Ophthalmomyiasis Externa Caused by Muscae Fly Larva in Deserts of the Thar

Keywords::

• Muscae fly
• Oestrus ovis
• ophthalmomyiasis
• Thar

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Erratum

To the editor:

We are reporting clinical manifestations of ophthalmic myiasis in 3 patients in Balesar/Shergarh village in Jodhpur district (Thar desert area) in Rajasthan, India. All 3 patients belonged to the same regional area/village. The clinical picture is that of a viral or allergic conjunctivitis with itching of the eye, tearing, and foreign body sensation. The larvae can be easily missed on routine examination as they are small and translucent and quickly avoid the slit lamp. External ophthalmomyiasis is deposition of fly larvae confined to conjunctiva, eyelid, and lacrimal ducts. Ophthalmomyiasis is not uncommon but underestimated in dry rural areas, and it is still frequently misdiagnosed as viral or allergic conjunctivitis. In our opinion this is the first report of ophthalmomyiasis in the Thar Desert. There have been sporadic reports of ophthalmomyiasis from the Indian subcontinent, but for the first time this is being reported from the deserts of the Thar.

We observed 3 cases of external ophthalmomyiasis from January to May 2011 at MDM Hospital, Jodhpur, the tertiary level ophthalmic center of western Rajasthan, the only one in this vast area of desert. Each patient was examined thoroughly and questioned in detail about the history and, in particular, symptoms related to the development of myiasis. Diagnosis of external ophthalmomyiasis was made by direct visualization of the highly motile and photophobic larvae, using a slit lamp. The major presenting symptoms were irritation, foreign body sensation, lacrimation, and redness. In each case, the symptoms began while the affected individual was working or playing on a farm. One of the patients was expeditious enough and had himself discovered 2 larvae in his conjuctival fornix. In one case, the eye involvement was bilateral and in the others unilateral and with motile larvae present in the conjunctival fornix and bulbar and only occasionally in palpebral conjunctiva. However, we found a predominance of right eye involvement in our small sample (Table 1). All patients were experiencing injections in the conjunctiva, lid edema, and sometimes chemosis. Visual acuity was also normal in all patients. There was no sign of any aggressive corneal involvement, such as corneal ulcer, or intraocular involvement, such as invasion into eye globe (ophthalmomyiasis interna).

TABLE 1  Details of patients diagnosed.

S no.	Age (years)	Sex	Date of diagnosis	Place of occurrence	No. of larvae found	Laterality and ocular structures involved
1	11	Male (child)	11 Jan 2011	Playing in fields	8	Bilateral
						Right eye: 7 larvae from upper and lower fornix, bulbar and palpebral conjunctiva, lower lid margin
						Left eye: 1 larva from lower lid margin
2	45	Male	4 Apr 2011	Working in fields	4	Unilateral
						Right eye: lower fornix, bulbar and palpebral conjunctiva, lateral canthus
3	25	Male	9 May 2011	Working in fields	4	Unilateral
						Right eye: lower fornix, bulbar and palpebral conjunctiva

After instillation of proparacaine eyedrops the larvae became paralyzed and after photographic documentation were taken out with a cotton-tipped applicator (see supplemental video found in the online edition of this article) and the eyes were washed with Ringer lactate solution. The entire cotton tip of the applicator was submerged in thioglycollate broth media (TG media). Soon after the submersion the larvae were seen freely motile in the fluid of the culture media. The media was sent for micobiological investigation. The larvae measured 1–2 mm in length and varied from 4 to 8 in number. They were mounted on a microscope slide and examined. On the basis of their spindle shape, translucent, segmented body, and two large dark oral hooks connected to a white cephalopharyngeal skeleton, the larvae were identified as first instars of Muscae fly (Diptera: Oestridae) (Figure 1). We were told by microbiologists that the larvae if grown in pork meat fat can mature to grow into pupae and then the adult; species identification would be certain then. On parasitological referral the larvae were identified as first instars of Oestrous ovis (sheep botfly).

