9 why do we fall ill


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9 why do we fall ill

  1. 1. C hapter 13 WHY DO WE FALL ILL Activity _____________ 13.1 the kidney is filtering urine, the brain is thinking. • We have all heard of the earthquakes All these activities are interconnected. For in Latur, Bhuj, Kashmir etc. or the example, if the kidneys are not filtering urine, cyclones that attack the coastal poisonous substances will accumulate. Under regions. Think of as many different such conditions, the brain will not be able to ways as possible in which people’s think properly. For all these interconnected health would be affected by such a disaster if it took place in our activities, energy and raw material are needed neighbourhood. from outside the body. In other words, food • How many of these ways we can think of is a necessity for cell and tissue functions. are events that would occur when the Anything that prevents proper functioning of disaster is actually happening? cells and tissues will lead to a lack of proper • How many of these health-related events activity of the body. would happen long after the actual It is in this context that we will now look disaster, but would still be because of the at the notions of health and disease. disaster? • Why would one effect on health fall into the first group, and why would another 13.1 Health and its Failure fall into the second group? 13.1.1 THE SIGNIFICANCE OF ‘HEALTH’ When we do this exercise, we realise thathealth and disease in human communities We have heard the word ‘health’ used quiteare very complex issues, with many frequently all around us. We use it ourselvesinterconnected causes. We also realise that as well, when we say things like ‘mythe ideas of what ‘health’ and ‘disease’ mean grandmother’s health is not good’. Ourare themselves very complicated. When we teachers use it when they scold us saying ‘thisask what causes diseases and how we prevent is not a healthy attitude’. What does the wordthem, we have to begin by asking what these ‘health’ mean?notions mean. If we think about it, we realise that it We have seen that cells are the basic units always implies the idea of ‘being well’. We canof living beings. Cells are made of a variety of think of this well-being as ef fectivechemical substances – proteins, carbo- functioning. For our grandmothers, being ablehydrates, fats or lipids, and so on. Although to go out to the market or to visit neighboursthe pictures look quite static, in reality the is ‘being well’, and not being able to do suchliving cell is a dynamic place. Something or things is ‘poor health’. Being interested inthe other is always happening. Cells move following the teaching in the classroom so thatfrom place to place. Even in cells that do not we can understand the world is called amove, there is repair going on. New cells are ‘healthy attitude’; while not being interestedbeing made. In our organs or tissues, there is called the opposite. ‘Health’ is therefore aare various specialised activities going on – state of being well enough to function wellthe heart is beating, the lungs are breathing, physically, mentally and socially.
  2. 2. 13.1.2 PERSONAL AND COMMUNITY ISSUES We need food for health, and this food will have to be earned by doing work. For this, BOTH MATTER FOR HEALTH the opportunity to do work has to be available.If health means a state of physical, mental Good economic conditions and jobs areand social well-being, it cannot be something therefore needed for individual health.that each one of us can achieve entirely on We need to be happy in order to be trulyour own. The health of all organisms will healthy, and if we mistreat each other anddepend on their surroundings or their are afraid of each other, we cannot be happyenvironment. The environment includes the or healthy. Social equality and harmony arephysical environment. So, for example, health therefore necessary for individual health. Weis at risk in a cyclone in many ways. can think of many other such examples of But even more importantly, human beings connections between community issues andlive in societies. Our social environment, individual health.therefore, is an important factor in ourindividual health. We live in villages, towns 13.1.3 DISTINCTIONS BETWEEN ‘HEALTHY’or cities. In such places, even our physical AND ‘DISEASE-FREE’environment is decided by our socialenvironment. If this is what we mean by ‘health’, what do Consider what would happen if no agency we mean by ‘disease’? The word is actuallyis ensuring that garbage is collected and self-explanatory – we can think of it asdisposed. What would happen if no one takes ‘disease’ – disturbed ease. Disease, in otherresponsibility for clearing the drains and words, literally means being uncomfortable.ensuring that water does not collect in the However, the word is used in a more limitedstreets or