Biology disease notes

What is a disease?
Any malfunctioning process which interferes with the normal functioning of the body is
called a disease. In other words, disease may be defined as a disorder in the physical,
physiological, psychological or social state of a person caused due to nutritional
deficiency, physiological disorder, genetic disorder, pathogen or any other reason.

OR

A disease is an abnormal condition that affects the body of an organism. It is often

constructed as a medical condition associated with specific symptoms and signs.

Types of diseases

• Infectious diseases
• Contagious diseases
• Food borne illness
• Communicable diseases
• Non-communicable diseases
• Airborne diseases
• Lifestyle disease
• Mental disorders
• Organic disease
• Water prone disease
 Infectious diseases
Infectious diseases are illnesses caused by pathogens in the body, primarily from soil,
contaminated water, and infected animals. They are transmissible or communicable
and include viruses, bacteria, fungi, protozoa, multicellular parasites, and prions.
Contagious diseases are easily transmitted through contact with ill individuals or their
secretions, making them a subset of infectious diseases.

Agents of infectious diseases

• Bacteria
• Viruses
• Protozoa (Protists)
• Fungi
• Helminths (Animals)

Contagious Disease
Infectious diseases that are easily spread from one person (or organism) to another
through direct or indirect contact. The ease of transmission is a key characteristic.

Agents of contagious diseases

• Viruses: Measles, influenza, chickenpox, COVID-19, norovirus.

• Bacteria: Strep throat, tuberculosis, MRSA, gonorrhoea.

• Fungi: Ringworm, athlete's foot.

• Parasites: Scabies, lice.

Food Borne Illness

Illness caused by consuming contaminated food or beverages.

Agents of food borne illness:

• Bacteria: Salmonella, E. coli, Campylobacter, Clostridium botulinum.
• Viruses: Norovirus, hepatitis A.
• Parasites: Giardia, Cryptosporidium, tapeworms.
• Toxins: Produced by bacteria (e.g., botulinum toxin, staphylococcal enterotoxin)
or naturally occurring in certain foods (e.g., some mushrooms).
 Communicable Diseases
This is essentially a synonym for infectious diseases. It refers to diseases that can be
transmitted from one person or animal to another, either directly or indirectly. The term
is often used interchangeably with "contagious," though not all communicable diseases
are equally contagious.

Agents of communicable disease:

The same as contagious diseases: viruses, bacteria, fungi, and parasites.

Non-Communicable Diseases (NCDs)

Diseases that are not caused by infectious agents and cannot be transmitted from
person to person. They are often chronic conditions.

Agents of non-communicable diseases:

• Genetic factors: Predisposition to certain cancers, heart disease.
• Lifestyle choices: Poor diet, lack of exercise, smoking, excessive alcohol
consumption.
• Environmental factors: Exposure to pollutants, carcinogens.
• Aging: Increased risk of certain diseases with age.

Airborne Diseases
Infectious diseases transmitted through the air by tiny droplets or particles
containing pathogens. These particles can remain suspended in the air for extended
periods.

Agents of airborne diseases:

• Viruses: Measles, chickenpox, influenza, tuberculosis (bacterial, but airborne
transmission).
• Bacteria: Tuberculosis.
• Fungi: Histoplasmosis, aspergillosis.

Lifestyle Diseases
Diseases primarily caused by unhealthy lifestyle choices. They are generally non-
communicable.

Agents of lifestyle diseases:

• Unhealthy diets high in processed foods, sugar, and saturated fats.
• Lack of physical activity.
• Tobacco use.
• Excessive alcohol consumption.
• Chronic stress.
 Mental Disorders (Mental Illnesses)
Conditions that affect a person's thinking, feeling, mood, or behavior.

Agents of mental disorders:

• Genetic factors: Predisposition to depression, schizophrenia.

• Biological factors: Chemical imbalances in the brain.

• Psychological factors: Trauma, stress, coping mechanisms.

• Environmental factors: Social and cultural influences.

• Note: While some mental health challenges can be influenced by external

events, they are not caused by transmissible pathogens.

