OCULAR SETARIOSIS IN A HORSE

Pashu Sandesh, 06 November 2023

A case study

Yogendra Singh¹, Ravi Prakash Goyal¹, Ranjit Kumar¹, Kh. Sangeeta Devi²,

Anil Kumar Gangwar³

1. M. V. Sc. Student       2. Assistant Professor          3. Professor & Head

Department of Veterinary Surgery and Radiology, College of Veterinary Science and Animal Husbandry, Narendra Deva University of Agriculture and Technology, Kumarganj-224 229, Ayodhya (UP)

1. ABSTRACT

A 4-year-old white horse was presented at the College, Veterinary Clinical Complex, Ayodhya, Uttar Pradesh, India, with impaired vision and cloudiness in the left eye. On close examination, a thread-like larva was seen in the anterior chamber of the eye and was later diagnosed as setariosis. Finally, the setaria was removed by surgery aspirating it with a 16 gauge needle. Ivermectin was administered at 200 µg/kg to avoid recurrence. Two setaria larvae were collected and recovery was uneventful. Opacity cleared in about 3 weeks.

2. INTRODUCTION

Ocular Setariosis in horses is reported from many parts of lndia including J & K [1]. It is an intra-ocular helminth parasite and is classified under nematodes. It is caused by the migration of immature stages of setaria labiato-papillosa (S. digitata) and setaria equi. In the sub-clinical stage lacrymation and conjunctivitis are seen followed by cloudiness of the cornea resulting in corneal opacity. Similar lesions are seen in Thalizia infection but the parasite was found either under the conjunctiva or in the vitreous cavity of the eyeball [2]. While setaria is seen in the conjunctival sac only and not in the aqueous chamber. The infection occurs in equines when infected mosquitoes feed around the eyes and deposit the infective larvae there, which enter and migrate in the anterior chamber of the eye [3] The damage to the eye is caused by the serrated cuticle of the worm and movement of larvae [4]. Ocular setariasis is usually treated surgically either by paracentesis or by aspiration [5]. Surgical treatment has been advocated & found successful [6], though medical treatment has been reported [7] 

3. ANAMNESIS

The owner reported that the animal has had a cloudy appearance in its left eye for three weeks, which is increasing day by day. The animal was shown to a local veterinarian previously. During clinical examination, cloudiness was observed in the left eye and on close examination, a thread-like larva was seen in the eye. Thereafter, the case was referred for surgical correction at the VCC unit. 

4. CLINICAL SIGNS

 Important clinical signs noted at the time of presentation included a snake-like, whitish parasite moving swiftly in the aqueous humour of the left eye, photophobia, corneal opacity, blepharospasm, mild lacrimation and head tilt, moderate depression, stiff gait and moderate fever (40°C).

Haematological data shows a decrease in erythrocyte (RBC) count, haemoglobin and haematocrit (PVC), together with leucocytosis and an accelerated erythrocyte sedimentation rate (ESR). Microscopic examination of wet blood films revealed one actively motile microfilariae per 50 µl sample. Knott’s test (a technique for the detection of microfilariae by haemolysis and concentration of blood samples) was performed and observed positive for microfilariae of the Setaria species [8].

5. TREATMENT

The animal was properly restrained in lateral recumbency under both general and regional anaesthesia using atropine (0.04 mg/kg), xylazine (1 mg/kg) and lignocaine 2% respectively. A 10 ml disposable syringe with an 18-gauge needle was inserted into the anterior chamber of the affected eye at the 6 o'clock position of the cornea about 5 mm apart from the limbus. Part of the aqueous humour was to be withdrawn before the parasite could be removed through a small incision window on the cornea. However, the needle got clogged immediately after the piston of the syringe was pulled out to withdraw the aqueous humour. When the needle was pulled out of the eye, the tail part of the worm plugged the needle. The entire parasite was then successfully removed from the eye. Then, the eye was treated with antibiotics. No additional surgical procedure was done to relieve the blindness of the affected eye. The worm removed was 4.9 cm long and was identified as S. digitata under light microscopic. After the removal of the parasite, 2-3 drops of dexamethasone and neomycin eye drops were applied to the eyes 3-4 times a day for 1 week. Ivermectin was administered at 200 µg/kg to avoid recurrence. The animal recovered without complications and was free of the parasite 6 months after treatment.

6. DISCUSSION

Adult Setaria equina are found inside the anterior chamber of the horse's eye. This filaroidea nematode, which is normally found inside the peritoneal cavity of horses, may cause serious intraocular damage [9]. Setaria equina has an indirect life cycle. Microfilaria are transmitted by blood-sucking insects.  The Larva of the parasite arrives in the anterior segment of the eye and grows into an immature adult. 

 Clinical signs attributed to ocular filariasis are caused by the resultant iridocyclitis which may be manifested by aqueous flare, hypopyon, photophobia, epiphora, miosis and corneal oedema. Often the parasite cannot be visualised because of the opacity of the cornea and aqueous humour. 

Diagnosis and treatment of Iridocyclitis of uncertain aetiology in a horse merit a careful examination, with a focal light source and magnification, for the presence of intraocular parasites. If opaque media prevents a thorough intraocular examination symptomatic treatment for the uveitis may be instituted and the examination repeated. The treatment of choice for intraocular filariasis has been surgical removal of the parasite followed by treatment for uveitis. Although ivermectin has recently been reported to be 80 per cent effective against adult S equina at a dose of 0.2 mg/kg bwt and 88 per cent effective at a dose of 0.5 mg/kg bwt [10].

8. REFERENCES

1. Bhadwal MS, Sharma RK, Singh. Equine intraocular parasite, Centaur. 1998; 24 (3): 81-83. 

2. Xue CN, Tian, Z Huang. "Thelazia callipaeda in human vitreous." Canadian Journal of Ophthalmology 2007;  42(6):884-885. 

3. Soulsby E. Helminths, Arthropods and Protozoa of Domesticated Animals.BailliereTinda, London. 1982; 1:316-319

4. Jaiswal S, Singh SY, SinghB, Singh, HN. Ocular setariosis in a horse in Intas Polivet. 2006; 7(1): 67-68. 

5. Lavach JD. Parasitic diseases. In Large Animal Ophthalmology. Philadelphia, Mosby. 1990; 1: 260-263

6. Bhardwaj HR, Bhadwal MS, Soodan JS, Surgical removal of the eye worm in a horse - A case report in Intas Polivet 2000; l(I): 101.

7. Moore CP, Sarazan RD, Whitly RD, Jackson WF. Equine ocular parasites a review. Equine vet. Journal. 1993;54(6): 76-85.

8. Slim MK, Fouad KA. Incidence of equine filariasis in Egypt. Veterinary Medical Journal of the Faculty of Veterinary Medicine, Cairo University 1964; 11: 113-11Jemelka ED. Removal of Setaria digitata from the anterior chamber of the equine eye. Vet. Med. Small Anim. Clin. 1976; 71:673-675

9. Levine N. Nematode Parasites of Domestic Animals and Man. Burgess Publishing Co, Minneapolis. 1968; 461,470-475, 481, 485. 

10. Klei TR, Torbet BJ, Ochoa R. Efficacy of ivermectin (22,23-dihydro avermectin B,) against adult Setaria equina and Onchocerca cervicalis in ponies. J. Parasitol.1980; 66: 859-861.