Abstract
The transmission of zoonotic filarial parasites by black flies has so far been reported in the Chiang Mai and Tak provinces, Thailand, and the bites of these infected black flies can cause a rare disease—human zoonotic onchocerciasis. However, species identification of the filarial parasites and their black fly vectors in the Chiang Mai province were previously only based on a morphotaxonomic analysis. In this study, a combined approach of morphotaxonomic and molecular analyses (mitochondrial cox1, 12S rRNA, and nuclear 18S rRNA (SSU HVR-I) genes) was used to clarify the natural filarial infections in female black flies collected by using human and swine baits from two study areas (Ban Lek and Ban Pang Dang) in the Chiang Mai province from March 2018 to January 2019. A total of 805 and 4597 adult females, belonging to seven and nine black fly taxa, were collected from Ban Lek and Ban Pang Dang, respectively. At Ban Lek, four of the 309 adult females of Simulium nigrogilvum were positive for Onchocerca species type I in the hot and rainy seasons. At Ban Pang Dang, five unknown filarial larvae (belonging to the same new species) were detected in Simulium sp. in the S. varicorne species-group and in three species in the S. asakoae species-group in all seasons, and three non-filarial larvae of three different taxa were also found in three females of the S. asakoae species-group. This study is the first to molecularly identify new filarial species and their vector black fly species in Thailand.
Highlights
Black flies (Diptera: Simuliidae) are a group of small hematophagous insects which vector several pathogens that are responsible for animal and human diseases, human onchocerciasis caused by the parasitic worm Onchocerca volvulus [1]
Our study revealed that S. nigrogilvum, collected at Ban Lek is a natural vector of O. sp. type I, which has previously been isolated from S. bidentatum in Japan and S. nigrogilvum in western Thailand [15,16]
We found that the positive female of S. sp. in the S. varicorne species-group (BPD1) was most likely to be a new black fly species belonging to the S. chumpornense subgroup
Summary
Black flies (Diptera: Simuliidae) are a group of small hematophagous insects which vector several pathogens that are responsible for animal and human diseases, human onchocerciasis (river blindness) caused by the parasitic worm Onchocerca volvulus [1]. Several black fly species have been reported to vector filarial worms of the genus Onchocerca that cause zoonotic onchocerciasis in humans. This infection is generally caused by a single immature adult worm of animal origin [2]. 37 human cases of zoonotic onchocerciasis have been reported globally, including in Europe, North America, North Africa, and East Asia [3]. O. jakutensis, which is a natural parasite of red deer, was reported in Poland [4].
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