Abstract
BackgroundThe Onchocercidae is a family of filarial nematodes with several species of medical or veterinary importance. Microfilariae are found in the blood and/or the dermis and are usually diagnosed in humans by microscopy examination of a blood sample or skin biopsy. The main objectives of this study were to evaluate whether filariae DNA can be detected in faecal samples of wild non-human primates (NHPs), whether the detected parasites were closely related to those infecting humans and whether filarial DNA detection in faeces is associated with co-infections with nematodes (Oesophagostumum sp. and Necator sp.) known to cause blood loss while feeding on the host intestinal mucosa.MethodsA total of 315 faecal samples from 6 species of NHPs from Cameroon and Gabon were analysed. PCRs targeted DNA fragments of cox1 and 12S rDNA genes, to detect the presence of filariae, and the internal transcribed spacer 2 (ITS2), to detect the presence of Oesophagostomum sp. and Necator sp. infections.ResultsAmong the 315 samples analysed, 121 produced sequences with > 90% homology with Onchocercidae reference sequences. However, 63% of the 12S rDNA and 78% of the cox1 gene sequences were exploitable for phylogenetic analyses and the amplification of the 12S rDNA gene showed less discriminating power than the amplification of the cox1 fragment. Phylogenetic analyses showed that the cox1 sequences obtained from five chimpanzee DNA faecal samples from Gabon and two from Cameroon cluster together with Mansonella perstans with high bootstrap support. Most of the remaining sequences clustered together within the genus Mansonella, but the species could not be resolved. Among the NHP species investigated, a significant association between filarial DNA detection and Oesophagostomum sp. and Necator sp. infection was observed only in gorillas.ConclusionsTo our knowledge, this is the first study reporting DNA from Mansonella spp. in faecal samples. Our results raise questions about the diversity and abundance of these parasites in wildlife, their role as sylvatic reservoirs and their potential for zoonotic transmission. Future studies should focus on detecting variants circulating in both human and NHPs, and improve the molecular information to resolve or support taxonomy classification based on morphological descriptions.
Highlights
The Onchocercidae is a family of filarial nematodes with several species of medical or veterinary importance
polymerase chain reaction (PCR) targeting the 12S rDNA and cox1 mitochondrial genes of filariae were run for all samples selected. 12S rDNA and cox1 sequences were obtained from 20 human patients and 7 of them were added for comparisons to the phylogenetic trees
Among the 315 samples analysed, 121 were positive by PCR (38%): 31 samples were positive for 12S rDNA only, 59 samples were positive for cox1 only, and 31 for both gene fragments (Table 2)
Summary
The Onchocercidae is a family of filarial nematodes with several species of medical or veterinary importance. Microfilariae are found in the blood and/or the dermis and are usually diagnosed in humans by microscopy examination of a blood sample or skin biopsy. Species belonging to genera such as Loa, Onchocerca, Wuchereria, Brugia and Mansonella are responsible for human or animal diseases such as loiasis, onchocerciasis or lymphatic filariasis. Some of these species are found in both humans and non-human primates (NHPs) [2]. If one considers the main species parasitizing humans, mf are detected by light microscopy examination of a blood sample (Loa loa, Wuchereria bancrofti, Brugia malayi and Mansonella perstans), or of a skin biopsy (Onchocerca volvulus and M. streptocerca), or both (M. ozzardi) [3]. Besides the microscopical identification of the parasites, various other techniques detecting antigens, antibodies or parasitic DNA are available and used either for the individual diagnosis or to assess the infection endemicity levels in communities
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