Intraocular parasitic infection occurs rarely but it may lead to ocular morbidity and, in some cases, cause blindness. The common ocular presentations are inflammation in the orbit, eye and adnexa, intraocular inflammation in both anterior and posterior segment. Myanmar is one of the endemic area and the commonest parasites found in Myanmar are Loa Loa (Nematodes-microfilaria), Gnathostoma (zoonotic nematodes) and cysticercosis (tissue dwelling cestodes).
A total 13 cases of intraocular helminthic infections were reported in Yangon Eye Hospital from 2001 to 2010; nine cases were found to have parasites in anterior segments and among the four cases of posterior segment parasitic infections - three cases with cysticercus and one case of Gnathostomal larva were confirmed by microbiology. Adult form of Loa Loa and Gnathostomal larva are the worms commonly found in anterior chamber. Posterior segment infestation is a rare occurrence and in definite cases the parasites were seen directly in the eye, removed from the eye and identified with microbiology. There are many unreported cases with indirect evidences like multiple iris holes, unexplained endogenous endophthalmitis in healthy young persons, and subretinal pigmented tracts in posterior pole are commonly seen in clinical practice without viable parasites seen in the eye.
Human gnathostomiasis, caused by migration of Gnathostoma larvae, is an important foodborne parasitic zoonosis that is endemic mainly in Asian countries where people consume raw freshwater fish. (Kannan, 1999) This infection can give rise to “cutaneous larva migrans” or “visceral larva migrans” syndromes. Being the first reported case from Myanmar (Gyi, 1960), human gnathostomiasis is endemic among Myanmar people who eat fermented or raw freshwater fish or shrimp, or marinated freshwater fish (second intermediate or paratenic host). However, it can also be presumed to enter a human host through drinking unpurified water containing an infected Cyclops (Khin, 1968).
The outbreak in Myanmar had been reported among Korean emigrants who developed migratory swellings and creeping eruptions on the back, abdomen, flank, and other cutaneous areas. (Chai et al, 2003) Moreover, Nomura et al, (2000) have reported the development of creeping eruptions in two Japanese visited Myanmar who consumed raw freshwater shrimps, and the third stage larva of Gnathostoma malaysiae detected in subcutaneous tissue of one of the 2 patients.
One definite case of Gnathostomal infestation was identified in Yangon Eye Hospital in ten years time. The patient first came to seek an advice for seeing floaters in his right visual field. Apart from it, his vision was perfect in both eyes. The symptom occurred intermittently and the dilated fundus examination revealed a small curved structure in the mid-cavity of vitreous. It was removed from the vitreous with Par-plana vitrectomy approach and was identified by microbiology as a third stage larva of Gnathostoma. The patient had well recovered from surgery and his vision remained unaffected.
Cysticercus infection is endemic in various part of the world including South East Asia, India, Eastern Europe, Central and South America. (Kaiaperumal, 2005)
Human cysticercosis is a parasitic infection caused by the larval form of the cestode, Taenia solium (pork tape worm). It is acquired by ingestion of contaminated food containing ova of T.solium. Human Cysticercosis mainly affects the central nervous system causing focal neurological deficit and signs of increased ICP in cerebral cysticercosis, and the eye and orbit (ocular cysticercosis). It can be asymptomatic for many years.
Intraocular cysticercosis in posterior segment usually presents with reduction of vision, seeing floaters, subretinal cysts and associated retinal detachment. It can even mimic with retinoblastoma when it occurs in a child. (Agarwal, 2003) When the intact cyst remains viable, it evokes a little or no inflammatory response. Once the cyst ruptures, an antigenic toxic material leaks from the cyst and induces an inflammatory reaction, such as vitritis, uveitis, and sometimes endophthalmitis.
We have three reported cases of cysticercus infestation that involved posterior segment in the past 10 years. All cases presented with unilateral reduced vision ranging from counting fingers to hand movement and severe intraocular inflammation. They all are young healthy men with no previous ophthalmic problem. All three patients presented with a cyst or two in retina. Inside the subretinal cyst there was a worm like structure and the surrounding RD was noted in a patient as shown in Fig 1.
Cysticerci are commonly detected by ophthalmoscopic examination, however, the use of ultrasonography was found to be of great aid to establish the diagnosis by supplementing and confirming the clinical findings. (Pochaczevsky, 1979) In our case, Ultrasound (A and B scan) was performed and had demonstrated a sonolucent well defined rounded cyst with central echodense structure within the cyst suggestive of Scolex with surrounding retinal detachment (Fig 2).
Surgical removal is the therapeutic approach in parasitic infection in the eye. However in our cases the patients received the initial medical treatment with topical steroids and cycloplegics to control the inflammation. Then the cysts were surgically removed successfully with PPV approach. Its identification was confirmed by Microbiology. Histological section showed a thin fibrous wall lined by germinal epithelium and there is an invaginated scolex in the lumen consistent with that of a cysticercus (Fig 3).
Anthelminthics (eg, albendazole, praziquantel) and oral corticosteroids have been found to be effective in cases with ocular cysticerci. In our patients, they were treated with a single dose of oral Albendazole (15 mg/kg/d) along with prednisolone for 4 weeks. The final visual outcome depends on the extent of damage by the parasites and the associated inflammation and retinal fibrosis. In one case of ours, the final best corrected visual acuity was only 6/60 due to tractional retinal folds in posterior pole in 3 months postoperative review (Fig 4).
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