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Diseases: Cause and Control
Health is a condition of complete physical, mental, and social well-being. On the other hand, a disease refers to a situation where the body's vital functions are disrupted, either physiologically or psychologically.
Categories of Diseases
- Endemic Disease: A disease is considered endemic when it is confined to a specific area and affects a small number of people. Examples include yellow fever and goitre.
- Epidemic Disease: An epidemic disease spreads from one place to another, leading to an outbreak that affects a large population simultaneously. An example of this is the plague.
- Pandemic Disease: When a disease occurs worldwide, it is classified as a pandemic disease. AIDS is an example of a pandemic disease.
- Sporadic Disease: A sporadic disease occurs in single, scattered cases. Examples include malaria and cholera.
- Communicable or Infectious Diseases: These diseases are caused by infectious agents or pathogens and can spread from one person to another. Examples include tuberculosis, chickenpox, and measles.
- Non-communicable or Noninfectious Diseases: These diseases do not spread from one person to another. Examples include beriberi, scurvy, and arthritis.
- Bacterial Diseases: Diseases caused by bacteria are known as bacterial diseases. Examples include cholera, tetanus, and syphilis.
- Viral Diseases: Diseases caused by viruses are referred to as viral diseases. Examples include poliomyelitis, mumps, and rabies.
- Protozoal Diseases: Diseases caused by protozoa are called protozoal diseases. Examples include malaria and amoebic dysentery.
- Parasitic Diseases: Diseases caused by parasitic worms are known as parasitic diseases. Examples include ascariasis and taeniasis.
- Food-borne Diseases: These diseases are caused by consuming food contaminated with chemical toxins or pathogens. Examples include taeniasis and trichinosis.
- Water-borne Diseases: Diseases caused by consuming contaminated water are called water-borne diseases. Examples include typhoid fever, cholera, and hepatitis A.
- Air-borne Diseases: These diseases spread through the air when droplets of pathogens are expelled due to coughing, sneezing, or talking. Examples include influenza and meningitis.
- Insect-borne Diseases: Diseases caused by pathogens transmitted by insects and ticks are known as insect-borne diseases. Examples include malaria and elephantiasis.
Diseases Caused by Bacteria
| Disease | Incubation Period | Mode of Transmission | Symptoms | Preventive Measures |
| Tuberculosis (Mycobacterium tuberculosis) | 2-10 weeks | Air, dust or the sputum of an infected person | 1. Wasting of the body occurs, resulting in loss of resistance and weakness 2. Loss of appetite and weight | The patient should be kept in isolation BCG (Bacillus Calmette Guerin) vaccine should be administered |
| Cholera (Vibrio cholerae) | Few hours to 6 days | Contaminated water, food and drinks; spread by flies | Severe stomach ache, diarrhoea with white, watery and foul smelling faecal waste and vomiting | Control of houseflies Personal hygiene, cleanliness of the surroundings and consumption of well-cooked, nutritious food 3. Anti-cholera injection |
| Tetanus (Clostridium tetani) | 4-20 days | Cuts or wounds in the skin; enters through the blood into the spinal cord | Painful contractions or spasms of muscles of neck and jaw Body becomes rigid and may even bend like a bow | Wounds and cuts should be cleaned immediately Anti-tetanus vaccine should be given |
| Syphilis (Treponema pallidum) | 1-12 weeks | Sexually transmitted or close contact | Skin rash; ulcers on the penis, rectum, lips, tongue and nipples Fever | Avoid sexual contact with an infected person Treatment of antibiotics, especially that of penicillin |
| Diphtheria (Corynebacterium diphtheriae) | 2-10 days | Droplet infection while coughing and sneezing, contact | Patient experiences pain in the throat, fever and difficulty in breathing | DPT vaccine Isolation of the patient |
| Typhoid (Salmonella typhi) | 7-21 days | Contaminated water, milk, through flies | Fever is usually high, especially in the afternoon, accompanied by cold Diarrhoea, nausea, vomiting, loss of appetite and constipation Rose-coloured rashes or eruptions appear on the chest and abdomen | Personal hygiene and cleanliness of the surroundings Typhoid vaccine should be given |
| Whooping cough (Haemophilus pertussis) | 10-15 days | Contact, droplet infection of the throat | Fever, cold with running nose and irritating cough Whoop is developed at the end of cough as a sudden bout of noisy breath Vomiting after injection of food | DPT vaccine or triple antigen is commonly given |
| Pneumonia (Diplococcus pneumoniae) | 1-3 days | Contact or by air | Difficulty in breathing Water accumulates in the lungs | Avoid fatigue, malnutrition and contact |
Diseases Caused by Bacteria
Leprosy (Mycobacterium leprae)
- Incubation Period: Several years
- Mode of Transmission: Contact, highly contagious
- Symptoms: Nervous loss of sensation, paralysis, and deformity
- Prevention: Vaccination
- Other Measures: Good nutrition and sanitation
Gonorrhea (Neisseria gonorrhoeae)
- Incubation Period: 3-10 days
- Mode of Transmission: Sexual contact
- Symptoms: Pain during urination, pus-like discharge in genital tubes
Diseases Caused by Protozoa
Malaria (Plasmodium falciparum)
- Incubation Period: About 3 weeks
- Mode of Transmission: Female Anopheles mosquito acts as a carrier
- Symptoms: Cold Stage: Sudden onset of fever Hot Stage: Body temperature may rise to 41°C (106°F) Sweating Stage: Profuse sweating and lowering of body temperature
- Prevention: Reduction or elimination of mosquito populations, prevention of mosquito bites using nets and repellents, drinking water boiled with neem leaves and inflorescence
Amoebic Dysentery or Amoebiasis (Entamoeba histolytica)
- Incubation Period: About 1 week
- Mode of Transmission: Food and water contaminated by flies, faeces of an infected person
- Symptoms: Diarrhoea or watery motions containing mucus or blood, abdominal pain, destruction of intestinal lining, constipation alternating with diarrhoea, stomach convulsions
