Oestrus ovis as a Cause of Red Eye in Aljabal Algharbi, Libya.

PURPOSE: To study the common presenting signs of external ophthalmomyiasis caused by Oestrus ovis larvae in Aljabal Algharbi province, Libya.
MATERIALS AND METHODS: A prospective non- comparative study was conducted from September 2009 to July 2010 at the Gharian outpatient clinic, Gharian, Aljabal Algharbi, Libya. The common presenting features of patients with external ophthalmomyiasis and data on the organism that caused the disease were collected.
RESULTS: Twenty one cases diagnosed with external ophthalmomyiasis were recorded. There were fourteen males (66.67%) and seven females (33.33%) in the cohort. The mean age was 14.29 ± 3.46 years (range, 8 years to 22 years: males; 13.39 ± 3.03 years and females; 16.67 ± 3.75 years). The main complaint was redness (100.00%), itching (71.43%) and tearing (57.14%). Twelve patients (57.14%) were from rural areas and 9 patients (42.9%) were from urban areas. The causative organism was found to be first instar of Oestrus ovis larvae.
CONCLUSION: External ophthalmomyiasis caused by Oestrus ovis can cause red eye in patients from Aljabal Algharbi, Libya and requires careful examination to ensure early diagnosis and proper treatment.

INTRODUCTION

Myiasis due to Oestrus ovis is a well-known zoonotic disease that affects a variety of animals. Human myiasis affects mainly individuals in rural areas such as shepherds and farmers.1 Myiasis is the infestation of living or dead tissues and organs of vertebrates by larval stages of certain dipterous flies.2 There are two main types of myiasis: external and internal myiasis. External myiasis includes cutaneous myiasis which is more common than ocular and aural myiasis. Internal myiasis includes gastric, intestinal and urogenital infestation.3

Conjunctival myiasis is the most frequent expression of ocular myiasis.4 Ocular myiasis is clinically divided into external ophthalmomyiasis in which the infestation is restricted to the conjunctiva, and internal ophthalmomyiasis which affects the choroid and retina.5

The most common cause of external ocular myiasis is the larvae of sheep botfly, Oestrus ovis.6–8 Oestrus ovis is an obligate parasite of sheep and goats. Occasionally, humans become accidental hosts.8–12 The clinical features may be mistaken for periorbital cellulitis or acute conjunctivitis.1013

The severity of myiasis depends on the location of the infestation. In external ophthalmomyiasis, the sequelae are mostly benign and self limiting. However, in cases of internal ophthalmomyiasis caused by larvae from other species such as Hypoderma, the larvae can penetrate the sclera and burrow into subretinal space leading to iridocyclitis, endophthalmitis or loss of vision.68

Oestrus ovis myiasis is endemic in sheep and goats in tropical areas such as North Africa and south Asia.2 The prevalence and cause of ocular myiasis remains unknown in Libya.19 In this prospective study, we report the common presenting features of external ophthalmomyiasis affecting individuals in Aljabal Algharbi province, Libya and determine Oestrus ovis larvae as the cause.

MATERIALS AND METHODS

Aljabal Algharbi, one of the Libyan provinces, is located south west to the Libyan capital Tripoli and consists of thirty five sub provinces. Gharian is considered as the largest sub province. This prospective non- comparative study was conducted from September 2009 to July 2010 at Gharian outpatient clinic, Gharian, Aljabal Algharbi, Libya. Data on 21 patients diagnosed with external ophthalmomyiasis were collected.

All patients were required to sign a written informed consent. A written questionnaire was administered which included queries on age, gender, locality (rural or urban), history of contact with animals and their presenting symptoms.

Anesthetic eye drop (4% cocaine) was applied one to two times in 5 min intervals to immobilize the organism which was removed by fine smooth forceps under slit lamp observation by the ophthalmologist. Affected eyes were irrigated frequently with 500 ml of normal saline and patients were advised to apply topical ciprofloxacin 0.3% and dexamethasone 0.1% four times a day to prevent secondary bacterial infection and to reduce inflammation. Patients were advised to present to the emergency room if they felt a moving foreign body or pain in their eyes and to follow up at the ophthalmology clinic to avoid any possible complication or recurrence.

Organisms were sent in a small vial containing 70% ethanol to the department of parasitology where they were mounted on a microscope slide and examined carefully by light microscopy. The organisms were identified as the first instar larvae of Oestrus ovis.

RESULTS

Twenty one cases of external ocular ophthalmomyiasis were recorded. There were fourteen males (66.67%) and seven females (33.33%). The mean age was 14.29 ± 3.46 years (range, 8 years to 22 years). The mean age of the males was 13.39 ± 3.03 years and that of females was 16.67 ± 3.75 years. Twelve patients (57.14%) were from rural areas and 9 patients (42.86%) were from urban areas. Fifteen cases (71.43%) had contact with sheep, four cases (19.05%) had contact with goats and two cases (9.52%) had contact with other animals (cats and dogs). The number of larvae removed ranged from 1 to 7 (mean 3.38). Most cases (71.42%) presented in spring and summer. The majority of patients reported an insect buzzing around their face or striking them in the eye immediately before the occurrence of symptoms. Symptoms were similar to conjunctivitis with pain, itching, redness and tearing in the affected eyes [Figure 1a].

