Chapter 5 — ରୋଗ ଓ ତାହାର ନିରାକରଣ (Diseases and Their Prevention)

The World Health Organisation defines health as a state of complete physical, mental and social well being, and not merely the absence of disease or infirmity. A healthy person's body works well, without pain or weakness, he is able to do his work and enjoy it, his mind is at ease and he gets on with the people around him. Health is therefore not a matter of the body alone. A student who is free of illness but sleepless with worry, or who has no friends and feels unwanted, is not fully healthy. And a person who is physically fit but lives in a community that has no clean water, no drainage and constant quarrels is likely soon to lose his health as well. The word disease literally means 'dis-ease', a state of discomfort, in which the normal functioning of the body or mind is disturbed.

Health depends on several conditions. First, the physical environment: clean air, safe drinking water, proper disposal of garbage and sewage, and a house free of damp, smoke and mosquitoes. A village where refuse is dumped in the open and the drains overflow will have more diarrhoea, more malaria and more worms than one that is kept clean, however careful each family may be inside its own house. Second, nutrition: the body needs a balanced diet of adequate quantity to grow, to work and to resist infection; the hungry child falls ill more often and recovers more slowly. Third, personal habits: bathing, washing hands before eating and after using the toilet, brushing teeth, wearing clean clothes, sleeping enough, exercising, and avoiding tobacco, alcohol and drugs. Fourth, social conditions: a job, a secure income, education, freedom from fear and violence, and good relations with family and neighbours. Since these conditions are shared, health is a community matter as much as an individual one, and public health measures, water supply, sanitation, immunisation, control of mosquitoes and health education, do more to keep a population healthy than all the hospitals put together.

Health has both individual and social importance. To the individual it means the capacity to learn, to work, to earn and to enjoy life; to a family it means income and freedom from the cost of illness; to the nation it means a productive workforce and lower spending on treatment. Illness, on the other hand, brings pain, loss of work and wages, expense on medicines, and sometimes permanent disability or death. This is why prevention, which is cheaper and kinder than cure, is the theme of the whole chapter. The signs by which we recognise that something is wrong are called symptoms (what the patient feels: headache, fever, loose motions, cough) and signs (what the doctor finds: a rash, a swollen liver, an abnormal blood count). Symptoms tell us that there is a disease; they seldom tell us which one, and a doctor uses the history, the examination and laboratory tests to reach a diagnosis.

Diseases are classified in several ways, and the classifications overlap.

On the basis of duration, a disease is acute if it lasts a short time, days or a few weeks, and then either ends in recovery or in death: common cold, influenza, typhoid, cholera, measles. It is chronic if it lasts a long time, months or years, and often the whole of life: tuberculosis, leprosy, diabetes, asthma, arthritis, elephantiasis. Acute diseases may be severe while they last but usually leave no lasting damage; chronic diseases have far greater effects on health, because their long duration weakens the body, prevents work and study, drains the family's money and may cause permanent disability. A cold for a week does not affect a child's growth; tuberculosis for two years does.

On the basis of cause, a disease is infectious (communicable) if it is caused by a living agent, a microbe or a parasite, that can pass from one person to another; malaria, tuberculosis, cholera, influenza, AIDS and COVID-19 are infectious. The agent may spread directly, through the air, by touch or by sexual contact, or indirectly, through water, food, soil, objects or an insect vector. A disease is non-infectious (non-communicable) if it is not caused by an agent that can be passed on; it arises from within the body or from the person's habits and environment. Non-infectious diseases include:

• Deficiency diseases, caused by lack of a nutrient in the diet: anaemia (iron), goitre (iodine), rickets (vitamin D), scurvy (vitamin C), night blindness (vitamin A), beri-beri (vitamin B1), kwashiorkor and marasmus (protein and energy).
• Degenerative diseases, caused by the wearing out of organs with age or misuse: heart disease, hypertension, stroke, arthritis, cataract.
• Metabolic and hormonal diseases: diabetes, obesity, thyroid disorders.
• Allergies, an over reaction of the body to harmless substances: asthma, hay fever, eczema.
• Cancers, uncontrolled multiplication of the body's own cells.
• Mental illnesses such as depression and schizophrenia, and injuries and poisonings.

On the basis of origin, a congenital disease is present from birth, caused by a defect in the genes (haemophilia, colour blindness, thalassaemia, sickle cell anaemia, which is common in western Odisha) or by damage during pregnancy (cleft lip, some heart defects, defects caused by the mother's rubella infection); congenital diseases are lifelong and usually cannot be cured, though their effects may be managed. An acquired disease develops after birth. Congenital diseases caused by genes may be hereditary, passed from parent to child; acquired diseases are never passed on in this way, though an infectious disease may pass from mother to baby.

Finally, diseases may be endemic, always present at a low level in an area, as malaria is in many districts of Odisha; epidemic, when the number of cases suddenly rises far above the usual level, as in an outbreak of cholera after floods; and pandemic, an epidemic spread across countries and continents, as with influenza in 1918 and COVID-19 in 2020. Sporadic diseases occur as scattered single cases.

