Ophthalmomyiasis - an overview | ScienceDirect Topics (2024)

Ocular Myiasis (Including Ophthalmomyiasis, Orbital and Palpebral Myiasis).

Ocular myiasis refers to infestations of the eye or periorbital tissue by larvae and represents less than 5% of human myiasis cases. When larvae remain outside the eye, it is termed ophthalmomyiasis externa, whereas penetration of the eye itself is termed ophthalmomyiasis interna, a severe condition that can lead to blindness. Dermatobia hominis very occasionally causes ophthalmomyiasis externa, with eyelid and conjunctival involvement.

Orbital myiasis in humans is commonly caused by the ovine nasal botfly, Oestrus ovis and the Russian botfly, Rhinoestrus purpureus, which are found in most sheep farming communities. Victims usually have the sensation of being struck in the eye by an insect or by a small foreign object. A few hours later, a painful inflammation develops, causing an acute catarrhal conjunctivitis. Ocular symptoms, such as foreign body sensation, irritation, redness and photophobia, have been reported. The conjunctivitis can vary from mild to severe pseudo-orbital cellulites. Features of the conjunctivitis included pale oedema, linear superficial punctate and keratopathy.

UVEITIS CAUSED BY INSECT-INDUCED DISEASE

Ophthalmomyiasis is the ocular disorder caused by infestation with fly larvae, most commonly the larval form of the sheep botfly Oestrus ovis. Maggots may be seen in the conjunctival fornix (cul-de-sac) or inside the eye. Internal ophthalmomyiasis can be diagnosed by noting a motile larva in the anterior chamber, vitreous, or subretinal space. The maggot may leave trails (“railroad tracks”) behind throughout the retina. A mild inflammatory response in the anterior chamber (e.g., iritis, iridocycl*tis) or vitreous may occur. Treatment is surgical removal of the larva. Corticosteroids may be used to treat the accompanying intraocular inflammation.^65,159

Ophthalmomyiasis

Ophthalmomyiasis is the result of an invasion of dead or living vertebrate animal tissue by fly larvae into the eye. Genera commonly associated with human myiasis include Dermatobia, Gasterophilus, Oestra, Cordylobia, Chrysomya, Wohlfahrtia, Cochliomyia, and Hypoderma (Francesconi and Lupi, 2012). It is common in rural farming regions. Myiasis usually follows a seasonal pattern, in accordance with the insect's life cycle, i.e., most cases occur during spring and summer in temperate climates (e.g., Europe, Northern America and Northern Africa) (Padhi et al., 2017).

Many flies do not lay their eggs on humans but on other insects, animals or objects that may come into contact with skin. Female flies retain their eggs within their body until they hatch. Once they hatch the larvae can burrow into the skin and develop and grow into mature larvae. Although some flies are attracted to open wounds some species infest unbroken skin (Francesconi and Lupi, 2012). When they occur in the eye, larval infections are usually restricted to the conjunctiva and cornea. There are three categories of ophthalmomyiasis: ophthalmomyiasis externa, ophthalmomyiasis interna and orbital myiasis.

Symptoms vary based on the biology of the larvae, the location in the eye, and route of penetration. Ophthalmomyiasis externa refers to the superficial infection of ocular tissue, i.e., conjunctival involvement. Patients typically experience itching, pain, conjunctival hyperemia, lid edema, lacrimation and foreign body sensation (Anane and Hssine, 2010). These signs may mimic conjunctivitis. This type of ocular myiasis is typically mild, self-limited and benign.

Ophthalmomyiasis interna is an infection involving the anterior or posterior segment of the eye. The fly larva may be seen in the anterior segment, vitreous and/or subretinal space (Jakobs et al., 1997). This type of infection is not common and clinically appears as anterior uveitis, sometimes accompanied by posterior segment inflammation. Patients may present with iritis, retinal detachment or subretinal tracks. Symptoms usually include red eye, vision loss, floaters, pain and scotomas (Francesconi and Lupi, 2012).

