Efficacy of a spot-on formulation containing moxidectin 2.5%/imidacloprid 10% for the treatment of Cercopithifilaria spp. and Onchocerca lupi microfilariae in naturally infected dogs from Portugal

Development of an indirect ELISA for the serodiagnosis of canine infection by Onchocerca lupi

Onchocerca lupi is a zoonotic filarioid parasite of dogs and cats with widespread distribution. A specific non-invasive diagnostic assay for the detection of O. lupi infections remains unavailable. This study aimed to assess the accuracy, specificity, and sensitivity of an ELISA test designed using nine peptides from two O. lupi proteins. Sera (n = 54) collected from O. lupi infected dogs from endemic areas (Portugal and USA), alongside sera from dogs positive for Dirofilaria immitis, D. repens, Cercopithifilaria bainae, and Acanthocheilonema reconditum (n = 53) from a non-endemic area for O. lupi, as well as from helminth-free dogs (n = 60), were tested. The checkerboard titration method was applied for the optimization of peptide concentrations and conjugate anti-dog dilutions. Sensitivity, specificity, and optimal cut-off values were calculated using ROC curve analysis. All peptides reacted against sera of O. lupi, with no correlation between optic density (OD) values and microfilariae (mfs) loads. Sensitivity and specificity values ranging from 85.45 to 100%, and 88.89% to 100%, respectively, were recorded for all peptides examined, with 100% specificity and sensitivity observed for peptides 40_3, 40_5, 130_3, 120_3 and 40_1, 130_5, respectively. The maximum cut-off value was observed for peptides 40_5 (0.765) and 40_3 (0.708). Testing of sera from dogs positive for other filarioids resulted in lower OD values (up to 1.565) for peptides 40_3 and 40_5 when compared with O. lupi (up to 2.929). The availability of this assay will be of value in epidemiological studies of canine O. lupi infection in both endemic and non-endemic areas, and in assessing the risk for zoonotic transmission.

Development and validation of a long-read metabarcoding platform for the detection of filarial worm pathogens of animals and humans

BACKGROUND

Filarial worms are important vector-borne pathogens of a large range of animal hosts, including humans, and are responsible for numerous debilitating neglected tropical diseases such as, lymphatic filariasis caused by Wuchereria bancrofti and Brugia spp., as well as loiasis caused by Loa loa. Moreover, some emerging or difficult-to-eliminate filarioid pathogens are zoonotic using animals like canines as reservoir hosts, for example Dirofilaria sp. 'hongkongensis'. Diagnosis of filariasis through commonly available methods, like microscopy, can be challenging as microfilaremia may wane below the limit of detection. In contrast, conventional PCR methods are more sensitive and specific but may show limited ability to detect coinfections as well as emerging and/or novel pathogens. Use of deep-sequencing technologies obviate these challenges, providing sensitive detection of entire parasite communities, whilst also being better suited for the characterisation of rare or novel pathogens. Therefore, we developed a novel long-read metabarcoding assay for deep-sequencing the filarial nematode cytochrome c oxidase subunit I gene on Oxford Nanopore Technologies' (ONT) MinION™ sequencer. We assessed the overall performance of our assay using kappa statistics to compare it to commonly used diagnostic methods for filarial worm detection, such as conventional PCR (cPCR) with Sanger sequencing and the microscopy-based modified Knott's test (MKT).

RESULTS

We confirmed our metabarcoding assay can characterise filarial parasites from a diverse range of genera, including, Breinlia, Brugia, Cercopithifilaria, Dipetalonema, Dirofilaria, Onchocerca, Setaria, Stephanofilaria and Wuchereria. We demonstrated proof-of-concept for this assay by using blood samples from Sri Lankan dogs, whereby we identified infections with the filarioids Acanthocheilonema reconditum, Brugia sp. Sri Lanka genotype and zoonotic Dirofilaria sp. 'hongkongensis'. When compared to traditionally used diagnostics, such as the MKT and cPCR with Sanger sequencing, we identified an additional filarioid species and over 15% more mono- and coinfections.

CONCLUSIONS

Our developed metabarcoding assay may show broad applicability for the metabarcoding and diagnosis of the full spectrum of filarioids from a wide range of animal hosts, including mammals and vectors, whilst the utilisation of ONT' small and portable MinION™ means that such methods could be deployed for field use.