open spaces? meaning. We talk of disease when we can find So, if there is a great deal of garbage a specific and particular cause for discomfort.thrown in our streets, or if there is open drain- This does not mean that we have to know thewater lying stagnant around where we live, absolute final cause; we can say thatthe possibility of poor health increases. someone is suffering from diarrhoea withoutTherefore, public cleanliness is important for knowing exactly what has caused the looseindividual health. motions. We can now easily see that it is possible Activity _____________ 13.2 to be in poor health without actually suffering from a particular disease. Simply not being • Find out what provisions are made by diseased is not the same as being healthy. your local authority (panchayat/ ‘Good health’ for a dancer may mean being municipal corporation) for the supply able to stretch his body into difficult but of clean drinking water. • Are all the people in your locality able graceful positions. On the other hand, good to access this? health for a musician may mean having enough breathing capacity in his/her lungs to control Activity _____________ 13.3 the notes from his/her flute. To have the opportunity to realise the unique potential • Find out how your local authority in all of us is also necessary for real health. manages the solid waste generated in So, we can be in poor health without there your neighbourhood. being a simple cause in the form of an • Are these measures adequate? identifiable disease. This is the reason why, • If not, what improvements would you suggest? when we think about health, we think about • What could your family do to reduce societies and communities. On the other the amount of solid waste generated hand, when we think about disease, we think during a day/week? about individual sufferers.WHY DO WE FALL ILL 177
  3. 3. Q uestions 13.2.2 ACUTE AND CHRONIC DISEASES 1. State any two conditions The manifestations of disease will be different essential for good health. depending on a number of factors. One of the 2. State any two conditions most obvious factors that determine how we essential for being free of disease. perceive the disease is its duration. Some 3. Are the answers to the above diseases last for only very short periods of questions necessarily the same time, and these are called acute diseases. We or different? Why? all know from experience that the common cold lasts only a few days. Other ailments can13.2 Disease and Its Causes last for a long time, even as much as a lifetime, and are called chronic diseases. An example13.2.1 WHAT DOES DISEASE LOOK LIKE? is the infection causing elephantiasis, which is very common in some parts of India.Let us now think a little more about diseases.In the first place, how do we know that there Activity _____________ 13.4is a disease? In other words, how do we know • Survey your neighbourhood to find out:that there is something wrong with the body? (1) how many people suffered fromThere are many tissues in the body, as we acute diseases during the last threehave seen in Chapter 6. These tissues make months,up physiological systems or organ systems (2) how many people developed chronicthat carry out body functions. Each of the diseases during this same period,organ systems has specific organs as its parts, (3) and finally, the total number ofand it has particular functions. So, the people suf fering from chronicdigestive system has the stomach and diseases in your neighbourhood.intestines, and it helps to digest food taken • Are the answers to questions (1) and (2) different?in from outside the body. The musculoskeletal • Are the answers to questions (2) andsystem, which is made up of bones and (3) different?muscles, holds the body parts together and • What do you think could be the reasonhelps the body move. for these differences? What do you think When there is a disease, either the would be the effect of these differencesfunctioning or the appearance of one or more on the general health of the population?systems of the body will change for the worse.These changes give rise to symptoms and 13.2.3 C HRONIC DISEASES AND POORsigns of disease. Symptoms of disease are the HEALTHthings we feel as being ‘wrong’. So we have aheadache, we have cough, we have loose As we can imagine, acute and chronicmotions, we have a wound with pus; these diseases have different effects on our health.are all symptoms. These indicate that there Any disease that causes poor functioning ofmay be a disease, but they don’t indicate what some part of the body will affect our generalthe disease is. For example, a headache may health as well. This is because all functionsmean just examination stress or, very rarely, of the body are necessary for general health.it may mean meningitis, or any one of a dozen But an acute disease, which is over very soon,different diseases. will not have time to cause major effects on Signs of disease are what physicians will general health, while a chronic disease willlook for on the basis of the symptoms. Signs do so.will give a little more definite indication of As an example, think about a cough andthe presence of a particular disease. cold, which all of us have from time to time.Physicians will also get laboratory tests done Most of us get better and become well withinto pinpoint the disease further. a week or so. And there are no bad effects on 178 SCIENCE
