The origin of major human infections and the crucial role of person-to-person spread

Abstract

In discussions of the origin of new infectious diseases, prominence is usually given to dramatic infections acquired from animals (Lassa fever, Marburg and Ebola viruses) or from the environment (legionellosis). But these infections do not spread from human to human, and their impact on mankind can never be catastrophic. If a new infectious agent is to pose a major threat to the human species, it will need to kill tens or hundreds of millions of people over a short period of time (a few years), before vaccines and antimicrobial agents can be developed or effective blocks to transmission established. The 1918 influenza pandemic (total deaths about 20 million) almost came into this world-shaking category, but many of the deaths were presumably due to secondary bacterial pneumonia and this was the pre-antibiotic era. A similar airborne pandemic occurring today could spread globally within weeks by air transport and would have a greater impact. Smallpox arose long before the world became one from an infectious disease point of view, and although it caused devastating epidemics it did not have the opportunity to develop into the ‘major threat’ category. A significant proportion of people recovered, less virulent strains of virus (variola minor) appeared, and an effective vaccine not only kept it under control in many continents but finally eliminated it from the world. The plague (Yersinia pestis) influenced the course of history in Asia and Europe [1] but oven in its respiratory form could not in those days be transferred rapidly from continent to continent.

Introduction: Conceptualizing and Partitioning the Emergence Process of Zoonotic Viruses from Wildlife to Humans

“…The arboviruses, yellow fever virus, and the four dengue serotypes circulate in a human-tohuman transmission cycle mediated by anthropophilic H V s after introduction by bridging H V s feeding on infected primate H R s (de Silva et al 1999;Wolfe et al 2001;Monath 1989;Downs 1982); these viruses appear closely related to the wild type viruses circulating in sylvatic cycles, although regional variation is apparent (Bryant and Barrett 2003). Viral adaptation to the human H R appears in most cases to be critical to developing a virus with pandemic potential (Mims 1991(Mims , 1995. The introduction of avian-like gene segments into preexisting, aerosol-transmitted, human influenza A viruses, or alternatively, the introduction of key genetic components into preexisting avian viruses (see the chapter by Webby et al, this volume) may be prerequisite to pandemic influenza A emergence (Claas 2000).…”

Explaining viral pandemics with help from Theology and Physics - Alternative Hypotheses.

“…[Any other vector transmitting the SARS-CoV-2 virus, like mosquitoes, fleas, etc., will alter the dynamics of this argument, a limiting factor of this study]. Such epidemics which involve 'chance encounters' will end up eliminating large numbers of the population during their first episode of interaction (Mims 1991;1995). Subsequently, humans end up taking precautions to prevent a recurrence of similar episodes by the same (pathogen)…”

Determining the safety of microbial cultures for consumption by humans and animals

“…However, there is no evidence whatever indicating that gene mutations, chromosome rearrangements, or epigenetic changes that can occur in pure cultures that are isolated and maintained in a closed system, will induce a non-pathogenic microbe to become pathogenic. This is because pathogenicity, as discussed above, is a complex process that depends on the acquisition and expression of virulence factors and/or toxin genes (Wang et al, 2013;Hill, 2012;Henderson and Martin, 2013;Leeber et al, 2010;Falkow, 1997;Rahme et al, 1995;Mims, 1991) which cannot occur spontaneously in a closed system.…”

“…In contrast to opportunistic pathogens, which cause illness only rarely in compromised hosts, a true pathogenic microorganism has an intrinsic capability to cross or evade non-compromised host barriers (e.g., intact skin and a normally functioning immune system) and thereby infect individuals who would otherwise be considered healthy (Falkow, 1997;Mims, 1991). True pathogens are able to do this because they possess and express genes for virulence factors, which are defined as pathogen-produced substances that promote the establishment and maintenance of disease (http:// www.msu.edu/course/mmg/301/Lec32.pdf) Pathogenic microorganisms may also produce toxins that induce illness apart from infection per se.…”