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Indian Journal of Medical Microbiology, Vol. 27, No. 3, July-September, 2009, pp. 182-184 Special Article Microbes, the moon, and A/H1N1 Desikan Prabha Department of Microbiology, Bhopal Memorial Hospital and Research Centre, Raisen Bypass Road, Karond, Bhopal - 462 038, Madhya Pradesh Date of Submission: 25-May-2009 Code Number: mb09059 PMID: 19584496 On November 14, 2008, the Moon Impact Probe successfully separated from the moon-orbiting Chandrayaan-I at 20:06 and descended towards the lunar South Pole. The probe impacted Shackleton Crater, releasing sub-surface debris that could be analyzed for the presence of water. The excitement generated was palpable. Following the success of Chandrayaan-I, India now plans to launch a second unmanned moon mission by early 2012. The enterprise is expected to cost nearly Rs 500 crore. Man is at his innovative best when trying to locate potential ecosystems to utilize for his own survival. His primary need is to establish his place and purpose in the universe. To fulfill this need, the most important material required is biological in nature. Man will stop at nothing in his search for it. It is an instinctive urge that compels him to look for potentially hospitable environs to survive and propagate. His current home, the Earth, is rapidly being depleted of resources. Each generation of humans is now confronted with new challenges that affect their continued existence. These are the wages of our evolutionary success. However, to attain success, man has consistently pushed at the frontiers of his knowledge and his immediate environment. It has been necessary to do this to gain access to surroundings that would facilitate survival of future generations. Driven by a primal need to survive and multiply, the costs of such ventures have rarely mattered. There are deep similarities between the ethos of space exploration and activities of the latest bug on the block - the H1N1 Swine influenza virus. Many swine influenza viruses are a result of re-assortment and their genes are composed of human and avian and/or swine virus genes. Both human and avian influenza viruses occasionally transmit to pigs, and pigs serve as "mixing vessels" for the virus. The virus then exchange genetic material, leading to the production of a new "hybrid" virus potentially pathogenic to humans. [1] The H1N1 Swine influenza virus responsible for the current epidemic of influenza has a genetic mosaic derived from swine, bird and human influenza viruses. The CDC refers to it as a swine influenza A (H1N1) triple reassortant virus, A/Wisconsin/87/2005 H1N1. [2] This virus has been evolving for a long time, probably moving from birds to swine, and then to humans, aided in its transformation by the ecology of industrial-scale pig farming in North America. Transmission to new species of hosts is a major microbial strategy for survival and propagation. The philosophy behind this strategy is the same as that underlying our attempts to learn more about our neighbors in space. We are looking for new land to conquer, with new reserves of biological material to utilize for human survival and propagation. Microbes colonise new hosts with the same objective. As of May 2, 2009, 15 countries have officially reported 615 cases of influenza A (H1N1) infection. Of these, Mexico has reported 397 confirmed human cases of infection, including 16 deaths, and the United States Government has reported 141 laboratory confirmed human cases, including one death. Obviously, the virus is still evolving, and moving, and its ultimate trajectory cannot be seen right now. Over the past few decades, in addition to trips to the moon, there have been a number of exorbitantly expensive Mars missions. Quite a few have failed. In 1993, NASA′s billion dollar Mars Observer simply disappeared. Six years later, twin missions consisting of the $165 million Mars Climate Orbiter and the Mars Polar Lander ended in disaster. One burned up in the Martian atmosphere and the other smashed into the planet. Only three of humanity′s 11 landing attempts on Mars have succeeded. Our attempts at colonizing a new host, as it were, are still very immature. Perhaps we could take some cues from the grand masters of the game - the much maligned microbes. How does a microbe choose a new species of host? What kind of research goes into the identification of a potentially hospitable host? How does the organism decide the most effective route of infection? Which factors decide the kind of mutations required to make a pathogen suitably virulent for invasion of a new environment? What is the level of aggression required to colonize a new host? How does the organism fend off the innate hostility of the host′s natural defenses? Once colonized, how is the aggression toned down to maintain a successful relationship with the host? The answers may give us pointers to help us start and maintain a meaningful relationship with our neighbours in space. Microbes have a huge head start on us when it comes to intelligent techniques for survival. Their journey through evolution has been far longer than even the history of our species. Billions of years ago, they utilized the key elements - hydrogen, carbon, oxygen, nitrogen and sulphur through transformation cycles and became pioneering life forms on earth. Past masters at adapting to any environment, they rapidly colonized any suitable home. Large and dynamic microbial communities lived and multiplied inside other life forms - plants, animals or humans. They evolved a remarkable genetic versatility that enabled them to circumvent barriers to their continued existence. Horizontal gene traffic via plasmids and bacteriophages within and between microbial species maintained communication of vital information. Each new microbial strain demonstrated a greater versatility at survival techniques than the previously existing strains. A striking example is the virus that caused the epidemic of SARS, or severe acute respiratory syndrome, a few years ago. The indictment of a corona virus was a surprising twist in the tale of SARS and in the history of our knowledge of corona viruses. The first corona virus, isolated in 1937, was the avian infectious bronchitis virus. Since then, its cousins were found to