  4. 4. our health. We do not lose weight, we do not would not lead to loose motions. But they dobecome short of breath, we do not feel tired become contributory causes of the disease.all the time because of a few days of cough Why was there no clean drinking waterand cold. But if we get infected with a chronic for the baby? Perhaps because the publicdisease such as tuberculosis of the lungs, services are poor where the baby’s familythen being ill over the years does make us lives. So, poverty or lack of public serviceslose weight and feel tired all the time. become third-level causes of the baby’s We may not go to school for a few days if disease.we have an acute disease. But a chronic It will now be obvious that all diseasesdisease will make it difficult for us to follow will have immediate causes and contributorywhat is being taught in school and reduce causes. Also, most diseases will have manyour ability to learn. In other words, we are causes, rather than one single cause.likely to have prolonged general poor healthif we have a chronic disease. Chronic diseases 13.2.5 INFECTIOUS AND NON-INFECTIOUStherefore, have very drastic long-term effects CAUSESon people’s health as compared to acutediseases. As we have seen, it is important to keep public health and community health factors in mind13.2.4 CAUSES OF DISEASES when we think about causes of diseases. We can take that approach a little further. It isWhat causes disease? When we think about useful to think of the immediate causes ofcauses of diseases, we must remember that disease as belonging to two distinct types. Onethere are many levels of such causes. Let us group of causes is the infectious agents,look at an example. If there is a baby suffering mostly microbes or micro-organisms.from loose motions, we can say that the cause Diseases where microbes are the immediateof the loose motions is an infection with a causes are called infectious diseases. This isvirus. So the immediate cause of the disease because the microbes can spread in theis a virus. community, and the diseases they cause will But the next question is – where did the spread with them.virus come from? Suppose we find that thevirus came through unclean drinking water. Things to ponderBut many babies must have had this unclean 1. Do all diseases spread to peopledrinking water. So, why is it that one baby coming in contact with a sick person?developed loose motions when the other 2. What are the diseases that are notbabies did not? spreading? One reason might be that this baby is not 3. How would a person develop thosehealthy. As a result, it might be more likely diseases that don’t spread by contactto have disease when exposed to risk, whereas with a sick person?healthier babies would not. Why is the babynot healthy? Perhaps because it is not well On the other hand, there are also diseasesnourished and does not get enough food. So, that are not caused by infectious agents. Theirlack of good nourishment becomes a second- causes vary, but they are not external causeslevel cause of the disease the baby is suffering like microbes that can spread in thefrom. Further, why is the baby not well community. Instead, these are mostlynourished? Perhaps because it is from a internal, non-infectious causes.household which is poor. For example, some cancers are caused by It is also possible that the baby has some genetic abnormalities. High blood pressuregenetic difference that makes it more likely can be caused by excessive weight and lackto suffer from loose motions when exposed of exercise. You can think of many otherto such a virus. Without the virus, the genetic diseases where the immediate causes will notdifference or the poor nourishment alone be infectious.WHY DO WE FALL ILL 179
