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 Table of Contents  
Year : 2021  |  Volume : 18  |  Issue : 4  |  Page : 203-208

The resilience of microbes – Man's great enemies

Department of Community Health and Primary Care, Lagos University Teaching Hospital, University of Lagos, Lagos, Nigeria

Date of Submission30-Sep-2021
Date of Acceptance12-Oct-2021
Date of Web Publication09-Dec-2021

Correspondence Address:
Prof. Akin Osibogun
Department of Community Health and Primary Care, Lagos University Teaching Hospital and College of Medicine, University of Lagos, Lagos
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jcls.jcls_39_21

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More than 1400 microbes are known to cause disease in man and are therefore classified as pathogenic microbes. Only 12% of microbes on earth are responsible for the emerging and re-emerging diseases. All infectious agents have adapted routes for exiting from their reservoirs of infection because that is the only way there can be a perpetuation of their species. Factors aiding the seeming resilience of microbes include microbial evolution and adaptation, human susceptibility, climate and weather, changing ecosystem, human demography and behaviour amongst others. Therefore, man must recognize that the war against microbes is likely going to be there permanently. If we are careless however, the microbes may make life uncomfortable for man and change how we live drastically. A strengthened health intelligence system will support an early warning system that gives clear pictures of what is on the ground and what is evolving. This will also monitor the environment including the water supply system, the sewage, the soil, and the air for evidence of microbes that may be pathogenic to man. We must also mount a robust anthropological surveillance to monitor human behavior as it may affect disease transmission and must search for and deploy effective antimicrobial agents. Overall, we must develop the human capacity that will efficiently deliver our selected strategies to detect, prevent, and mitigate the impact of microbes on human health.

Keywords: Enemy, man, microbes, resilience

How to cite this article:
Osibogun A. The resilience of microbes – Man's great enemies. J Clin Sci 2021;18:203-8

How to cite this URL:
Osibogun A. The resilience of microbes – Man's great enemies. J Clin Sci [serial online] 2021 [cited 2022 Aug 18];18:203-8. Available from: https://www.jcsjournal.org/text.asp?2021/18/4/203/332068

Presented at the 17th Annual Scientific Conference and Gathering of the Faculty of Clinical Sciences, College of Medicine, University of Lagos.

Date: Wednesday 28th July 2021

Venue: Old Great Hall, College of Medicine of University of Lagos, Lagos.

  Introduction Top

Distinguished ladies and gentlemen, do permit me to save time by adopting the already established protocol. I am indeed happy to be here to deliver this lecture because of its relevance and its timeliness. I thank the organizers for bringing up my name and the Dean, FCS, for accepting.

I have chosen this particular topic so as to remind us of the very difficult situation the entire world has been in for the past 18–20 months and to emphasize even when the COVID-19 pandemic ends, the world will still be at the risk of future pandemics.

I am hoping that this presentation will bring to fore again what we need to do to combat this pandemic and prepare ourselves for future ones. I do not intend to sound like a prophet of doom on this issue when I cannot even claim to be a prophet! On the contrary, the facts seem obvious if only we are prepared to pay the necessary attention.

When the U.S. Surgeon General William Stewart in 1969 declared and I quote him, “we can now close the book on infectious diseases,” and when this declaration was followed in 1980 by our eradication of smallpox – a disease that killed as many as 500 million in the 20th century alone – we had cause to be confident. We also celebrated in Nigeria when in 2014 we eradicated Guinea worm in Nigeria and this was followed a few years later with Nigeria being certified polio free. Yours truly had the privilege of serving on the Presidential Committee for the Certification of Guinea Worm Eradication in Nigeria.

It has been argued that human triumphalism and overconfidence in success in previous battles against microbes was responsible for the disastrous impact of the COVID-19 outbreak in the USA and Europe. While the then President of the USA seemed not to believe much in science, the Prime Minister of the United Kingdom had the erroneous belief that the SARS-COV-2 virus would just manifest like the common cold and go away within some time. These were costly assumptions.

With the benefit of hindsight, I think we must chide ourselves for ignoring the cautious words of Girolamo Frascatoro some 450 years ago when he spoke about Syphilis, thus “there will come yet other new and unusual ailments in the course of time. Moreover, this disease will pass away, but it later will be born again and be seen by our descendants.” Frascatoro had warned us 450 years ago about emergence and re-emergence of diseases and henceforth we must be determined in our preparedness.