- Prevention: Keeping food covered to avoid fly contamination, controlling fly populations, using clean, boiled, and cooled water for drinking, avoiding spicy and fried foods
Sleeping Sickness (Trypanosomiasis)
- Incubation Period: From 3 days to 3 weeks
- Mode of Transmission: Bite of the Tsetse fly
- Symptoms: Swollen, red, painful nodule at the site of the fly bite, fever, headache, itchiness, joint pain in the first phase, mood changes, anxiety, insomnia in the later phase
- Prevention and Treatment: Insect control measures, administration of drugs such as melarsoprol, pentamidine, and suramin
Diseases Caused by Parasitic Worms
Ascariasis (Ascaris lumbricoides)
- Incubation Period: About 4-8 weeks
- Mode of Transmission: Soil, food, and water contaminated with eggs of the female worm; flies act as carriers
- Symptoms: Bleeding in liver, heart, lungs, sudden contraction of muscles, fever, and anaemia
- Prevention: Maintenance of personal hygiene, using boiled, cooled, and fresh water for drinking
Taeniasis (Taenia solium)
- Incubation Period: About 8-14 weeks
- Mode of Transmission: Consumption of infected pork and beef
- Symptoms: Extreme weakness
- Prevention: Avoiding raw meat, cooking meat at a temperature greater than 140°F for about 5 minutes, freezing meat
Filariasis/Elephantiasis (Filarial worm Wuchereria bancrofti)
- Incubation Period: 4 weeks to 1 year
- Mode of Transmission: Bite of the Culex mosquito
- Symptoms: Characteristic swelling in the arms, legs, and chest, swollen legs resembling those of an elephant, inflammation of lymph glands and lymph vessels, enlargement of limbs/ankle, fever with chills
- Prevention and Treatment: Avoiding mosquito bites, eradication of the vector, use of antibiotics and anti-inflammatory analgesics
Differences between Viruses and Bacteria
| Viruses | Bacteria |
| Very small | Larger |
| Visible only under an electron microscope | Visible under a light microscope |
| Non-cellular | Single-celled |
| Have no metabolism | Have metabolism |
| Do not take in any food | Take in food by absorption |
| Do not grow and divide | Grow and divide to produce more bacteria |
| Can be crystallized | Cannot be crystallized |
| Command the host cell to produce virus | Self-reproducing |
| All produce diseases in man, animals or plants | Some harmless, some useful and some disease-producing |
Common Viral Diseases
Poliomyelitis (Polio virus)
- Incubation Period: 7-14 days
- Mode of Transmission: Excreta or secretion of the nose; incubates in the intestine, passes to the brain through the blood vessels
- Symptoms: Muscle paralysis of legs, common cold, sore throat, fever, fatigue, headache, vomiting, and reddening of the throat
- Prevention: Vaccination, polio vaccine
Mumps (Myxovirus parotitis)
- Incubation Period: 12-26 days
- Mode of Transmission: Contact, contaminated food or milk and air
- Symptoms: Characteristic painful swelling of salivary glands, pain while opening the mouth, earache, headache, and fever
- Prevention: Vaccination of gamma globulin, complete isolation
Rabies (Rhabdovirus)
- Incubation Period: 30 days or more
- Mode of Transmission: Mad dog bite (canine disease)
Infectious Diseases and their Prevention
A disease that is caused by the infection of pathogen like bacteria, virus, fungi, parasites or prions is known as infectious disease. Infectious diseases can be spread from one person to another through air, water, food, physical contact, or other means. In this chapter, we will discuss some major infectious diseases, their symptoms, and preventive measures.
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FAQs on Revision Notes: Diseases: Cause And Control
| 1. What are the common causes of diseases? |  |
Ans. Diseases can be caused by various factors, including pathogens such as bacteria, viruses, fungi, and parasites. Other causes may include genetic factors, environmental influences, lifestyle choices (such as diet and exercise), and exposure to toxins or pollutants. Understanding these causes is essential for effective prevention and control measures.
| 2. How can infectious diseases be controlled and prevented? | |
Ans. Infectious diseases can be controlled through several measures, including vaccination, which helps to build immunity against specific pathogens. Good hygiene practices, such as regular handwashing, can prevent the spread of infections. Additionally, proper sanitation and safe food handling are crucial. Public health initiatives that promote awareness and education about disease prevention also play a significant role.
| 3. What are non-communicable diseases, and how can they be managed? | |
Ans. Non-communicable diseases (NCDs) include conditions such as heart disease, diabetes, and certain cancers, which are not caused by infectious agents. Management of NCDs typically involves lifestyle modifications, including a balanced diet, regular physical activity, and avoiding tobacco and excessive alcohol consumption. Regular health check-ups can help in early detection and management of these diseases.
| 4. Why is it important to understand the life cycle of pathogens? | |
Ans. Understanding the life cycle of pathogens is crucial for developing effective treatments and preventive measures. By knowing how pathogens reproduce and spread, healthcare professionals can identify vulnerable points to interrupt transmission. This knowledge aids in creating vaccines, treatments, and public health strategies that target specific stages of a pathogen's life cycle.
| 5. What role do environmental factors play in the spread of diseases? | |
Ans. Environmental factors, such as climate, pollution, and urbanization, significantly impact the spread of diseases. For example, changes in climate can affect the habitats of vectors like mosquitoes, leading to increased transmission of diseases such as malaria and dengue fever. Pollution can also exacerbate health problems, making certain populations more susceptible to respiratory and other diseases. Understanding these factors is vital for effective disease control strategies.
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