[A new onchocercal parasite, Onchocerca alcis n. sp., parasite of the moose Alces alces in Sweden]

Redescription of Onchocerca lupi (Spirurida: Onchocercidae) with histopathological observations

BACKGROUND

Onchocerca lupi is a dog parasite of increasing zoonotic concern, with new human cases diagnosed in Turkey, Tunisia, Iran, and the United States. Information about the morphology of this nematode is scant and a detailed re-description of this species is overdue. In addition, histopathological data of potential usefulness for the identification of O. lupi infections are provided.

METHODS

Male and female nematodes, collected from the connective tissue of a dog, were examined using light microscopy and scanning electron microscopy (SEM), and an histological evaluation was performed on biopsy samples from periocular tissues.

RESULTS

The morphological identification was confirmed by molecular amplification and partial sequencing of cytochrome oxidase subunit 1 gene. This study provides the first comprehensive morphological and morphometric description of O. lupi from a dog based on light microscopy, SEM, molecular characterization, and histological observations.

CONCLUSIONS

Data herein presented contribute to a better understanding of this little known parasitic zoonosis, whose impact on human and animal health is still underestimated. The presence of granulomatous reactions only around the female adult suggests that the release of microfilariae from the uterus might be the cause of the inflammatory reaction observed.

Defining parasite biodiversity at high latitudes of North America: new host and geographic records for Onchocerca cervipedis (Nematoda: Onchocercidae) in moose and caribou

Background

Onchocerca cervipedis is a filarioid nematode of cervids reported from Central America to boreal regions of North America. It is found primarily in subcutaneous tissues of the legs, and is more commonly known as ‘legworm’. Blackflies are intermediate hosts and transmit larvae to ungulates when they blood-feed. In this article we report the first records of O. cervipedis from high latitudes of North America and its occurrence in previously unrecognized host subspecies including the Yukon-Alaska moose (Alces americanus gigas) and the Grant’s caribou (Rangifer tarandus granti).

Methods

We examined the subcutaneous connective tissues of the metacarpi and/or metatarsi of 34 moose and one caribou for parasitic lesions. Samples were collected from animals killed by subsistence hunters or animals found dead in the Northwest Territories (NT), Canada and Alaska (AK), USA from 2005 to 2012. Genomic DNA lysate was prepared from nematode fragments collected from two moose. The nd5 region of the mitochondrial DNA was amplified by PCR and sequenced.

Results

Subcutaneous nodules were found in 12 moose from the NT and AK, and one caribou from AK. Nematodes dissected from the lesions were identified as Onchocerca cervipedis based on morphology of female and male specimens. Histopathological findings in moose included cavitating lesions with multifocal granulomatous cellulitis containing intralesional microfilariae and adults, often necrotic and partially mineralized. Lesions in the caribou included periosteitis with chronic cellulitis, eosinophilic and lymphoplasmacytic infiltrate, and abundant granulation associated with intralesional adult nematodes and larvae. Sequences of the nd5 region (471bp), the first generated for this species, were deposited with Genbank (JN580791 and JN580792). Representative voucher specimens were deposited in the archives of the United States National Parasite Collection.

Conclusions

The geographic range of O. cervipedis is broader than previously thought, and extends into subarctic regions of western North America, at least to latitude 66°N. The host range is now recognized to include two additional subspecies: the Yukon-Alaska moose and Grant’s caribou. Accelerated climate change at high latitudes may affect vector dynamics, and consequently the abundance and distribution of O. cervipedis in moose and caribou. Disease outbreaks and mortality events associated with climatic perturbations have been reported for other filarioids, such as Setaria tundra in Fennoscandia, and may become an emerging issue for O. cervipedis in subarctic North America.

Subconjunctival zoonotic onchocerciasis in man: aberrant infection with Onchocerca lupi?

