Abstract
BackgroundCutaneous dirofilariosis is a canine mosquito-borne zoonosis that can cause larva migrans disease in humans. Dirofilaria repens is considered an emerging pathogen occurring with high prevalence in Mediterranean areas and many parts of tropical Asia. In Hong Kong, a second species, Candidatus Dirofilaria hongkongensis, has been reported. The present study aimed to compare mitochondrial genomes from these parasites and to obtain population genetic information.Methods and FindingsComplete mitochondrial genomes were obtained by PCR and Sanger sequencing or ILLUMINA sequencing for four worms. Cytochrome oxidase subunit 1 sequences identified three as D. repens (all from Europe) and one as C. D. hongkongensis (from India). Mitochondrial genomes have the same organization as in other spirurid nematodes but a higher preference for thymine in the coding strand. Phylogenetic analysis was in contradiction to current taxonomy of the Onchocercidae but in agreement with a recent multi-locus phylogenetic analysis using both mitochondrial and nuclear markers. D. repens and C. D. hongkongensis sequences clustered together and were the common sister group to Dirofilaria immitis. Analysis of a 2.5 kb mitochondrial genome fragment from macrofilaria or canine blood samples from Europe (42), Thailand (2), India (1) and Vietnam (1) revealed only small genetic differences in the D. repens samples including all European and the Vietnam sample. The Indian C. D. hongkongensis and the two Thai samples formed separate clusters and differences were comparatively large.ConclusionGenetic differences between Dirofilaria spp. causing cutaneous disease can be considerable whereas D. repens itself was genetically quite homogenous. C. D. hongkongensis was identified for the first time from the Indian subcontinent. The full mitochondrial genome sequence strengthens the hypothesis that it represents an independent species and the Thai samples might represent another cryptic species, Candidatus Dirofilaria sp. ‘Thailand II’, or a quite divergent population of C. D. hongkongensis.
Highlights
The genus Dirofilaria contains several filarial nematode species that use various carnivores as definitive hosts
While D. immitis is distributed in the Americas, Mediterranean area, many parts of Asia and Africa as well as Australia, D. repens is limited to the old world with endemic areas in Southern and Eastern Europe, many parts of Asia and presumably Africa, there is only sparse information for the latter continent [4]
A new Dirofilaria species, Candidatus Dirofilaria hongkongensis has been proposed as a causative agent of subcutaneous or subconjunctival dirofilariosis in humans in Hong Kong and was detected in dogs [5, 6]
Summary
The genus Dirofilaria contains several filarial nematode species that use various carnivores as definitive hosts. Wang et al [8] showed that the odds of D. immitis prevalence increased significantly with increased temperature and precipitation in the USA, which suggests that the parasites will be found often in tropical climate zones. This is further corroborated by the fact that most of the known Dirofilaria species described currently have only been reported from countries with tropical climate [9, 10]. The present study aimed to compare mitochondrial genomes from these parasites and to obtain population genetic information
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