Why does a person fall ill? The obvious answer for an infectious disease is that a microbe entered the body. But this answer is incomplete, because in a village where every child drinks the same water only some fall ill with diarrhoea, and of a hundred people exposed to the tuberculosis bacterium only a few develop the disease. Disease usually has more than one cause, arranged in levels.

The immediate cause is the agent that directly produces the disease: the cholera bacterium, the malaria parasite, the dengue virus, the lack of vitamin C. Without this agent the particular disease cannot occur. But the immediate cause acts only when other conditions allow it. These are the contributory causes, the second level. A child got diarrhoea because he drank contaminated water; the water was contaminated because the village has no sewage system and the well is beside the drain; the child was badly affected because he was already undernourished and his body could not resist; he was undernourished because his family is poor. Each of these is a contributory cause, and the whole chain, from the poverty and lack of sanitation of the community through the child's poor nutrition to the microbe in the water, is the true explanation of his illness.

Contributory causes may be grouped:

• Environmental: unsafe water, poor sanitation, open defecation, overcrowding, stagnant water breeding mosquitoes, polluted air, unsafe working conditions.
• Nutritional: undernutrition lowers resistance to every infection; the malnourished child dies of measles that a well fed child shrugs off.
• Personal: lack of hygiene, smoking, alcohol, drugs, lack of exercise, unsafe sexual behaviour, refusal of vaccination.
• Genetic: inherited weaknesses that make some people susceptible to diabetes, hypertension, certain cancers or allergies.
• Social and economic: poverty, ignorance, lack of health services, discrimination, war and displacement.

The distinction matters for prevention. A doctor treats the immediate cause with a medicine; a community prevents the disease by removing the contributory causes. Killing the cholera bacterium in one patient cures him; supplying clean water to the village prevents cholera in everyone. This is why public health depends on engineers, teachers and elected bodies as much as on doctors. It also explains why the same disease may be mild in a healthy person and fatal in a weak one, and why the poor, who face the most contributory causes, suffer most from disease. The chain of causation is a favourite examination question and should be answered with a concrete example: microbe, the way it reached the patient, why the patient was vulnerable, and the social condition behind that.

For non-infectious diseases the same logic applies. The immediate cause of a heart attack is the blocking of an artery; the contributory causes are smoking, a fatty diet, lack of exercise, obesity, diabetes, high blood pressure, stress and family history, and most of these can be changed.

Infectious diseases are caused by living organisms that enter the body, multiply there and damage it. Such organisms are called pathogens (disease producers), and the relationship in which one organism lives in or on another and harms it is parasitism. The pathogens belong to five groups, and it is important to know the group, because the treatment differs for each.

Viruses are the smallest, 20 to 300 nanometres, not made of cells, and consisting only of a coat of protein around a core of DNA or RNA. They cannot grow or multiply outside a living cell; they enter a cell, take over its machinery to make thousands of copies of themselves, and burst or damage it. Because they have no metabolism of their own, antibiotics do not act on them; viral diseases are prevented by vaccines and treated by rest, care and a few antiviral drugs. Viral diseases include the common cold, influenza, measles, mumps, chickenpox, polio, rabies, dengue, chikungunya, hepatitis A and B, Japanese encephalitis, AIDS and COVID-19.

Bacteria are single celled prokaryotes, 1 to 10 micrometres, that multiply rapidly by binary fission in the body and damage it by the toxins they produce or by destroying tissue. They are killed by antibiotics, such as penicillin, streptomycin, tetracycline and amoxicillin, which block processes such as cell wall formation or protein synthesis that bacteria have and human cells do not. Bacterial diseases include tuberculosis, cholera, typhoid, diphtheria, whooping cough, tetanus, leprosy, plague, pneumonia, anthrax and many diarrhoeas and skin infections.

Fungi are eukaryotes that grow as threads or as yeasts on the skin, nails, hair and mucous membranes and, in weakened patients, in the lungs and internal organs. They cause ringworm, athlete's foot, dandruff, thrush (candidiasis) and aspergillosis. They are treated with antifungal drugs, and they flourish in damp, dirty conditions.

Protozoa are single celled eukaryotes, larger than bacteria and mostly living in blood or the intestine. Plasmodium causes malaria, Entamoeba histolytica causes amoebic dysentery, Giardia causes giardiasis (a persistent diarrhoea), Trypanosoma causes sleeping sickness and Leishmania causes kala azar. They are treated with specific antiprotozoal drugs such as chloroquine and metronidazole.

Helminths (worms) are multicellular animals, some large enough to see, that live as parasites in the intestine, blood or tissues: roundworm (Ascaris), hookworm, pinworm, tapeworm (Taenia), the filarial worm Wuchereria which causes elephantiasis, and the liver fluke. They cause anaemia, malnutrition and obstruction, and are treated with deworming drugs such as albendazole, which the school health programme gives twice a year.

