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

Abstract

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.

Figure 1

Onchocerca lupi. A) Anterior part, female, lateral view. B) Cephalic extremity, female, lateral (B1) and dorsoventral view (B2), respectively. C) Oesophago-intestinal junction, male, lateral view. D) Tail, male, ventral view. E) Posterior end, male, sinistral view. F) Right spicule, dextral view. G) Terminal part of female genital system, lateral view; note microfilariae in the ovejector. Scale-bars in micrometers.

Figure 2

Onchocerca lupi, light microscopy. A) Cephalic extremity, male, lateral view. B) Posterior end and right spicule, dextral view. C) Region of vulva, lateral view; note oesophago-intestinal junction (arrowhead) and vulva (arrow). D1-3) Variations in the structure of the cuticle along the body of a female: at the level of appearance of first ridges and striae (D1), at the level close to the anterior body end, characterized by full formation of ridges and striae (D2), and from a mid-body fragment (D3); note cuticular ridges (arrowheads) and striae (arrows). E) Microfilaria in ovejector. Scale-bars in micrometers.

Figure 3

Onchocerca lupi, SEM. A) Cephalic extremity, female, lateral view; note labial papillae (arrowheads), cephalic papillae (arrows) and amphid (asterisk). B) Cephalic extremity, female, apical view; note labial papillae (arrowheads), cephalic papillae (arrows) and amphid (asterisk). C) Posterior end, male, dextral view; note caudal papillae (arrowheads) and the abnormally situated eight papilla. D) Vulva. E & F) Cuticular ridges on anterior and mid-body fragments, respectively, note the interruption of cuticular ridges in the lateral fields. Scale-bars in micrometers.

Figure 4

Ocular and periocular tissue, histopathology. Collapsed eye with four sections of Onchocerca lupi in the subconjunctival tissue (arrows) (H&E, scale-bar = 500 μm).

Figure 5

Periocular tissue, histopathology. In the subconjunctival sac there is a section of a coiled female of Onchocerca lupi, note the uteri filled with eggs containing well-developed microfilariae (arrows) or eggs in earlier stage of development (arrowheads), a faint intestine, atrophied muscle and lateral hypodermal chords (H&E, scale-bar = 100 μm).

Figure 6

Connective periocular tissue of a dog, histopathology. Transverse section of an adult male of Onchocerca lupi, note the intestine below the vas deferens (H&E, scale-bar = 20 μm).

Figure 7

Connective periocular tissue of a dog, histopathology.Onchocerca lupi microfilaria (arrow) near a small vessel (H&E, bar = 50 μm).