Orbital myiasis is a severe infestation characterized by the intraocular invasion of maggots from the eyelid myiasis. Eyelid tumors are the most common predisposing factor for this type of ophthalmomyiasis (Çaça et al., 2006; Cavușoglu et al., 2009; Jain et al., 2007). Patients typically present with proptosis, congestion, chemosis and discharge (Padhi et al., 2017).

Diagnosis is made via patient history and physical examination. Establishing a history of a patients recent close contact with farm animals (specifically sheep or goats) in a rural area may aid diagnosis (Nimir et al., 2012). Additionally, a slit lamp exam may reveal small translucent larvae up to 5mm in length on the conjunctiva. Because the larvae are photophobic, it is prudent to examine the eye and discharge under moderate slit lamp illumination and high magnification (Francesconi and Lupi, 2012). Ocular myiasis should be considered in cases of unilateral foreign body sensation.

The mainstay of treatment is the removal of the larvae, often at the slit lamp, with topical analgesics and antibiotics. Removal of the larvae may be difficult due to their strong attachment to tissue. Corticosteroids may be used to treat inflammation. Symptoms tend to resolve immediately after removal of the larvae. In severe cases, exenteration may be required to prevent the intracranial extension of tissue destruction (Francesconi and Lupi, 2012).

Ophthalmomyiasis

The term ophthalmomyiasis refers to the infestation of the eye by the larval forms of flies (maggots) of the order Diptera. Ophthalmomyiasis externa indicates infestation of the conjunctiva, whereas ophthalmomyiasis interna (posterior or anterior) means infestation inside the globe.⁸³ Usually, these larval forms are obligate tissue parasites that require the host's tissue to complete their developmental cycle. In addition to humans, the usual hosts for these larvae include cattle, deer, sheep, horses, and reindeer. The larvae may get to the eye via a vector such as an adult fly that carries the larvae or eggs to the region, or by touching of the ocular region with hands contaminated with the larvae. Most patients do not give a history of being ‘bitten.’ The larva is thought to bore through the coats of the eye until they come to rest within. However, an early report by DeBoe⁸⁴ described the emergence of the larva from the optic nerve head into the vitreous. A handful of cases have been described in the literature.

Seventeen patients with ophthalmomyiasis externa were seen by Amr and colleagues⁸⁵ in northern Jordan. These occurrences were due to the sheep nasal botfly, Oestrus ovis; the symptoms were mild to severe conjunctivitis, cellulitis, and lacrimation. Four cases due to O. ovis in Kuwait both before and after Operations Desert Shield and Desert Storm were reported.⁸⁶ Another species involved is Cochliomyia hominivorax,⁸⁷ whose larvae can lie over the conjunctiva and can be removed with a cotton swab⁸⁸ (Fig. 17-6).

With ophthalmomyiasis interna the invading larva may initially cause little or no pain, but discomfort and an intraocular inflammatory reaction can certainly occur,⁸⁹ particularly after its death.⁹⁰ The characteristic features of ophthalmomyiasis interna include the presence of subretinal tracks^91,92 along with the finding of an encysted larva either subretinally or even free floating in the vitreous. Without finding the maggot in the eye, a definitive diagnosis cannot be made; the maggot is white or semitranslucent, segmented, and tapered at both ends.⁹¹ Vision may be lost because of macular hemorrhage, optic nerve invasion by the maggot, or retinal detachment. Jakobs and colleagues⁹³ reported a patient with a larva that appeared to enter the eye via the optic nerve, migrated subretinally yielding tracts, and then apparently entered the optic nerve again. Billi and co-workers⁹⁴ reported such a case after cataract extraction, conjecturing that the site of entry into the eye was the surgical wound. The organism was removed from the eye by vitrectomy and thought to be of the Sarcophagidae family of flies. Interestingly, no retinal pigment epithelium tracking was noted. Campbell and colleagues⁹⁵ reported that an interesting retinopathy that resembled ophthalmomyiasis interna was seen in 10% of a sample Chamorro population examined on the island of Guam. In addition, this retinopathy was found in 50% of a population with amyotrophic lateral sclerosis–parkinsonism–dementia complex. Although the retinopathy appears to be similar to the changes seen with parasitic infestation, they were not able to establish a definitive diagnosis despite obtaining eyes for histologic study.

