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Management of ophthalmomyiasis externs: case report
Management of ophthalmomyiasis externa: case report Michael Ashenhurst, MD, FRCSC; Shamek Pietucha, * BSc
H
uman cases of myiasis (infestation by fly larvae) are rarely observed in North America. We report a case of orbital ophthalmomyiasis externa in a 50-year-old woman following a trip to Belize. Surgical excision was accomplished with a combination of topically applied lidocaine gel and local anesthesia. CASE REPORT
Our patient presented with severe pain, periorbital erythema and edema of the lower eyelid on returning from Belize. Medical management of her initial mosquito bite did not improve the situation. On further examination, a fistulous tract of erythema with periorbital edema was noted around the lower eyelid region. Detailed slit-lamp examination of the eyelid region showed a breathing apparatus of a larva. Ocular examination was otherwise unremarkable, with normal visual acuity, extraocular motility and fundus findings. A diagnosis of ophthalmomyiasis externa was made (Fig. 1). We applied 2% lidocaine gel (AstraZeneca Canada Inc., Mississauga, Ont.) topically for 5 minutes to anesthetize the larva. On cessation of larva movement, lidocaine was injected subcutaneously into the infraorbital nerve territory. We dissected down into the lower lid starting at the fistular tract and extending
horizontally for about 15 mm. The larva was found to be positioned horizontally and was surrounded by a fibrous capsule. The capsule was incised and a nonmotile larva was observed. Removal was atraumatic. The wound was closed with interrupted Monocryl sutures (Ethicon Inc., Somerville, NJ), and 2 mg of dexamethasone was injected subcutaneously at the end of the procedure. Based on the morphologic features and the pattern of spinous rings, the larva was identified as that of the human botfly, Dermatobia hominis (Fig. 2). COMMENTS
Myiasis refers to larval infestation with Diptera, an order of insects that includes the flies, gnats and mosquitoes. Ophthalmomyiasis is the invasion of mammalian periocular tissues by fly larvae (maggots). Most reported cases of ocular myiasis have been external to the globe, called ophthalmomyiasis externa. 1,2 Involvement within the globe, ophthalmomyiasis interna, is a severe condition that may lead to blindness and death.3.4
From the Department of Ophthalmology, University of Calgary, Calgary, Alta.
*At the time of writing, Mr. Pietncha was a second-year medical student at the University of Calgary. Originally received June 19, 2003 Accepted for publication Nov. 20, 2003 Correspondence to: Shamek Pietucha, 103-804 18 Ave. SW, Calgary AB T2T 008; [email protected] This article has been peer-reviewed.
Can J Ophthalmol 2004;39:285-7
Ophthalmomyiasis externa-Ashenhurst et al
Fig. I-Patient before larva extraction. A fistulous track with a white breathing spiracle of the larva is evidenced in the centre of the lid swelling.
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Ophthalmomyiasis externa-Ashenhurst et al
Fig. 2-lntact Dermatobia hominis larva. Note typical concentric hooks.
