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Editor,—Human ocular invasion by non-human filarial parasites has been reported for more than 200 years.1 2However, only just over a handful have actually been removed, described and identified in detail.3-6 Furthermore, theDipetalonema species that have been described in three cases were thought to be from the body cavity of the natural hosts—the porcupine and the beaver.4 5 7 8
This report describes a case of Dipetalonema reconditum (usually associated with canine filariasis) in the human eye. It is noteworthy that this worm has morphological similarities to the canine heartworm Dirofilaria imitis, which in the past has been described in the human eye5 9 but not satisfactorily identified.10
A 62 year old white resident of suburban Victoria, Australia, presented with a red and irritated right eye of 2 weeks' duration. This was exacerbated after a rural walking trip and did not improve with topical lubrication. He also noted mild diplopia on extreme right gaze. On examination, the visual acuity was 6/6 in the right eye and 6/4 in the left. There was mild limitation of right eye abduction. Localised bulbar conjunctival erythema and chemosis were noted inferotemporally in the right eye near the insertion of the lateral rectus. Slit lamp biomicroscopy revealed a slithering, clear, thread-like mobile mass in the subconjunctival space of the inflamed area (Fig 1 and video report (see BJOwebsite)). Intraocular pressure and the rest of the ocular examination, including anterior and posterior segments, were unremarkable. Previous history included pyrexia of unknown origin (PUO) and lancinating headaches 5 months previously. Investigation results then of note included erythrocyte sedimentation rate (ESR) 96 mm in the first hour, C reactive protein (CRP) 411 mg/l, and trace proteinuria. He improved on intravenous ceftriaxone, metronidazole, and oral roxithromycin. He had also had another period of PUO and suffered with chronicGiardia infection.
The worm was removed following localised peritomy under topical local anaesthesia using lignocaine 2%, phenylephrine 10%, and phospholine iodide 12.5% (in an attempt to paralyse the worm). The specimen was removed alive and intact and sent in normal saline for identification. Laboratory examination revealed a worm measuring 32 mm in length with morphological features consistent with an unfertilised adult femaleD reconditum.
Patient investigations including thick and thin blood film, full blood count, ESR, CRP electrolytes, liver function tests, and chestx ray were all within normal limits. His pet dogs were found to be serologically negative forDipetalonema.
He was treated with oral mebenazole, topical prednisolone acetate 1%, and chloramphenicol before the worm's identification. Two weeks following removal of the worm the diplopia had resolved and residual fibrosis of the conjunctiva at the site of removal was noted.
Dipetalonema reconditum is a nematode that is commonly found to be endemic in dogs' subcutaneous tissues. Worldwide distribution includes the United States, Italy, and Africa. Its infestation in dogs, the only definitive host, is not clinically significant, although they may manifest an elevated eosinophil and leucocyte count. This manifestation may result in false positives in test for circulating Dirofilaria imitismicrofilariae, also known as the dog heartworm. The differentiation of these two worms is important as Dirofilariais pathogenic to canines. Knott's test11 is used to detect these microfilaria serologically. Identification of these two adult worms is by their staining patterns with acid phosphatase:Dipetalonema stains evenly whileDirofilaria concentrates the acid phosphatase in two regions.
The Dipetalonema reconditum microfilarium averages about 250–270 μm in length and 4–4.5 μm in width with a round curved body, a distinguishing cephalic hook, and a blunt anterior end. Adult males average 13 mm in length and females 17–32 mm.12
Dipetalonema has an indirect life cycle with development of infective larvae that are carried by fleas (genusCtenocephalides,Pulex), ticks (Rhipicephalus sanguineus), and lice (Linognathus). Dogs are infected when bitten by the fleas. The microfilarium circulates in the blood as a first stage larva. The larval life cycle lasts 61–68 days. The adult worm tends to infect the subcutaneous tissues.12 Other less common sites of infestation include the body cavities and the kidneys.
Our case represents human subconjunctival infestation with an adult unfertilised D reconditum; this is, to our knowledge, the first report in the literature. The literature reveals three other documented cases ofDipetalonema species infestation in the human eye; however, none of them was D reconditum. The chronic nature and slow onset of the symptoms implies that this infestation excited a slow and limited inflammatory reaction within the ocular tissues.
There is no documented treatment for this infestation; ivermectin and milbemycin are recommended. Other control measures include flea, louse, and tick control. Hitherto, there has not been any documented public health significance. The incidence of D reconditum infestation in Australian dogs has significantly decreased since the introduction of the heartworm prevention programme as the treatment for D immitis also eliminates the D reconditum. As the serology in our patient's dogs was negative for D reconditum, one can postulate he was infected via a flea bite in his rural walking; however, we have no confirmative history. There is no documentation of the incidence of D reconditum in the Australian wildlife. As it is a self limiting condition, the definitive treatment is removal of the worm.
The authors thank Dr Harsha Sheorey, microbiologist at St Vincent's Hospital, Melbourne, for his help in identifying the organism.
Website extra A video report is on the BJO website. It shows the undulating appearance of the right bulbar conjunctival surface in a 62 year old white male as the Dipetalonema reconditum remains mobile immediately before removal following localised peritomy www.bjophthalmol.com