Human Ocular Onchocerca lupi Infection Diagnosed in Norway

Human zoonotic disease caused by Onchocerca lupi is rare but increasingly reported in the literature. Human infections with the nematode (round worm) O. lupi have been confirmed in 13 humans in Europe, Tunisia, Turkey, Iran and the USA.1-3 The parasite’s life cycle is not fully understood, but the parasite is transferred from animal to human through a vector, most likely the blackflies (Simuliidae).2 Most frequent presentation in animals and humans are ocular findings including variably painful subconjunctival swellings and nodules containing immature or mature worms affecting the eye or adjacent structures. Occasionally, extradural masses affecting the spinal cord have been seen in humans.1,4 Diagnosis is achieved by microscopy of excised adult female worms which exhibit a particular cuticular structure. Molecular analysis by polymerase chain reaction (PCR) with sequencing of the PCR product can confirm the species. Treatment consists of surgical worm removal, sometimes accompanied by anthelmintic, antibiotic and anti-inflammatory therapy.

structure was protruded from the lesion (Figure 1). The lesion was explored by slit lamp, and a 4-5 cm long structure thin as a sewing thread was extracted using fine forceps under local anesthetic. Later, the structure was identified as the adult roundworm O. lupi by microscopy and PCR with subsequent sequencing at the Public Health Agency and the National Veterinary Institute, Sweden and University of Zürich, Switzerland. Eosinophil blood cell count was normal. The laboratories saw no microfilariae within the worm on direct microscopy, hence our O. lupi was not considered a gravid female worm ( Figure 2). The patient was seen at the Department of Infectious Diseases, OUH, and no extraocular clinical manifestations were noticed; thus, no further investigations or treatments were recommended. The patient was treated with topical steroids in tapering doses and seen at regular intervals. His symptoms were gradually resolved. At 6 months follow-up, the patient was symptom free and the only ophthalmological finding was slight hyperemic vessels in the area of previous worm removal.

