Onchocerca jakutensis Filariasis in Humans

We identified Onchocerca jakutensis as the causative agent of an unusual human filariasis in a patient with lupus erythematosus. To our knowledge, this is the first case of human infection with O. jakutensis and the first human case of zoonotic onchocercosis involving >1 worm.

Z oonotic fi larial infestations occur worldwide, and in most reported cases the involved species are members of the genus Dirofi laria. However, zoonotic Onchocerca infections are rare and to date only 13 cases (originating from Europe, Russia, the United States, Canada, and Japan) have been described. In all of these cases only 1 immature worm was found, and the causative species was identifi ed as O. gutturosa, O. cervicalis, O. reticulata, or O. dewittei japonica on the basis of morphologic and in some cases serologic parameters (1)(2)(3)(4). O. cervicalis and O. reticulata are found in the ligaments of the neck and extremities of horses, O. gutturosa is typically found in the nuchal ligaments of cattle, and O. dewittei japonica is found in the distal parts of the limbs and adipose tissue of footpads of wild boars.
We identifi ed the causative agent of a zoonotic Onchocerca infection with multiple nodules in a patient with systemic lupus erythematosus (SLE) who had been receiving hemodialysis. The parasite was identifi ed in paraffi n-embedded tissue samples by PCR and DNA sequence analysis.

The Study
The patient was a 59-year-old woman with SLE who had developed multiple nodules on the neck and face over several years. Because of major renal insuffi ciency, she also had been receiving hemodialysis 3 times per week (3.5 hours) for >10 years. The fi rst clinical differential diagnoses were cutaneous SLE, nephrogenous dermatopathy, calciphylaxis, and calcinosis. The clinical picture was obscured by secondary infl ammations and ulcerations caused by selfinfl icted trauma. Multiple sampling attempts by cutaneous core biopsies resulted in histologic diagnosis of unspecifi c, secondary infl ammatory changes. Deep surgical excision of 1 subcutaneous nodule on the scalp indicated subcutaneous helminthosis (Figure). The patient was treated with ivermectin and subjected to 2 plastic surgeries for facial reconstruction, after which she recovered.
At this point, species identifi cation of the causative agent was still pending. A history of travel anamnesis and location of the nodules indicated a possible Dirofi laria infection, but a specifi c PCR showed negative results. Morphologic features of the few available sections suggested Onchocerca spp. To our knowledge, multiple nodules had never been reported in cases of infection with zoonotic Onchocerca. Because a defi nitive morphologic identifi cation of the causative nematode was not possible, molecular identifi cation from DNA isolated from the only available material (formalin-fi xed and paraffi n-embedded tissue) was conducted.
To evaluate the causative genus, universal fi larial primers were constructed on the basis of fi larial sequences available in GenBank (primer FILfw 5′-CGGTGATATT-GGTTGGTCTC-3′ for the fi rst internal transcribed spacer region and primer FILrev 5′-CTAGCTGCGTTCTTCATC-GATC-3′ for the 5.8S rRNA gene). PCR and sequencing were performed and a similarity matrix was calculated after multiple sequence alignment (5).
The DNA fragment obtained was 226 bp and showed greatest similarities to Onchocerca sequences, ranging from 87% to 95%. Similarities to Wuchereria, Brugia, Mansonella, Dirofi laria, and Acanthocheilonema were lower, ranging from 75% to 80%. Assignment to the genus Onchocerca was obvious, but species identifi cation still posed a problem because published O. volvulus sequences showed higher similarities among each other (98.8%-100%) than with our sequence. The only exception was a clinical O. volvulus strain (OvNod1-3) from Bolo, Cameroon, which showed 94.8% sequence similarity. However, the authors of that report indicated that their strain might be a zoonotic Onchocerca sp. (6).

Conclusions
The limiting factor in identifying the causative agent in our patient was the nature of the sample material. Because only a few formalin-fi xed and paraffi n-embedded sections were available, morphologic identifi cation was not possible. PCR-based identifi cation was restricted because DNA has a tendency to degrade when stored in formalin, which limits the length of the target sequence to ≈300 bp and limits its discriminatory power (9). A different approach with 3 PCRs, 1 for genus identifi cation and 2 for species identifi cation, and primers for highly variable multicopy targets enabled us to accurately identify the causative agent as O. jakutensis.
To our knowledge, O. jakutensis has never been identifi ed as an agent of human fi lariasis. It has been identifi ed as a rare parasite of red deer in Germany, Poland, and Russia, and may also be found in other northern European countries (10). Our patient came from the United States and had traveled all over Europe. She could thus have acquired the infection in several different locations.
Two fi ndings for this patient were particularly unusual and obscured the identifi cation of the parasite. The fi rst fi nding was that she had, in contrast to all previous human cases of zoonotic onchocercosis, multiple nodules. The second fi nding was that her face (periorbital and buccal), neck, and scalp were affected, although zoonotic fi lariae are typically found in similar or identical tissues as in their natural hosts (11). O. jakutensis is usually found in tissues of the outer thigh and caudal part of the back; >2 nodules per infected host are rare (12,13). It is unlikely that these fi ndings are associated with greater virulence of O. jakutensis than of other zoonotic Onchocerca spp. However, parasite virulence might be related to the patient having had autoimmune disease since childhood and as a result having received long-term immunosuppressive therapy. The immune status of the patient was further impaired by renal insuffi ciency for >10 years. However, no data exist on the immune status of patients in any of the previously reported cases of infection with zoonotic Onchocerca spp. For other nematodes, e.g., Strongyloides stercoralis, a correlation between immune status of the patient and severity of disease is well established. One report describes more severe skin manifestations caused by O. volvulus in HIV patients (14).
We have identifi ed a zoonotic infestation with an Onchocerca sp. that can cause disease in humans. The combination of impaired immunity and unusually progressing infestation highlights a new aspect of zoonotic fi lariasis.