Morphological and Molecular Characterization of the House Dust Fauna and its Forensic Importance for the Kingdom of Saudi Arabia

Abstract

Over 200 mite species, known collectively as House Dust Mites (HDM), are highly synanthropic, living specifically in human dwellings, in mattresses and other upholstered furniture. Their forensic value is enhanced by their microhabitat specificity. Therefore, mites are omnipresent, yet very environmental specific. This applies also but not exclusively to rape or sexual assault cases, since they have a preference for human secretions, including semen and saliva. The correct and accurate identification of mites is key in the analysis of trace evidence. House dust mite species can be linked to indoor crimes and may provide clues on the crime itself. The acaro-fauna of dwellings in the Kingdom of Saudi Arabia (KSA), its biodiversity in general and for Pyroglyphydae (Astigmata) mites in particular have been studied in this research in three climatic regions. The highest abundance of a diverse fauna of Pyroglyphidae mites was found in the Coastal Area and the Highlands. One particular morpho-species was identified as new and it is described in chapter 2. Dermatophagoides saudi sp. nov, was specific to one geographical region in KSA (chapter 3). When associated with a crime, this mite can act as a forensic marker of location, provenance. Moreover, in the investigation of crime scenes and during the forensic analysis of traces the use genetics tools, and specifically microsatellites to identify populations that can link to suspects, victims or locations use more often non-human biological trace evidence; and mites (Acari) are the most ubiquitous traces in crime scenes. Microsatellites are genetic markers characterised by multiple repeats of short nucleotide strings. Perhaps the most challenging step into utilising the house dust fauna as trace evidence is the collection of reasonable number of mites as well as the amounts of mite DNA, that will allow downstream molecular reactions -especially considering the small size of the mites and their samples. This study addressed this challenge and three preservation methods of HDM, for their further DNA extraction and microsatellite studies were considered (Chapter 4). Clearly the method that considers the direct homogenisation of mites from dust, without fixatives was the most promising. DNA of mite specimens was extracted successfully from one and multiple mites (pooled) (Chapter 5). However, the quality and quantity of DNA varied and is positively correlated to the number of mites pooled. v Microsatellite markers previously described for the most ubiquitous domestic mite, Dermatophagoides farinae (Acari, Pyroglyphidae) have been therefore tested in laboratory reared D. farinae (Df), and in D. farinae, D. pteronyssinus and D. saudi sp. nov. from wild colonies, from UK and KSA (Chapter 5). Therefore, cross species specificity was also tested. Primers and their microsatellite regions (as identified previously on the genome) were tested using 125 previously defined primer pairs for D. farinae. Varying PCR conditions were tried. Sixty three percent (63%) of the primers correctly amplified, for the first time microsatellites for D. farinae. A lower number of primers were also successful for the other two species of Dermatophagoides, including the new species from KSA. The idea is to enable future research to determine if mite population genotypes can be linked to specific houses, localities and to hosts from different cultural and geographical backgrounds.