Figure 1

(a) Red eye as the main complaint. (b) The whole larva with translucent segmented body and large dark oral hooks connected to a cephalopharyngeal skeleton (×100). (c) Magnified view showing the anterior part of the maggot with a pair of dark oral hooks (×400)

The main complaints were redness (100.00%), itching (71.43%) and tearing (57.14%). Symptoms included red eye, itching with the sensation of mobile foreign body in the eyes, and tearing. Meticulous ophthalmologic examination by slit lamp biomicroscope revealed white organisms moving rapidly across the conjunctiva or the cornea with tendency to scatter from the light beam which helped confirm the clinical diagnosis of external ophthalmomyiasis.

Marked improvement in signs and symptoms occurred after the removal of all larvae. Larvae were white translucent and measured approximately 1.1 mm in length and 0.3 mm in width [Figure 1b]. Each larva consisted of an anterior end with a pair of large, horn-like dark oral hooks connected to cephalopharyngeal skeleton [Figure 1c]. The body of the larva was segmented; each of these segments has minute dark spines arranged as intersegmented bands [Figure 1b and c]. There were 22 to 25 terminal hooks arranged in two scallops in the terminal segment. These morphologic features were consistent with the first instar of Oestrus ovis. In all cases, the Oestrus ovis larvae did not develop beyond the first instar.

DISCUSSION

Human myiasis is clinically categorized into six types: dermal and subdermal, facial cavity, wound (or traumatic), gastrointestinal, vaginal, and generalized myiasis. Human myiasis is caused by three dipetran families which include Osteridae, Calliphoridae, and Sarcophagidae.14

In our study, the causative organisms were identified as Oestrus ovis larva which is the most common cause of ophthalmomyiasis. This outcome concurs with previous studies of ophthalmomyiasis.5–1315

Morphologically, Oestrus ovis (sheep nasal botfly) is a large yellowish gray fly from 10 to 12 mm long. Oestrus ovis larvae are capable of parasitizing host immediately after birth. In its normal life cycle, the adult female sheep nasal botfly deposits larvae around the nostrils of sheep and goats, larvae migrate into the sinuses. There, they mature by going through three progressive developmental larval stages (instars). After several months, the third instar (mature larval stage) passes out of the sheep and goat nostrils and pupate on the ground. Adult flies emerge from the pupa approximately 3-6 weeks later and live for approximately one month. The sheep botfly deposits larvae near eyes of human with a stream of larvae while it is flying.810

Our observation that the Oestrus ovis larvae developed to the first instar concurs with Corrin et al.5 and Ali et al.16 Both of these studies516 found that the Oestrus ovis larvae develop in the nasopharyngeal cavities and frontal sinuses of livestock; however, in humans the larvae are incapable of developing beyond the first stage and causing external or internal ophthalmomyiasis.516 Similar to a previous study,15 we confirmed that most of the patients were involved in agricultural activites and/or were sheep (or goat) farmers.

We found more residents of rural areas (12 patients; 57.14%) than urban areas were infected. Additionally, the association between larval infection and agricultural areas was clearly evident with 80.95% of patients had either visited or were living in agricultural areas immediately prior to the appearance of symptoms. This observation is similar to Dorchies17 who found that human infection by O. ovis is generally considered to be accidental.

However, 71.43% of patients in our study did have direct contact with sheep which may indicate infection may not be accident. Hira et al.18 and Masoodi et al.19 found greater frequency of ophthalmomyiasis in sheep rearing areas and reported that myiasis is an occupational disease among farmers and shepherds.

In our study, the main complaints were red eye (100.00%), itching (71.43%) and tearing (57.14%) indicating a severe irritation to the affected eye. These symptoms correlate with the morphology and the behavior of larvae. Indeed, while the larvae are moving on the conjunctiva and the cornea of affected eye, their oral hooks and spines irritate eyes of the unnatural hosts such as humans and dogs.5

Treatment initially aimed to immobilize the larvae in order to facilitate removal. This was achieved by the application of local anesthetic eye drops and removal at the slit lamp. The second step was to relieve symptoms and prevent secondary infection by instilling topical antibiotics and anti-inflammatory drugs. The sequence of treatment agrees with Thakur et al. approach.15 Follow-up examination was recommended to avoid post-treatment complications or recurrence as proposed by Anane and Hssine.4

Red eye was the main complaint in all cases of ocular myiasis which should be considered as an occupational disease among farmers and shepherds in Aljabal Algharbi, Libya. Therefore awareness of the sequalae of ocular myiasis will help prevent and control this disease. Additionally ophthalmologists must be aware of the clinical picture of this disease especially during spring and summer for timely diagnosis and prompt management.