Thelaziasis
Thelaziasis | |
---|---|
Other names | Thelaziosis |
Infectious disease |
Thelaziasis is the term for infestation with
Signs and symptoms
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.[3][4]
Cause
Life cycle
In the uterus of the adult female, the embryos develop into first-stage larvae (L1), which remain in the eggshell (sheath).
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.[6]
Hosts and geographic range
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.[7]
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
Diagnosis
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."[8]
Treatment
Because they live so close to the outside of the body, Thelazia is one of the few
Topical treatment of livestock,
For the treatment of human cases, removal of the worm is suggested. Topical treatment with
In canines, prevention against canine thelaziosis by monthly administrations of a combination of milbemycin oxime and afoxolaner (NexGard Spectra) has been found effective.[11]
Prevalence
By one author's count, 257 human cases of Thelazia callipaeda had been reported worldwide by the year 2000,[12] though thelaziasis is still considered to be a rare disease.
Various livestock and wildlife surveys suggest that thelaziasis is quite common among animals.
- A slaughterhouse survey in Canada found that about one-third (32%) of cattle over an eight-month period were infested with eyeworms.[13]
- A survey of horses in Kentucky revealed a 42% rate of infestation with Thelazia lacrymalis.[14]
- In Wyoming and Utah, a survey of hunter-harvested mule deer found 15% to be infested by Thelazia californiensis.[15]
- A survey of various sites in Italy found 23-60% of dogs, 5% of foxes and 4 out of 4 cats to be infested with Thelazia callipaeda.[16]
- In a study of dogs living in western Spain, 39.9% of the dogs were found to have Thelazia callipaeda worms living in their eyes.[17]
References
- ^ PMID 18394285.
- PMID 15639731.
- PMID 30349847.
- ^ "A Second Case of Human Conjunctival Infestation With Thelazia gulosa and a Review of T. gulosa in North America". academic.oup.com. 22 October 2019.
- ISBN 0-85199-421-0.
- S2CID 22281032.
- PMID 29436343.
- ^ PMID 4546457.
- ^ "Merck Veterinary Manual".
- ^ "Merck Veterinary Manual".
- PMID 30644355.
- PMID 10777285.
- PMID 7189135.
- PMID 10936545.
- S2CID 38137704.
- PMID 14580802.
- PMID 21791108.