infect cattle, pigs, horses, turkeys, cats, dogs, rats and mice. The first human family member was cultivated from nasal cavities. The two identified ones, OC43 and 229E, are thought to cause 30% of all cases of common cold, depending upon the year. These are are divided into three groups based on cross reactivity of antibodies and genome sequencing. The genome sequence of the new SARS associated corona virus showed that it did not fit into any of the groups. [3] It was a new virus in itself. That brought us to the question of where the virus came from. One possibility was that it was a mutant human corona virus that acquired new virulence factors. The other possibility was that it could be an animal corona virus that aquired mutations which enable it to infect human cells. A third possibility was that it was a recombinant of two human corona viruses or a human corona virus and an animal corona virus. Antibodies to the SARS associated corona virus were found in the serum of patients with SARS during their convalescence, but not in human serum samples banked before the outbreak. [4] This suggested that the virus was new to the human population. The nucleotide sequence of the SARS associated corona virus genome differed substantially from sequences of all known corona viruses. Thus, it is reasonable to assume that the virus had been infecting some animal species for a long time - and then jumped to humans, where it found a favorable environment. Was the jump accidental - or a well researched and superbly orchestrated move? The latter is more likely. With a genome of more than 30,000 nucleotides, corona virus may be fairly shrewd. A new pathogen emerges through mutation or recombination. A new virus typically shares some antigens with ancestors and also has new, novel surface antigens. This helps them evade the prevailing herd immunity created by their relatives in their new host. The temporal dynamics of a successful invasion by the new virus into a virgin population can be established by applying the equation Ro = βr∩/(αµδ). Here, Ro is the rate at which infected cells generate new infected cells in very early stages after exposure - when most cells are uninfected. β is the rate of cell division, r is the replication rate of the virus within its host cell, ∩ is the rate at which uninfected cells are produced by the host, and α, µ, and δ are the death rates of infected cells, uninfected cells and free virus respectively. The genotype of a successful new pathogen must ensure production of phenotypes with properties capable of ensuring Ro greater than one to establish itself in a new host. [5] Following this, successful survival in the new host depends on a variety of factors including antigenic constitution, the ability to replicate within the host and the capacity to survive an immunological onslaught. Clearly, there is a calculated precision in microbial colonization of new species of hosts, a precision that is probably far more evolved than that visible in our tentative forays into outer space. Over the years, certain characteristics have been identified which contribute to the overall success of microbial pathogens. Some characteristics of concern pertain to Darwinian forces which favour competitive survival. Others pertain to anthropocentric forces which, in turn, favour shared survival. This means that on one hand, ′survival of the fittest′ is the predominant philosophy. On the other hand, there is the notion that a successful pathogen drifts towards commensalism in its relationship with its natural host. It is an appropriate mix of both that goes towards the making of a successful pathogen. The pathogen decides the quantum of either ingredient in the mix at each stage of evolution to ensure successful survival of future generations. A key feature of microbial philosophy is that complete utilization of all the resources in the new host is detrimental to the survival of the organism. It is, therefore, necessary for the host to survive and renew resources in order to provide sustenance for the offspring of the organism. Microbes were aware of this long before man even thought of the consequences of depletion of non renewable sources of energy on earth, and this is probably why epidemics and pandemics necessarily come to an end. Obviously, microbes are much more intelligent than we realize, and the current outbreak caused by the H1N1 Swine Influenza virus may teach us a few lessons before coming to an end. Be that as it may, with world attention focused on H1N1 swine flu, it is easy to forget the threat still posed by H5N1 and other strains of flu. Immunity to H1N1 will not offer protection to H5N1 if that also becomes readily transmissible between humans. [6] As H1N1 spreads to areas where H5N1 is endemic, do we face an even greater challenge-that of re-assortment of the two viruses and the threat of another pandemic? The answers lie within the virus itself. Intellect, the magnitude of which we assumed was unique to humans, developed gradually over millions of years. Intellect is what influences nature to modify and change instinctive behavior to result in the kind of behavior that would provide optimum benefit (survivability). Evidently, intellect is not the exclusive domain of humans. We have a lot to learn from other life forms which have a longer evolutionary history. Conservation of precious resources, strategic planning, frugality, efficiency and coordination - these are only a few of the important lessons in survival that we need to learn from microbes. Micro-organisms have been around on this planet much longer than we have. Over centuries, they have grappled with a wide variety of predicaments and onslaughts and have emerged victorious. They are survivors par excellence. With a wealth of experience, they have survival skills that we have ignored for far too long. We have been extremely patronizing of their mores and have been guilty of placing them lower down on the evolutionary scale. Perhaps we need to go down on our knees, to the level of microbes, to learn the essentials of survival and achieve the spectacular without the arrogance that has become synonymous with, the species, Homo sapiens. References
Copyright 2009 - Indian Journal of Medical Microbiology |
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