Why do we fall ill – 2 (Cause & Prevention of Diseases)

Causes of Disease

            Disease may be caused due to several reasons like due to pathogens such as virus or bacteria; or due to internal factors such as genetic mutation; or even due to our negligence.  We may classify the causes in various ways, e.g.

1. Immediate cause and Contributory cause.

Immediate cause: The organisms that enter our body and causes disease is called immediate cause. For example, virus, bacteria, protozoa etc.

Contributory cause: The secondary factors which lead these organisms enter our body are known as contributory cause. For example, dirty water, unclear surroundings, contaminated food, improper nourishment, poverty, poor standard of living etc.

2. Infectious and Non-infectious Cause

Infectious causes:  

They include the agents like microbes or micro-organisms as the immediate causes which spread the disease from an infected person to a healthy person. Diseases that are caused by are called infectious diseases.

Examples are Tuberculosis, tetanus, Common cold, AIDS, etc.

Non-infectious causes: 

The disease which does not spread by contact between infected and healthy person is called non-infectious disease.

Examples are Cancer, genetic abnormalities, high blood pressure, etc.

In text questions of Class 9 Science NCERT Textbook – Page 180

Q 1. List any three reasons why you would think that you are sick and ought to see a doctor. If only one of these symptoms were present, would you still go to the doctor? Why or why not?
Answer: The 3 reasons why one would think that he is sick are—(1) headache, (2) cold and cough, (3) loose-motions.
            This indicates that there may be a disease but does not indicate what the disease is. So one would still visit the doctor for the treatment and to know the cause of above symptom.
            Even in case of single symptom one needs to go to the doctor to get proper treatment.

Q 2. In which of the following case do you think the long-term effects on your health are likely to be most unpleasant?  If you get jaundice; If you get lice; or If you get acne.Why?
Answer: In the above cases, lice and acne are acute problems of our health which can be cured in short duration. But jaundice is the disease that can have most unpleasant effect on our health as it affects the most important organ of our body i.e., liver. This disease is a chronic one.

Infectious Agents

When a disease causing organism enters our body it causes infection, it multiplies and grows in the body called host.  Some of the agents and diseases caused by them are listed here.

Bacteria           Tuberculosis, tetanus, typhoid, cholera

Virus                AIDS, polio, chicknenpox, rabies, measles

Fungi               Skin diseases

Protozoan        Malaria, amoebiasis, kala-azar

Worm              Filariasis

Means of Spreading Infectious Diseases:

How does the Disease manifest itself*

            Different species of microbes seem to have evolved to home in on different parts of the body. In part, this selection is connected to their point of entry.

• If they enter from the air via the nose, they are likely to go to the lungs.  This is seen in the bacteria causing tuberculosis.
• If they enter through the mouth, they can stay in the gut lining like typhoid causing bacteria. Or they can go to the liver, like the viruses that cause jaundice.

            But this needn’t always be the case.

• An infection like HIV, that comes into the body locally, will spread to lymph nodes all over the body.
• Malaria-causing microbes, entering through a mosquito bite, will go to the liver, and then to the red blood cells.
• The virus causing Japanese encephalitis, or brain fever, will similarly enter through a mosquito bite. But it goes on to infect the brain.

The signs and symptoms of a disease will depend on the tissue or organ which the microbe targets.

• If the lungs are the targets, then symptoms will be cough and breathlessness.
• If the liver is targeted, there will be jaundice.
• If the brain is the target, we will observe headaches, vomiting, fits or unconsciousness.

            But in HIV infection, the virus goes to the immune system and damages its function. Thus, many of the effects of HIV-AIDS are because the body can no longer fight off the many minor infections that we face everyday. Instead, every small cold can become pneumonia. Similarly, a minor gut infection can produce major diarrhoea with blood loss. Ultimately, it is these other infections that kill people suffering from HIV-AIDS.  AIDS stands for Acquired Immunodeficiency Syndrome. It is caused by the Human Immunodeficiency Virus or HIV.

