Module 15 Microbes and Diseases PDF

MODULE 15 MICROBES AND DISEASES Andes, A.T. Department of Zoology, University of Ilorin, Ilorin, Nigeria Introduction Microbe is a noun coined from micro-organism, i.e. organisms that canno...

MODULE 15 MICROBES AND DISEASES Andes, A.T. Department of Zoology, University of Ilorin, Ilorin, Nigeria Introduction Microbe is a noun coined from micro-organism, i.e. organisms that cannot be seen with the naked eye. They exist as single cells or cell clusters and can be appreciated with the aid of special gadgets such as the microscope. They form a very large and diverse group of organism that combines plant and animal features. They include bacteria, fungi, viruses and protozooans. Microbes play very important roles in nature than their small size suggest. They form a significant integral part of the community that ensure interaction between living and non-living components and hence the sustenance of all ecosystems. They ensure the synthesis and degradation of special organic substances in the course of their existence. Man has over the years taken advantage of this in a number of ways such as the production of beer, yogurt and antibiotics, baking, soak away system, etc. Learning Outcomes By the end of this module, you should be able to: (i) give the definition and various groups of microorganisms; (ii) identify various microbial reservoir; (iii) explain ways by which microbes can invade a susceptible host; (iv) differentiate between pathogenicity and normal human flora; (v) establish ways or routes of transmission of microbes; and (vi) analyse the etiology and prevention of various microbial diseases Main Body Introduction This module introduces you to meaning of Microorganism, Host Invasion, Pathogenicity, Reservoirs, Transmission and Microbial Diseases. This will be discussed under 2 units. Unit 1 Microorganisms Subunit 1 Host Invasion Subunit 2 Pathogenicity Subunit 3 Reservoirs Unit 2 Microorganisms Subunit 2 Transmission Subunit 3 Microbial Diseases Unit 1: Microorganisms Contents 1.0 Introduction 2.0 Learning Outcomes 3.0 Main Contents 3.1 Host Invasion, 3.2 Pathogenicity 3.3 Subunit 1 Reservoirs, 4.0 Summary 5.0 Self-Assessment Questions 6.0 Tutor Marked Assessment 7.0 Further Reading 1.0 Introduction This unit introduces Host Invasion and pathogenicity. 2.0 Learning Outcomes By the end of this unit, you should be able to: (i) define and various groups of microorganisms; (ii) explain ways by which microbes can invade a susceptible host; (iii) Reservoirs; and (iv) differentiate between pathogenicity and normal human flora 3.0 Main Content 3.1 Host Invasion Microbes play very important roles in nature than their small size suggest. They form a significant integral part of the community that ensure interaction between living and non-living components and hence the sustenance of all ecosystems. They ensure the synthesis and degradation of special organic substances in the course of their existence. Man has over the years taken advantage of this in a number of ways such as the production of beer, yogurt and antibiotics, baking, soak away system, etc. Human microflora occur on the skin, orifices, i.e. mouth, nose, anus, vagina etc; body fluids such as saliva, blood, semen etc., as well as, in the tissues. Most of these form normal body microflora, in which case their presence is not harmful to their host. The detrimental or pathogenic forms, however, elicit disease condition i.e. an alteration in the host system resulting in the loss of productivity, in man as a result of the interaction with the microbe. This disease possibility necessitates a discussion on Microbes and Diseases, believing that a thorough understanding of the etiology of microbial disease of man will reduce their incidence and therefore enhance human livelihood. To elicit disease condition, microbes must establish contact, multiply and colonise its host either superficially or in the tissue. To achieve this, they require to have conquered the series of defence mechanisms put up by an unwilling host. The most prominent of this is the impenetrable skin that serves as barrier. The determined microbes, however, make their way in by adhering to the surface and producing chemical substances (enzymes) that break the barrier for them. Some of them take advantage of skin lacerations by way of wounds, while others reside in obscured spaces with restricted access but clement environment such as the mouth, anus and vagina. Microbes are known to show preferences for site of occurrence. e.g. Nisseria gonorrhea, a microbe causing sexually transmitted disease known as Gonorrhea. which sticks strongly to the inner lining of the urinogenital tract than any other place. 