  Agents of Disease Top

Disease is an abnormality in the anatomy or physiology of a part or the whole of an organism. Illness, on the other hand, is the totality of the response of man to actual or perceived disease. I will not dwell much on this distinction this morning beyond mentioning that it is possible for a man to have a disease and not show signs and symptoms of the disease. It is also possible for a man not to have any disease but to play every role of the ill.

Generally, diseases are classifiable into two broad categories – communicable and noncommunicable.

Communicable diseases are those that can be transmitted from one human being to another. Such diseases are in general characterized by the presence of a biologic agent which either by itself in full or part or by its product can be transmitted to a new and susceptible host. The key points to note are – a biologic agent, a reservoir of infection, a route of transmission, and a susceptible host. I will come back to these key points later because of their importance in the prevention and control of communicable diseases.

Noncommunicable diseases are those that are not transmissible from one person to another, for example, diabetes mellitus, hypertension, and sickle cell disease. Please note that inheriting sickle cell genes from one's parents not viewed as transmission in the context defined above. Noncommunicable diseases have however been associated with predisposing and exposure factors.

As for biologic agents of disease, we have recognized prions, viruses, rickettsia, bacteria, fungi, protozoa, and helminthes. We are familiar with all these and I will not spend time on them except to mention that prions are protein elements that are associated with disease causation e.g., the Creutzfeldt-Jacob Disease (or Mad Cow Disease).

Distinguished ladies and gentlemen, as our knowledge increases, so do our definitions change. Today, cervical cancer which we had always known as a noncommunicable disease has now been associated with the human papillomavirus. This new knowledge has led to the development of an HPV vaccine which is now applied for the prevention of cervical cancer. Some link has also been established between prostatic cancer and sexually transmitted diseases including the HPV. Cancer of the liver has now been associated with the Epstein–Barr virus and the possibility is there that if we can develop a suitable vaccine against this virus, we may just be able to prevent some of the liver cancers.

Please note my careful choice of words as I have only said we may be able to prevent some of the liver cancers through appropriate vaccines. This is so because noncommunicable diseases have a multiplicity of causative or associated factors unlike communicable diseases that are always related to an identifiable biologic agent.

More than 1400 microbes are known to cause disease in man, and these are therefore classified as pathogenic microbes. A majority of the microbes on earth are benign to man and some may actually be beneficial to the ecosystem. Of the 1400 pathogens, only about 12% are responsible for emerging and re-emerging diseases.

An emerging disease is one that has newly appeared in a population or that has been known for some time but is rapidly increasing in incidence or geographic spread or occurrence. A re-emerging disease is one that once was a major health problem in a particular country or globally, and then declined in incidence, but is again becoming a public health problem.

  The chain of infection Top

For infectious diseases to thrive, the following elements of the chain of infection must be present:

  • A biologic agent
  • A reservoir of infection
  • A route of exit from the reservoir A mode of transmission
  • A new and susceptible host
  • A route of entry into the susceptible host.

I have earlier provided a listing of the various classes of biologic agents – viruses, bacteria, etc., and I rely on you to recall and possibly add to the list if I had left out any. The reservoir of infection can be an already infected person or an animal in the case of zoonotic diseases or part of the environment as in tetanus whose spores can be found in the soil.

All infectious agents have adapted routes for exiting from their reservoirs of infection because that is the only way there can be a perpetuation of their species. It will be catastrophic for the species if the agents were to die with their host. Hence, in the course of the disease in the host, progenies of the infective agent must find a way of exiting from the host and being subsequently transmitted to a new and susceptible host.

Some infectious agents exit from their infected hosts through the gastrointestinal tract, for example, typhoid and cholera; some exit through the respiratory tract, for example, tuberculosis and measles; others are assisted to exit through the assistance of blood-sucking vectors such as mosquitoes in the cases of malaria and yellow fever. Others burrow their way to exit through the skin as in Guinea worm while others exit through the reproductive tract, for example, chlamydia and other sexually transmitted infections (STIs).