  5. 5. The ways in which diseases spread, and Peptic ulcers and the Nobel prize the ways in which they can be treated andFor many years, everybody used to think prevented at the community level would bethat peptic ulcers, which cause acidity– different for different diseases. This wouldrelated pain and bleeding in the stomach depend a lot on whether the immediateand duodenum, were because of lifestyle causes are infectious or non-infectious.reasons. Everybody thought that a Qstressful life led to a lot of acid secretionin the stomach, and eventually causedpeptic ulcers. uestions Then two Australians made a discovery 1. List any three reasons why youthat a bacterium, Helicobacter pylori, wasresponsible for peptic ulcers. Robin Warren would think that you are sick and(born 1937), a pathologist from Perth, ought to see a doctor. If only oneAustralia, saw these small curved bacteria of these symptoms were present,in the lower part of the stomach in many would you still go to the doctor?patients. He noticed that signs of Why or why not?inflammation were always present around 2. In which of the following case dothese bacteria. Barry Marshall (born 1951), you think the long-term effects ona young clinical fellow, became interested your health are likely to be mostin Warren’s findings and succeeded incultivating the bacteria from these sources. unpleasant? In treatment studies, Marshall and • if you get jaundice,Warren showed that patients could be • if you get lice,cured of peptic ulcer only when the • if you get acne.bacteria were killed off from the stomach. Why?Thanks to this pioneering discovery byMarshall and Warren, peptic ulcer diseaseis no longer a chronic, frequently disabling 13.3 Infectious Diseasescondition, but a disease that can be curedby a short period of treatment withantibiotics. 13.3.1 INFECTIOUS AGENTS We have seen that the entire diversity seen in the living world can be classified into a few groups. This classification is based on common characteristics between different organisms. Organisms that can cause disease are found in a wide range of such categories of classification. Some of them are viruses, some are bacteria, some are fungi, some are single-celled animals or protozoans. Some For this achievement, Marshall and diseases are also caused by multicellularWarren (seen in the picture) received the organisms, such as worms of different kinds.Nobel prize for physiology and medicinein 2005. 180 SCIENCE
  6. 6. Fig. 13.1(a): Picture of SARS viruses coming out (see arrows for examples) of the surface of an infected cell. The white scale line represents 500 nanometres, which is half a micrometre, which is one- thousandth of a millimetre. The scale line gives us an idea of how small the things we are looking at are. Fig. 13.1(d): Picture of Leishmania, the protozoan Courtesy: Emerging Infectious organism that causes kala-azar. The Deseases, a journal of CDC, U.S. organisms are oval-shaped, and each has one long whip-like structure. One organism (arrow) is dividing, while a cell of the immune system (lower right) has gripped on the two whips of the dividing organism and is sending cell processes up to eat up the organism. The immune cell is about ten micrometres in diameter.Fig. 13.1(b): Picture of staphylococci, the bacteria which can cause acne. The scale of the image is indicated by the line at top left, which is 5 micrometres long.Fig. 13.1(c): Picture of Trypanosoma, the protozoan organism responsible for sleeping sickness. The organism is lying next to Fig. 13.1(e): Picture of an adult roundworm (Ascaris a saucer-shaped red blood cell to give lumbricoides is the technical name) from an idea of the scale. the small intestine. The ruler next to it Copyright: Oregon Health and Science shows four centimetres to give us an University, U.S. idea of the scale.WHY DO WE FALL ILL 181
  7. 7. Common examples of diseases caused by But viruses do not use these pathways atviruses are the common cold, influenza, all, and that is the reason why antibiotics dodengue fever and AIDS. Diseases like typhoid not work against viral infections. If we have afever, cholera, tuberculosis and anthrax are common cold, taking antibiotics does notcaused by bacteria. Many common skin reduce the severity or the duration of theinfections are caused by different kinds of disease. However, if we also get a bacterialfungi. Protozoan microbes cause many infection along with the viral cold, takingfamiliar diseases, such as malaria and kala- antibiotics will help. Even then, the antibioticazar. All of us have also come across intestinal will work only against the bacterial part ofworm infections, as well as diseases like the infection, not the viral infection.elephantiasis caused by diffferent species ofworms. Activity _____________ 13.5 Why is it important that we think of thesecategories of infectious agents? The answer • Find out how many of you in your classis that these categories are important factors had cold/cough/fever recently.in deciding what kind of treatment to use. • How long did the illness last? • How many of you took antibiotics (askMembers of each one of these groups – your parents if you had antibiotics)?viruses, bacteria, and so on – have many • How long wer e those who tookbiological characteristics in common. antibiotics ill? All viruses, for example, live inside host • How long were those who didn’t takecells, whereas bacteria very rarely do. Viruses, antibiotics ill?bacteria and fungi multiply very quickly, while • Is there a difference between