Forensic DNA Analysis of Mixed Mosquito Blood Meals: STR Profiling for Human Identification

SIMPLE SUMMARY: Blood-fed mosquitoes found at crime scenes can provide human blood traces for genetic analysis that aid in forensic investigations. Because a mosquito can obtain its blood meal from two or more sources, this study aims to determine whether it is possible to obtain a human DNA profile from the blood meal of a single Culex pipiens mosquito experimentally fed on mixed blood of human male-female or human-mice. Twenty-four human STR loci were amplified over a complete digestion profile post-feeding. Data revealed that full, complete, and partial STR profiles could be obtained from all blood meal types up to 12, 24, and 36 h post-feeding, respectively. The mixed human–animal blood maximized the DNA degradation and, thus, impaired STR identification beyond 36 h until they became poorly detectable at 48 h post-feeding. These results indicate that human DNA can be obtained from mosquito blood meals, even if it is mixed with non-human blood, for up to 36 h post-feeding. ABSTRACT: Mosquito vectors captured at a crime scene are forensically valuable since they feed on human blood, and hence, human DNA can be recovered to help identify the victim and/or the suspect. This study investigated the validity of obtaining the human short tandem repeats (STRs) profile from mixed blood meals of the mosquito, Culex pipiens L. (Diptera, Culicidae). Thus, mosquitoes were membrane-feed on blood from six different sources: a human male, a human female, mixed human male-female blood, mixed human male-mouse blood, mixed human female-mouse blood, and mixed human male-female-mouse blood. DNA was extracted from mosquito blood meals at 2 h intervals up to 72 h post-feeding to amplify 24 human STRs. Data showed that full DNA profiles could be obtained for up to 12 h post-feeding, regardless of the type of blood meal. Complete and partial DNA profiles were obtained up to 24 h and 36 h post-feeding, respectively. The frequencies of STR loci decreased over time after feeding on mixed blood until they became weakly detectable at 48 h post-feeding. This may indicate that a blood meal of human blood mixed with animal blood would contribute to maximizing DNA degradation and thus affects STR identification beyond 36 h post-feeding. These results confirm the feasibility of human DNA identification from mosquito blood meals, even if it is mixed with other types of non-human blood, for up to 36 h post-feeding. Therefore, blood-fed mosquitoes found at the crime scene are forensically valuable, as it is possible to obtain intact genetic profiles from their blood meals to identify a victim, a potential offender, and/or exclude a suspect.