The metagenomic approach and causality in virology

Castrignano, Silvana Beres; Nagasse-Sugahara, Teresa Keico

Since then, some modifications of these postulates have been proposed, including the following: the acknowledgment of viruses as infectious agents (they were unknown in Koch's time), 7, 19 of the importance of the study of antibodies (presence and time of appearance), 19 of the possibility of disease prevention using vaccines against the virus, 10 of the importance of epidemiological studies, 10 and of the concept that several factors, and not only a single cause, can contribute to disease development. 7 Owing to the advances in molecular biology techniques, proposals to amend Koch's postulates from the 80s onwards included criteria based on microbial genetics. 9, 13, 16 Among these recent propositions, both the criteria of Mokili et al, 16 based on the comparison of metagenomic characteristics among infected and healthy individuals, and the criteria of Lipkin, 13 who grouped laboratory, clinical and epidemiological data into three certainty levels to establish an association between pathogens and diseases, considered the inoculation of the infectious agent in a healthy individual as INTRODUCTION a criterion for the confirmation of causality (this criterion was inherited from Koch's postulates). However, because of ethical issues, it is not possible to inoculate a suspected pathogen in human beings, and with exceptions such as the SARS-related human coronavirus, few etiological agents have a susceptible experimental animal model. 2 Moreover, Lipkin 13 suggested an alternative to this rule from Koch's postulates and indicated that a causal association can be confirmed if the disease can be attenuated or prevented with the use of microorganismspecific vaccines, drugs, or antibodies.