The treatment of ophthalmomyiasis must be tailored to the ocular findings. If the worm is situated in the anterior chamber it should be removed as quickly as possible, as it may migrate elswehere in the eye.⁹⁶ A Fuchs’ heterochromic iridocycl*tis has been been described after a case of ophthalmomyiasis interna posterior.⁹⁷ Saraiva and colleagues⁹⁸ reported a case of the removal of a worm from the anterior segment, and histology showed the larva to be covered with macrophages and foreign body giant cells (Fig. 17-7). The granulomatous reaction cleared with removal of the worm. In the case of an immobile subretinal worm, with no inflammatory disease and good vision, the ophthalmologist may elect to follow the patient. However, if there is a severe inflammatory reaction, antiinflammatory therapy should be instituted. Hemorrhage may require a vitrectomy because it may indicate that the larva is alive and migrating. If the larva can be visualized in the subretinal space, and if the decision is made to treat it, Gass and Lewis⁹¹ have recommended the use of photocoagulation over removal of the organism by sclerotomy. Others have suggested either laser or vitrectomy.⁹⁹ Forman and colleagues¹⁰⁰ described a case of a 16-year-old patient with a subretinal fly larva in which the larva was killed with argon laser therapy. The patient's visual acuity improved from 20/200 to 20/20. Syrdalen and colleagues¹⁰¹ reported that removal of a reindeer warble fly larva through a pars plana opening after vitrectomy freed the surrounding vitreous attachments. Others have reported a caribou botfly infecting an eye.⁹⁹ The patient retained good vision. However, the visual result varies, depending on whether the macula and the optic nerve were involved in the process.⁹³

Ophthalmomyiasis

The term ophthalmomyiasis refers to infestation of the eye by the larval forms of flies (maggots) of the order Diptera. Ophthalmomyiasis externa is infestation of the conjunctiva, whereas ophthalmomyiasis interna (posterior or anterior) is infestation inside the globe.⁸⁴ Usually, these larval forms are obligate tissue parasites that require the host’s tissue to complete their developmental cycle. In addition to humans, the usual hosts for these larvae include cattle, deer, sheep, horses, and reindeer. The larvae may get to the eye via a vector, such as an adult fly that carries the larvae or eggs to the region, or through touching of the ocular region with hands contaminated by the larvae. Most patients do not report being “bitten.” The larva is thought to bore through the coats of the eye until they come to rest within. However, an early report by DeBoe⁸⁵ described the emergence of the larva from the optic nerve head into the vitreous. A few cases have been described in the literature.

Seventeen patients with ophthalmomyiasis externa were seen by Amr etal.⁸⁶ in northern Jordan. These occurrences were caused by the sheep nasal botfly Oestrus ovis; the symptoms were mild to severe conjunctivitis, cellulitis, and lacrimation. Four cases of O. ovis infection in Kuwait, both before and after Operations Desert Shield and Desert Storm, were reported.⁸⁷ Another species involved is Cochliomyia hominivorax,⁸⁸ whose larvae can lie over the conjunctiva and can be removed with a cotton swab⁸⁹ (Fig. 18.6).

With ophthalmomyiasis interna, the invading larva may initially cause little or no pain, but discomfort and an intraocular inflammatory reaction can certainly occur,⁹⁰ particularly after its death.⁹¹ The characteristic features of ophthalmomyiasis interna include the presence of subretinal tracks,^92,93 along with the finding of an encysted larva either subretinally or even free floating in the vitreous. Without finding the maggot in the eye, a definitive diagnosis cannot be made; the maggot is white or semitranslucent, segmented, and tapered at both ends.⁹² Vision may be lost because of macular hemorrhage, optic nerve invasion by the maggot, or retinal detachment. Jakobs etal.⁹⁴ reported the case of a patient with a larva that appeared to have entered the eye via the optic nerve, migrated subretinally yielding tracts, and then apparently entered the optic nerve again. Billi etal.⁹⁵ reported such a case after cataract extraction, conjecturing that the site of entry into the eye was the surgical wound. The organism, which was removed from the eye with vitrectomy, was thought to be of the Sarcophagidae family of flies. Interestingly, no RPE tracking was noted. Campbell etal.⁹⁶ reported that an interesting retinopathy that resembled ophthalmomyiasis interna was seen in 10% of a sample Chamorro population examined on the island of Guam. In addition, this retinopathy was found in 50% of a population with the amyotrophic lateral sclerosis (ALS)–parkinsonism–dementia complex. Although the retinopathy appeared to be similar to the changes seen with parasitic infestation, Campbell etal. were not able to establish a definitive diagnosis despite obtaining eyes for histologic study.