The group also decides how fast the disease develops and how it spreads. Viruses and bacteria multiply in hours, so their diseases come on quickly; worms take weeks to mature. Some pathogens, such as the cold virus, stay near their point of entry; others, such as the typhoid bacterium and the malaria parasite, spread through the blood to the whole body. Different pathogens attack different organs and produce different symptoms, which the next topics describe.

An infectious disease can spread only if the pathogen has a way of leaving one person and reaching another. These routes of transmission are the key to prevention, because if the route is blocked the disease cannot spread even though the microbe still exists. Diseases spread by these routes are called communicable. There are two broad modes, direct and indirect.

Direct transmission passes the pathogen from person to person without an intermediate:

• Through the air (droplet infection): when a patient coughs, sneezes, laughs or talks, tiny droplets of saliva and mucus carrying microbes are thrown into the air and breathed in by people nearby, or settle on surfaces and are picked up on the hands. Common cold, influenza, measles, chickenpox, mumps, diphtheria, whooping cough, tuberculosis, pneumonia and COVID-19 spread this way, and spread fastest in crowded rooms, buses, schools and slums. Covering the mouth when coughing, a mask, ventilation and distance break the route.
• Through physical contact: skin diseases such as scabies, ringworm and leprosy, and eye infections such as conjunctivitis, pass by touch or through shared towels, combs and clothes; rabies passes through the bite of an infected animal.
• Through sexual contact: syphilis, gonorrhoea, hepatitis B and HIV/AIDS pass from one partner to another; HIV and hepatitis B also pass through infected blood transfusion, shared needles and razors, and from an infected mother to her baby during pregnancy or birth.

Indirect transmission uses a vehicle or a carrier:

• Through water: when the excreta of a patient reach drinking water through open defecation, leaking sewers, floods or a well beside a latrine, the pathogens are swallowed by everyone who drinks it. Cholera, typhoid, dysentery, diarrhoea, hepatitis A and polio are water borne. Safe water supply, toilets and boiling or chlorinating water break the route, and these diseases explode after floods and cyclones in Odisha.
• Through food: food contaminated by dirty hands, flies, dust or unsafe water, or stale food in which bacteria have multiplied, carries the same diseases as water, as well as food poisoning and worm eggs; hand washing, covering food and cooking thoroughly prevent it.
• Through vectors: a vector is an animal, usually an insect, that carries the pathogen from one host to another. The female Anopheles mosquito carries malaria, the Aedes mosquito carries dengue and chikungunya, the Culex mosquito carries filariasis and Japanese encephalitis, the housefly carries cholera and typhoid germs on its legs from excreta to food, the rat flea carries plague, the sand fly carries kala azar and the tsetse fly carries sleeping sickness. Controlling the vector, by draining stagnant water, spraying, nets and covered food, controls the disease.
• Through soil and objects: tetanus spores in soil enter wounds; hookworm larvae in soil penetrate bare feet; contaminated needles, surgical instruments and blood carry hepatitis and HIV.

Knowing the route tells us the answer. Airborne diseases need ventilation, masks and vaccination; water and food borne diseases need sanitation and clean water; vector borne diseases need mosquito control; contact diseases need hygiene and safe behaviour. No amount of medicine given after the event replaces these simple barriers.

Mosquito borne diseases are the biggest infectious disease burden of Odisha, which for years reported more malaria cases than any other Indian state, mainly from the forested tribal districts of the south and west. Three mosquitoes carry three sets of diseases.

Malaria is caused by the protozoan parasite Plasmodium, of which four species infect man: P. vivax, the commonest and mildest; P. falciparum, the most dangerous, which causes cerebral malaria and most deaths, and which is the main species in Odisha; and P. malariae and P. ovale. The parasite is transmitted by the bite of the female Anopheles mosquito, which needs blood to develop its eggs and bites between dusk and dawn. When an infected mosquito bites, it injects the parasites (sporozoites) into the blood; they go to the liver, multiply there for a week or two, then enter the red blood cells, where they multiply and burst the cells in cycles of 48 hours (72 for P. malariae). The bursting releases toxins and produces the characteristic periodic fever: a cold stage with violent shivering, a hot stage with high fever and headache, and a sweating stage in which the temperature falls, repeating every second or third day. Destruction of red cells causes anaemia and enlargement of the spleen; P. falciparum may block the brain capillaries and cause unconsciousness, convulsions and death. The diagnosis is confirmed by seeing the parasite in a stained blood film or by a rapid diagnostic kit, and the treatment is with chloroquine, quinine or artemisinin combination drugs, which the government supplies free. Prevention has three parts: avoiding bites, by sleeping under insecticide treated bed nets, using repellents and screening windows; killing adult mosquitoes by spraying insecticides on walls; and stopping breeding, by draining stagnant water, filling pits, covering tanks, adding larva eating fish (Gambusia) to ponds and spraying oil on water surfaces. Odisha's malaria cases have fallen sharply since mass distribution of bed nets and village level testing began.