*In addition to these tissue-specific effects, there will be other common effects too by which the disease manifests itself.

            Most of these common effects depend on the fact that the body’s immune system is activated in response to infection. An active immune system recruits many cells to the affected tissue to kill off the disease-causing microbes.

            This recruitment process is called inflammation.

Inflammation: When an active immune system release many cells to the affected tissue to fight off the disease-causing microbes it is called inflammation. Local effects caused on body due to inflammation are—swelling, pain, fever and redness.

            Inflammations help in the localization of the issue and prevent it from spreading.

Severity of Disease

            Severity of disease manifestations depend on the number of microbes in the body. If the number of microbes is very small, the disease manifestations may be minor or unnoticed. But if the number is large, the disease can be severe enough to be life-threatening.

            The immune system is a major factor that determines the number of microbes surviving in the body.  We will discuss about the immune system in detail at the end of the lesson.

PRINCIPLES OF TREATMENT

1. To reduce the effects of the diseases

            By taking medicines to bring down the effects of the disease like fever, pain, etc. and by taking complete rest to conserve the body’s energy so that body may concentrate on eliminating the microbes.

            But in addition to the method one needs to take medication to kill the microbes. So, second step is:

2. To kill the cause of the disease

By taking suitable antibiotics and drugs which kill the disease causing microbes.

            [In order to cure us antibiotics are largely used by doctors practicing modern medicine.  Though there are several other very effective ways of treatment which do not use antibiotics e.g. Ayurveda, Homeopathy etc. but that is out of course for this class. Coming to Antibiotics.  What are they?]

Antibiotics

            These are the chemicals that block biochemical pathways important for bacteria.  They are antimicrobial drugs produced from other organisms, such as fungus and some bacteria. 

Mode of action of Antibiotic:           

            The antibiotics function by one or more of the following ways:

• Inhibiting of Cell Wall Synthesis of the pathogen (a most common mechanism).
• Inhibition of Protein Synthesis (Translation) required for growth of the pathogens. (second largest class).
• Alteration of their Cell Membranes.
• Inhibiting their metabolic Activity.
• Inhibition of their Nucleic Acid Synthesis.

            [A word of caution regarding use of antibiotics.  Either don’t use it or if use it then do the complete prescribed course lest the pathogens become immune to that medicine.  Don’t stop the medicine unless doctor suggests].

            Antibiotics do not work against viral infections as the viruses do not have their own biochemical mechanisms [but depend upon that of the host.  But other streams of medicine mentioned above do cure the so called viral infections too].

            Why don’t we have anti viral medicines?

            Making an anti-viral medicines is harder than making an antibacterial medicine because viruses have few biochemical mechanisms of their own. They enter our cells and use our machinery for their life processes. This means that there are relatively few virus-specific targets to aim at. Despite the limitations, there are now effective anti-viral drugs, for example, the drugs that keep HIV infection under control.

Mircorbes causing the disease

            Before starting any treatment we need to know the mircorbes causing the problem.  The required list follows: 

Pathogens

            Pathogens are external agents that cause diseases in other organisms. This pathogen includes harmful microbes or microorganism such as bacteria, virus, fungi or protozoa.

Vector

            Vectors are those organisms that carry a pathogen from the host to a recipient. Mosquito, rats and mice are some of the common vectors that carry infectious diseases.

Bacteria

            Bacteria are microorganisms that are seen in almost all environmental condition. Not all bacteria are harmful. Some bacteria are also beneficial to human beings. Bacteria are beneficial for digestion, nitrogen fixation, extracting antibiotics from them – they are used to make medicines also, etc.

            Few of the common diseases caused by bacteria are cholera, typhoid, pneumonia, tuberculosis etc.

Virus

            A virus is a microorganism that is always pathogenic in nature. They do not have their own machinery to replicate. Therefore they enter the host cell and replicate their; and in the process destroy the host cell. Few of the common diseases spread by the viruses are cold, influenza, dengue fever etc.