The treatment of ophthalmomyiasis must be based on the ocular findings. If the worm is found in the anterior chamber, it should be removed as quickly as possible because it may migrate to other areas of the eye.⁹⁷ Heterochromic iridocycl*tis has been described after a case of ophthalmomyiasis interna posterior.⁹⁸ Saraiva etal.⁹⁹ reported a case where a worm was removed from the anterior segment, with histology showing the larva to be covered with macrophages and foreign body giant cells (Fig. 18.7). The granulomatous reaction cleared with removal of the worm. In the case of an immobile subretinal worm, with no inflammatory disease and good vision, the ophthalmologist may elect to only observe the patient. However, if there is a severe inflammatory reaction, anti-inflammatory therapy should be initiated. Hemorrhage may require vitrectomy because it may indicate that the larva is alive and migrating. If the larva can be visualized in the subretinal space and if the decision is made to treat it, Gass and Lewis⁹² have recommended the use of photocoagulation versus removal of the organism with sclerotomy. Others have suggested either laser or vitrectomy.¹⁰⁰ Forman etal.¹⁰¹ described the case of a 16-year-old patient with a subretinal fly larva, which was killed with argon laser therapy. The patient’s visual acuity improved from 20/200 to 20/20. Syrdalen etal.¹⁰² reported that removal of a reindeer warble fly larva through a pars plana opening after vitrectomy freed the surrounding vitreous attachments. There is also a report of a caribou botfly infecting an eye and the patient retaining good vision.¹⁰⁰ However, the visual result varies, depending on whether the macula and the optic nerve were involved in the process.⁹⁴

Myiasis – Chapter 124

Ocular involvement by larvae of flies is called ophthalmomyiasis. Ocular involvement in humans has been reported with a number of fly species, including Oestrus ovis (“sheep bot fly”), Gasterophilidae (“horse bot fly” or “horse warble fly”), Wohlfahrtia magnifica (“sheep maggot fly”), Chrysomyia bezziana (“screwworm fly”), Cordylobia anthropophaga (“tumbu fly”), and Dermatobia hominis, among others. Ocular disease occurs from deposition of eggs by flies or by secondary vectors, such as mosquitoes. Larvae emerge and penetrate the periocular and ocular tissues. Ocular involvement of the orbit, eyelid, or conjunctiva is called “ophthalmomyiasis externa.”¹⁰⁸ “Ophthalmomyiasis interna” implies that larvae have invaded deep ocular structures (Fig. 135.50).¹⁰⁹ Such involvement may be either anterior or posterior. Larval migration can result in conjunctivitis, keratitis, scleritis, iritis, vitritis, subluxation of the lens, uveitis, and vitreal hemorrhage. Subretinal involvement may result in retinal detachment and hemorrhages. Retinal scarring and “track” formation may result. Involvement may be bilateral.

Specific diagnosis is confirmed by pathologic examination of recovered larvae or of subsequently matured flies. Treatment of ophthalmomyiasis externa involves mechanical removal of the larva(e) with careful searching for the presence of additional intranasal or intraocular larvae. Ophthalmomyiasis interna may be treated with laser photocoagulation or with surgery. Topical and systemic steroids may be used to minimize local inflammatory reactions.