For some vector-borne infectious agents, it is the same vector which assisted their exit that is also responsible for their transmission to the new and susceptible host. The mode of entry into the new host will also be through the bite of such a vector as it tries to take its next blood meal. For disease agents exiting through the respiratory tract such as Mycobacterium tuberculosis, the air is their transmission agent as they are carried within some distance in droplets. Disease agents exiting through the gastrointestinal tract are transmitted through the contamination of food and water by the infective agents and new susceptible hosts now ingest the contaminated food or drink the contaminated water.

  The Natural History of Infectious Diseases Top

When a new person is in contact with an infectious agent, the infection can become established or aborted depending on the dose of the invading organism and the immune status or resistance of the new host. If the infection is established, it then elicits a set of responses from the host which manifests as the signs and symptoms of that disease. These responses are the consequences of the interaction between the infective agent and the host. Some responses include fever and some include pus formation signifying the efforts of the body to fight the invading organisms. Some invading organisms affect the integrity of blood vessels and thereby cause bleeding as in hemorrhagic fevers.

That period between the invasion of the susceptible host by the infectious agent and the manifestation of the signs and symptoms of disease is referred to as the incubation period. During this period, the infected person is capable of transmitting the infective agent to other new and susceptible hosts.

Once infected, the body in some cases is able to develop antibodies that may successfully checkmate the infective agents. From this disease state, the body may thus either recover if it is able to overcome the invading agent, or go into chronicity or death. From chronicity, the body may also go into recovery, persistence, or death.

In some infectious diseases, the body is able to recover but yet continues to harbor the infectious agent and is capable of transmitting to a new and susceptible host. This state of infection is referred to as a carrier state.

Our knowledge of the chain of infection and the natural history of infectious diseases is what we can rely on in our battle against invading microbes. This knowledge explains how it is possible to be vaccinated and yet get infected and also be able to transmit the virus

  Factors Aiding the Seeming Resilience of Microbes Top

The Institute of Medicine in the United States published in 2003 a report titled “Microbial Threats to Health: Emergence, Detection and Response” and this report identified several factors contributing to the emergence and re-emergence of infectious diseases and the following are adapted from that publication:

Microbial evolution

Microbes appear to have been originally able to grow and multiply in different environments and hosts, but some microbes have been able to jump species such that microbes that had lower animals as their hosts in which they caused diseases, are now able to infect man and cause disease. Some that were also known to cause disease in man have now been identified as able to cause disease in lower animals. Hence, we now talk about zooanthroponosis and anthropozoonosis and both refer to diseases shared between man and animals [Table 1].
Table 1: Examples of rodent-transmitted diseases

Click here to view

By hiding outside human populations and at times hiding in animals of economic value to man, pathogenic microbes have made it difficult for man to exterminate them. Of the over 1400 pathogens known to cause disease in man, about 12% are emerging and re-emerging infectious diseases. Of these emerging and re-emerging diseases, about 60% are related to zoonoses or diseases of animals shared with man.

Another way in which microbes have tricked man, is by changing their route of transmission. For example, Trachoma used to be largest cause of blindness in man but is now also possibly the most common sexually transmitted infection globally! It is possible that man's behaviour could have supported the success of the organism.

Microbial adaptation

In their quest for survival, microbes evolve or acquire antibiotic resistance genes that allow bacteria to survive exposure to antibiotics. Mutation of genetic materials and the horizontal transfer of virulent strains from one microbe to another have also been identified as survival mechanisms for microbes, for example, the evolution of the multidrug-resistant TB [Figure 1].
Figure 1: Microbial adaptation
Source: National Institute of Allergy and Infectious Diseases, “http://www.niaid.nih.gov/

Click here to view

Human susceptibility

Man's immune status is often lowered at the extremes of age and also by the presence of some other chronic diseases which then makes it easier for an invading organism to be able to establish itself because of the immunocompromised state.

Climate and weather

Climatic change including increasing temperature may make it possible for certain vectors that hitherto could not survive in a particular geographic area to now survive and facilitate the transmission of diseases. Climate change can also alter the agricultural practices of man and consequently bring him in closer contact with the agents of disease. Climate change can also alter the agricultural practices of man and consequently bring him in closer contact with the agents of disease.

Changing ecosystem

This is also related to the effects narrated under climate change as environmental changes affect predator density and may therefore facilitate an increase in the population of vectors of disease.

