To better plan for forensic investigation strategies of an event, capitalizing on past experiences can shed light on current practices and the direction of future research. Two illustrative examples, neither of them bioterrorism acts, are the Sverdlovsk anthrax incident and the case of a dentist with AIDS who may have infected patients with HIV Both required epidemiological investigation and molecular biology to resolve.
The first case explores the sources of anthrax spores from an anthrax epidemic. In April 1979 in Sverdlovsk, Russia, a loud explosion occurred at a military compound. Several days later, residents downwind from this compound developed high fever and had difficulty breathing. The persons affected lived or worked downwind and within a narrow zone, approximately 4 km south and east of the military facility. At least 200 patients died. Medical doctors identified the outbreak as pulmonary anthrax. Government officials, in contrast, declared that the outbreak was caused by consumption of meat from a cow suffering from the disease. Thus, there was a discrepancy regarding the cause of the anthrax epidemic; either it was due to consumption of tainted meat or it was the result of a release of aerosolized anthrax from a bioweapons factory (a Biological Weapons Convention treaty violation).
Patient fatalities did not display the symptoms of gastric or skin anthrax, which would likely have been the result of handling or eating contaminated beef. Investigations also revealed that sheep and cattle in six different villages as far as 50 km southeast of the facility also died of anthrax. Autopsies of human victims revealed severe pulmonary edema and toxemia. DNA analysis suggested that the patients were exposed to several anthrax strains simultaneously, which is atypical for a natural infection in a cow. The available evidence supported that the cause of the disease was anthrax from an accidental release from the compound, a Russian bioweapons facility.39,40 The release of the anthrax spores apparently occurred only once and may have taken no more than a few minutes.
The second case describes attempts to determine the cause and source of HIV in patients that implicated a Florida dentist with AIDS. A number of people from Florida became HIV-infected in the late 1980s. Their histories did not indicate lifestyles or practices that would put them at high risk for exposure to HIV41 An epidemiologic investigation indicated that the HIV transmission occurred during invasive dental care from a dentist with AIDS. The dentist was first identified as HIV-positive in 1986.4243 The HIV-positive patients had invasive procedures performed by the dentist after he had been diagnosed with AIDS. The precise mode of HIV transmission was unknown; the only data implicating him as the source are that multiple patients who contracted HIV visited that same dentist.
To provide further insight into whether or not the dentist transmitted HIV to his patients, bioinformatics/phylogenetics were employed. DNA sequence data from the HIVs from lymphocytes from each of the patients, the dentist, a local control group, and an outgroup were aligned and compared. The basis of the phylogenetic comparison is that sequences that are more similar are more closely related and share a more recent common ancestry than the sequences from other lineages.43,44 The analysis showed that the HIV nucleotide sequences from a number of the patients were closely related (although not exactly the same) to those from the dentist and were distinct from viruses obtained from control patients living in the same geographic area as the dental practice. The data strongly support (but not necessarily conclusively) that the patient HIV is closely related to the HIV from the dentist contracted the virus from the dentist.45
For other microorganisms that do not mutate as rapidly, more similar sequences may be required for an association. Further, a lower evolutionary rate of divergence suggests that a larger segment of the genome of many microbes must be sequenced (or at least typed for the informative sites). Thus, it is important to increase efforts in genetics studies to gain a better understanding of the degree of variation among pathogenic agents so that circumstantial evidence for attribution can be strengthened.
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