The detection of an Apicomplexan (order Neogregarinorida) pathogen in the dust mite Acarus siro – a novel host-pathogen relationship : Implication to dust mite life cycle and allergen extract purity

Abstract

Rationale While evaluating the purity of mite cultures using degenerate primers for 18S rDNA, a 1710bp region amplified from cultures of Acarus siro showed close sequence homology to neogregarine parasites instead of the mite 18S sequence. Cultures where this was amplified from had mites that were relatively dormant. They were also significantly slower to expand compared to non-infected cultures. Methods The identity of the parasite was further investigated through microscopic observation and phylogenetic analysis using parsimony and maximum likelihood analysis with 23 other protists. Results Sequence divergence between the putative parasite reported herein and an uncultured alveolate was 6.6% and between the parasite and Ophriocystis elektroscirrha (neogregarine parasite of the Monarch butterfly) was 8.1%. Sequence divergence between the putative neogregarine parasite and the nearest eugregarine taxon, Monocystis agilis, is 17.5%. Slide preparations of mites cleared with lactic acid revealed larger structures compatible with gametocyts. Gametocysts were uniform, oval and measured 20×17 μm in size and contained 8–13 hyaline structures suggestive of developing oocysts. Conclusions The placement of the unknown organism is highly suggestive that this is a previously unrecognized and unnamed neogregarine parasite that infects the tissue of A. siro. Based on its phylogenetic placement in the trees within the neogregarine clade and the structures observed under light microscopy, the pathogen is suggested to be in the order Neogregrinorida, making this a novel host-parasite relationship in the Acari. The identification of such a parasite in mites has implications on purity of allergen extracts derived from dust mite cultures.