Human demographics and behavior

Increasing human population and overcrowding make it easier for the spread of diseases. Commercial sex work and newly defined sexual practices and behavior, for example, multiplicity of sexual partners and male-to-male practices, will result in increased exposure to agents of diseases.

Economic development and land use

Widespread deforestation can lead to encroachment on the reservoir of some infectious agents. The continuous clearing of forests and bushes brings man into further contact with some animal reservoirs of disease.

Technology and industry

Refrigeration and packaging of food for distribution globally also means that infective agents can be distributed globally through such a food distribution chain.

International travel and commerce

Most microbes cannot move or move long distances and this fact alone would have limited their ability to cause havoc in large populations. Viruses in particular cannot move and in fact cannot be accurately described as living things. However, many microbes are moved most times by man and his activities or by air and vectors. Man's design of efficient travel modes has also supported the efficient dissemination of the agents of disease! Thus, the first cases of SARS-COV-2 infection were reported in Wuhan district in China in December 2019, and by January to February 2020, all the continents had received the virus. The first case in Nigeria was reported on February 27, 2020, in a patient who came in from Italy 2 days earlier. Our major wave of infection came with flights arriving from Europe and the USA between March 9 and 15, 2020, because those regions were then currently experiencing massive outbreaks. A direct flight from London to Lagos is under 6 h!

Breakdown of public health infrastructure

One major defining feature of the protracted Ebola epidemic in Liberia, Sierra Leone, and Guinea is the collapsed public health infrastructure in those countries. This has made it difficult for the epidemic that was reported since March 2014 to have remained out of control in those countries until external help has been poured into those countries. On the other hand, the presence of a relatively functional health infrastructure in Lagos and Rivers States in Nigeria was significantly contributory to our ability to contain the Ebola virus within 3 months after its importation into the country in July 2014.

Poverty and social inequality

Poverty and social inequity will lead to people living in areas that are overcrowded and with poor sanitary facilities as well as deprive them of access to resources that are preventive of diseases. Poverty will also expose people to activities and behavior that increase exposure to health risks.

War and famine

Wars cause a lot of social disruptions and damages to physical infrastructure such as water and electricity supply, thus paving the way for the spread of diseases. Rape and abuses during wars also aid the spread of diseases as was clearly documented during the Rwandan War when so many raped women gave birth to many HIV-infected babies. We are yet to know what the full picture is in the parts of Nigeria affected by the insurgency.

Lack of political will

Lack of political will at times delay the prompt allocation of resources to contain emerging diseases until the diseases get out of hand. An example was the Ebola outbreak in West Africa that claimed over 11,000 lives. It took a while for the WHO to declare an emergency compared to the urgency with which the body convened an emergency meeting when SARS had claimed <300 lives in 2003. National governments also at times are slow to recognize their responsibilities. There are many arguments suggesting tardiness at the onset in handling the current COVID-19 pandemic, and the results have been the pandemic we now have to deal with.

Intent to harm

Bioterrorists could cause the release of an infective agent into populations and thereby cause the emergence or re-emergence of an infectious disease. The use of anthrax through the post in the United States in 2011 is one example.

  In Conclusion, What can Man do? Top

The first and main thing is for us to recognize that the war against microbes is likely going to be there permanently as we all form part of an ecosystem. We must however control the theaters of the war if man is to live a somewhat predictable and minimally comfortable life as we understand it. If human life is allowed to be short and cut down by disease, it will affect the quality and meaning of life as we understand it. Therefore, the microbes must be continually engaged on all fronts!

Science has indeed made a lot of progress including the discovery of penicillin and other potent weapons against microbes. Perhaps, one of the game-changer discoveries was the discovery of the structure of DNA by James Watson and Francis Crick in 1953. The duo determined the double-helix nature of DNA and the mechanism through which it could copy itself and serve as the basis of hereditary information.

The work of Rosalind Franklin and Maurice Wilkins in creating images of DNA through X-ray diffraction enabled Watson to finally determine the binding of adenine, thymine, guanine, and cytosine in forming the ladder rungs of the helix structure. All this work earned Watson, Crick, and Wilson the Nobel Prize in 1962. Franklin had died in 1958 and could not share in the Prize.