these twoworms multiply very slowly in comparison. groups?Taxonomically, all bacteria are closely related • If yes, why? If not, why not?to each other than to viruses and vice versa.This means that many important lifeprocesses are similar in the bacteria group 13.3.2 MEANS OF SPREADbut are not shared with the virus group. As a How do infectious diseases spread? Manyresult, drugs that block one of these life microbial agents can commonly move fromprocesses in one member of the group is likely an affected person to someone else in a varietyto be effective against many other members of ways. In other words, they can beof the group. But the same drug will not work ‘communicated’, and so are also calledagainst a microbe belonging to a different communicable diseases.group. Such disease-causing microbes can As an example, let us take antibiotics. spread through the air. This occurs throughThey commonly block biochemical pathways the little droplets thrown out by an infectedimportant for bacteria. Many bacteria, for person who sneezes or coughs. Someoneexample, make a cell-wall to protect standing close by can breathe in thesethemselves. The antibiotic penicillin blocks droplets, and the microbes get a chance tothe bacterial processes that build the cell-wall. As a result, the growing bacteria become start a new infection. Examples of suchunable to make cell-walls, and die easily. diseases spread through the air are theHuman cells don’t make a cell-wall anyway, common cold, pneumonia and tuberculosis.so penicillin cannot have such an effect on We all have had the experience of sittingus. Penicillin will have this effect on any near someone suffering from a cold andbacteria that use such processes for making catching it ourselves. Obviously, the morecell-walls. Similarly, many antibiotics work crowded our living conditions are, the moreagainst many species of bacteria rather than likely it is that such airborne diseases willsimply working against one. spread. 182 SCIENCE
  8. 8. inevitable that many diseases will be transmitted by other animals. These animals carry the infecting agents from a sick person to another potential host. These animals are thus the intermediaries and are called vectors. The commonest vectors we all know are mosquitoes. In many species of mosquitoes, the females need highly nutritious food in the form of blood in order to be able to lay mature eggs. Mosquitoes feed on many warm-blooded animals, including us. In this way, they can transfer diseases from person to person.Fig. 13.2: Air-transmitted diseases are easier to catch the closer we are to the infected person. However, in closed areas, the droplet nuclei recirculate and pose a risk to everybody. Overcrowded and poorly ventilated housing is therefore a major factor in the spread of airborne diseases. Diseases can also be spread throughwater. This occurs if the excreta from someonesuffering from an infectious gut disease, suchas cholera, get mixed with the drinking waterused by people living nearby. The cholera-causing microbes will enter new hoststhrough the water they drink and causedisease in them. Such diseases are muchmore likely to spread in the absence of safesupplies of drinking water. Fig. 13.3: Common methods of transmission of The sexual act is one of the closest diseases.physical contact two people can have witheach other. Not surprisingly, there aremicrobial diseases such as syphilis or AIDS 13.3.3 O RGAN - SPECIFIC AND TISSUE -that are transmitted by sexual contact from SPECIFIC MANIFESTATIONSone partner to the other. However, suchsexually transmitted diseases are not spread The disease-causing microbes enter the bodyby casual physical contact. Casual physical through these different means. Where do theycontacts include handshakes or hugs or go then? The body is very large whensports, like wrestling, or by any of the other compared to the microbes. So there are manyways in which we touch each other socially. possible places, organs or tissues, where theyOther than the sexual contact, the AIDS virus could go. Do all microbes go to the same tissuecan also spread through blood-to-blood or organ, or do they go to different ones?contact with infected people or from an Different species of microbes seem to haveinfected mother to her baby during pregnancy evolved to home in on different parts of theor through breast feeding. body. In part, this selection is connected to We live in an environment that is full of their point of entry. If they enter from the airmany other creatures apart from us. It is via the nose, they are likely to go to the lungs.WHY DO WE FALL ILL 183
