**8. Eye infections caused by ectoparasites**

#### **8.1. Myiasis**

Myiasis is an infection caused by larvae of flies. It is common in tropical and subtropical areas. It is known as ophthalmomyiasis when ocular structures are involved. Ophthalmomyiasis is categorized into three clinical categories (ophthalmomyiasis externa, ophthalmomyiasis interna and orbital myiasis), depending on the location of larvae in the eyes. Several genera have been reported to cause myiasis such as *Dermatobia*, *Gasterophilus*, *Oestra*, *Cordylobia*, *Chrysomyia*, *Wohlfahrtia*, *Cochliomyia* and *Hypoderma* [1]. Significantly, larvae causing ophthal‐ momyiasis belong to the genus *Hypoderma* [16]. *Three cases of external* ophthalmomyiasis, two due to *Oestrus ovis and one due to Cochliomyia hominivorax* were reported earlier from North India [17]. *Oestra ovis* also known as sheep nasal botfly is responsible for causing ophthalmo‐ myiasis externa in shepherding areas [244–247]. It mainly involves eyelids, conjunctiva, lacrimal sac and nasolacrimal ducts. Most common clinical feature is the foreign body sensation and may be associated with conjunctivitis and keratitis.

Diagnosis is established by the identification of the maggots. Treatment usually involves the surgical removal of the maggots. Medical treatment involves just one oral dose (150 to 200 µg/ kg of body weight) of ivermectin [16]. However, the use of ivermectin for the treatment of myiasis is an off-label treatment in many countries and should be used for selected cases. The side effects such as dermal eruptions, fever, dizziness, migraines and muscular pains are common. Antibiotics and steroids may also be required to prevent the inflammation and superadded bacterial infection. Opthalmomyiasis interna [248] is caused by the invasion of the ocular structures leading to uveitis, lens dislocation and retinal detachment. Diagnosis is established by visualizing the migratory tracks along subretina by the ophthalmoscopy. Symptoms persist if not treated. Serious complications may also occur such as lens dislocation and retinal detachment due to invasion of tissue [1]. Steroid therapy is advocated if there is severe inflammation, and surgical removal is performed in severe cases. Orbital myiasis is seen in patients who are not able to maintain good personal hygiene [16]. Treatment is directed at removal of maggots and control of secondary infection. Preventive measures include mainte‐ nance of good sanitation conditions and proper disposal of waste material to control the flies in surrounding areas.

#### **8.2. Lice**

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

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

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

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‐

prevalent in sub-Saharan Africa, China and South Asia (Figure 20) [8].

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

of choice for all forms of schistosomiasis [8].

74 Advances in Common Eye Infections

ed frogs legs [243].

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

Important genera of the lice causing human infestation belong to *Pediculus* and *Phthirus.* Geographical areas where *Phthiriasis palpebrarum* is commonly found have been depicted in Table 1 and Figure 21. Eggs or nits laid down by lice glue themselves to body hairs or clothing fibers. Nymphs emerge from eggs and feed on the host, causing pruritis. Eyebrows and eyelashes are most commonly, involved. Excoriation marks along with small erythematous papules aid in diagnosis. Nits can be found at the base of eyelashes, substantiating the clinical diagnosis. Symptoms persist if not treated. Eyelid disease is treated by petrolatum and noneyelid involvement may be treated with lindane, permethrin, pyrethrin or malathion [1].

*Phthiriasis palpebrum;* Tick infestation.

**Figure 21.** World map showing geographical areas endemic for ocular ectoparasites. *Phthiriasis palpebrarum*; Tick infes‐ tation.

#### **8.3. Ticks**

Ticks belonging to the class Arachnida are important vectors for the transmission of several infections to humans [1]. Geographical regions where ticks' infestation has been reported are depicted in Table 1 and Figure 21. Ticks complete their life cycle in three different stages, i.e. larva, nymph and adult, and all the life cycle stages require blood meals. Ticks have been reported to attach to ocular structures that may appear as meibomian gland mass. Symptoms persist if not treated. Treatment includes removal of ticks, and tick bite granuloma may resolve after several weeks.

#### **9. Summary**

Ocular parasitic infections are of medical importance worldwide because of significant morbidity rates, and if not diagnosed and treated on time could lead to vision loss. High index of clinical suspicion is required to establish the diagnosis for further confirmation by laboratory techniques followed by specific treatment. Direct demonstration of the parasite is possible in few ocular parasitic infections, while in few, specific clinical features such as changes in retina on direct ocular examination may point toward specific diagnosis. Serology has limited role in the diagnosis as most of the ocular parasitic infections are localized in the eye. Utility of different diagnostic techniques in various parasitic ocular infections has been summarized in Table 2. Although reports reveal that the serology for antibody detection and/or molecular techniques for parasite DNA detection, when applied directly on the ocular tissues, aqueous or vitreous humor usually confirm the diagnosis, these techniques have its own merits and demerits. IgG immunoblot technique has been applied for the diagnosis of ocular toxoplas‐ mosis with some success, and it is suggested that local antibody production is presumed to have occurred, if immunoreactive bands are detected in the aqueous humor but not in the serum [249]. Future reports in this direction may throw further light on its utility. Moreover, application of Western blotting technique may be possible only in limited diagnostic centers.

Report on "Diagnostic Approach to Ocular Toxoplasmosis" revealed in conclusion that the clinical diagnosis of ocular toxoplasmosis may be supported by laboratory tests in 60–85% of cases, depending on the time of sampling. Analysis of the aqueous humor is particularly helpful in patients with atypical lesions or in individuals who are irresponsive to specific therapy. Even so, a laboratory confirmation of the clinical diagnosis is not achieved in 15–40% of cases [72].

