Evaluation Of The Etiologic Agent

The type of pathogen or toxin detected in an outbreak can signal intentional misuse. For example, Staphylococcal enterotoxin B (SEB) has been weaponized due to its relative stability. But Staphylococcal enterotoxin A is more commonly found as a naturally occurring cause of foodborne illness. Therefore, the occurrence of illness due to SEB should raise considerable interest in an outbreak investigation.

Presence of multiple pathogens within a clinical specimen or within one outbreak of illness can also indicate unnatural occurrence. Analysis of preserved human tissue specimens from Sverdlovsk contained four different strains of the anthrax bacillus.20 Such multistrain occurrence is a highly improbable event in a naturally occurring disease outbreak, and was considered strong evidence that the anthrax was manufactured.

Microbes are dynamic organisms, and are therefore constantly changing in response to natural selection pressures in their environment. It is often possible to determine the laboratory or geographic origin and character of microbes by use of strain typing, molecular biology tools, and antibiotic resistance patterns. For example, there are seven major serotypes of foot-and-mouth disease virus, and these have definite geographic distributions throughout the world. Ribotyping of Yersinia pestis was useful in ruling out a terrorist attack by Kashmir separatists in the pneumonic plague epidemic in Surat in 1994. Similarly, when parties to the war in Northern Bosnia accused each other of biological warfare during the 1995 tularemia epidemic, strain typing revealed the etiologic agent to be type B Francisella tularensis var palaeartica, which is endemic in Bosnia.65 Pathogen banks at various diagnostic reference centers and collaborating centers associated with the OIE and WHO maintain strain typing and molecular characterization information.

If the etiologic agent differs from agents found naturally, detailed molecular analysis may be able to indicate whether or not the organism has been genetically or otherwise modified.

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