Human DNA from Mosquitos?

So let me tell you all a little bit about me. I am a PhD Candidate at Sam Houston State University in the forensic science program. My concentration is in Forensic DNA and my research topic is human identification (HID) following mass disasters. However, I figured I should probably branch off to new topics, but first I thought I would start with an interesting read I found a little while ago titled, “Identification of person and quantification of human DNA recovered from mosquitoes (Culicidae)” by Garan Curic, et al. The article is a short communication about obtaining human DNA from the gut of mosquitoes. The study apparently stemmed from a case of a dead body found on the beach and the only evidence linking the victim to the suspect was a mosquito found at the suspect’s house that contained the blood of the victim. The use of human DNA from mosquitoes may sound weird. However, forensic science is all about the probative value of evidence. Any little piece of evidence is important if it can help tell the story of a crime committed, especially if it’s the only probative evidence found. I thought it would be a good article for those of you interested in forensic DNA because it touches on common DNA analyses for HID and a common problem that we face, such as DNA degradation.

Common DNA analysis in crime labs consists of (1) evidence collection and sampling, (2) DNA purification, (3) quantification, (4) amplification, and (5) short tandem repeat (STR) typing. The main criteria for successful STR typing is single source DNA of sufficient quantity and quality. Extracting human DNA from the gut of a mosquito could be an issue. We work with nanograms and picograms of DNA, and although that seems very small, degraded or low amounts of DNA makes STR typing more difficult. According to the article, the very little amount of human DNA in the gut of a mosquito is digested by digestive enzymes and bacterial activity. However, they were able to obtain full profiles up to 32-48 hours after feeding. Any time longer than that, they were only able to obtain partial DNA profiles. They were able to obtain more reportable alleles after reanalysis of these samples by increasing the number of cycles during amplification and using a mini-STR kit, which are common techniques used to overcome DNA degradation. I found it odd that they discussed DNA profiling before quantitation but anyway, the quantity of human DNA decreased as the digestion period increased. Low amounts of human DNA were reported (<1pg/uL in some cases). However, successful STR typing usually requires 500pg/uL to 1ng/uL of DNA. The solution is concentrating the purified DNA to obtain more DNA per microliter.

In conclusion, human DNA obtained from the gut of mosquitoes is suitable for STR typing more than three days after the feeding. I thought that was pretty interesting. It reminds me of another article that was able to obtain DNA from the worm in tequila. Look it up if you’re interested. Here’s a link to a brief description about it: http://www.scienceagogo.com/news/20100110033959data_trunc_sys.shtml. By the way, that’s sorta the basis of my research with Dr. Sheree Hughes-Stamm.