Fig. 3-White eggs of D. hominis glued to abdomen of carrier fly.B
Ophthalmomyiasis externa has been associated with larvae of D. hominis, Oestrus ovis (sheep nasal bot), Cordylobia anthropophaga (tumbu fly), C. rodhaini (Lund's fly), Cochliomyia hominivorax (New World screwworm fly) and other insects, including Cuterebra species (rodent or rabbit bots) and Hypoderma bovis (cattle grub).5 These represent obligatory parasites, whose larval stages can occur only in the living tissue of animal or human hosts. The method of transmission and tissue affected vary with the species of parasite; sites include the nasopharynx, gut, eyes, genitourinary system and auditory canal. Some of the parasites may live in either necrotic or living tissue. 5 Our patient was infected with D. hominis, the most common cause of cutaneous myiasis in tropical and neotropical regions of Central and South America. 6 The adult D. hominis is 12 mm to 18 mm in length and has a yellow head, blue-grey thorax and metallic blue abdomen. The life cycle of D. hominis begins with an
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unusual process called phoresis, in which the female botfly captures a day-biting mosquito or other bloodsucking arthropod and, in midair, lays approximately 10 to 50 eggs (bots) on its abdomen, attached with a glue-like secretion2 .4,7 (Fig. 3). When the arthropod takes a blood meal from a warm-blooded human or other mammal, the temperature-sensitive larvae hatch onto the skin of the victim and then, 5 to 10 minutes later, burrow into the skin via the bite wound or a hair follicle. 4 A small lesion resembling an insect bite then develops. A central breathing pore is seen within the furuncular lesion, which grows up to 2 cm in diameter and 1 cm in height. As evidenced in our patient, the bot positions itself head down and breathes through caudal respiratory spiracles (Fig. 2). Concentric rows of backward-projecting hooks make the bot difficult to dislodge. Patients frequently feel crawling sensations and significant pain if the bot is irritated. Commonly, there is serous purulent exudate from the pore. Secondary infection is rare owing to bacteriostatic secretions produced in the gut of the larva. Various methods of larva extraction have been suggested. Suffocation techniques have been successfully used to starve the larva of oxygen, leading to eventual death and removal with forceps. Substances used to occlude the breathing hole include heavy oil, petroleum jelly, beeswax, liquid paraffin, raw meat, nail polish, butter, mineral oil, chewing gum and adhesive tape. 6 ,9 The drawback to this treatment is that in response to occlusion of the breathing hole, the larva shifts within the furuncle, causing excessive pain to the patient. An alternative technique is the injection of lidocaine at the base of the furuncle. The localized swelling forces the larva to the surface, where it can be grasped and removed. 9 Surgical extraction is the preferred treatment as retention of larval material from incomplete removal can cause chronic irritation and infection. We found the use of topically administered lidocaine gel before subcutaneous injection of lidocaine to be very effective. When the gel was applied, the larva was neutralized and was unable to use its projecting hooks. This made the extraction comfortable for the patient without the undue irritation associated with attempting to remove a live larva. Furthermore, surgical removal minimized surrounding tissue disturbance, leading to proper wound closure and healing. As the frequency of world travel increases, the occurrence of myiasis may increase in North America. It is important to obtain a detailed travel
Ophthalmomyiasis externa-Ashenhurst et al history and to perform prompt surgical excision. We found the topical use of lidocaine gel to be of particular benefit to the patient in larva removal. 'Early detection of ophthalmomyiasis extema may ,avoid possible wound infection and reduce the chances of orbital scarring, with potential need for oculoplastics repair.
Dermatobia hominis larvae following travel to Brazil. Int J DermatoI1996;35(2):121-3.
5. 6.
7. REFERENCES
1.
2. 3.
4.
Rodrigues MM, Weiss CB, Muncy DW. Ophthalmomyiasis of the eyelid caused by Cuterebra larva. Am J OphthalmoI1974 ;78:1024-6. Millikan LE. Myiasis. Clin DermatoI1999;17:191-5. Slusher MM, Holland WD, Weaver RG, Tyler ME. Ophthalmomyiasis interna posterior: subretinal tracks and intraocular larvae. Arch OphthalmoI1979;97(5) :885-7. Tsuda S, Nagaji J, Kurose K, Miyasato M, Sasai Y, Yoneda Y. Furuncular cutaneous myiasis caused by
8.
9.
Sherman RA. Wound myiasis in urban and suburban United States. Arch Intern Med 2000;160(13):2004-14. Goodman RL, Montalvo MA, Reed JB, Scribbick FW, McHugh CP, Beatty RL, et al. Anterior orbital myiasis caused by human botfly (Dermatobia hominis). Arch OphthalmoI2000;118(7):1002-3 . Gordon PM, Hepburn NC, Williams AE, Bunney MH. Cutaneous myiasis due to Dermatobia hominis: a report of six cases. Br J DermatoI1995;132:811-4. The Veterinary Parasitology Images Gallery: Arthropoda: Insecta and Acari. Available: http://icb.usp.br/-marcelcp/ (accessed 2004 Feb 5). Shorter N, Werninghaus K, Mooney D, Graham A. Furuncular cuterebrid myiasis. J Pediatr Surg 1997; 22(10):1511-3.