3.2 Pathogenicity Microbes initiate some level of alterations in the host's system as a result of their activities. Some of these activities are aimed at improving their survival chances in the areas of food acquisition and avoidance of the host's defense actions. Some of these activities include: Production of excretory wastes that may be intolerable to the host and hence referred to as toxins Deprivation of the host of its nutrients Confiscation of host tissue for personal use by the microbe. e.g. viral infections Destruction of the host tissue, e.g. anemia resulting from malaria infection Initiation of tissue changes that may lead to cancers or tumors and Reduction of host immune response thereby giving room for opportunistic infections. 3.3 Reservoirs Microbes reside temporarily in one or more natural environments known as reservoirs. The major reservoirs are water, soil, atmosphere, humans, domestic and wild animals. In their bid to survive they move from one reservoir to the other and become successful when established in their host. Diseases that are contractible by humans from other animals are termed zoonotic diseases. 4.0 Summary The unit drive the discussed on Host invasion, Pathogenicity and reservoirs. 5.0 Self-Assessment Questions (SAQs) (i) give the definition and various groups of microorganisms; (ii) explain ways by which microbes can invade a susceptible host; (iii) reservoirs; and (iv) differentiate between pathogenicity and normal human flora 6.0 Tutor Marked Assessment Write concise notes on: i. Host invasion ii. Pathogenicity iii. Reservoirs 7.0 Further Reading Brock, T. D., M. T. Martinko and J. Parker (1994) Biology of micro-organisms. Prentice Hall, New Jersey: 909pp. Cheng, T. C. (1973) General Parasitology. Academic Press, London,.965pp. Godman, A. and A. Gutteridge (1978) A New Health Science for Africa. Longman, London. 255pp. Unit 2 Microorganisms and Microbial Diseases Contents 1.0 Introduction 2.0 Intended Learning Outcomes (Objectives) 3.0 Main Contents 3.1 Transmission 3.2 Microbial Diseases 4.0 Summary 5.0 Self-Assessment Questions 6.0 Tutor Marked Assessment 7.0 Further Reading 1.0 Introduction.This unit will further discuss microorganisms and its transmission and the kinds of diseases that can result as a means of that. 2.0 Learning Outcomes By the end of this unit, you should be able to: (i) establish ways or routes of transmission of microbes; and (ii) analyse the etiology and prevention of various microbial diseases 3.0 Main Contents 3.1 Transmission The essence of successful transmission bid is to ensure the establishment of the offspring or progenies of a particular microbe in another host of the same kind; a mission that entails movement across reservoirs. They, therefore, utilize media that are inevitably used by their prospective host such as air, water, food, etc... The following four basic ways are often employed: Contaminated food and water (Oral-faecal route) Ingestion of contaminated food and water is a popular mode of microbial transmission. Faecal contamination is usually the source of such pathogens, as they reside mostly in the alimentary canal and they are voided out via the anus. They gain access to drinking water or food owing to inadequate sanitary procedures or sometimes directly when one licks unclean hands after visiting the toilet. Contamination of the respiratory tract (Respiratory route) Pathogenic microbes may find their way to the host's respiratory tract, irritate the host and force it to sneeze or cough. These activities, as well as, talking and throwing out sputum are primarily meant to protect the unwilling host, but they aid the transference of the microbes to other hosts in form of droplets in the atmosphere. The pathogens are successfully transmitted when a prospective host inhales such droplet. Most of the pathogens remain active and infective even after the droplet had dried up and they could be transported by wind. Direct contact with infected persons, animals or contaminated objects Pathogens frequently utilize the opportunity of contact to get across to a new host. Such a pathogen is described as-a contagion. Such contacts may be direct or indirect, e.g. sexual intercourse, kissing, sharing of toiletries, renting of dresses, etc. The entry may be via open wound, e.g. Tetanus bacteria from soil. Inoculation through the skin Pathogens may take advantage of the interaction between blood sucking parasite of man and man. The microbe makes itself available to the vector when it feeds on human blood. It is then transmitted to another host while consuming blood from its new host. Such pathogens usually grow and multiply in the vector. e.g. Plasmodium and Anopheles mosquito. 