometimes reserved for pathological mite-infestation of nonhuman mammals. Thus, mange includes mite-associated skin disease in domestic mammals, in livestock, and in wild mammals (for example, foxes, coyotes, cougars and wombats. Severe mange caused by mites has been observed in wild bears. Since mites belong to the arachnid subclass Acari, another term for mite infestation is acariasis.
Baylisascaris is a genus of roundworms that infect more than fifty animal species.
Haemonchus contortus, also known as the barber's pole worm, is a very common parasite and one of the most pathogenic nematodes of ruminants. Adult worms attach to abomasal mucosa and feed on the blood. This parasite is responsible for anemia, oedema, and death of infected sheep and goats, mainly during summer in warm, humid climates.
Ascaris suum, also known as the large roundworm of pig, is a parasitic nematode that causes ascariasis in pigs. While roundworms in pigs and humans are today considered as two species with different hosts, cross-infection between humans and pigs is possible; some researchers have thus argued they are the same species. Ascariasis is associated with contact to pigs and pig manure in Denmark.
Dirofilaria immitis, also known as heartworm or dog heartworm, is a parasitic roundworm that is a type of filarial worm, a small thread-like worm, that causes dirofilariasis. It is spread from host to host through the bites of mosquitoes. There are four genera of mosquitoes that transmit dirofilariasis, Aedes, Culex, Anopheles, and Mansonia. The definitive host is the dog, but it can also infect cats, wolves, coyotes, jackals, foxes, ferrets, bears, seals, sea lions and, under rare circumstances, humans.
Acanthocheilonema is a genus within the family Onchocercidae which comprises mainly tropical parasitic worms. Cobbold created the genus Acanthocheilonema with only one species, Acanthocheilonema dracunculoides, which was collected from aardwolf in the region of South Africa in the nineteenth century. These parasites have a wide range of mammalian species as hosts, including members of Carnivora, Macroscelidea, Rodentia, Pholidota, Edentata, and Marsupialia. Many species among several genera of filarioids exhibit a high degree of endemicity in studies done on mammalian species in Japan. However, no concrete evidence has confirmed any endemic species in the genus Acanthocheilonema.
Dioctophyme renale, commonly referred to as the giant kidney worm, is a parasitic nematode (roundworm) whose mature form is found in the kidneys of mammals. D. renale is distributed worldwide, but is less common in Africa and Oceania. It affects fish eating mammals, particularly mink and dogs. Human infestation is rare, but results in kidney destruction, usually of one kidney and hence not fatal. A 2019 review listed a total of 37 known human cases of dioctophymiasis in 10 countries with the highest number (22) in China. Upon diagnosis through tissue sampling, the only treatment is surgical excision.
Lungworms are parasitic nematode worms of the order Strongylida that infest the lungs of vertebrates. The name is used for a variety of different groups of nematodes, some of which also have other common names; what they have in common is that they migrate to their hosts' lungs or respiratory tracts, and cause bronchitis or pneumonia. The lungworm will gradually damage the airways or lung tissue by inciting an inflammatory reaction inside the tissue. Ultimately, the parasites survive and reproduce in the respiratory tissues. The category is thus more a descriptive than a precisely taxonomic one.
Capillaria plica is a parasitic nematode which is most often found in the urinary bladder, and occasionally in the kidneys, of dogs and foxes. It has also been found in the domestic cat, and various wild mammals. Its presence usually produces no clinical symptoms, but in some cases, it leads to hematuria, cystitis, or difficulty in urination.
Capillaria hepatica is a parasitic nematode which causes hepatic capillariasis in rodents and numerous other mammal species, including humans. The life cycle of C. hepatica may be completed in a single host species. However, the eggs, which are laid in the liver, must mature outside of the host body prior to infecting a new host. So the death of the host in which the adults reach sexual maturity, either by being eaten or dying and decomposing, is necessary for completion of the life cycle.
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". Adults are usually found in the eyelids, tear glands, tear ducts, or the so-called "third eyelid". Occasionally, they are found in the eyeball itself, either under the conjunctiva 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.
Thelazia 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.
Trichostrongylus species are nematodes, which are ubiquitous among herbivores worldwide, including cattle, sheep, donkeys, goats, deer, and rabbits. At least 10 Trichostrongylus species have been associated with human infections. Infections occur via ingestion of infective larvae from contaminated vegetables or water. Epidemiological studies indicate a worldwide distribution of Trichostrongylus infections in humans, with the highest prevalence rates observed in individuals from regions with poor sanitary conditions, in rural areas, or who are farmers / herders. Human infections are most prevalent in the Middle East and Asia, with a worldwide estimated prevalence of 5.5 million people.
Milbemycin oxime, sold under the brand name Interceptor among others, is a veterinary medication from the group of milbemycins, used as a broad spectrum antiparasitic. It is active against worms (anthelmintic) and mites (miticide).
Angiostrongylus vasorum, also known as French heartworm, is a species of parasitic nematode in the family Metastrongylidae. It causes the disease canine angiostrongylosis in dogs. It is not zoonotic, that is, it cannot be transmitted to humans.
Lotilaner, sold under the brand name Xdemvy, is an ectoparasiticide (anti-parasitic) medication used for the treatment of blepharitis caused by infestation by Demodex. It is used as an eye drop.
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.
Phortica variegata is a species of vinegar fly in the family Drosophilidae. Phortica and related fly species are perhaps best known for their behaviour of feeding on the lacrimal secretions of mammals. As a consequence of this behaviour, P. variegata can serve as a vector of Thelazia callipaeda roundworms.
Nematode infection in dogs - the infection of dogs with parasitic nemamotodes - are, along with tapeworm infections and infections with protozoa, frequent parasitoses in veterinary practice. Nematodes, as so-called endoparasites, colonize various internal organs - most of them the digestive tract - and the skin. To date, about 30 different species of nematode have been identified in domestic dogs; they are essentially also found in wild dog species. However, the majority of them often cause no or only minor symptoms of disease in adult animals. The infection therefore does not necessarily have to manifest itself in a worm disease (helminthosis). For most nematodes, an infection can be detected by examining the feces for eggs or larvae. Roundworm infection in dogs and the hookworm in dogs is of particular health significance in Central Europe, as they can also be transmitted to humans (zoonosis). Regular deworming can significantly reduce the frequency of infection and thus the risk of infection for humans and dogs.