  9. 9. This is seen in the bacteria causing minor gut infection can produce majortuberculosis. If they enter through the mouth, diarrhoea with blood loss. Ultimately, it isthey can stay in the gut lining like typhoid- these other infections that kill peoplecausing bacteria. Or they can go to the liver, suffering from HIV-AIDS.like the viruses that cause jaundice. It is also important to remember that the But this needn’t always be the case. An severity of disease manifestations depend oninfection like HIV, that comes into the body the number of microbes in the body. If thevia the sexual organs, will spread to lymph number of microbes is very small, the diseasenodes all over the body. Malaria-causing manifestations may be minor or unnoticed.microbes, entering through a mosquito bite, But if the number is of the same microbewill go to the liver, and then to the red blood large, the disease can be severe enough to becells. The virus causing Japanese life-threatening. The immune system is aencephalitis, or brain fever, will similarly enter major factor that determines the number ofthrough a mosquito bite. But it goes on to microbes surviving in the body. We shall lookinfect the brain. into this aspect a little later in the chapter. The signs and symptoms of a disease willthus depend on the tissue or organ which 13.3.4 PRINCIPLES OF TREATMENTthe microbe targets. If the lungs are thetargets, then symptoms will be cough and What are the steps taken by your family whenbreathlessness. If the liver is targeted, there you fall sick? Have you ever thought why you sometimes feel better if you sleep for somewill be jaundice. If the brain is the target, we time? When does the treatment involvewill observe headaches, vomiting, fits or medicines?unconsciousness. We can imagine what the Based on what we have learnt so far, itsymptoms and signs of an infection will be if would appear that there are two ways to treatwe know what the target tissue or organ is, an infectious disease. One would be to reduceand the functions that are carried out by this the effects of the disease and the other to killtissue or organ. the cause of the disease. For the first, we can In addition to these tissue-specific effectsof infectious disease, there will be other provide treatment that will reduce thecommon effects too. Most of these common symptoms. The symptoms are usuallyeffects depend on the fact that the body’s because of inflammation. For example, we canimmune system is activated in response to take medicines that bring down fever, reduceinfection. An active immune system recruits pain or loose motions. We can take bed rest somany cells to the affected tissue to kill off the that we can conserve our energy. This willdisease-causing microbes. This recruitment enable us to have more of it available to focusprocess is called inflammation. As a part of on healing.this process, there are local effects such as But this kind of symptom-directedswelling and pain, and general effects such treatment by itself will not make the infectingas fever. microbe go away and the disease will not be In some cases, the tissue-specificity of the cured. For that, we need to be able to kill offinfection leads to very general-seeming the microbes.effects. For example, in HIV infection, the How do we kill microbes? One way is tovirus goes to the immune system and use medicines that kill microbes. We have seendamages its function. Thus, many of the earlier that microbes can be classified intoeffects of HIV-AIDS are because the body can different categories. They are viruses, bacteria,no longer fight off the many minor infections fungi or protozoa. Each of these groups ofthat we face everyday. Instead, every small organisms will have some essentialcold can become pneumonia. Similarly, a biochemical life process which is peculiar to 184 SCIENCE
  10. 10. that group and not shared with the other we can get some easy answers. For airbornegroups. These processes may be pathways for microbes, we can prevent exposure bythe synthesis of new substances or respiration. providing living conditions that are not These pathways will not be used by us overcrowded. For water-borne microbes, weeither. For example, our cells may make new can prevent exposure by providing safesubstances by a mechanism different from drinking water. This can be done by treatingthat used by bacteria. We have to find a drug the water to kill any microbial contamination.that blocks the bacterial synthesis pathway For vector-borne infections, we can providewithout affecting our own. This is what is clean environments. This would not, forachieved by the antibiotics that we are all example, allow mosquito breeding. In otherfamiliar with. Similarly, there are drugs that words, public hygiene is one basic key to thekill protozoa such as the malarial parasite. prevention of infectious diseases. One reason why making anti-viral In addition to these issues that relate tomedicines is harder than making anti- the environment, there are some other generalbacterial medicines is that viruses have few principles to prevent infectious diseases. Tobiochemical mechanisms of their own. They appreciate those principles, let