Ophthalmomyiasis

10.5 Myiases

Concerning arthropods, neurological and ocular manifestations of fascioliasis may give rise to confusion mainly with brain myiasis and ophthalmomyiasis. Myiases are infestations by dipterous larvae (maggots) that feed on dead or living vertebrate tissues for a variable period. They induce specific and nonspecific immune responses of the hosts with practical implications in the diagnosis (Otranto, 2001). Although serological tests are available, myiasis diagnosis is basically made by finding and carrying out a characteristic morphological identification of the larvae of the Diptera.

Brain myiasis in humans appears to be rare. Only very few cases of brain myiasis in humans have been reported worldwide (Terterov et al., 2010), including fatal cases in intracerebral myiasis. Infestations of the nose and ears are extremely dangerous because they provide the larvae with access to brain tissue. Aural myiasis causing meningitis and brain infestations have been reported (Yuca et al., 2005). In cases of brain penetration by the larvae, the fatality rate has been mentioned to be as high as 8% (Noutsis and Millikan, 1994). Severe complications may also be related to the involvement of the skull base (Arbit et al., 1986; Caça et al., 2003; Ciftcioglu et al., 1997; Werminghaus et al., 2008).

Aural myiasis occurs frequently in children and less frequently in adults, especially when mentally retarded (Baynder et al., 2010). Larval stages of Calliphora sp., Lucilia sericata, and Musca domestica have been found to be involved with myiasis of the nose, paranasal sinuses, pharynx, and ears (Kaczmarczyk et al., 2011). Sarcophaga has also been listed as causing mystic scalp and skull infection (Arbit et al., 1986). Fatal scalp myiasis caused by Cochliomyia hominivorax having reached the brain cavity has been reported (Oliva et al., 2007).

Larvae of species of Hypoderma appear to be of particular importance in intracerebral myiasis, mainly in children (Doby and Beaucournu, 1970; Kalelioglu et al., 1989; Lewicka-Urbanska, 1955; Pouilaude et al., 1980). Hypoderma larvae can penetrate into the brain, causing cerebral haematoma and clinical signs. The severity of hypodermiasis relies on the fact that intraocular and nervous locations accompanied by paraplegia have also been reported. The migration of the larval stages of Hypoderma may take place through the central nervaxis, involving a neurological syndrome with rachidian hypereosinophilia of several weeks, until the appearance of larvae under the skin and a reincrease of blood eosinophilia. Finally, eosinophils of the cephalorachidian fluid may thus participate in a paraneoplastic syndrome. Hypoderma lineatum gives rise to linear dermatitis chiefly at the level of the head, for example, behind the ear, whereas Hypoderma bovis gives rise to mobile ambulatory tumours with gelatinous oedema and finally giving rise to a pseudofuruncular lesion containing the larval stage (Doby and Beaucournu, 1970). The differential diagnosis between fascioliasis and hypodermiasis may sometimes pose serious difficulties, mainly in cases of myiasis with deep tissue infections or abortive forms and in overlapping endemic areas such as western France. Computerized tomography shows the haematoma, and carotid angiography shows the absence of a vascular malformation, but these examinations do not allow aetiological diagnosis of myiasis. Diagnosis is indicated by seroimmunological examinations and/or by the discovery of the larva during operation (Pouilaude et al., 1980). In those cases, only the use of a Fasciola-specific serological test may confirm the fascioliasis diagnosis of the patient.

Unlike the rarity of brain myiases, there are numerous cases of eye myiasis reported from many regions, including both developed and developing countries. Ocular involvement or ophthalmomyiasis is seen to occur in about 5% of all cases of myiasis. Most commonly, larvae attack the external surface of the eyes or ocular adnexa, for example, the lids, conjunctiva, or lacrimal ducts (external ophthalmomyiasis). External ophthalmomyiasis is often a benign self-limiting disease that may usually be remedied without complications. However, outbreaks of human external ophthalmomyiasis have also been reported (Dunbar et al., 2008).