Organic Disease:
A disease that involves a physical or structural change in the organs or tissues of the
body. This contrasts with functional diseases, where symptoms exist without detectable
physical abnormalities.

Agents of organic disease:

• Infections: Bacterial infections causing organ damage.

• Genetic abnormalities: Cystic fibrosis, sickle cell anemia.

• Injuries: Trauma leading to tissue damage.

• Environmental factors: Exposure to toxins causing organ damage.

Waterborne Diseases:
Illnesses caused by consuming contaminated water.

Agents of waterborne disease:

• Bacteria: Vibrio cholerae (cholera), Salmonella typhi (typhoid fever), E. coli.

• Viruses: Hepatitis A, rotavirus, norovirus.

• Protozoa: Giardia lamblia, Cryptosporidium parvum.

• Parasitic worms: Roundworms, tapeworms.

Congenital disease:
The disease which is present from birth (e.g. hole in the heart in infants). They are
caused by some genetic abnormality or metabolic disorder or malfunctioning of an
organ.

Acquired disease:
The disease which may occur after birth during one’s lifetime.

Acquired diseases may generally be classified into :

(i) Infectious diseases: The diseases which can be transmitted from diseased
healthy person to e.g. measles.
(ii) Degenerative diseases: The diseases caused by the malfunction of some
vital organs of the body e.g. heart failure.
(iii) Deficiency diseases: These are caused due to nutritional deficiency such as
that of minerals or vitamins in the diet e.g. anaemia (Fe), Beri- Beri (vitamin
B). You have read about such diseases in an earlier lesson 27.
(iv) Cancer: This is an abnormal, uncontrolled and unwanted growth of cells. e.g.
breast cancer.

Acquired diseases are studied under two categories

(i) Communicable diseases: The diseases which can be transmitted from an

infected person to a healthy person.
(ii) Non-communicable diseases: These diseases do not spread from an affected
person to a healthy person.

Modes of Spread of Communicable Diseases

Communicable diseases spread from the infected person to a healthy person in the
following ways.
Direct transmission

The pathogens of diseases infect a healthy person directly without an intermediate

agent. It can take place by various means such as,

(i) Direct contact between the infected person and the healthy person:
Diseases like smallpox, chicken pox, syphilis, gonorrhoea spread through direct
contact.
(ii) Droplet infection: The infected person throws out tiny droplets of mucus by
coughing, sneezing or spitting. These droplets may contain the pathogen. By
inhaling the air containing the droplets, a healthy person may get the infection.
Diseases like common cold, pneumonia, influenza, measles, tuberculosis and
whooping cough spread through droplet infection.
(iii) Contact with soil contaminated with disease-causing viruses and bacteria.
Health
(iv) Animal bite: Viruses of rabies are introduced through the wound caused by the
bite of rabid animals, especially dogs. The virus is present in the saliva of the
rabid animals.

Indirect transmission occurs when pathogens travel to humans via intermediate

agents. These methods include:

(i) Vectors like houseflies, mosquitoes, and cockroaches. For example, houseflies can
carry cholera-causing germs from infected feces to food, leading to infection in healthy
individuals.

(ii) Air-borne pathogens can enter the body through inhaling contaminated air or dust,
as seen with epidemic typhus.

(iii) Object-borne transmission happens through contaminated items like toys or

utensils.

(iv)Water-borne transmission occurs when drinking water is contaminated with disease-

causing pathogens, such as those causing cholera or hepatitis.

Pathogen - A living organism which causes a disease.

Parasite - An organism which gets food and shelter from host.

Host - The living body on which the disease• producing organism takes shelter.

Infestation - Presence of many parasitic organisms on the surface of the host or on

clothing.
Vector - An organism that harbours a pathogen and may transmit it to another person
(e.g. mosquitoes and malaria).

Carrier - An organism that does not harbour the pathogen but transmits it to another
(e.g. housefly and cholera).

Reservoir - An organism that harbours pathogens in large numbers without suffering.

Epidemic - Spreading of a disease among many people causing significant loss of life in
one area for a period (e.g. plague).

Endemic - A disease regularly found among a particular group of people (e.g. goitre in a
specific locality).