In the past few decades, 10 cases of cryptic, zoonotic onchocerciasis, including two subconjunctival infections, have been reported in man. In the majority of cases, Onchocerca cervicalis, O. gutturosa or O. dewittei, which normally infect horses, cattle and wild boar, respectively, were responsible for the lesions. However, the taxonomic status of the parasites involved in the two subconjunctival infections, both of which were European, has never been unambiguously determined. In such infections, the acute phase appears to be characterized by conjunctivitis. A single, strongly coiled, immature, female worm was found incorporated in a large granulomatous nodule, in the ocular and peri-ocular tissues, in the chronic stage of each of the two eye infections. Several, patent, sporadic cases of subconjunctival O. lupi infection have recently been reported in dogs. In terms of the location of the worms, clinical signs and histopathology, these canine infections were very similar to those seen in the two human patients with eye infection. When the parasites recovered from human eyes were compared morphologically with the Onchocerca spp. infecting animals in Europe, they appeared to be most similar to O. lupi. Although O. lupi is normally a parasite of dogs, it may thus also be responsible for aberrant, zoonotic, subconjunctival infections in man.

Canine ocular onchocercosis in Hungary

An adult male mongrel dog that had spent its entire life in Hungary, was found to have infection with filaroid nematodes of the genus Onchocerca. The gravid male and female parasites were embedded in bean-sized granulomatous masses on the conjunctiva and the sclera of both eyes. The cuticle of females consisted of two separated layers in longitudinal sections, the external layer bearing ridges and the internal layer showing striations. The ridges were marked, rounded in shape, and the ratio of body diameter to the distance between ridges varied between 7:1 and 10:1. At midbody of the worms, two striations could be seen between each pair of ridges: one under every ridge and one between neighbouring ridges. Numerous exceptionally small (96.4 microm x 6.4 microm) microfilariae were seen in the uteri of females and the surrounding tissues and isolated from skin biopsy materials. The morphology and location of the parasite and histopathological lesions of the Hungarian case were similar to that described in dogs in the United States. This case is the first documented ocular Onchocerca infection in dogs outside the western United States. Thus, onchocercosis should be considered in the differential diagnosis of ocular and periocular nodules in dogs also in Europe.

Ocular Onchocerca infections in two dogs in western United States

Two dogs, one from California and one from Arizona, were found to have aberrant infections caused by filarial nematodes of the genus Onchocerca. In both cases, the parasites are localized in or near the eye. In one case the worm was located in the cornea and was surgically removed. In the second case, a very marked granulomatous reaction was induced in the retrobulbar space, mimicking an abscess. This eye was enucleated. The worms in both instances were female, and were gravid, i.e. contained microfilariae in utero, indicating that a male worm(s) had been present and mating had occurred. The exact identity of the species of Onchocerca responsible cannot be determined, although the features observed are most like Onchocerca lienalis of cattle. These cases represent the fourth and fifth such cases reported from the US, and are especially interesting because of the unusual location of the worms, the small number of recognized cases, and the similarity to a recent zoonotic human infection.

Zoonotic Onchocerca (Nematoda:Filarioidea) in the cornea of a Colorado resident

OBJECTIVE

A female patient, resident in the state of Colorado, presented with iritis of the right eye. Slit-lamp examination showed the presence of a thin, threadlike worm entwined in the cornea. The patient was taken to surgery for removal of the parasite.

DESIGN

A case report.

INTERVENTION

A 3-mm-long supertemporal incision was made in the cornea and further dissected until the worm could be grasped and removed by gentle traction.

RESULTS

The worm, a filarial nematode, was identified as a member of the genus Onchocerca, most likely Onchocerca cervicalis, a natural parasite of horses. The patient had an uneventful recovery, and 1 week after surgery, her visual acuity, intraocular pressure, and corneal edema were all resolving.

CONCLUSION

In the United States and elsewhere, most cases of zoonotic filarial infection involving the eye are caused by Dirofilaria or Dipetalonema-like worms. However, the current case was caused by a species of Onchocerca. This is the first case of zoonotic Onchocerca from the eye to be reported, only the second case of zoonotic Onchocerca in the United States, and the seventh case worldwide. The worm was removed surgically, and the patient had an uneventful recovery.