Fungi

            Fungi are a group of organisms which are eukaryotic in nature and saprophytic in nutrition (live on dead or decaying organic matter). They could be either unicellular or multicellular organism. Many common skin infections such as ringworm, nail infection, etc are examples of Fungal diseases.

Parasites

            A parasite is an organism that lives in another organism, called the host, and often harms it. It is dependent on its host for survival – it has to be in the host to live, grow and multiply.  Examples are tape worm, round worm etc.  They enter our body and take away the digested food from us in turn depleting us of nutrition and making us ill.

PRINCIPLES OF PREVENTION

            All of what we have talked about so far deals with how to get rid of an infection in someone who has the disease. But there are three limitations of this approach to dealing with infectious disease.

• Once someone has a disease, their body functions are damaged and may never recover completely.
• Treatment will take time, which means that someone suffering from a disease is likely to be bedridden for some time even if we can give proper treatment.
• The person suffering from an infectious disease can serve as the source from where the infection may spread to other people. This leads to the multiplication of the above difficulties.

            It is because of such reasons that prevention of diseases is better than their cure.

            How can we prevent diseases? There are two ways, one general and one specific to each disease.

General ways of preventing infections      

            The general ways of preventing infections mostly relate to preventing exposure. How can we prevent exposure to infectious microbes? If we look at the means of their spreading, we can get some easy answers.

• For airborne microbes, we can prevent exposure by providing living conditions that are not overcrowded.
• For water-borne microbes, we can prevent exposure by providing safe drinking water. This can be done by treating the water to kill any microbial contamination.
• For vector-borne infections, we can provide clean environments. This would not, for example, allow mosquito breeding. In other words, public hygiene is one basic key to the prevention of infectious diseases.
• In addition to them the immune system of our body is normally fighting off microbes. Becoming exposed to or infected with an infectious microbe does not necessarily mean developing noticeable disease. So, one way of looking at severe infectious diseases is that it represents a lack of success of the immune system. The functioning of the immune system, like any other system in our body, will not be good if proper and sufficient nourishment and food is not available.  So the basic principle of prevention of infectious disease is the availability of proper and sufficient food for everyone.  Proper nourishment or healthy diet that includes all the necessary nutrients as well as vitamins and minerals is necessary for better functioning of our immune system.

A few words on the immune system.

The Immune System

            An immune system is the part of the body that provides protection against infection from pathogens, invading foreign substances and other toxins.  The immune system includes the following:

1. Skin and Mucous Membranes

            Skin and Mucous membranes act as the layer of defence. While skin protects the body externally, mucous membrane protects the insides of the body.

2. WBC

            WBC or the White blood cells are called Leucocytes or Leukocytes. They are the important components of our immune system and are present in the blood and lymph.  They function by attacking and killing the pathogens and protect our body by making it free from pathogens and infections.  The different types of White blood cells found in the blood are neutrophils, lymphocytes, monocytes, basophils, ad eosinophils. These blood cells have specialized functions.

3. Macrophages and NK Cells

            Macrophages are large and specialized cells of the immune system.  These cells are produced in response to infections or due to the development of damaged or dead cells. They attack cancer cells through destruction and ingestion. Natural Killer Cells bind to the enemy cell and they dissolve the membrane so the enemy cell can no longer function.

4. Dendritic Cells

            Dendritic cells create the memory and carry information about the pathogens to the liver, spleen, lymph nodes for preparing them to fight / produce the fighters.]

IMMUNIZATION – The Specific way of preventing infections        

            They relate to a peculiar property of the immune system that usually fights off microbial infections.

Story of small pox

            [Let us cite an example to try and understand this property. These days, there is no smallpox (Chechak) anywhere in the world. But as recently as a hundred years ago, smallpox epidemics were not at all uncommon. In such an epidemic, people used to be very afraid of coming near someone suffering from the disease since they were afraid of catching the disease. However, there was one group of people who did not have this fear. These people would provide nursing care for the victims of smallpox. This was a group of people who had had smallpox earlier and survived it, although with a lot of scarring. In other words, if you had smallpox once, there was no chance of suffering from it again.]