FIGURE 1  (a) High-magnification microbiology laboratory photographs of larva that we retrieved from the conjuctival cul de sac of our patient. Note the spindle shape, translucent, segmented body, and two large dark oral hooks connected to a white cephalopharyngeal skeleton. The larvae were identified as first instars of Muscae fly, suspected Oestrus ovis (Diptera:Oestridae). [Courtesy Dr. Prabhu Prakash, MD, Professor, Microbiology, Dr SN Medical College, Jodhpur, India]. (b) Microbiology laboratory photographs of another larva that we retrieved from the conjuctival cul de sac of same patient. (c) High-magnification view of oral segment. (d) Removal of larva with cotton-tipped applicator under local anesthesia. (e) Larva on the lid margin. Video: We can see the larva in the inferior conjuctival fornix, freely mobile, which was removed with sterile cotton-tipped applicator under proparacaine local anesthesia. The entire cotton-tipped applicator with the larva was submerged in TG media in a test tube chamber. A few seconds after submersion the larva was found freely moving in the fluid of the culture media. A total of 3 larvae were removed from this patient.

For the patient an antibiotic and steroid eyedrops were started. Following removal of all larvae, the symptoms resolved drastically within a few hours or days. Instillation of petroleum jelly or turpentine oil can also be used as they arrest the larval breathing by hypoxia for cutaneous infections and orbital myiasis and then larvae run out in search of fresh air. These have not been approved for ocular use and were not used in our patients.

Myiasis can be of three types: obligatory, facultative, and accidental. Obligatory myiasis is mainly caused by botfly larvae (Dermatobia, Condylobia, Oestrus) as they do not get enough nutrition from the parent fly. Botfly larva causes myiasis mainly in animals, and human infection is a zoonosis. Dermatobia hominis larvae are spread by mosquitoes as the female lays its eggs on mosquito wings. It is the most common cause of myiasis in humans. Condylobia anthropophagia is spread by urine and feces. Facultative myiasis is caued by blowflies (Phormia, Lucilia, Musca). Some facultative larvae of Lucilia serrica secretes bacteriolytic enzymes and is used for sterilization of infected wounds! Accidental myiasis usually involves housefly larvae on wound dressings and Eristaris in the anal canal.

Ophthalmic myiasis is due to deposition and inhabitation of dipterous larvae in the human eye. Various species of flies are able to cause ophthalmomyiasis, including Oestrus ovis (sheep nasal botfly), housefly (Musca domestica), latrine fly (Fannia), and cattle botfly (Hypoderma).^1,2 Oestrus ovis is the most common reported till now—90% of these as a cause of ophthalmic myiasis in humans—but there may be wide geographical variation.³ Ophthalmic myiasis due to Oestrus ovis was described for the first time in 1947 by James.⁴ More cases have been reported from the Mediterranean, India, and also from Russia, Iran,⁵ Serbia, Africa,⁶ Oman, and America. Grammer et al.³ and Masoodi et al.¹ described cases of external ophthalmomyiasis caused by Oestrous ovis in farmers living in close contact with sheep and goats.

Ophthalmomyiasis mostly occurs in rural areas, where people live in close contact with cattle. Involvement by Oestrus ovis is in the form of external ophthalmomyiasis only, which is confined to the conjunctiva, eyelid, and lacrimal ducts, as first instar larvae have no bite organs and are unable to secrete proteolytic enzymes.⁶ Identification of the species is important to estimate the risk of penetration of the globe. Larvae from some other species, such as Hypoderma¹ or Chrysomyia bezziana can penetrate the eye globe and cause endophthalmitis and iridocyclitis, and may even lead to blindness. They are capable of living in eye fluid, and cause symptoms by crawling on the eyeballs with the help of anterior hooks and by their curved mandibular barbs and body spines, which cause much irritation.

Symptoms, such as severe eye irritation, redness, foreign body sensation, pain, lacrimation, and swelling of the lids, season of occurrence, and also predominance of young male patients and 1 boy in our case series are similar to those described in other reports.^1–3 Complications such as corneal ulcer, invasion into the eye globe, and decreased vision are not usual and none of these complications were encountered in our patients.

We should suspect larval conjunctivitis in rural areas, especially during spring and summer, in patients presenting with viral or allergic conjunctivitis or following a history of something falling in the eye. As the larvae are small and translucent and the slit-lamp beam makes them run away, they can be easily misdiagnosed on routine examination. This is the first clinical reporting of ophthalmomyiasis by Muscae fly in the Thar Desert to the best of our knowledge.

Notice of Correction: Changes have been made to the author order and affiliations and a correspondence address has been added to the previously published version of this article since its original online publication in March 2012.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

SUPPLEMENTAL MATERIAL

A video of this procedure is available in the online edition of this article.