us ask aenter our cells and use our machinery for question we have not looked at so far.their life processes. This means that there Normally, we are faced with infectionsare relatively few virus-specific targets to aim everyday. If someone is suffering from a coldat. Despite this limitation, there are now and cough in the class, it is likely that theeffective anti-viral drugs, for example, the children sitting around will be exposed to thedrugs that keep HIV infection under control. infection. But all of them do not actually suffer from the disease. Why not?13.3.5 PRINCIPLES OF PREVENTION This is because the immune system of our body is normally fighting off microbes. WeAll of what we have talked about so far deals have cells that specialise in killing infectingwith how to get rid of an infection in someone microbes. These cells go into action each timewho has the disease. But there are three infecting microbes enter the body. If they arelimitations of this approach to dealing with successful, we do not actually come downinfectious disease. The first is that once with any disease. The immune cells managesomeone has a disease, their body functions to kill off the infection long before it assumesare damaged and may never recover major proportions. As we noted earlier, if thecompletely. The second is that treatment will number of the infecting microbes istake time, which means that someone controlled, the manifestations of disease willsuffering from a disease is likely to be be minor. In other words, becoming exposedbedridden for some time even if we can give to or infected with an infectious microbe doesproper treatment. The third is that the person not necessarily mean developing noticeablesuffering from an infectious disease can serve disease.as the source from where the infection mayspread to other people. This leads to the So, one way of looking at severe infectiousmultiplication of the above difficulties. It is diseases is that it represents a lack of successbecause of such reasons that prevention of of the immune system. The functioning of thediseases is better than their cure. immune system, like any other system in our How can we prevent diseases? There are body, will not be good if proper and sufficienttwo ways, one general and one specific to each nourishment and food is not available.disease. The general ways of preventing Therefore, the second basic principle ofinfections mostly relate to preventing prevention of infectious disease is theexposure. How can we prevent exposure to availability of proper and sufficient food forinfectious microbes? everyone. If we look at the means of their spreading,WHY DO WE FALL ILL 185
  11. 11. Activity _____________ 13.6 immunisation. • Conduct a survey in your locality. Immunisation Talk to ten families who are well-off Traditional Indian and Chinese medicinal and ten who are very poor (in your systems sometimes deliberately rubbed the estimation). Both sets of families skin crusts from smallpox victims into the should have children who are below skin of healthy people. They thus hoped five years of age. Measure the heights of these children. Draw a graph of the to induce a mild form of smallpox that height of each child against its age would create resistance against the for both sets of families. disease. • Is there a difference between the Famously, two centuries ago, an groups? If yes, why? English physician • If there is no difference, do you think named Edward that your findings mean that being Jenner, realised well-off or poor does not matter for that milkmaids health? who had had cowpox did not These are the general ways of preventing catch smallpoxinfections. What are the specific ways? They even duringrelate to a peculiar property of the immune epidemics.system that usually fights off microbial Cowpox is a veryinfections. Let us cite an example to try and mild disease.understand this property. Jenner tried These days, there is no smallpox deliberately givinganywhere in the world. But as recently as a cowpox to peoplehundred years ago, smallpox epidemics were (as he can be seen doing in the picture), andnot at all uncommon. In such an epidemic, found that they were now resistant topeople used to be very afraid of coming near smallpox. This was because the smallpoxsomeone suffering from the disease since they virus is closely related to the cowpox virus.were afraid of catching the disease. ‘Cow’ is ‘vacca’ in Latin, and cowpox is However, there was one group of people ‘vaccinia’. From these roots, the wordwho did not have this fear. These people wouldprovide nursing care for the victims of ‘vaccination’ has come into our usage.smallpox. This was a group of people who hadhad smallpox earlier and survived it, although We can now see that, as a general principle,with a lot of scarring. In other words, if you we can ‘fool’ the immune system intohad smallpox once, there