In uncommon circ*mstances, the maggots may penetrate into the eyeball itself (internal ophthalmomyiasis) or may involve the orbit (orbital myiasis), which may result in serious damage and often lead to severe loss of vision, blindness, or even loss of the eye, mainly in cases of larvae with burrowing habits that can give rise to very destructive forms of ophthalmomyiasis, especially in debilitated patients (Chodosh and Clarridge, 1992; Khurana et al., 2010; Verstrynge and Foets, 2004). Ophthalmomyiasis interna may be further subdivided into anterior and posterior based on the presence of the larva in the anterior or posterior segment of the eye, respectively. However, posterior migration of an anterior larva has also been reported (Miratashi et al., 1997; Sharifipour and Feghhi, 2008). The unpredictable behaviour of the larva inside the eye results in difficulty in making treatment decisions.

Fly species of the genera Calliphora, Lucilia, Sarcophaga, Gasterophilus, Hypoderma, Musca, Callitroga, Cuterebra, Dermatobia, Chrysomya, Wohlfahrtia, and Oedemagena are known to cause internal ophthalmomyiasis in humans (Lagace-Wiens et al., 2008; Syrdalen and Stenkula, 1987; Thakur et al., 2009; Verstrynge and Foets, 2004). Diagnosis is made by surgery and identification of the dipteran larva involved.

Myiasis of body cavities

Myiasis of this type includes infestation of the eye, auditory canal, nasopharynx, and associated sinuses. Ophthalmomyiasis is usually caused by Oestrus ovis. It occurs in cooler latitudes of the northern and southern hemispheres in rural areas. Ophthalmomyiasis interna involves the eyeball, whereas ophthalmomyiasis externa is a relatively mild disease, characterized by conjunctivitis, lid edema, and superficial punctate keratopathy in response to movement of the larvae across the external surface of the eyeball. Patients commonly complain of acute foreign-body sensation with lacrimation, often with abrupt onset. Mild pain and inflammation follow for 10 days, but the infestation is self-limited and benign. Invasion of the eyeball and severe external inflammation occasionally occur. Non-O. ovis eye disease may be more severe. Larvae may appear within the cornea, lens, anterior chamber, or vitreous, but rarely undergo continued development when the eyeball has been entered. A rare devastating consequence is retinitis involving the macula, with fibrosis leading to blindness. Occasionally, enucleation or exenteration is required.

In nasal myiasis, the initial symptoms are swelling, tickling pain, and nasal obstruction, associated with a sensation of “crawling.” Epistaxis is common, but the discharge soon becomes purulent and fetid. The most important species of flies in nasal myiasis are C. hominivorax, C. bezziana, and D. hominis. Extensive tissue destruction may follow. External auditory myiasis is usually seen in infants and debilitated individuals. Local irritation is the rule, with invasion of the tympanic membrane being rare. Infestation of the nose and ears is extremely dangerous because of the possibility of penetration into the brain: the fatality rate is approximately 8%. Nasal myiasis may complicate leprosy patients: first, the loss of the sneezing reflex and second, the inability to clean the nose properly on account of severe hand deformity.

Myiasis

Larvae of flies invading various parts of the human body may cause a disease called myiasis. Usually the larvae of tumbu fly (Cordylobia anthroprophaga) or botfly (Dermatobia hominis) are the most important causes of cutaneous or subcutaneous myiasis, rarely ophthalmomyiasis and, even rarer, secondary infection in the periorbital tissue, including meninges. The same applies to infestation with screwworms (genus Callitroga) and related species which usually affect sheep, cats, dogs, etc., in rare cases also malnourished humans. These larvae lead to purulent rhinitis, even sinusitis, osteomyelitis, and finally potentially fatal meningitis.

The sheep botfly (Oestrus ovis, rarely also Wohlfahrtia species) may cause ophthalmomyiasis externa or interna which, per se, can lead in malnourished patients to periorbital invasion, secondary infection, and even meningitis and brain abscess (Jelinek et al., 1995; Robbins and Khachemoune, 2010).

Similarly, a chronic otitis may be the “ground” for myiasis leading to exacerbation of the external otitis leading to otitis media and even mastoiditis and progression into the intracranial space, causing meningitis, epidural or subdural empyema, or even brain abscess (Sampson et al., 2001; Messahel et al., 2010).

Radical extirpation/removal of all maggots may prevent further spread of secondary infections (Clyti et al., 2008).