**7. Trematodes infections**

#### **7.1. Fascioliasis**

Fascioliasis is a food-borne parasitic infection caused by trematodes that mainly affect liver. It is acquired by eating metacercaria of *Fasciola hepatica* encysted on leaves that are eaten raw. Two important species are *Fasciola hepatica* and *F. gigantica*. The life cycle includes release of eggs from adult flukes that further develop into miracidia, sporocysts, rediae, cercariae and metacercariae as shown in Figure 19. The parasite passes its life cycle in two different hosts: sheep, goat, cattle and man act as definitive host and snails of the genus *Lymnaea* act as intermediate host. The eggs are passed out in the feces of definitive hosts that mature in water. Ciliated miracidium develops inside each egg in 2–3 weeks. Miracidium after getting released from egg finds its way to its suitable intermediate host. Inside the lymph spaces of the molluscan host, the miracidium passes through stages of sporocyst, two generations of rediae and finally to the stage of cercariae. The mature cercariae escape from the snail into the water and encyst (metacercariae) in blades of grass or water-cress, which is ingested by herbivorous animals and occasionally by man. On entering the digestive tract, the metacercariae excyst in the duodenum and migrate through intestinal wall into peritoneal cavity. It further traverses through liver capsule, parenchyma and ultimately settle in the biliary passages, where it mature into adults. The eggs are liberated in the feces through bile, completing the life cycle.

**Figure 19.** Life cycle of *Fasciola* (Diagrammatic representation).

Opthalmofascioliasis is the term used for those cases in which eye infection is directly caused by migrant ectopic fasciolid fluke. All other patients with ocular manifestations due to fasciolids located in liver or other organs should be classified as fascioliasis with ocular implications. Although ocular involvement in fascioliasis is rare, cases have been reported from France, Spain, Italy, Austria, Belgium, United Kingdom, Algeria, Tunisia, Iran, Uzbeki‐ stan, Korea, China, Argentina, Chile, Peru, Brazil and Guatemala (Figure 20) [239]. Symptoms and signs usually relate to the affected eye and may cause conjunctival hyperaemia, corneal oedema, dilated episcleral vessels, paralysis of extraocular muscles, decrease in perception of light, deep anterior chamber with flare, uveitis and so on. Diagnosis is established directly by visualization of leaf-shaped like organism in the eye or by studying the morphological features of the surgically removed worm. Eosinophilia, positive serology by ELISA or presence of eggs in stools may aid in diagnosis. Severe complications may occur if not treated. Early surgical intervention is associated with rapid response and reasonable final visual acuity [14]. Thus, ophthalmological manifestations have been known to be cured with surgical treatment without any antiparasitic treatment [14]. However, triclabendazole is the drug of choice if medical treatment is required.

#### **7.2. Schistosomiasis**

The symptoms and signs depend on the location of the cyst in the target organ. Most common ocular finding is the development of proptosis due to the presence of intraorbital space occupying lesion. This may further lead to exposure to keratitis and ulceration of the cornea. Other complications due to the local invasion of the expanding cyst may lead to erosion of orbital wall, optic atrophy and optic neuritis. Subretinal hydatid cyst has been reported. In

The diagnosis depends on the clinical findings suggestive of hydatid cyst on ocular examina‐ tion and confirmed by radiological techniques such as ultrasonography, CT scan and/or MRI [232, 233]. "Double wall" sign is a characteristic of orbital hydatid cyst seen by ultrasonography [232]. Serology may also aid in diagnosis. However, in majority of the commercially and inhouse serological assays, hydatid fluid is the main antigenic component and sensitivity of IgG-ELISA reported in various studies varies from 64.8 to 100%, while specificity varies from 87.5 to 100%. Purified and recombinant antigens are also being tried for developing ELISA with high sensitivity and specificity [234]. Fine needle aspiration cytology can also be performed