Pandemic - A disease found all over the world (e.g. AIDS).

Interferon - Proteins produced by infected cells to prevent further development of a

virus.

Inoculation - Introduction of antigenic material into the body to prevent disease.

Vaccination - Injection of a weak strain of a specific bacterium to secure immunity (also

called immunization).

Incubation period - The time between pathogen entry and appearance of disease
symptoms.

Symptoms - Specific signs that help identify the disease in the organism.

Diseases caused by viruses

1. Chickenpox is caused by the chickenpox virus and spreads through contact or scabs.
Symptoms include fever, rash, and vesicles. There is no vaccine, but keeping patients
isolated, sterilizing utensils, and burning fallen scabs can help. One infection grants
lifelong immunity.

2. Measles is caused by the Rubeola virus and spreads through air. Symptoms include a
cold and rashes. Patients should be isolated and maintain cleanliness.

3. Poliomyelitis is caused by the polio virus through contaminated food or water,

causing paralysis. Vaccination is the key prevention strategy.

4. Rabies is caused by a rabies virus from dog bites, leading to severe symptoms.
Immunizing dogs and giving anti-rabies vaccines are preventive measures.

5. Hepatitis is caused by the Hepatitis B virus from contaminated water. Vaccination is

available, and proper hygiene is essential.
6. Influenza is a respiratory illness caused by a mutating virus. Symptoms involve fever
and fatigue. Annual vaccination and treatment for symptoms are important.

7. Dengue is a virus spread by Aedes mosquitoes, causing fever and severe pain.
Symptoms appear 3 to 14 days after a bite. Diagnosis is through blood tests. Prevent by
controlling mosquito habitats.

Diseases caused by Bacteria

1) Tuberculosis
Mycobacterium tuberculosis
Airborne (sputum, cough, sneeze)
2• 10 weeks
Symptoms
• Persistent fever and coughing
• Chest pain with blood in sputum
• General weakness
Prevention and Cure
• Isolation of patient
• BCG vaccination for children

2) Typhoid
Salmonella typhi
Contaminated food and water
1• 3 weeks
• Clean, airy living conditions
• Antibiotics for treatment
Symptoms
• Continuous fever and headache
• Slow pulse rate
• Reddish rashes on the belly
Prevention and Cure
• Anti• typhoid inoculation
• Avoid exposed food and drinks
• Maintain sanitation and cleanliness
• Proper disposal of patient excreta
• Antibiotics for treatment
 3) Cholera
Vibrio cholerae
Contaminated food and water (housefly carrier)
6 hours to 2• 3 days
Symptoms
• Acute diarrhoea and watery stool
• Muscular cramps
• Loss of minerals, dehydration
Prevention and Cure
• Cholera vaccination
• Provide electrolytes (ORS)
• Proper washing and cooking of food
• Dispose of vomit and excreta
• Prevent flies on food

4) Diphtheria
Corynebacterium diphtheriae
Airborne (droplet infection)
2• 4 days
Symptoms
• Slight fever, sore throat
• Tough membrane obstruction in the throat
Prevention and Cure
• Immediate medical attention
• DPT vaccine for babies
• Dispose of infected discharges
• Antibiotics under supervision
• Isolate infected child

5) Leprosy
Mycobacterium leprae
Prolonged contact with infected person
1• 5 years
Symptoms
• Skin lesions
• Nodules and ulcers
• Deformities of fingers and toes
• Loss of sensation in affected areas
Prevention and Cure
• Keep children away from infected parents
• Medicines to arrest the disease
Diseases caused by protozoans
1) Malaria is caused by the Malarial parasite from the Plasmodium species,
transmitted by female Anopheles mosquitoes. Symptoms include headache,
fever, chills, weakness, and anaemia, with severe cases leading to death.
Prevention includes using mesh doors, mosquito nets, and eliminating standing
water.

2) Amoebiasis is caused by Entamoeba histolytica from contaminated food and

water, causing intestinal ulcers, abdominal pain, and diarrhoea. Prevention
focuses on sanitation and washing food, with antibiotics for treatment.

