Dipetalonema reconditum in the human eye
T Huynh, J Thean, R Maini1
Royal Victorian Eye and Ear Hospital and 1Centre for Eye Research Australia, Melbourne, Australia
Correspondence to: Dr T Huynh MBBS, Royal Victorian Eye and Ear Hospital, 32 Gisborne St, East Melbourne, Victoria 3002, Australia
Accepted for publication: 15 July 2001
Ocular invasion by the nematode Dipetalonema reconditum in a 62-year-old patient who presented with a red and irritated right eye of 2 weeks duration. Slit-lamp biomicroscopy revealed a slithering, clear, thread-like mobile mass in the subconjunctival space of the inflamed area. The specimen was removed alive and intact, measuring 32mm in length with morphological features consistent with an unfertilised adult female D. reconditum.
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Human ocular invasion by non-human filarial parasites have been reported for more than 200 years1,2. However, only just over a handful have actually been removed, described and identified in detail.3-6. Furthermore, the Dipetalonema species that have been described in three cases were thought to be from the body cavity of the natural hosts, the porcupine and the beaver4,5,7,8.
This case 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 identified10.
A 62-year-old caucasian resident of suburban Victoria 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 on the right and 6/4 on the left. There was mild limitation of right eye abduction. Localised bulbar conjunctival erythema and chemosis was 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 (Figure and Video). 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 five months previously. Investigation results then of note included ESR 96mm/h, CRP 411mg/L and trace proteinuria. He improved on intravenous ceftriaxone, metronidazole and oral roxithromycin. He had also had another period of PUO and suffered with chronic Giardia.
The worm was removed following localised peritomy under topical local anaesthetic using lignocaine 2%, phenylephrine 10% and phospholine iodide 12.5% (in an attempt to paralize the worm). The specimen was removed alive and intact and sent in normal saline for identification. Laboratory examination revealed a worm measuring 32mm in length with morphological features consistent with an unfertilised adult female D. reconditum.
Patient investigations including thick and thin blood film, full blood count, ESR, CRP electrolytes, liver function tests and chest x-ray were all within normal limits. His pet dogs were found to be serologically negative for Dipetalonema.
He was treated with oral mebenazole, topical prednisolone acetate 1% and chloramphenicol prior to the worm�s identification. Two weeks following removal of the worm the diplopia had resolved and residual fibrosis of the conjunctiva at 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 definite host, is not clinically significant, although they may manifest an elevated eosinophil and leukocyte count. This manifestation may result in false positives in test for circulating Dirofilaria immitis microfilariae, also known as the dog heartworm. The differentiation of these two worms is important as Dirofilaria is pathogenic to canines. Knott�s test11 is used to detect these microfiliaria serologically. Identification of these two adult worms is by their staining patterns with acid phosphatase: Dipetalonema stains evenly, whilst Dirofilaria concentrates the acid phosphatase in two regions.
The Dipetalonema reconditum microfilarium averages about 250-270�m in length and 4-4.5�m in width with a round curved body, a distinguishing cephalic hook and a blunt anterior end. Adult males average 13mm in length and females 17-32mm12.Dipetalonema has an indirect life cycle with development of infective larvae that are carried by fleas (genus Ctenocephalides,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 to 68 days. The adult worm tends to infect the subcutaneous tissues12. 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 of this in the literature. The literature reveals three other documented cases of Dipetalonema species infestation in the human eye, however none of them were 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 heart worm prevention program 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.
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