Discussion
This is the fourteenth verified and published case of human O. lupi infection and the first patient diagnosed in Northern Europe to our knowledge. However, the infection was most likely imported from Turkey where O. lupi is endemic.
Onchocerca is a genus of nematodes (roundworms) with 34 different species, which primarily parasitize nonhuman hosts. 5 The only well-established species known to cause human infection is O. volvulus, which causes onchocerciasis, also known as river blindness, primarily in Africa. 6 In 1967, a new species infecting a wolf (Canis lupus cubanensis) was described in Russia and was named O. lupi. 7 The taxonomy of this parasite is as follows: phylum Nematoda, order Spirurida, family Onchocercidae, genus Onchocerca, and species Onchocerca lupi. 7 The first confirmed human cases of O. lupi were recorded in Turkey. 5,8,9 The life cycle of the parasite is not fully understood but believed to be similar to that of O. volvulus. According to Lok et al, 10 Onchocerca spp. present two phases: one in blackflies (vector-immediate hosts) and another in definitive hosts (humans and animals). When vectors take a blood meal on an infected definitive host, these ingest microfilariae. The microfilariae develop to the third stage-infective larva (L3) in the mouth parts of the blackflies. This larval stage is infective to vertebrate definitive hosts. When infected blackflies take a subsequent blood meal from an uninfected vertebrate, the L3-larva is transmitted to a new vertebrate.
The most frequent clinical findings in animals and humans are, as in our case, unilateral or asymmetrical, variably painful subconjunctival swellings and nodules containing immature or mature worms affecting the eye and/or adjacent tissues accompanied by conjunctival hyperemia. 2 Occasionally, subcutaneous nodules and masses affecting the spinal cord have been observed in humans. 1,4,11 Differential diagnose of the ocular findings include orbital cellulitis, retro bulbar abscess, nodular episcleritis and periorbital neoplasia. When a roundworm is identified, the main differential diagnosis is Dirofilaria repens. Dirofilariasis affects the eye in similar ways as O. lupi and has been reposted to affect human eyes in more cases than O. lupi. 12,13 The diagnosis is usually accidental when a filarial worm is excised from a nodule. The difficulties in recognizing O. lupi may arise from the fact that the infection is unknown to the examiner, whether the excised worm is immature, damaged during excision or fixed in Formalin, which may hamper molecular analysis. 14 Diagnosis of O. lupi is achieved by microscopy of excised adult female worms which exhibit a particular cuticular structure. We found molecular analysis of the worm to be helpful in species determination. 2 To the best of our knowledge, microfilariae have not been verified in human blood, but gravid female worms have been seen in humans. 1 In animals, searching for microfilariae in blood smears has been shown to be unrewarding. 15,16 Skin snips are commonly used but show low sensitivity in light infections. Blood eosinophilia is common but not always seen, as illustrated in our case. 2 Diagnosis remains challenging in the absence of reliable non-invasive diagnostic tests. 4 There are no evidence-based treatment algorithms for human O. lupi infection. 1 In general, treatment consists of surgical worm removal and/or anthelminthic, antibiotic and anti-inflammatory therapy. 2 Since data on the treatment of O. lupi is scarce, recommendations for medical therapy of O. lupi are based primarily on what is known about the treatment of 0. Volvulus. 17 In human onchocerciasis (river blindness), bacterial endosymbionts of the genus Wolbachia are believed to be essential for embryogenesis of microfilariae, and might therefore constitute an additional therapeutic target. Also, Figure 1. Clinical Presentation. Clinical presentation of the patient before worm removal. Roundworm in the superonasal quadrant of the left eye located partly subconjunctival, partly exposed. Conjunctival injection and hyperemia present. Wolbachia has been searched in O. lupi, [18][19][20][21][22] and in nodules containing O. lupi nematodes removed from naturally infected dogs, Wolbachia-like endobacteria has been detected by electron microscopy. 23 Doxycycline is known to make female worms of O. volvulus sterile by its antibacterial effect on the Wolbachia endosymbiont, which is required for reproduction and the long-term survival of the parasite. 24 The anthelmintic drug ivermectin is microfilaricidal, so it may prevent symptomatic manifestations of river blindness caused by inflammatory reactions to dying microfilariae in subcutaneous tissue of the skin and the conjunctiva of the eye; it may also hinder transmission to blood-feeding blackflies. 25 Since standardized treatment regimens for O. lupi infections are lacking, we opted to treat our patient with surgical removal of the parasite and tapering doses of topical steroids alone. Our worm did not contain microfilariae on direct microscopy, hence treatment with ivermectin was deemed unnecessary. On the other hand, one may argue that a single dose of ivermectin in this case would stop possible transmission of unrecognized microfilariae to susceptible humans or mammals if the patient was bitten by the appropriate vector while in Turkey. Postoperative Doxycycline treatment in order to sterilize the worm seemed inappropriate since the worm was removed in toto and there was no sign of multiple infection. In our opinion, based on available published literature, there is not enough data supporting the need for anti-helminthic or antibiotic therapy. Our patient recovered completely within six months post-surgery and after tapering out topical steroids.

Conclusion
Globalization with increased movement of people, food, livestock and pets combined with environmental and climate changes has led to the rapid expansion of emerging infections throughout the world. Human zoonotic infections with O. lupi have been increasingly recognized, yet they are still rare. However, the number of cases may be underestimated due to lack of knowledge and diagnostic tools. Furthermore, Dirofilaria, another filarial nematode, may have been wrongly identified as the cause of subconjunctival and periorbital masses such as the one seen in our patient. It is important to alert the scientific community, doctors, veterinarians, ophthalmologists, health service workers and the public about this poorly known emerging zoonotic disease which may also affect humans. Studies are needed to determine regular and potential definitive hosts and vectors of O. lupi in different areas in order to understand the reservoir, the transmission patterns and the seasonality of this zoonosis. Furthermore, research is needed to better define the burden of disease, identify targeted prevention strategies, and develop easily available diagnostic tools and therapeutic modalities.

Authors' Contributions
ARS and TS removed the worm and did the clinical follow up at the ophthalmological department. FOP advised, ARS and TS about the diagnostics of worm identification and contributed to the clinical follow up of the patient at the Department of Infectious Diseases, OUS. TL contributed to the molecular analysis of the worm and provided the lupe photograph of the worm (Figure 2). All authors discussed the case and contributed to the final manuscript.