3) Filariasis is caused by the filarial worm from mosquito bites. Symptoms include
fever, swelling, and "elephantiasis" in limbs. Prevention involves mesh barriers
and proper covering of water containers, with drugs available for treatment.

Non-Communicable diseases
1) Diabetes mellitus
• Diagnosed by blood test or urine test.
Causes of Disease
• Less insulin secretion from the pancreas.
• Mental stress.
• Heredity from parents to children.
Symptoms of Disease
• High blood glucose levels.
• Frequent urination.
• Increased thirst and hunger.
Reduced healing capability of injuries.
• General body weakness.
• Diabetic coma in extreme cases.
Prevention and Cure
• Maintain healthy body weight.
• Follow a regulated diet.
• Avoid sugar and high carbohydrates.
• Insulin injections before meals as prescribed by a doctor.
 2) Cardiovascular Diseases
Common Causes
• Cholesterol deposits in coronary arteries.
• Reduced blood supply and oxygen to heart muscles.
• Stress and strain.
• Obesity.
Symptoms
• Persistent high blood pressure (BP)
• It may damage the arteries of kidney.
• In extreme cases the arteries may burst, or blindness may be caused.
• It may also cause paralysis.
Prevention and Cure
• Do not build up mental tension.
• Low fat diet should be taken.
• Weight of the body must be kept under control.
• Good eating habits should be cultivated
• Medicines may be taken as per doctor’s advice.

2 b) Coronary Heart Disease Symptoms

• Severe chest pain and breathlessness.
• Nausea and vomiting.
• Excessive sweating.
• Possible blood clot formation.
Coronary Heart Disease Prevention and Cure
• Low saturated fat diet.
• Healthy eating habits.
• Control body weight.
• Avoid smoking, alcohol, and drugs.
• Undergo treatment by a qualified doctor.
• Diagnosed by Electrocardiogram (ECG) and possible bypass surgery in severe cases.

3) Osteoporosis
Symptoms
• Often asymptomatic until a fracture occurs.
• Spine fractures can cause severe pain and chronic back issues.
• Risk of hip fractures from minor accidents.
Treatment
• Vitamin D and calcium supplements.
• Bed rest to prevent worsening.
• Dietary and lifestyle changes advised.
• Exercise under professional guidance.
 4) Cancer
Causes
• Unknown definitive cause, but certain genes may become cancer-causing.
• Heavy smoking, alcohol use, and tobacco chewing.
• Consistent skin irritation.
Tumour Types
Harmless and non-spreading.
Rapidly spreading and serious.
Symptoms
• Persistent lumps or thickening in tissues.
• Irregular bleeding or discharge.
• Non-healing sores.
• Changing moles or warts.
• Persistent cough or difficulty swallowing.
Prevention and Cure
• Annual cancer check-ups.
• Medical treatment as needed.
• Avoid smoking, alcohol, and tobacco.
• Regular lifestyle for health.

5) Allergy
Characteristics
• Hypersensitivity to foreign substances (allergens).
• Common allergens include pollen, animal dander, drugs, and Odors.
Symptoms
• Sneezing, breathlessness, watery eyes, throat irritation.

Sexually transmitted diseases

Sexually transmitted diseases are transmitted through sexual contact. They spread via
mucous membranes and secretions of sexual organs, throat, and rectum. Examples
include syphilis, gonorrhoea, and AIDS.

