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Q: Can mosquito blood DNA be used to detect crimes?
Krishna: There was a case report from China (1). We really can't confirm the authenticity of this story because it was reported by news agencies:
The police in China caught a burglar in an interesting way. They found dead mosquitoes at the house where the theft had taken place and used the blood stains on the wall to trace him through his DNA. The burglar had squashed the mosquitoes while leaving the house, a report in Global Times said. The burglary took place in Fuzhou, in Fujian province, on June 11, according to the report.
The police said that when they arrived at the house, they found that the door was closed from the inside and that the thief had entered the apartment from the balcony.
Quoting the police, South China Morning Post (SCMP) said that the thief stole several valuable items. The cops also found that the man spent the night at the house after finding some noodles and egg shells in the kitchen.
The blood samples were carefully extracted by the police from the wall and sent for DNA analysis. The police confirmed that the DNA samples belonged to a suspect with a surname Chai who has a criminal record.
Another case was reported from Finland ( 6)
However, one of my friends, who is a forensic scientist who deals with DNA testing, says this could be possible.
And, there are scientific studies regarding this (2, 3, 5).
Human blood extracted from mosquitoes remains viable for DNA analysis up to two days after feeding, research shows (4). Forensic scientists, who can examine human blood from a mosquito's stomach and match the DNA to determine who was bitten. This technique can help police work out who was at a crime scene and in the future, might provide evidence that can be used to convict offenders. But questions remain about how long it takes a mosquito to digest human blood and how long before the DNA becomes unrecognizable. By examining DNA in blood digested by two different species of mosquito over a range of times after feeding, the scientists were able to trace back blood samples to individual volunteers, even after two days of digesting in the mosquito. After roughly three days the mosquitoes completely digested the blood (5).
Criminal traces commonly found at crime scenes may present mixtures from two or more individuals. The scene of the crime is important for the collection of various types of traces in order to find the perpetrator of the crime. Hematophagous mosquitoes (hematophagous arthropods obtain blood from a vertebrate in a variety of ways, ranging from simple biting with chewing-type mouthparts, to penetration of the skin with tubular sucking mouthparts that are of a diameter that is small enough to cannulate blood vessels) found at crime scenes can be used to perform genetic testing of human blood and aid in suspect investigation.
One study showed that human DNA profiles could be obtained from hematophagous mosquitos at 24 h following the blood meal. It is possible that hematophagous mosquitoes can be used as biological remains at the scene of the crime, and can be used to detect human DNA profiles of up to four individuals (2).
In another study (3) a total of 26 female hematophagous mosquitoes were identified as Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus; researchers were able to obtain 11 forensically valid genetic profiles, with a minimum of 0.028203 ng/μL of human DNA. Thus, the results of this study showed that it was possible to correlate human genetic information from mosquitoes with the volunteer reference samples, which validates the use of this information as forensic evidence. Furthermore, they observed mixed genetic profiles from one mosquito. Therefore, it is clearly important to collect these insects indoors where crimes were committed, because it may be possible to find intact genetic profiles of suspects in the blood found in the digestive tract of hematophagous mosquitoes for later comparison to identify an offender and/or exclude suspects.
So mosquito blood DNA can be used to detect crimes under certain conditions.
5. Yuuji Hiroshige, Masaaki Hara, Atsushi Nagai, Tomoyuki Hikitsuchi, Mitsuo Umeda, Yumi Kawajiri, Koji Nakayama, Koichi Suzuki, Aya Takada, Akira Ishii, Toshimichi Yamamoto. A human genotyping trial to estimate the post-feeding time from mosquito blood meals. PLOS ONE, 2017; 12 (6): e0179319 DOI: 10.1371/journal.pone.0179319