Cutaneous Distribution and Circadian Rhythm of Onchocerca lupi Microfilariae in Dogs

Abstract

BackgroundAmong the arthropod-borne nematodes infesting dogs, Onchocerca lupi (Spirurida: Onchocercidae) is of increasing zoonotic concern, with new human cases of infection diagnosed in Turkey, Tunisia, Iran and the USA. Knowledge of the biology of this nematode is meagre. This study aimed at assessing the distribution and periodicity of O. lupi microfilariae from different body regions in naturally infested dogs.Methodology/Principal FindingsSkin samples were collected from six dogs infested with O. lupi but without apparent clinical signs. Two skin samples were collected from 18 anatomical regions of dog 1 at necropsy. In addition, single skin biopsies were performed from the forehead, inter-scapular and lumbar regions of dogs 2–6, in the morning, afternoon, and at night. Two aliquots of the sediment of each sample were microscopically observed, microfilariae counted and morphologically and molecularly identified. Most of the 1,667 microfilariae retrieved from dog 1 were in the right ear (59.6%), nose (26.5%), left ear (6.7%), forehead (3.0%), and inter-scapular (2.9%) regions. In dogs 2–6, the overall mean number of microfilariae was larger on the head (n = 122.8), followed by the inter-scapular (n = 119.0) and lumbar (n = 12.8) regions. The overall mean number of microfilariae was larger in the afternoon (153.4), followed by night (75.4) and morning (25.8).Conclusions Onchocerca lupi microfilariae were more common in the head (i.e., ears and nose) than in the remaining part of the dog's body, indicating they tend to aggregate in specific body regions, which are the best sites to collect skin samples for diagnostic purposes. The periodicity pattern of microfilariae of O. lupi and their concentration in specific body regions is most likely a result of the co-evolution with their as-yet-unknown vector. The detection of skin microfilariae in asymptomatic animals, suggests the potential role of these animals as carriers and reservoirs of O. lupi.

The Emergence of ZoonoticOnchocerca lupiInfection in the United States – A Case-Series

“…Onchocerca lupi appears to lack the host-specificity found in many other filarial parasites. It is known to reproduce in dogs and cats [17, 21] and has been found to do so in humans in these case-series. This finding could have serious implications for efforts to reduce the risk of infection in humans as there could be other, as yet not identified mammalian species that could serve as a reservoir to maintain risk of infection in humans.…”

Aberrant laryngeal location of Onchocerca lupi in a dog

“…in the trachea of a dog from Greece [17]. The diagnosis of O. lupi infection relies on the ophthalmologic examination of clinically suspect dogs, along with the detection of microfilariae from skin snip biopsy sediment performed on the head, ears and nose region [18]. Microfilariae have to be differentiated from those of other filarial nematodes, namely Cercopithifilaria bainae, Cercopithifilaria grassi, Cercopithifilaria sp.…”

“…II or Dirofilaria spp. [18]. Additionally, imaging tools such as ultrasounds scan, computed tomography and magnetic resonance imaging can be used [19].…”

Intraocular localization ofOnchocerca lupiadult worm in a dog with anterior uveitis: A case report

“…As the ocular signs of this parasitic disease are not pathognomonic, especially in the acute cases, and the skin snips obtained from the periocular skin are not always rewarding, the diagnosis also may be made by the presence of visible white subconjunctival thread‐like parasites or fragments. However, recently published material suggests that skin snip tests from the patient's ear tip are the most sensitive site for diagnosis . In chronic cases, diagnosis can be made by periocular skin snips collected from the head and by histopathology of the subconjunctival nodules or cysts .…”