Key words: myiasis, ophthalmomyiasis externa, botfly, lidocaine gel
CAN J OPHTHALMOL-VOL. 39, NO.3, 2004
287
H
uman cases of myiasis (infestation by fly larvae) are rarely observed in North America. We report a case of orbital ophthalmomyiasis externa in a 50-year-old woman following a trip to Belize. Surgical excision was accomplished with a combination of topically applied lidocaine gel and local anesthesia. CASE REPORT
Our patient presented with severe pain, periorbital erythema and edema of the lower eyelid on returning from Belize. Medical management of her initial mosquito bite did not improve the situation. On further examination, a fistulous tract of erythema with periorbital edema was noted around the lower eyelid region. Detailed slit-lamp examination of the eyelid region showed a breathing apparatus of a larva. Ocular examination was otherwise unremarkable, with normal visual acuity, extraocular motility and fundus findings. A diagnosis of ophthalmomyiasis externa was made (Fig. 1). We applied 2% lidocaine gel (AstraZeneca Canada Inc., Mississauga, Ont.) topically for 5 minutes to anesthetize the larva. On cessation of larva movement, lidocaine was injected subcutaneously into the infraorbital nerve territory. We dissected down into the lower lid starting at the fistular tract and extending
horizontally for about 15 mm. The larva was found to be positioned horizontally and was surrounded by a fibrous capsule. The capsule was incised and a nonmotile larva was observed. Removal was atraumatic. The wound was closed with interrupted Monocryl sutures (Ethicon Inc., Somerville, NJ), and 2 mg of dexamethasone was injected subcutaneously at the end of the procedure. Based on the morphologic features and the pattern of spinous rings, the larva was identified as that of the human botfly, Dermatobia hominis (Fig. 2). COMMENTS
Myiasis refers to larval infestation with Diptera, an order of insects that includes the flies, gnats and mosquitoes. Ophthalmomyiasis is the invasion of mammalian periocular tissues by fly larvae (maggots). Most reported cases of ocular myiasis have been external to the globe, called ophthalmomyiasis externa. 1,2 Involvement within the globe, ophthalmomyiasis interna, is a severe condition that may lead to blindness and death.3.4
From the Department of Ophthalmology, University of Calgary, Calgary, Alta.
*At the time of writing, Mr. Pietncha was a second-year medical student at the University of Calgary. Originally received June 19, 2003 Accepted for publication Nov. 20, 2003 Correspondence to: Shamek Pietucha, 103-804 18 Ave. SW, Calgary AB T2T 008; [email protected] This article has been peer-reviewed.
Can J Ophthalmol 2004;39:285-7
Ophthalmomyiasis externa-Ashenhurst et al
Fig. I-Patient before larva extraction. A fistulous track with a white breathing spiracle of the larva is evidenced in the centre of the lid swelling.
285
Ophthalmomyiasis externa-Ashenhurst et al
Fig. 2-lntact Dermatobia hominis larva. Note typical concentric hooks.
Fig. 3-White eggs of D. hominis glued to abdomen of carrier fly.B
Ophthalmomyiasis externa has been associated with larvae of D. hominis, Oestrus ovis (sheep nasal bot), Cordylobia anthropophaga (tumbu fly), C. rodhaini (Lund's fly), Cochliomyia hominivorax (New World screwworm fly) and other insects, including Cuterebra species (rodent or rabbit bots) and Hypoderma bovis (cattle grub).5 These represent obligatory parasites, whose larval stages can occur only in the living tissue of animal or human hosts. The method of transmission and tissue affected vary with the species of parasite; sites include the nasopharynx, gut, eyes, genitourinary system and auditory canal. Some of the parasites may live in either necrotic or living tissue. 5 Our patient was infected with D. hominis, the most common cause of cutaneous myiasis in tropical and neotropical regions of Central and South America. 6 The adult D. hominis is 12 mm to 18 mm in length and has a yellow head, blue-grey thorax and metallic blue abdomen. The life cycle of D. hominis begins with an
286
CAN J OPHTHALMOL-VOL. 39, NO.3, 2004