1 AIDS (Acquired Immune Deficiency Syndrome)

It is a pandemic disease. The word “immune deficiency” signifies that the immune
system becomes very weak. It is a disease of cell-mediated immune system of the body.
Lymphocytes are the main cells of the immune system i.e. T-lymphocytes and B-
lymphocytes. ‘Helper T’ lymphocytes play a great role in regulating the immune system.
Damages to or destruction of ‘Helper’ lymphocytes leads to the development of a
cellular immune deficiency which makes the patient susceptible to wide variety of
infections.
Mode of Transmission
• Sexual contact with an infected person.
• Sharing syringes with an infected person.
• Blood transfusions with HIV-infected blood.
• Organ transplants from an infected person.
• Artificial insemination.
• Mother to newborn during birth.
Incubation Period
28 months (15 to 57 months range).
Symptoms
• Lung diseases (e.g., tuberculosis).
• Skin cancer.
• Nerve damage.
• Brain damage impacting memory and speech.
• Reduced platelets causing haemorrhage.
• Swollen lymph nodes, fever, and weight loss in severe cases.
• Full-blown AIDS may lead to death within three years.
Prevention and Cure
• No known medicine or vaccine for HIV.
• Avoid sexual contact with infected individuals.
• Use disposable syringes.
• Ensure blood transfusions are HIV-free.
• Avoid prostitution and homosexuality.
• Always use condoms during intercourse.
Control
• AIDS can be detected by ELISA test.
• Partner notification for examinations.
• Education about STDs.
Serological screening for groups (e.g., blood)
donors).
Syphilis
Causative organism
• Treponema pallidum (a long corkscrew bacteria)
Mode of spread
• Sexual contact with an infected person
Incubation period
• Symptoms appear in about 10-90 days, usually noticed in 3-4 weeks
Symptoms
• Fever and sores on skin, throat, and urogenital areas
• Rashes on hands, feet, and palms
• White patches in the mouth
• Acne-like warts in the groin
• Patchy hair loss
• Serious symptoms may affect organs after about 10 years
Prevention and cure
• Have sexual intimacy with only one person
• Avoid prostitution and homosexuality
• Practice abstinence and use condoms
• Seek medical treatment and maintain personal hygiene

Gonorrhoea
Gonorrhoea is a sexually transmitted disease that often involves urethra, vagina or
penis, cervix, anus, and throat, as its target sites
Causative organism
• Neisseria gonorrhoeae, a gonococcus bacterium
cervix, rectum, mouth
Modes of spread
• Multiple sex partners increase risk
• Any unprotected sex is risky
• Contact with sores of an infected person is risky
Incubation period
• About 2-5 days after infection
Symptoms
• Inflammation of mucous membrane in the urinogenital tract
• Burning sensation while urinating and urethral discharge
• Rectal discomfort
• Joint pain
• Rashes on palms, mild sore throat
• Potential sterility in females
Prevention and cure
• Have sexual contact with only one person
• Avoid prostitution and homosexuality
• Use antibiotics as prescribed by a doctor
• Gonorrhoea primarily affects males in the urethra, anus, throat, joints, and eyes
• Most victims are teenagers and young adults
gonococcal septicaemia (blood poisoning)

Drug abuse and its prevention

What is a drug?
• A drug is a chemical substance altering body and mind functions.
• It can be a pharmaceutical preparation or a natural substance.
What is drug abuse?
• Medications are used for treating diseases.
• Drug abuse occurs when drugs are used without medical reasons or supervision,
causing harm.
• Commonly abused substances include cough syrups, pain killers, and tranquillisers.
• Abuse may involve chemicals with no medical use, like glue and solvents.
• Severity depends on quantity, method, and frequency of use.
• Drug abuse causes serious physical, emotional, and social issues.
What are the effects of drug abuse?
instant or quick feelings of well• being and drowsiness.
physical and mental damage, academic and employment failure, damaged
relationships, financial ruin, STI risks, and increased accident chances.
• Addicts focus solely on getting their next dose, often leading to crimes.
WHAT YOU HAVE LEARNT
• Diseases are broadly classified into two categories–Acquired (Occur after birth)
and congenital (present from birth).
• Infectious diseases are transmitted from a diseased person to a healthy person
and degenerative diseases are due to malfunctioning of some organs.
• Cancer is uncontrolled growth of cells.
• Acquired diseases are studied in two categories of communicable and
noncommunicable diseases.
• Communicable diseases are transmitted and may be caused by virus, bacteria,
protozoa or helminths (worms).
• Non-communicable diseases are not transmitted from a diseased person to a
healthy person.
• Diseases which spread by sexual contact are called sexually transmitted
diseases (STD).
• AIDS is caused by HIV.
• Gonorrhoea is caused by a bacterium (Neisseria gonorrhoeae). Syphilis is
caused by a long, corkscrew bacterium (Treponema pallidum).