By the year 2003, the entire human genome had been decoded and, by the year 2020, a lot of speed had been gained with DNA sequencing capability. Following the first reported COVID-19 case in Nigeria on February 27, 2020, I had a live interview on Channels TV in March 2020 and I informed the audience that a vaccine will be developed against the virus within a short time. That statement was taken with a pinch of salt by many based on the fact that vaccine development took far longer than that in the past.

However, the Chinese had already provided the full sequence of the SARS-COV-2 and all that researchers needed to do was to look what part of the DNA we could use to develop a vaccine that will enable the human body produce immune responses without developing the disease based on the knowledge of what was now possible with genomics.

It is most likely that the microbes also need man to survive and may never quite succeed in exterminating humanity. If we are careless however, the microbes may make life uncomfortable for man and change human nature and how we live drastically. Life in the era of COVID-19 in the past 20 months shows that much. We must therefore constantly be reminded of the words of Girolamo Frascatoro and keep ourselves in a state of watchfulness and preparedness.

Preparedness is the state of being ready to act. In the infectious disease disaster context, it broadly refers to the ability to detect a pathogen, act to prevent its spread, and mitigate disease in humans (or animals or plants). Please note that the One Health concept recognizes that microbes that can be pathogenic in man can have their reservoirs in man, animal, and the environment. If we are to effectively control, effective epidemiological and laboratory capabilities are required to enable us to detect and prevent the spread of pathogenic microbes. A strengthened health intelligence system will support an early warning system that gives clear pictures of what is on the ground and what is evolving. Even where resources are limited, a good characterization of an outbreak can help in preventing its further spread through identification of populations at risk and measures to interrupt transmission.

The health intelligence system must also monitor the environment including the water supply system, the sewage, the soil, and the air for evidence of microbes that may be pathogenic to man. This is a form of ecologic surveillance. During the Polio Eradication Campaign, we took samples from drainage systems for laboratory evaluation and search for polio virus.

In addition to ecologic surveillance, we must also mount a robust anthropological surveillance to monitor human behavior as it may affect disease transmission. Human behavior remains the most complex and difficult intervention area in our war against the microbes.

Moreover, in order to reduce the reservoir of infection as well as relieve human suffering, we must search for and deploy effective antimicrobial agents. We must provide treatment and hope to the affected.

Overall, we must develop the human capacity that will be able to efficiently deliver our selected strategies to detect, prevent, and mitigate the impact of microbes on human health. Preparedness requires resource deployment and preparedness is cheaper in the long run than when a country is caught unprepared!

Distinguished ladies and gentlemen, as Disraeli said, “If you can't simply explain it, then you don't damn understand it.” I hope I have been able to present the issues as simply as possible.[8]

Thank you for your attention.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Cunha BA. Historical aspects of infectious diseases, part I. Infect Dis Clin North Am 2004;18:XI-V.  Back to cited text no. 1
Kenrad E. Nelson and Carolyne F. Williams, Early History of infectious Diseases, Jones and Bartlett Publishers.  Back to cited text no. 2
Inhorn MC, Brown PJ. The Anthropology of Infectious Diseases: International Health Perspective. Australia: Gordon and Breach Publishers; 1995.  Back to cited text no. 3
Brachman PS. Infectious diseases – Past, present, and future. Int J Epidemiol 2003;32:684-6.  Back to cited text no. 4
Santajit S, Indrawattana N. Mechanisms of Antimicrobial Resistance in ESKAPE Pathogens. Biomed Res Int. 2016;2016:2475067. doi: 10.1155/2016/2475067.  Back to cited text no. 5
Munita JM, Arias CA. Mechanisms of Antibiotic Resistance. Microbiol Spectr. 2016;4:10.1128/microbiolspec.VMBF-0016-2015. doi: 10.1128/microbiolspec.VMBF-0016-2015.  Back to cited text no. 6
Bowale A, Abayomi A, Idris J, Omilabu S, Abdus-Salam I, Adebayo B, et al. Clinical presentation, case management and outcomes for the first 32 COVID-19 patients in Nigeria. Pan Afr Med J 2020;35:24.  Back to cited text no. 7
Abayomi A, Odukoya O, Osibogun A, Wright O, Adebayo B, Balogun M, et al. Presenting symptoms and predictors of poor outcomes among 2,184 patients with COVID-19 in Lagos State, Nigeria. Int J Infect Dis 2021;102:226-32.  Back to cited text no. 8


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