Symptoms persist if not treated [236]. Surgical removal of the cyst is the treatment of choice. Medical therapy includes administration of albendazole or mebendazole to prevent the recurrences due to the contents of the cyst leaking into the surgical sites [237]. If the cyst is accidently ruptured, in situ irrigation with hypertonic saline should be performed. However,

Fascioliasis is a food-borne parasitic infection caused by trematodes that mainly affect liver. It is acquired by eating metacercaria of *Fasciola hepatica* encysted on leaves that are eaten raw. Two important species are *Fasciola hepatica* and *F. gigantica*. The life cycle includes release of eggs from adult flukes that further develop into miracidia, sporocysts, rediae, cercariae and metacercariae as shown in Figure 19. The parasite passes its life cycle in two different hosts: sheep, goat, cattle and man act as definitive host and snails of the genus *Lymnaea* act as intermediate host. The eggs are passed out in the feces of definitive hosts that mature in water. Ciliated miracidium develops inside each egg in 2–3 weeks. Miracidium after getting released from egg finds its way to its suitable intermediate host. Inside the lymph spaces of the molluscan host, the miracidium passes through stages of sporocyst, two generations of rediae and finally to the stage of cercariae. The mature cercariae escape from the snail into the water and encyst (metacercariae) in blades of grass or water-cress, which is ingested by herbivorous animals and occasionally by man. On entering the digestive tract, the metacercariae excyst in the duodenum and migrate through intestinal wall into peritoneal cavity. It further traverses through liver capsule, parenchyma and ultimately settle in the biliary passages, where it mature into adults. The eggs are liberated in the feces through bile, completing the life cycle.

it causes local inflammatory reaction that may lead to atrophy of optic nerve [238].

severe cases, blindness may also occur [231].

72 Advances in Common Eye Infections

for establishing the diagnosis [235].

**7. Trematodes infections**

**7.1. Fascioliasis**

Schistosomiasis, or bilharziasis, is caused by trematode flatworm of the genus *Schistosoma*. Freshwater snails release the larval forms in the water, which penetrate the skin of human host

Fascioliasis; Schistosomiasis; Philopthalmosis; *Clinostomum lacramalitis; Alaria mesocercariasis*

**Figure 20.** World map showing geographical areas endemic for ocular trematode infections.

while swimming, bathing, fishing and even domestic chores such as laundry and herding livestock. In the human body, the larvae mature into adult schistosomes, which reside in the blood vessels. Eggs released by females are passed out of the body in the urine or feces. It is prevalent in sub-Saharan Africa, China and South Asia (Figure 20) [8].

Ocular involvement is not the usual site that is involved in schistosomiasis, but cases have been reported where Schistosoma ova or even the adult worm can reach the systemic circula‐ tion and can lodge itself at ectopic sites such as eyes. Although schistosomiasis is very common, ocular cases are rare. It can cause uveitis or subretinal granuloma [240]. Diagnosis is established by direct demonstration of eggs/cercariae in the eye. Detection of eggs in the urine and feces may aid in establishing the diagnosis. Symptoms persist if not treated. Praziquantel is the drug of choice for all forms of schistosomiasis [8].

#### **7.3. Other rare ocular infections by trematodes**

The cases of acute nodular conjunctivitis and anterior chamber granuloma formation have been documented, which are caused by endemic water-borne trematode infection. The identification of the remnants of parasites aspirated from such cases revealed that these parasites belong to the genus *Philophthalmus* that are known to parasitize birds [25, 241]. Humans acquire infection accidently while bathing or playing in contaminated water. Conjunctival nodules heal spontaneously, and anterior chamber nodules can be treated with topical/oral corticosteroids. Surgical removal is recommended in cases having large nod‐ ules. First human case of *Clinostomum* lacramalitis was reported in Thailand [242]. Human cases of intraocular infection with mesocercariae of *Alaria americana* and other *Alaria* mesocercariae have been reported in patients who had ingested undercooked contaminat‐ ed frogs legs [243].