Dengue is caused by a virus carried by the Aedes aegypti mosquito, which has black and white striped legs, breeds in clean stored water in pots, coolers, tyres and flower vases, and bites by day. It produces sudden high fever, severe headache and pain behind the eyes, joint and muscle pain so intense that the disease is called break bone fever, and a rash. In the dangerous form, dengue haemorrhagic fever, the platelet count falls, bleeding occurs from the gums and skin, and the patient may collapse from loss of fluid. There is no specific drug; treatment is rest, fluids and careful monitoring of platelets, and aspirin must be avoided. Chikungunya, carried by the same mosquito, causes fever and crippling joint pain that may last months. Prevention is entirely by eliminating breeding places: emptying and scrubbing water containers weekly (the 'dry day'), covering tanks, and protecting from day time bites.

Filariasis (elephantiasis) is caused by the worm Wuchereria bancrofti, transmitted by the Culex mosquito, which breeds in dirty drain water. The adult worms block the lymph vessels, and over years the legs, arms or scrotum swell enormously. It was once common in coastal Odisha and is being eliminated by mass annual doses of the drugs DEC and albendazole. Culex also carries Japanese encephalitis, a viral infection of the brain from pigs and birds, prevented by a vaccine given to children in affected districts.

Tuberculosis (TB) is caused by the bacterium Mycobacterium tuberculosis, discovered by Robert Koch in 1882, and it remains the infectious disease that kills the most adults in India, which has about a quarter of the world's cases. The bacterium spreads through the air: a patient with TB of the lungs throws out bacilli in the droplets of his cough, sneeze and speech, and the bacilli, which are tough and survive for hours in the dust of a dark room, are inhaled by others. Overcrowded, dark, badly ventilated houses, poor nutrition, smoking, diabetes and HIV infection all make a person more likely to develop the disease after infection; most infected people wall off the bacteria and never fall ill, but the bacteria can wake up years later when resistance falls.

Pulmonary TB, the commonest form, produces a persistent cough for more than two weeks, often with sputum and sometimes with blood, evening fever, night sweats, loss of appetite and steady loss of weight, chest pain and breathlessness. The bacteria destroy lung tissue and form cavities. TB can also attack the lymph nodes of the neck (scrofula), the bones and spine, the intestine, the kidneys, the skin and the coverings of the brain (TB meningitis, which is often fatal in children). Diagnosis is by examining the sputum under the microscope for the acid fast bacilli, by newer rapid molecular tests, by a chest X-ray and by the tuberculin skin test.

TB is curable, but the treatment is long. A combination of antibiotics, isoniazid, rifampicin, pyrazinamide and ethambutol, is taken daily for six months or more, and the whole course must be completed even though the patient feels well after a few weeks; stopping early lets the surviving bacteria grow back resistant to the drugs, and multi drug resistant TB, which needs two years of toxic treatment, is now a serious problem. To ensure completion, the national programme uses DOTS, directly observed treatment, in which a health worker watches the patient swallow the medicine, and supplies the drugs free through every health centre. Prevention includes the BCG vaccine given to every newborn, which protects children against the severe forms; early detection and treatment of cases so that they stop spreading the bacilli (a patient becomes non infectious within weeks of starting treatment); covering the mouth when coughing and not spitting in public; good ventilation and sunlight in houses; adequate nutrition; and screening the contacts of every patient.

Other important airborne diseases share the same route and the same preventive principles. Influenza (flu), a virus that changes every year, causes fever, body ache, cough and cold, and spreads in epidemics every winter and monsoon; it is dangerous to the old and to those with heart or lung disease, and vaccines are updated yearly. The common cold is caused by hundreds of different viruses, which is why there is no vaccine. Measles, a viral fever with a red rash that starts behind the ears, kills undernourished children through pneumonia and diarrhoea and is prevented by the MR vaccine. Diphtheria, whooping cough (pertussis) and pneumonia are bacterial and are prevented by vaccines and treated by antibiotics. Chickenpox, mumps and COVID-19 are viral. For all of them: cover coughs, keep the sick child at home, ventilate rooms, and vaccinate.

Water and food borne diseases follow the faecal oral route: the pathogen leaves the body of a patient or carrier in the faeces, reaches water or food through open defecation, flies, dirty hands or leaking sewage, and enters a new host through the mouth. They are the diseases of poor sanitation, and in Odisha they rise sharply every monsoon and after every flood. Together, the diarrhoeal diseases are the second largest killer of children under five in India.

Cholera is caused by the comma shaped bacterium Vibrio cholerae, whose toxin makes the intestine pour out water and salts. The disease begins suddenly with profuse, painless, watery diarrhoea like rice water, vomiting and severe cramps; a patient can lose many litres of fluid in a day, and without replacement dies of dehydration and shock within hours. Epidemics follow floods and fairs, and Odisha has had many. Treatment is immediate rehydration with ORS or intravenous fluid, and antibiotics shorten the illness; prevention is safe water, sanitation, hand washing, fly control and an oral vaccine in high risk areas.