3.2 Microbial Diseases Microbes and the diseases initiated by them are numerous; however, some of the examples of these diseases shall be reviewed with emphasis on those that are of common occurrence in Nigeria. The diseases have been grouped on the basis of their causative agent into bacterial fungal, viral and protozoan diseases. The name, location in the host, mode of transmission, part of the host body affected, clinical manifestation, treatment and prevention of each disease are described briefly. Viral diseases: These are caused by the smallest organism described, i.e. virus. They can not be seen under the common light microscope. They are obligate parasites that show evidence of living only when in their host. Outside their host they are inert; hence they me regarded as organisms at the borderline between living and non-living things. Viruses usually occur, live and multiply within the cell of its host and they take over the control of such cells from their respective nuclei and from the host. Thus one of the general characteristics of viruses is their ability to alter the working method or system of the cells of a host. Table 1 shows a summary of the etiology of six common viral diseases and possible treatments and preventive measures. Viral diseases are usually difficult to treat owing to the fact that they reside within the host's cell where drugs cannot be tolerated. An effective drug at this point may kill the host cell before the virus. More emphasis is, therefore, placed on prevention, which ensures that the pathogens do not find their way into the host cell. When they do, however, the microbe is usually left for the host's immune system to handle. Table 1: Etiology, treatment and prevention of some viral diseases of man Causative Part of Method of Disease Type Clinical body Prevention and agent manifestation spread treatment affected Polio picorna Headache, Intestine Droplet Vaccination, boil virus fever, Paralysis and nervous infection, water for all system feacal purpose contamination Measles Paramyxo Fever, nose and Skin and Droplet Isolation of patients, virus eye discharge, Intestine infection avoiding overcrowding, rashes, improving ventilation, coughing, death vaccination Yellow fever Arbovirus Fever, Blood, liver, Mosquito Vaccination, avoiding headache, kidney vectors mosquito bite yellow eyes Smallpox Venola virus High fever, skin Respiratory Droplet Vaccination, improved blister and tract, blood, infection, ventilation, avoiding rashes, death skin wound overcrowding, patient contagion isolation Common cold Rhinovirus Running nose, Respiratory Droplet Patient isolation, (catarrh) headache, tract infection improved ventilation sneezing avoiding overcerowding AIDS HIV (Human Inability to The immune Contagion in Controlled sexual Immuno- defend self system body fluid activity, avoidance of deficiency against other body fluid contact virus) disease Bacterial Diseases: Several human diseases are caused by bacteria of various types. Bacteria are among the smallest living organisms. They are the first group of micro-organisms to be discovered as a disease causing organism. Most of them gain entry into their host via the mouth, nose, vagina, anus or lacerated skin. They obtain their food from their host by secreting enzymes that break down food substances to simpler forms that are readily absorbed by them. They also secrete waste products that are usually toxic to their host. Table 2 gives specific information on the etiology, clinical manifestation, treatment and prevention of some common bacterial diseases of man. Table 2: Etiology, treatment and prevention of some bacterial diseases of man Causative Part of Method of Disease Type Clinical body Prevention and agent manifestation spread treatment affected Cholera Vibrio cholorae Gut irritation, Alimentary Faecal Provision of good severe canal contaminated water, good personal diarrhea, food and water, hygiene. deg=hydration, vectors Use of antibiotics death (housefly) ORT Leprosy Bacillus sp Loss of Skin and Droplet Isolation of sensation, sore nervous infection, infected individuals, on skin, loss of system prolonged feeding well, use flesh and bone close contact of drugs Tuberculosis Mycobacterium Irritation of the Lungs Droplet Feeding well, tuberculosis respiratory infection, Vaccination, tract, coughing milk sourced (BCG) use of from infected antibiotics cattle Pneumonia Pneumococcus Chest pain, Lungs and Droplet Isolation of infected sp high fever, respiratory infection individuals, avoid constant tract overcrowding, use of coughing antibiotics Gonorrhea Neisseria Difficulty in Reproductive Contagion Restricted intercourse, gonourrhoeve urinating in organ, eyes of by sexual avoiding contact with men, sterility infants contact infected