April 05, 2024
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Ocular parasitosis consistently perplexes ophthalmologists due to its varied and unpredictable presentations. The elusive nature of the disease ensures it remains concealed unless actively sought out through diligent examination.
Gnathostomiasis is a rare zoonotic infection in which humans are the paratenic host. Human gnathostomiasis is caused by ingestion of third-stage larva of the nematode, which may be found in raw or poorly cooked meat or in contaminated water. A live intraocular nematode is rare and mostly reported from Southeast Asian countries.
Figure 1. Clinical slit lamp photograph showing endothelial pigmented keratic precipitates (a). Live worm seen stuck in iris at 2 clock hours (b).
Source: Dhivya Ashok Kumar, MD, FRCS, FICO, FAICO, Anjana Chandran, MBBS, DNB, Amar Agarwal, MS, FRCS, FRCOphth, and Ashvin Agarwal, MD
We are reporting a case of a live worm hooked in the iris of a patient with recurrent uveitis and how it was managed successfully. This case is reported because of its rarity and clinical importance.
Case summary
A 34-year-old woman presented to the outpatient department with complaints of redness, pain, watering and diminution of vision in the left eye for the past week, associated with headache. She gave a history of recurrent similar episodes in the past 6 months for which topical medications were taken. She had no significant medical history or any history of trauma to the eye.
On examination, distance Snellen visual acuity was 6/6 in the right eye and 6/6 p in the left eye. On slit lamp examination, the right eye was normal. The left eye showed ciliary congestion, central large keratic precipitates and pigments on the endothelium (Figure 1a). The anterior chamber had 2+ cells and flare, and retrolental cells were seen. The iris revealed two defects in the midperiphery, one at 7 clock hours and another at 2 clock hours, which had a live motile worm hooked in it (Figure 1b). IOP was 30 mm Hg in the left eye. Fundus examination of the left eye revealed grade 1 vitritis. B-scan ultrasonography was normal except for the mild vitreous echoes. Anterior segment OCT (Figure 2) was performed for location, and widefield fundus photographs were taken to document any posterior segment involvement of the left eye. No worms were seen in the posterior segment.
Figure 2. Anterior segment OCT showing live worm (green arrow).
Under peribulbar anesthesia, a clear corneal incision was made. The worm was extracted using MST forceps (Figure 3b) and was sent for microscopy and histopathological examination. The worm was short and stout, reddish-brown and cylindrical, measuring approximately 0.5 cm. The histopathology report showed larval tissue with four hooklets, morphology suggestive of Gnathostoma (Figure 4).
Figure 3. Live worm seen intraoperatively under peribulbar anesthesia (a) and removed with MST forceps (b).
Figure 4. Histopathology slide attained with hematoxylin and eosin showing the worm with hooklets.
The patient was given oral albendazole 400 mg once daily for 2 weeks, a tapering dose of oral prednisolone (starting with 40 mg once daily for a week followed by a tapering dose by 10 mg every week), topical prednisolone acetate eye drops, homatropine eye drops, moxifloxacin 0.5% eye drops and dorzolamide-timolol combination eye drops. Routine blood investigations were normal. Routine urine and stool examination did not reveal any egg, worm or larva. The patient followed up after 1 week with no sequelae (Figure 5).
Figure 5. Postoperatively, one can see preexisting iris hole formed by motile worm (yellow arrow) (a) and current removed site showing lamellar iris atrophy (b).
Human gnathostomiasis
Several species of parasitic worms in the genus Gnathostoma cause human gnathostomiasis, which is commonly diagnosed in Southeast Asia and has also been found elsewhere in Asia, South and Central America, and some areas of Africa. The first case of gnathostomiasis was reported from Thailand in 1889 and was attributed to Gnathostoma spinigerum. The primary cause of infection is eating undercooked or raw freshwater fish, eels, frogs, birds and reptiles. Common infection manifestations are swelling under the skin and increased levels of eosinophils in the blood. In rare cases, the parasite may enter the liver, the eye, and the nerves, spinal cord or brain. Changes in eating habits and improvements in disease reporting may explain the increase in reports of human gnathostomiasis.
Amar Agarwal
Ocular manifestations
If Gnathostoma larvae enter the eye, they can lead to external and internal ocular lesions with inflammation, subarachnoid hemorrhage and possibly visual loss. Intraocular gnathostomiasis has also been associated with macular scarring, rupture of the nasal branch of the central retinal artery, and retinal tear with choroidal hemorrhage near the optic disc. Characteristic features include iris holes, uveitis and subretinal hemorrhage with subretinal tract, and clinical manifestations may include eyelid edema, conjunctival pain and conjunctival erythema. Larvae in the eyes can be visualized and are generally found in the anterior chamber. If the larvae are surgically removed, visual performance can be recovered.
Parasitic infestation is a major health problem in tropical countries. Common ocular parasites are Toxocara, Onchocerca, Wuchereria, Ancylostoma, Loa, Dirofilaria, Gnathostoma and Angiostrongylus. Chronic eye inflammation and increased IOP can be due to the presence of the live worm or the immune reaction. Successful treatment involves early and complete removal of the worm, which can be challenging due to the motility of the worm.
Conclusion
In instances of recurrent iridocyclitis, it may be prudent to consider parasitic uveitis as a potential differential diagnosis. Systemic treatment with anthelmintic drugs and steroids is recommended in cases of parasitic uveitis. Stool examination, radiological imaging and high-resolution ultrasonography are recommended to rule out systemic involvement. In the management of cases like this, the crucial focus lies in the extraction of the live worm.
- References:
- Barua P, et al. Indian J Med Microbiol. 2007;doi:10.4103/0255-0857.34775.
- Biswas J, et al. Retina. 1994;doi:10.1097/00006982-199414050-00009.
- Kannan KA, et al. Indian J Ophthalmol. 1999;47(4):252-253.
- Liu GH, et al. Parasit Vectors. 2020;doi:10.1186/s13071-020-04494-4.
- Nawa Y, et al. J Trop Med Parasitol. 2010;33:77-86.
- Parasites – gnathostomiasis (Gnathostoma infection). https://www.cdc.gov/parasites/gnathostoma/index.html. Accessed March 7, 2024.
- Pillai GS, et al. Am J Trop Med Hyg. 2012;doi:10.4269/ajtmh.2012.11-0719.
- Rawat P, et al. Indian J Ophthalmol. 2016;doi:10.4103/0301-4738.181747.
- For more information:
- Amar Agarwal, MS, FRCS, FRCOphth, director of Dr. Agarwal’s Eye Hospital and Eye Research Centre, is the author of several books published by SLACK Books, sister company of Healio publisher Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at [email protected]; website: www.dragarwal.com.
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