Typhoid (enteric fever) is caused by Salmonella typhi, which passes through the intestine into the blood. It produces a fever that rises step by step over a week to a high, continuous level, with headache, weakness, abdominal pain, constipation or diarrhoea, a coated tongue and sometimes rose coloured spots on the trunk; untreated, it may perforate the intestine in the third week. It is diagnosed by blood culture or the Widal test and treated with antibiotics. Recovered patients may remain healthy carriers who shed the bacteria in their stools for years and infect others through the food they handle, as the cook 'Typhoid Mary' famously did; food handlers must therefore be tested and hygienic. A vaccine is available.

Diarrhoea, the passing of three or more loose stools a day, is caused by many organisms: rotavirus (the commonest cause in infants, now prevented by a vaccine), E. coli, Shigella (bacillary dysentery, with blood and mucus in the stool), Entamoeba (amoebic dysentery) and Giardia. Whatever the cause, the danger is the same: dehydration. The signs are thirst, dry mouth, sunken eyes, loss of skin elasticity, little urine and, in infants, a sunken fontanelle and lethargy. The life saving treatment is oral rehydration solution (ORS), a packet of glucose and salts dissolved in a litre of clean water, given in sips after every loose stool; a home substitute is a fistful of sugar and a pinch of salt in a glass of boiled water. Zinc tablets shorten the illness, feeding must continue, and antibiotics are needed only for dysentery. ORS has saved crores of children and is the cheapest medicine ever made.

Hepatitis A and E are viral infections of the liver spread through contaminated water and food, producing fever, nausea, loss of appetite, dark urine and jaundice (yellow eyes and skin); they clear up with rest and diet, and hepatitis A has a vaccine. (Hepatitis B and C, by contrast, spread through blood and sexual contact.) Polio, a virus that enters by the mouth and can paralyse the limbs, was once common and has been eliminated from India by the oral polio vaccine given on pulse polio days. Worm infestations, roundworm, hookworm and pinworm, also spread by faecal contamination of soil, food and hands.

Prevention of all these diseases is the same short list, and it is the responsibility of the community: a safe, protected water supply (or boiling, filtering or chlorinating water at home); toilets for every household and an end to open defecation, which is the aim of the Swachh Bharat programme; proper disposal of garbage and control of flies; washing hands with soap after the toilet and before food; covering food, avoiding cut fruit and stale food from the street, and cooking thoroughly; and the available vaccines.

Rabies is a viral disease of the nervous system transmitted through the saliva of an infected animal, almost always by the bite of a rabid dog in India, and sometimes by cats, monkeys, jackals or bats. The virus travels along the nerves from the bite to the brain, taking anywhere from ten days to a year depending on the distance and depth of the bite. Once symptoms appear, fever, restlessness, painful spasms of the throat at the sight or sound of water (hydrophobia), excessive saliva, convulsions and paralysis, the disease is always fatal. But it is completely preventable. After any bite or scratch the wound must be washed immediately and thoroughly with soap and running water for ten to fifteen minutes, which removes much of the virus, and the person must go to a health centre for the anti rabies vaccine, a course of injections in the arm on days 0, 3, 7, 14 and 28, together with rabies immunoglobulin into the wound for severe bites. The biting animal, if it can be found, is observed for ten days. Vaccination of dogs, control of stray dogs and educating children not to tease or approach unknown animals reduce the risk.

AIDS (acquired immuno deficiency syndrome) is caused by the human immunodeficiency virus (HIV), which attacks and destroys the helper T lymphocytes of the immune system. HIV is transmitted in only four ways: through unprotected sexual contact with an infected person; through infected blood, by transfusion of untested blood or by sharing needles and syringes, as among drug users, or through unsterilised razors and tattoo needles; from an infected mother to her baby during pregnancy, birth or breast feeding; and through infected organ transplants. It is not spread by touch, hugging, sharing food and utensils, coughing, mosquito bites, toilets or swimming pools, and people with HIV can live and work with everyone else without any risk to them. After infection there may be a flu like illness, then a silent period of years during which the virus multiplies and the number of helper T cells falls. When the immune system collapses, the person develops the infections that a healthy body would repel, tuberculosis, pneumonia, persistent diarrhoea, fungal infections of the mouth, and certain cancers, together with fever, weight loss and swollen glands; this stage is AIDS, and it is these opportunistic infections that kill. There is no cure and no vaccine, but antiretroviral drugs, given free by the government, suppress the virus so well that an infected person can live a normal span and cannot transmit it. Prevention means faithfulness to one uninfected partner or the use of condoms, testing of all donated blood, using only new disposable syringes and sterilised instruments, treating infected pregnant women to protect the baby, and above all education and an end to the stigma that stops people from being tested.