was no chance of developing a memory for a particular infectionsuffering from it again. So, having the disease by putting something, that mimics the microbeonce was a means of preventing subsequent we want to vaccinate against, into the body.attacks of the same disease. This does not actually cause the disease but This happens because when the immune this would prevent any subsequent exposure to the infecting microbe from turning intosystem first sees an infectious microbe, it actual disease.responds against it and then remembers it Many such vaccines are now available forspecifically. So the next time that particular preventing a whole range of infectiousmicrobe, or its close relatives enter the body, diseases, and provide a disease-specificthe immune system responds with even means of prevention. There are vaccinesgreater vigour. This eliminates the infection against tetanus, diphtheria, whooping cough,even more quickly than the first time around. measles, polio and many others. These formThis is the basis of the principle of the public health programme of childhood 186 SCIENCE
  12. 12. immunisation for preventing infectious humans and animals. Find out thediseases. plan of your local authority for Of course, such a programme can be the control of rabies in your Quseful only if such health measures are neighbourhood. Are these measuresavailable to all children. Can you think of adequate? If not, what improvements would you suggest?reasons why this should be so? Some hepatitis viruses, which causejaundice, are transmitted through water. uestionsThere is a vaccine for one of them, hepatitis 1. Why are we normally advised toA, in the market. But the majority of children take bland and nourishing foodin many parts of India are already immune when we are sick?to hepatitis A by the time they are five years 2. What are the different means byold. This is because they are exposed to the which infectious diseases arevirus through water. Under these spread?circumstances, would you take the vaccine? 3. What precautions can you take in your school to reduce the Activity _____________ 13.7 incidence of infectious diseases? 4. What is immunisation? • Rabies virus is spread by the bite of infected dogs and other animals. There 5. What are the immunisation are anti-rabies vaccines for both programmes available at the nearest health centre in your locality? Which of these diseases are the major health problems in your area? What you have learnt • Health is a state of physical, mental and social well-being. • The health of an individual is dependent on his/her physical surroundings and his/her economic status. • Diseases are classified as acute or chronic, depending on their duration. • Disease may be due to infectious or non-infectious causes. • Infectious agents belong to different categories of organisms and may be unicellular and microscopic or multicellular. • The category to which a disease-causing organism belongs decides the type of treatment. • Infectious agents are spread through air, water, physical contact or vectors. • Prevention of disease is more desirable than its successful treatment. • Infectious diseases can be prevented by public health hygieneWHY DO WE FALL ILL 187
  13. 13. measures that reduce exposure to infectious agents. • Infectious diseases can also be prevented by using immunisation. • Effective prevention of infectious diseases in the community requires that everyone should have access to public hygiene and immunisation. Exercises 1. How many times did you fall ill in the last one year? What were the illnesses? (a) Think of one change you could make in your habits in order to avoid any of/most of the above illnesses. (b) Think of one change you would wish for in your surroundings in order to avoid any of/most of the above illnesses. 2. A doctor/nurse/health-worker is exposed to more sick people than others in the community. Find out how she/he avoids getting sick herself/himself. 3. Conduct a survey in your neighbourhood to find out what the three most common diseases are. Suggest three steps that could be taken by your local authorities to bring down the incidence of these diseases. 4. A baby is not able to tell her/his caretakers that she/he is sick. What would help us to find out (a) that the baby is sick? (b) what is the sickness? 5. Under which of the following conditions is a person most likely to fall sick? (a) when she is recovering from malaria. (b) when she has recovered from malaria and is taking care of someone suffering from chicken-pox. (c) when she is on a four-day fast after recovering from malaria and is taking care of someone suffering from chicken-pox. Why? 6. Under which of the following conditions are you most likely to fall sick? (a) when you are taking examinations. (b) when you have travelled by bus and train for two days. (c) when your friend is suffering from measles. Why?188 SCIENCE