Eyeworm infection commonly caused by Thelazia spp, is a parasitic condition affecting the eyes of various animals, including cattle, goats, horses, dogs, and cats. This condition, known as eyeworm infection, can occasionally affect humans, who serve as aberrant hosts for Thelazia spp. These parasitic nematodes belong to the genus Thelazia, with several species known to infect cattle.
Species and Vectors
The primary Thelazia species that affect goats and other animals include:
| Species | Vector | Affected Animal(s) | Country/Region |
| Thelazia gulosa | Face flies (Musca autumnalis) | Cattle, Goats | North America, Europe |
| Thelazia lacrymalis | Cattle, Horses, Goats | North America, Europe, Asia | |
| Thelazia skrjabini | Cattle, Dogs, Goats | Europe, Asia | |
| Thelazia californiensis | Lesser house fly (Fannia canicularis) | Dogs, Cats, Humans | North America, particularly Western USA |
| Thelazia callipaeda | Fruit flies (Phortica variegata) | Dogs, Cats, Humans, Goats | Europe, Asia, particularly China, Korea, Japan, and parts of Europe |
Thelazia species are transmitted by vectors and their possible hosts.
Life Cycle and Transmission
Eye worm infection thelazia worms have a complex life cycle involving both an intermediate host (flies) and a definitive host (goats). The life cycle is as follows:
- Eggs and Larvae: Adult worms in the eyes of infected goats release larvae.
- Fly Vector: These larvae are ingested by flies when they feed on the tears and secretions from the eyes of infected goats.
Life Cycle
Diagram illustrating the life cycle of Thelazia worms in cattle, horses, dogs, cats, and humans.
- Adult Worms in the Eye:
- Adult Thelazia worms reside in the conjunctival sac and tear ducts of the goat’s eye. They can also be found in the eyelids and nictitating membrane.
- Female worms produce larvae (L1) that are released into the tears and other ocular secretions.
- Intermediate Host (Fly):
- Face flies (Musca autumnalis) or fruit flies (Phortica variegata) feed on the tear secretions of infected goats, ingesting the L1 larvae.
- Inside the fly, the larvae develop into infective third-stage larvae (L3) over a period of about 2-4 weeks, depending on environmental conditions.
- Transmission to New Host:
- When the fly feeds on the eyes of another goat, the L3 larvae are deposited onto the new host’s eye.
- The larvae then migrate to the conjunctival sac or tear ducts, where they mature into adult worms, completing the cycle.
Transmission
- Direct Contact: Transmission occurs when an infected fly feeds on the tears and eye secretions of a goat, transferring the larvae.
- Seasonality: The prevalence of Thelazia infection is often higher during warm seasons when fly activity is increased.
- Environmental Factors: Conditions that support the proliferation of the fly population, such as warm and moist environments, enhance the transmission of Thelazia.
Symptoms and Diagnosis
- Symptoms in Goats:
- Conjunctivitis (inflammation of the conjunctiva)
- Increased tear production (epiphora)
- Swelling of the eyes
- Sensitivity to light (photophobia)
- Visible worms in the conjunctival sac or tear ducts
- Diagnosis:
- Clinical examination of the eye for the presence of worms.
- Microscopic examination of eye secretions to detect larvae.
- Serological tests to identify antibodies against Thelazia species.
Treatment and Control
- Treatment:
- Anthelmintics such as ivermectin or moxidectin can be effective in treating Thelazia infections.
- Topical treatments or eye drops containing anti-parasitic medications may also be used.
- Control:
- Fly control measures, such as insecticide sprays and fly traps, to reduce the vector population.
- Regular inspection and treatment of infected animals is necessary to prevent the spread of the parasite.
- Maintaining clean and dry living conditions to reduce the breeding sites for flies.
Understanding the life cycle and transmission of Thelazia worms is crucial for developing effective control and treatment strategies to protect the health of goats.
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