unusual process called phoresis, in which the female botfly captures a day-biting mosquito or other bloodsucking arthropod and, in midair, lays approximately 10 to 50 eggs (bots) on its abdomen, attached with a glue-like secretion2 .4,7 (Fig. 3). When the arthropod takes a blood meal from a warm-blooded human or other mammal, the temperature-sensitive larvae hatch onto the skin of the victim and then, 5 to 10 minutes later, burrow into the skin via the bite wound or a hair follicle. 4 A small lesion resembling an insect bite then develops. A central breathing pore is seen within the furuncular lesion, which grows up to 2 cm in diameter and 1 cm in height. As evidenced in our patient, the bot positions itself head down and breathes through caudal respiratory spiracles (Fig. 2). Concentric rows of backward-projecting hooks make the bot difficult to dislodge. Patients frequently feel crawling sensations and significant pain if the bot is irritated. Commonly, there is serous purulent exudate from the pore. Secondary infection is rare owing to bacteriostatic secretions produced in the gut of the larva. Various methods of larva extraction have been suggested. Suffocation techniques have been successfully used to starve the larva of oxygen, leading to eventual death and removal with forceps. Substances used to occlude the breathing hole include heavy oil, petroleum jelly, beeswax, liquid paraffin, raw meat, nail polish, butter, mineral oil, chewing gum and adhesive tape. 6 ,9 The drawback to this treatment is that in response to occlusion of the breathing hole, the larva shifts within the furuncle, causing excessive pain to the patient. An alternative technique is the injection of lidocaine at the base of the furuncle. The localized swelling forces the larva to the surface, where it can be grasped and removed. 9 Surgical extraction is the preferred treatment as retention of larval material from incomplete removal can cause chronic irritation and infection. We found the use of topically administered lidocaine gel before subcutaneous injection of lidocaine to be very effective. When the gel was applied, the larva was neutralized and was unable to use its projecting hooks. This made the extraction comfortable for the patient without the undue irritation associated with attempting to remove a live larva. Furthermore, surgical removal minimized surrounding tissue disturbance, leading to proper wound closure and healing. As the frequency of world travel increases, the occurrence of myiasis may increase in North America. It is important to obtain a detailed travel
Ophthalmomyiasis externa-Ashenhurst et al history and to perform prompt surgical excision. We found the topical use of lidocaine gel to be of particular benefit to the patient in larva removal. 'Early detection of ophthalmomyiasis extema may ,avoid possible wound infection and reduce the chances of orbital scarring, with potential need for oculoplastics repair.
Dermatobia hominis larvae following travel to Brazil. Int J DermatoI1996;35(2):121-3.
5. 6.
7. REFERENCES
1.
2. 3.
4.
Rodrigues MM, Weiss CB, Muncy DW. Ophthalmomyiasis of the eyelid caused by Cuterebra larva. Am J OphthalmoI1974 ;78:1024-6. Millikan LE. Myiasis. Clin DermatoI1999;17:191-5. Slusher MM, Holland WD, Weaver RG, Tyler ME. Ophthalmomyiasis interna posterior: subretinal tracks and intraocular larvae. Arch OphthalmoI1979;97(5) :885-7. Tsuda S, Nagaji J, Kurose K, Miyasato M, Sasai Y, Yoneda Y. Furuncular cutaneous myiasis caused by
8.
9.
Sherman RA. Wound myiasis in urban and suburban United States. Arch Intern Med 2000;160(13):2004-14. Goodman RL, Montalvo MA, Reed JB, Scribbick FW, McHugh CP, Beatty RL, et al. Anterior orbital myiasis caused by human botfly (Dermatobia hominis). Arch OphthalmoI2000;118(7):1002-3 . Gordon PM, Hepburn NC, Williams AE, Bunney MH. Cutaneous myiasis due to Dermatobia hominis: a report of six cases. Br J DermatoI1995;132:811-4. The Veterinary Parasitology Images Gallery: Arthropoda: Insecta and Acari. Available: http://icb.usp.br/-marcelcp/ (accessed 2004 Feb 5). Shorter N, Werninghaus K, Mooney D, Graham A. Furuncular cuterebrid myiasis. J Pediatr Surg 1997; 22(10):1511-3.
Key words: myiasis, ophthalmomyiasis externa, botfly, lidocaine gel
CAN J OPHTHALMOL-VOL. 39, NO.3, 2004
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