Microbial Forensics Host Factors

Steven e. Schutzer

Department of Medicine, University of Medicine and Dentistry of New Jersey—New Jersey Medical School, Newark, New Jersey

Consider the diagnosis of a disease caused by a biothreat. Multiple questions arise immediately. One question is whether it is a natural event or an intentional attack. Knowledge of the host response can potentially answer some questions depending upon the pathogen involved. Some of these questions include who else was exposed, who else may have been vaccinated for protection, how long ago was the person infected, and were other persons who are close to the individual also infected before or after the index case? Aside from public and personal health concerns, these questions seek to categorize individuals as possible victims versus perpetrators. It is the aim of this chapter to present the elements of the host response in a simplified fashion that in the right context has high potential to bring answers to these questions.

Microbial forensics has a primary aim to identify the biological agent, its source, and the individuals responsible for a biothreat event.1 Analytic approaches differ when the suspected biothreat agent is encountered in a container or the environment, as opposed to a human or animal. Trace element, pollen, growth media, latent fingerprint, and microbial and nonmicrobial nucleic acid analysis are all applicable to the container and environmental sample.2 However, once the microbe or its toxin is in the living host, it is no longer possible to analyze all of the preceding items except the microbial nucleic acid. Nevertheless, the host response to the biological agent is available for analysis. This is akin to other forensic studies where physical traces of bite marks, scratches, wound trajectories, and sizes of wounds are often surrogate evidence of the teeth, fingernails, and bullets.3 The forensic pathologist is already familiar with these. Those involved with epidemiologic and diagnostic issues will be more familiar with the host response. In the context of microbial forensics it is important to integrate all of these with intelligence information so that an authenticated piece of a puzzle may be included in the analytical and attribution picture.

Microbial Forensics

Copyright © 2005 by Elsevier Inc. All rights of reproduction in any form reserved.

The host response to a foreign substance is often a well orchestrated series of events designed to protect the individual from harm. Modern techniques help us elucidate the pathways and components of the host response. The immune system and its components are a mainstay of our protection against infections and malignancies.4,5 Inflammation is often an unpleasant side effect as the immune system contains and eradicates a microbe or foreign tissue. Specific arms of the immune system can be used as markers in favor or against the presence of an infection. The humoral or antibody response to an invading microbe is an example. Some of the antibodies that are produced have a protective effect with other parts of the immune-inflammatory system and are responsible for eradicating the infection. Other antibodies may not be as effective in this role. However, in their ability to recognize unique and specific structures of a microbe, they serve as beacons that a microbe was recently present or was present in the distant past. Substances such as antibiotics which can rapidly kill a microbe may modify the immune response by removing the infectious driving force for a full-scale response. In clinical medicine and veterinary medicine, measurement of the immune response helps the diagnostician decide what infection was present and how recently. In these situations the intention is to provide treatment. For other pieces of the puzzle, the forensic scientist may exploit parts of the immune response to discover who is likely a victim of an attack and who might be responsible. This chapter will discuss the basics of the host immune response that can have utility in the microbial forensic sense. Examples will provide a sense of what information is achievable and what is not likely to provide clues with a high degree of certainty.

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