Several other diseases follow the same routes. Hepatitis B, a virus that damages the liver and can cause cancer, spreads exactly as HIV does and is far more infectious; a vaccine given to every infant prevents it. Syphilis and gonorrhoea are bacterial sexually transmitted diseases curable with antibiotics. Tetanus enters through wounds contaminated with soil or dung, producing lockjaw and fatal spasms; it is prevented by the tetanus toxoid vaccine, which every child receives and every injured person and pregnant woman is given. Skin diseases such as scabies (a mite that burrows and itches at night), ringworm and leprosy (a slow bacterial disease of skin and nerves, curable by multi drug therapy) spread by close contact and shared clothing, and the eye infection conjunctivitis spreads on hands and towels.

Not all diseases come from outside. A body that does not receive the nutrients it needs falls ill just as surely as one invaded by a microbe. Deficiency diseases are non-communicable diseases caused by the lack of one or more essential nutrients, proteins, vitamins or minerals, in the diet, or by their poor absorption. They are common in India wherever poverty, ignorance and a monotonous diet of cereal alone exist, and they fall hardest on children, adolescent girls and pregnant and nursing mothers. Many of them are 'hidden hunger': the child does not look starved, yet lacks iron, iodine or vitamin A and pays for it in growth, learning and resistance to infection.

Protein energy malnutrition (PEM) is the gravest. Kwashiorkor appears in children of one to three years who are fed on starchy gruel with almost no protein after weaning: the child has a swollen belly and puffy face and legs from fluid (oedema), thin discoloured hair, patchy skin, stunted growth, apathy and frequent infections. Marasmus results from a lack of both energy and protein in infants: the child is a skeleton of skin and bone, with wasted muscles, an old man's face, no fat and constant hunger. Both are treated with energy rich, protein rich feeding under medical care, and both are prevented by breast feeding, timely and adequate complementary foods with pulses, milk, eggs and oil, and the supplementary nutrition of Anganwadi centres and mid day meals.

Vitamin deficiencies each have a characteristic disease:

Mineral deficiencies are the most widespread of all. Lack of iron causes anaemia, a shortage of haemoglobin, which shows as pallor of the tongue, nails and eyelids, weakness, breathlessness on exertion and poor concentration; more than half of Indian women and children are anaemic, worsened by hookworm and malaria, and it is prevented by green leafy vegetables, jaggery, pulses and meat, the weekly iron folic acid tablets given in schools, and deworming. Lack of iodine causes goitre, a swelling of the thyroid gland in the neck, and in children born to iodine deficient mothers, cretinism, with stunted body and mind; it was common in hilly and flood plain areas where the soil has no iodine and is prevented by the universal use of iodised salt. Lack of calcium weakens bones and teeth, and lack of fluoride causes dental caries, while excess fluoride in ground water, as in parts of western Odisha, causes fluorosis with mottled teeth and stiff joints. The prevention of all deficiency diseases is a balanced diet containing cereals, pulses, milk, vegetables, fruits, oil and where possible eggs, fish or meat, and the public programmes that supply what the poorest cannot buy.

As infectious diseases are brought under control and people live longer, a second group of diseases has become the main cause of death in India, including Odisha: the non-communicable diseases (NCDs), which are not caused by any microbe and cannot be passed on, but arise from the way we live, from ageing and from heredity. The four biggest are cardiovascular disease, diabetes, cancer and chronic lung disease, and they share a small set of preventable risk factors: tobacco, unhealthy diet, physical inactivity and alcohol, which produce obesity, high blood pressure, high blood sugar and high blood fats.

Hypertension (high blood pressure) is a persistent blood pressure above 140/90 mm Hg. It usually causes no symptoms for years, which is why it is called the silent killer, while it damages the arteries, heart, brain, kidneys and eyes; it is the main cause of stroke, the sudden loss of speech or movement when a brain artery blocks or bursts. It is caused by excess salt, obesity, stress, lack of exercise, alcohol and heredity, and is controlled by cutting salt, losing weight, exercise and daily tablets. Coronary heart disease is the narrowing of the arteries of the heart by fatty deposits (atherosclerosis) built up over years by smoking, a diet rich in fat and sugar, diabetes, high blood pressure and lack of exercise; a clot in a narrowed artery causes a heart attack, with crushing chest pain spreading to the arm and jaw, sweating and breathlessness, needing emergency treatment. India has the highest rate of heart attacks in young adults in the world.

Diabetes mellitus is a disorder in which the level of glucose in the blood is persistently high, because the pancreas produces too little of the hormone insulin (type 1, usually in children, needing insulin injections) or because the body's cells stop responding to it (type 2, in adults, now appearing in the young, and linked to obesity, sugary food and inactivity). Symptoms are frequent urination, thirst, hunger, weight loss, tiredness and slow healing of wounds; over years high sugar damages the eyes, kidneys, nerves, heart and feet. It is diagnosed by a blood sugar test and managed by diet, exercise, weight control, tablets and insulin. India has more than ten crore diabetics, and the number is rising fast in towns and cities.