body fluid, in both sexes use of antibiotics Syphilis Treponema Mental Reproductive Contagion by Restricted intercourse, poludium impairment, organ, eyes sexual contact avoiding contact with skin blisters, bones, joints, infected body fluid, use brain damage skin and heart of antibiotics Tetanus Clostridum Lockjam spasm Blood nerves Wound Improved personal tetanus and muscles contamination hygiene, putting iodine on fresh wounded surface Fungal Diseases: Disease causing fungi in man are few. Trichophyton sp causes 'ringworm' and 'athletes foot' diseases in children and adults, respectively. This fungus obtains its nourishment from the outer layer of the skin with the aid of root-like structures called hyphae. It gives a small dark or red patch that grows, but becomes restricted to the outer margin of a portion with restored skin colouration and without hair strands later, hence the name 'ringworm'. These patches frequently occur on the scalp, inside the thighs and armpits. On the scalp, it gives a scaly bald patch without hair strands. Fungal disease spreads by personal or indirect contact achieved by way of sharing clothing and other personal effects such as sponge, comb, socks etc. The best preventive measure is to ensure personal cleanliness and discourage the use of damp socks and cover shoes. They are frequently treated with antiseptic devices. Protozoan diseases: Protozoans are tiny single celled organisms. Most of them are free living. A few of them, e.g. Plasmodium sp are however parasitic and they cause malaria and trypanosomiasis (sleeping sickness), respectively in man. Malaria is caused by Plasmodium sp, a pathogen that resides in the blood of man. They colonize the red blood cell, feed within it, reproduce in it and break it open, thus destroying it. This destruction results in anaemia. The pathogens also produce toxins that initiate rigors associated with malaria fever. The pathogens gain access into human blood stream through the feeding action of female Anopheles mosquito, which acts as a vector. The mosquito collects the pathogen from an infected individual while sourcing for blood, develops the pathogen to an infective form and subsequently passes the infective pathogen to a healthy individual during blood sucking activity. The symptoms of the disease include fever, i.e. high body temperature, headache, pains especially at the joints, little and deeply coloured urine, etc. Due to the high level of debility involved, chronic sufferers are usually incapable of carrying out their daily chores and so it leads to significant economic losses. Prevention is only achievable by avoiding contact with mosquitoes. Taking drugs to prevent malaria lead to undesirable effects such as the development of resistant to Plasmodium strain that will not respond to the common antimalarial drugs, thus complicating the management of malaria. Treatment is readily achieved through the use of drugs. Trypanosomiasis: Trypanosoma resides in the blood stream of man where they obtain their food and reproduce. They produce toxin which makes the host sick. The microbes are transmitted from one human host to the other by Tsetse fly (Glossina sp) while prospecting for blood. Signs and symptoms of the disease include fever, emaciation, sleeping almost always and eventually death. Prevention involves avoidance of tsetse fly and treatment entails the use of drugs. 4.0 Summary Transmission is discussed and microbial diseases. The diseases have been grouped on the basis of their causative agent into bacterial fungal, viral and protozoan diseases. The name, location in the host, mode of transmission, part of the host body affected, clinical manifestation, treatment and prevention of each disease are described briefly. 5.0 Self-Assessment Questions (SAQs) (i) establish ways or routes of transmission of microbes; and (ii) analyse the etiology and prevention of various microbial diseases 6.0 Tutor Marked Assessment i. Group the diseases on basis of their causative agent, listing the name, location in the host, mode of transmission, part of the host body affected, clinical manifestation, treatment and prevention of each disease. ii. Analyse the etiology and prevention of various microbial diseases 7.0 Further Reading Green, N. P., G. W. Stout, D. J. Taylor and R. Soper (1984) Biological Sciences. Cambridge University Press.; London. 472pp. Jawetz, E. 1. L. Melnick and E. A. Adeberg (1980) Review of medical microbiology. Lenge Medical Publication. 593pp.: Stanier, R. Y., I. L Ingraham, M. L: Wheelis and P. R Painter (1987) General Microbiology. Macmillan Education Ltd., London, Sill ed. 690pp. Thomas, C, G A. (1983) Medical Microbiology, Balliere Tindall Cassel Ltd., Eastbourne BN21 3 UN. 405 pp.