Cercopithifilaria spp. of dogs: little known but prevalent filarioids beneath the skin

Filarioids of the genus Cercopithifilaria are little studied, yet widespread parasites, that are relatively unique in being one of the very few nematodes transmitted by hard ticks. These filarioids live in the subcutis while microfilariae are found in the dermis. Definitive hosts include domestic dogs as well as a wide range of vertebrates, such as ruminants, non-human primates, murids, marsupials, porcupines, viverrids, bears and lagomorphs. The genus Cercopithifilaria contains three taxa (i.e. C. bainae, C. grassii and a yet undescribed species, namely Cercopithifilaria sp. II) that are known to infect dogs worldwide, with their occurrence overlapping the distribution of the main tick vector, Rhipicephalus sanguineus sensu lato. In recent decades, more attention has focused on these filarioids since they have been associated with clinical signs of infection, such as dermatitis, chronic polyarthritis and cutaneous cysts, and possibly with facilitating infections caused by other tick-borne pathogens. Nevertheless, these parasites remain largely underdiagnosed in clinical practice due to the lack of awareness of veterinary practitioners and to major obstacles to their diagnosis. In this review, we have assessed currently available data on Cercopithifilaria spp. infecting dogs worldwide and discussed the biological, clinical and epidemiological aspects of these filarioids, with the overall aim to gain a better understanding of their potential role in skin diseases.

Autochthonous Onchocerca lupi infection of a domestic dog in Austria

Onchocerca lupi is an emerging canine ocular pathogen with zoonotic potential. In Europe, known endemic areas are the Iberian Peninsula and Greece, but the parasite has also been found in Romania, Hungary, and Germany. A 5-year-old Irish Wolfhound was presented in August 2021 with ocular discharge. A subconjunctival granulomatous nodule containing several nematode fragments was removed. Molecular analysis of the mitochondrial cytochrome c oxidase subunit I gene confirmed the presence of O. lupi genotype 1. This is the first report of autochthonous O. lupi infection in a dog from Austria.

Dermal microfilariae of dogs, jackals and cats in different regions of Iran

Background

Due to the complexity of retrieving skin-dwelling microfilariae, filarioids of dogs presenting dermal microfilariae (e.g. Cercopithifilaria spp., Onchocerca lupi) are relatively unknown compared to Dirofilaria spp. and Acanthocheilonema spp. whose microfilariae circulate in the blood. Although Cercopithifilaria spp. and O. lupi filarioids are distributed worldwide, there is a paucity of information on their occurrence in Iran. The aim of this study was to investigate these filarioids in a large population of dogs from different regions of Iran.

Methods

From October 2018 to September 2020, skin biopsies were obtained from dogs housed in shelters (n = 557) and privately owned dogs (n = 26) in seven provinces of Iran (Hamedan, Kermanshah, Yazd, Mazandaran, Khuzestan, Lorestan, Esfahan), as well as from three road-killed jackals (Canis aureus) and three cats (Felis catus) in Hamedan province. The skin biopsies were first soaked in saline solution at room temperature overnight, and examined for dermal microfilariae under the microscope. Positive skin specimens and sediments were tested by PCR for a 304-bp region of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene and amplicons were sequenced.

Results

Microfilariae of Cercopithifilaria spp. were found in skin biopsies of 32 of the 583 (5.5%) dogs tested, with infection rates of up to 25% in Kermanshah. No microfilariae were recovered from skin biopsy samples collected from dogs in Khorramabad and Ahvaz, nor from the examined jackals and cats. None of the privately owned dogs were found to be infected. Morphologic and morphometric characteristics of the microfilariae were consistent with C. bainae. Eighteen skin samples were positive for the cox1 gene, of which 15 sequences showed a nucleotide identity of 100% and three of 93.4% with the reference sequence of C. bainae available in GenBank (haplotype I; GenBank accession number: JF461457).

Conclusions

The data from this study broadens current knowledge on the geographical distribution of C. bainae in dogs in Middle Eastern countries. Further studies on different wild canine species in the country (e.g. jackal, fox, wolf) could provide further information on the epidemiology of these filarioids. A particular focus should be put on zoonotic O. lupi given the reports of its presence in human patients from this country.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05141-2.