Definition
Conjunctivitis caused by the presence of a spirurid nematode-like helminth in the conjunctival fornix and lacrimal apparatus of numerous mammals and birds.
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Causes
- Thelazia sp. Spiruroidea.
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Synonyms
Geographical distribution
- Asia (India, China, Korea, Japan),
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- Northern America (California) (Thelazia californiensis),
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- Exceptionally, Europe (France, North-West Italy) (Thelazia callipaeda).
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Transmission
- Via an intermediate host-carrier (common house fly) which ingests L1 larvae from the lacrimal secretions of a dog and deposits infectived L3 larvae on another animal, approximately 2-4 weeks later.
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- Prepatence: approximately one month.
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Predisposing Factors
- Pre-existing ocular infection attracting flies,
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- Animals living in groups,
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Presumptive diagnosis
- Conjunctivitis resistant to symptomatic treatment on an animal having lived in a risk-prone area.
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- Presence of small, whitish, mobile filaments, approximately 1-cm long (adult worms), on the inner side of the nictitating membrane or in the lacrimal film on the surface of the eye.
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Confirming diagnosis
- Identification with a microscope of adult worms extracted with fine pincers under local anaesthesia, preserved in 70% alcohol, and cleared with amman's lactophenol (specialist laboratory).
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- Presence of spirurid eggs or larvae in a conjunctival smear.
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Differential diagnosis
- Conjunctivitis caused by foreign bodies.
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- Erratic localization of Dirofilaria immitis, Angiostrongylus vasorum, or Spirocerca lupi on the eye.
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Prognosis
Treatment
- Topical symptomatic treatment following extraction of worms.
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- Antibiotic therapy via eye drops (neomycin, polymyxin b) until cured (more than 6 weeks).
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- Ivermectin (or any other endectocide) at the rate of 200 µg/kg SC (off-label use under the prescriber's responsibility) in dogs that are difficult to handle or in groups of dogs.
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Prevention
- Control of diptera in risk-prone areas.
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Thelazia keratoconjunctivitis: presence of whitish filaments on corneal surface. (© Mérial)
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