Cancer is the uncontrolled division of the body's own cells, forming a tumour that invades and destroys surrounding tissue and spreads to distant organs (metastasis). It is triggered by agents called carcinogens, tobacco in every form (smoked or chewed, the cause of most mouth, throat and lung cancer in India, and gutkha and khaini are epidemic in Odisha), alcohol, certain viruses (hepatitis B, HPV), radiation, some chemicals and heredity. Warning signs are a lump, a sore that does not heal, unusual bleeding, a persistent cough or hoarseness, a change in a wart or mole and unexplained weight loss; early cancers are curable by surgery, radiation and drugs, and screening for cervical, breast and mouth cancer saves lives. Asthma and chronic bronchitis, worsened by smoke from chulhas, dust and tobacco, and mental illnesses such as depression, complete the list.

The prevention of NCDs lies almost entirely in lifestyle: no tobacco in any form, no alcohol, a diet with less salt, sugar, fried food and refined flour and more vegetables, fruits, pulses and whole grains, at least thirty minutes of brisk physical activity every day, a healthy body weight, enough sleep, control of stress, and regular check ups of blood pressure and blood sugar after the age of thirty. Habits formed in school last a lifetime, which is why this topic is taught to Class 9.

When prevention has failed and a person is ill, treatment has two aims: to reduce the effects of the disease so that the patient is comfortable and out of danger, and to kill the cause so that the disease ends. The two go together, and neither alone is enough.

Reducing the effects is symptomatic or supportive treatment. Fever is brought down with paracetamol and sponging; pain is relieved; a patient with diarrhoea is given ORS to replace the fluid he is losing; a patient with pneumonia is given oxygen; a patient with dengue is watched for bleeding and given fluids; and every patient is given rest, a nourishing, easily digested diet and plenty of fluids, so that the body's own defences can do their work. Rest is not a luxury: a body that is fighting an infection needs its energy for the fight. Many viral diseases, the common cold, influenza, chickenpox, hepatitis A and dengue, have no drug that kills the virus, and supportive care is the whole treatment until the immune system clears the infection. Symptomatic treatment does not, however, remove the cause, and a fever that is suppressed with paracetamol while the malaria parasite multiplies untreated can end in death.

Killing the cause uses drugs that attack the pathogen without harming the patient. This is possible because each group of pathogens has some process that human cells lack. Antibiotics such as penicillin block the making of the bacterial cell wall, which human cells do not have, so bacteria burst while our cells are untouched; others block bacterial ribosomes or DNA copying. Antibiotics are therefore effective against bacterial diseases, typhoid, cholera, TB, pneumonia, but useless against viruses, which have no cell wall and no metabolism of their own. Antiviral drugs are few and specific, because a virus uses the host's own machinery, and anything that stops it tends to harm the host too; there are antivirals for HIV, herpes, influenza and hepatitis B and C. Antifungal drugs, antiprotozoal drugs such as chloroquine and artemisinin for malaria and metronidazole for amoebiasis, and anthelmintics such as albendazole for worms complete the set. Two rules govern their use. First, the right drug for the right organism, which requires a diagnosis, by examination and tests, not guesswork; antibiotics for a viral fever waste money and breed resistance. Second, the full course at the right dose, even after the patient feels better, because the survivors of a half course are the toughest organisms, and they multiply into a drug resistant strain that will not respond next time, in this patient or in anyone he infects. The rise of bacteria resistant to every common antibiotic, driven by careless prescribing and over the counter sales, is one of the gravest problems of modern medicine.

Treatment has limits. Some diseases, once established, cannot be cured, only controlled, as diabetes and hypertension are, or not at all, as rabies is. Some damage done by disease, the paralysis of polio, the destroyed lung of TB, the blindness of xerophthalmia, is permanent even when the cause is removed. Treatment is expensive, takes time, keeps the patient from work and school, and the patient suffers in the meantime. All of this is why the prevention of disease, the subject of the next topic, is always better than its cure.

Prevention is better than cure because it spares the patient the suffering, the cost and the permanent damage of disease, and because it protects the whole community at once. Prevention has two levels: general measures that protect against many diseases, and specific measures aimed at one disease.

General prevention works by blocking the routes of transmission described earlier and by keeping the body strong. For airborne diseases: uncrowded, ventilated, sunlit houses, covering coughs, masks during epidemics. For water and food borne diseases: safe drinking water, toilets and sewage disposal, garbage removal, fly control, hand washing with soap, and food hygiene. For vector borne diseases: draining stagnant water, bed nets, spraying, screens. For contact and blood borne diseases: personal hygiene, safe sex, sterile needles and tested blood. And for all diseases: a balanced diet, exercise, rest and freedom from tobacco and alcohol, because a well nourished body resists infection, and much of the difference between the rich and the poor in illness is a difference in nutrition and sanitation, not in medicines. These are the tasks of the household, the school, the panchayat and the state together.