In general, it can be concluded that the clinical awareness and multiple approaches/techniques for the confirmatory diagnosis of clinically suspected ocular parasitic infections may yield higher sensitivity and diagnostic efficacy, as suggested earlier [250].

Treatment depends on the causative agent and may involve surgical removal and/or medical treatment with antiparasitic drugs (Table 2). In few infections, steroids are also prescribed to prevent the damage from the inflammatory response associated with the dying parasites. Preventive strategies depend on the type of parasitic infection and mainly include control of vector population for vector borne parasitic infections, maintenance of good personal hygiene and providing awareness to people about ocular parasitic infections through information, education and communication (IEC).

**8.3. Ticks**

tation.

after several weeks.

*Phthiriasis palpebrum;* Tick infestation.

76 Advances in Common Eye Infections

**9. Summary**

Ticks belonging to the class Arachnida are important vectors for the transmission of several infections to humans [1]. Geographical regions where ticks' infestation has been reported are depicted in Table 1 and Figure 21. Ticks complete their life cycle in three different stages, i.e. larva, nymph and adult, and all the life cycle stages require blood meals. Ticks have been reported to attach to ocular structures that may appear as meibomian gland mass. Symptoms persist if not treated. Treatment includes removal of ticks, and tick bite granuloma may resolve

**Figure 21.** World map showing geographical areas endemic for ocular ectoparasites. *Phthiriasis palpebrarum*; Tick infes‐

Ocular parasitic infections are of medical importance worldwide because of significant morbidity rates, and if not diagnosed and treated on time could lead to vision loss. High index of clinical suspicion is required to establish the diagnosis for further confirmation by laboratory techniques followed by specific treatment. Direct demonstration of the parasite is possible in few ocular parasitic infections, while in few, specific clinical features such as changes in retina on direct ocular examination may point toward specific diagnosis. Serology has limited role in the diagnosis as most of the ocular parasitic infections are localized in the eye. Utility of different diagnostic techniques in various parasitic ocular infections has been summarized in Table 2. Although reports reveal that the serology for antibody detection and/or molecular techniques for parasite DNA detection, when applied directly on the ocular tissues, aqueous

The need of increased awareness and clinical suspicion of OPI for prompt and specific diagnosis followed by application of sensitive and specific diagnostic technique(s) for confir‐ mation and effective treatment are the main challenges.

The future research priorities need to be directed to study exact host-pathogen mechanisms, local immune responses and to establish more sensitive and specific diagnostic techniques. The molecular techniques can provide rapid diagnosis of multiple ocular parasitic infections and species identification for specific therapy. Multiplex PCR assay, if developed, can add new dimensions in the diagnosis. Efforts to develop animal models are desired that may further help to study the exact host-pathogen mechanisms, local immune responses and in developing new treatment strategies.




**Ocular protozoal infections**

78 Advances in Common Eye Infections

Acanthamoeba keratitis Microscopy, culture on non-

Chagas disease Blood smear, Buffy coat, culture,

Malaria Thin and thick blood film for

PCR

Leishmaniasis Microscopy of tissue smears,

Giardiasis Confirming by intestinal

infection

Onchocerciasis Slit-lamp examination, Biopsy of

Microsporidiosis Microscopy,

Ocular nematode infections

**Diagnosis Treatment**

a. Biguanides – PHMB (0.02%)

therapy of 3-4 weeks

60 days

days

and fluconazole

systemic infection.

skin or eye infection

c. Removal of adult worms

b. Chlorhexidine 0.02% in combination with aromatic diamidines such as 0.1% propamidine isethionate, 0.15% dibromopropamidine, hexamidine 0.1% and neomycin (Topical antimicrobials should be administered every hourly for first several days and there after frequency reduced to every 3 hours with a minimum duration of

c. Surgical treatment includes keratoplasty or its variation known as DALK (Deep Anterior Lamellar Keratoplasty)

a. Benznidazole 5-10 mg/kg daily in 2-3 divided doses for

b. Nifurtimox 15 mg/kg daily in 3 divided doses for 60-90

a. *Plasmodium vivax* – Chloroquine + primaquine b. *P. falciparum* – Artemisinin combination therapy (Artemisinin + sulfadoxine-pyrimethamine or artemisinin

Pentavalent antimonial compounds, liposomal amphotericin B, miltefosine (dose is weight dependent), paromomycin, azoles such as ketoconazole, itraconazole

Topical fumagillin bicylohexylammonium (Fumidil B) 3 mg/mL in saline (fumagillin 70 µg/mL) eye drops: two drops every 2 hours for 4 days, then two drops four times daily (investigational use only in United States) plus albendazole 400 mg orally twice daily for management of

Metronidazole, tinidazole, and nitazoxanide. Others include paromomycin, quinacrine, and furazolidone

a. Ivermectin: given every 6 months for the life span of the adult worm or as long as infected person has evidence of

b. New treatment: Doxycycline, before starting treatment

infection with *Loa loa* has to be ruled out

+ lumefantrine) as per WHO guidelines

nutrient plates (coated with bacteria)/ in flasks (PBS +Bacteria), PCR, Real-time PCR

xenodiagnoses and PCR

microscopy, antigen detection,

culture on NNN media, PCR

Immunofluorescence assay, PCR

skin to identify larvae, skin nodules examination for identification of adult worms, PCR, antibody detection


**Table 2.** Diagnosis and treatment of various ocular parasitic infections