             Having the disease once acts as a means of preventing subsequent attacks of the same disease. This happens because when the immune system first sees an infectious microbe, it responds against it and then remembers it specifically. So the next time that particular microbe, or its close relatives enter the body, the immune system responds with even greater vigour. This eliminates the infection even more quickly than the first time around. This is the basis of the principle of vaccination. 

Immunization

            Immunization is the process whereby a person is made immune or resistant to an infectious disease. Vaccines are the common means to immunize people.

            We can now see that, as a general principle, we can ‘fool’ the immune system into developing a memory for a particular infection by putting something, that mimics the microbe we want to vaccinate against, into the body. This does not actually cause the disease but this would prevent any subsequent exposure to the infecting microbe from turning into actual disease. Many such vaccines are now available for preventing a whole range of infectious diseases, and provide a disease-specific means of prevention. There are vaccines against tetanus, diphtheria, whooping cough, measles, polio and many others.

            These form the public health programme of childhood immunisation for preventing infectious diseases. Of course, such a programme can be useful only if such health measures are available to all children. So that full lot of immunized people grow up.

[A Word of caution with regards to Immunization – The Fever etc.

It is my suggestion not to take medication to bring down the fever etc. which appear after taking immunization doses of certain diseases. In fact fever appears as a symptom of our system fighting with the the germs injected while vaccination. It is possible that the fight becomes slow when other medications are done to suppress the fight. It might negate the immunization effort.]

In text questions from Textbook for Class 9 NCERT Science – Page 186

Q 1. Why are we normally advised to take bland (soft) and nourishing food when we are sick?
Answer: Because our body needs more and more energy to get newer cells made / released to overcome the infection, and replace the cells dying during the wear and tear of body organ. The nourishing food provides nutrients to our body that will further provide energy and make new cells. No spices in the food makes its digestion process faster, does not release acids in the body that can interfere in the treatment and cure.

Q 2. What are the different means by which infectious diseases are spread?
Answer: The different means by which infectious diseases get spread are:
(a) Through air: They are also called air-borne diseases. The air carries bacteria, virus and the diseases that can cause common cold, influenza, tuberculosis etc.
(b) Through food and water: When one eats/drinks contaminated food/water, that contains bacteria, virus, worm etc. it can cause diseases like cholera typhoid, hepatitis.
(c) Through contact: Many diseases spread by contact of infected person with the healthy person. Example, fungal infections, skin diseases, scabies etc.
(d) By sexual contact: Dreadly Diseases like syphilis, AIDS can be transmitted by this way.

(e) By body fluids: Fluids like blood, semen, mother’s milk, when infected,
can also transmit diseases like AIDS.
(f) By Vectors: The organism that spreads a disease by carrying pathogens from one place to another is called vector. Example, Female Anopheles mosquitoes are vectors that carry parasites called plasmodium which causes malaria.

Q 3. What precautions can you take in your school to reduce the incidence of infectious diseases?
Answer: The precautions that one can take in school to reduce the incidence of infectious diseases are
(a) By using handkerchief while coughing and sneezing.
(b) Washing hands before eating.
(c) Requesting the infected to stay at home.
(d) Getting vaccinated before the infection affects.
(e) Keeping the school surroundings clean, and checking for stagnant water and reporting it to teacher for further action.

Q 4. What is immunisation?
Answer: Immunization is the process whereby a person is made immune or resistant to an infectious disease. Vaccines are the common means to immunize people.

Q 5. What are the immunisation programmes available at the nearest health centre in your locality? Which of these diseases are the major health problems in your area?
Answer: The immunization programmes available at the nearest health care centres are:

Polio eradication programme

H1N1 screening programme for Swine Flue

Child immunization programme starts from 0 to 12 years.

In major areas tuberculosis cases are reported in a large number which is a major concern.