Specific prevention uses the body's own defence, the immune system. When a pathogen enters, white blood cells recognise its foreign proteins (antigens) and the lymphocytes make antibodies that attach to it and destroy it, while other cells kill infected cells. The first response is slow, and the patient falls ill; but the immune system keeps memory cells that remember the antigen, so that if the same pathogen ever enters again the response is immediate and overwhelming, and the person does not fall ill. This is immunity, and it is why one attack of measles, chickenpox or mumps protects for life. Vaccination (immunisation) tricks the immune system into building this memory without the disease. A vaccine contains the pathogen in a killed or weakened form, or a harmless piece of it, or its inactivated toxin (toxoid); it cannot cause the disease, but it carries the antigens, so the body makes antibodies and memory cells, and when the real pathogen comes it is destroyed at once. Edward Jenner made the first vaccine in 1796, using cowpox to protect against smallpox, and smallpox, which killed crores, was wiped from the earth by vaccination in 1980; polio has followed it out of India. Immunity produced by infection or vaccination is active and long lasting; immunity given by ready made antibodies, from mother to baby through the placenta and breast milk, or by injection of immunoglobulin after a dog bite or a tetanus prone wound, is passive and lasts only weeks.

India's Universal Immunisation Programme gives every child free vaccines on a schedule: BCG (tuberculosis) and the first oral polio and hepatitis B doses at birth; the pentavalent vaccine (diphtheria, pertussis, tetanus, hepatitis B and Hib) with oral polio and rotavirus at 6, 10 and 14 weeks; measles rubella and Japanese encephalitis (in endemic districts) at 9 months and 16 to 24 months; DPT boosters at 18 months and 5 years; tetanus and diphtheria at 10 and 16 years; and tetanus toxoid for every pregnant woman to protect the newborn. When most of a community is vaccinated, the pathogen cannot find enough susceptible people to spread, and even the few unvaccinated are protected; this is herd immunity, and it is lost when parents refuse vaccines. The card that records these doses is a child's most important health document.

The knowledge in this chapter is of use only if it is turned into habits, of the individual and of the community. Personal hygiene is the set of daily practices by which a person keeps his own body clean and healthy, and it is the first defence against infection.

• Hands carry more infection than anything else. Wash them with soap and water for twenty seconds before eating or cooking, after using the toilet, after handling animals or garbage, after coughing or blowing the nose, and on coming home; nails should be kept short and clean.
• Bathing daily removes sweat, dead skin and the fungi and mites that cause skin disease; hair should be washed regularly and combs not shared.
• Teeth should be brushed twice a day and the mouth rinsed after meals, to prevent caries, gum disease and the infections that spread from a bad mouth; sweets and gutkha should be avoided.
• Clothes and bedding should be washed and sunned, and footwear worn outdoors to prevent hookworm and injuries.
• Food and water: eat freshly cooked food, wash fruits and vegetables, cover food from flies and dust, avoid stale or roadside food, and drink water that is boiled, filtered or chlorinated.
• Coughing and spitting: cover the mouth with a handkerchief or the elbow, and never spit in public; spitting spreads TB.
• Rest, exercise and diet: eight hours of sleep, daily physical activity and a balanced diet keep the immune system strong.
• Habits: no tobacco in any form, no alcohol, no drugs; these are the causes of the greatest number of preventable deaths.

Community health (public health) is the responsibility of the village, the town and the state, because a person cannot be healthy alone in an unhealthy environment. Its elements are: a safe water supply, protected from contamination, tested and chlorinated; sanitation, a toilet in every house or a community toilet, an end to open defecation, and safe disposal of sewage; garbage management, regular collection, separation of wet and dry waste, composting and no dumping in the open; drainage, covered drains that do not stagnate, since every puddle breeds mosquitoes; vector control, spraying, source reduction and larvivorous fish in ponds; food safety, clean markets and inspection of eating houses; immunisation of every child and pregnant woman; health services, the sub centre, primary health centre and hospital, with ASHA and Anganwadi workers in every village who detect illness early, and the public distribution of nutrition; health education in schools and communities; and disease surveillance, the reporting of every case of an epidemic disease so that an outbreak is seen and stopped at once, as the Integrated Disease Surveillance Programme does. Odisha's health system, its ASHA workers, the mosquito net distribution, the Swachh Bharat toilets, the mid day meal and Mission Indradhanush immunisation drives, are all applications of these principles, and their results, the fall in malaria, in infant deaths and in diarrhoea, show that prevention works.

The student's part is not small. A student who washes his hands, keeps his surroundings clean, empties the water pots on the dry day, takes the deworming tablet and the iron tablet, gets vaccinated, refuses tobacco and tells his family what he has learnt, changes the health of a household; a school that does the same changes a village. The message of this chapter is that most disease is preventable, and that the prevention is largely in our own hands.