Common Diseases in Humans

What is Health?

Health is the state of complete physical, mental, and social well being.
Health increases productivity and ensures longevity.

Ways to Ensure Good Health

Balanced diet
Personal hygiene
Exercise
Awareness about prevention and control of diseases
Proper waste disposal and control of vectors
Vaccination

Why do Diseases Occur?

Genetic reasons − Innate deficiencies and inheritable defects
Infections
Sedentary life style − Junk food, consumption of alcohols/drugs, lack of exercise

Pathogenic Diseases

Pathogens are the parasites that enter the human body through various means, then multiply, and interfere with normal vital activities.

Bacterial Diseases

Typhoid

Pathogen − Salmonella typhi
Spreads through − Contaminated food and water
Site of infection − Small intestine
Symptoms − High fever, stomach pain, headache, loss of appetite, constipation, and intestinal perforations in severe cases
Confirmatory test − Widal test

Pneumonia

Pathogens − Streptococcus pneumoniae and Haemophilus influenzae
Spreads through − Droplets/aerosols released from infected person, sharing of glasses or utensils
Site of infection − Alveoli (gets filled with fluid, difficulty in breathing)
Symptoms − Fever, chills, cough, headache, lips and nails become grey in severe cases

Viral Diseases

Common cold

Pathogen − Rhino viruses
Site of infection − Nose and respiratory passage
Spreads through − Droplets released from coughing or sneezing, or contaminated objects
Symptoms − Nasal congestion and discharge, sore throat, cough, headache, tiredness

Protozoan Diseases

Malaria

Pathogen − Plasmodium sps. (P.vivax, P. falciparum, P. malaria)
Vector − Female Anopheles mosquito
Symptoms − High grade fever, chills

Amoebiasis

Pathogen − Entamoeba histolytica
Vector − Housefly
Site of infection − Large intestine
Symptoms − Constipation, abdominal pain, cramps, stools with mucous, and blood clots

Fungal Diseases

Ringworms

Pathogens − Genera Microsporum, Trichophyton, and Epidermophyton
Spreads through − Towels, clothes, comb (Fungus is acquired from soil)
Symptoms − Appearance of dry, scaly lesions on various body parts with intense itching

Diseases Caused by Worms

Ascariasis

Pathogen − Round worm, Ascaris
Spreads through − Water, vegetables, fruits contaminated by faeces of infected person
Symptoms − Internal bleeding, muscular pain, fever, anaemia, blockage of intestinal passage

Elephantiasis (filariasis)

Pathogen − Wuchereria (W.malayi and W.bancrofti)
Spreads through − Bite of female mosquito vector
Symptom − Chronic inflammation of the organs, usually the lymphatic vessels of lower limb

Life Cycle of Plasmodium

Plasmodium requires two hosts to complete its life cycle.
When female Anopheles mosquito bites a healthy human being, it releases Plasmodium, which lives in its body as sporozoite (infectious form).
The parasites multiply (asexual reproduction) in the liver cells and finally burst the liver cells. Sporozoites are released in blood.
Parasites enter RBCs and further multiply (asexual reproduction) here and finally burst RBCs also.
Bursting of RBCs is accompanied by release of a toxic substance called haemozoin (associated with fever and chills).
In the RBCs, only sporozoites change into gametocytes (sexual stage). Gametocytes multiply.
When the diseased person is bitten by a female Anopheles mosquito, gametocytes are introduced into the mosquito.
Gametocytes fertilise and develop inside the intestine of mosquito to form sporozoites.
Sporozoites are stored in the salivary glands of mosquito and are released into the healthy person who is bitten by this mosquito.

Immunity

What is immunity?

The ability of body to fight the disease-causing organisms is called immunity.

Types of immunity

Immunity is of two types − innate immunity and acquired immunity.
Innate immunity − It is present from the time of birth. It is non-specific. It consists of 4 kinds of barriers.

Physical barriers − Skin and mucus coating of respiratory, gastrointestinal, and urogenital tract prevent entry of microbes into body.
Physiological barriers − Acid in stomach, saliva in mouth, tears from eyes
Cellular barriers − Blood has leukocytes such as polymorpho nuclear leukocytes, monocytes, etc. and tissue has macrophages which phagocytose the microbes.
Cytokine barriers − Special proteins called interferons are secreted by virus-infected cells that prevent the further spread of viral infection.

Acquired immunity − It is acquired, which means that it is produced in response to an encounter with a pathogen based on memory. It is pathogen specific.

When a pathogen for the first time infects a person, low intensity immune response is generated (primary response).
When the same pathogen attacks again, intensified immune response in generated, thereby preventing the occurrence of disease (secondary response).
Acquired immunity involves two types of cells − B-lymphocytes and T- lymphocytes.
B-lymphocytes − Secrete proteins called antibodies in response to pathogens Antibodies are specialized proteins with 4 peptide chains (2 light and 2 heavy), hence denoted as H2L2. IgA IgM, IgE, etc. are examples of some of the antibodies. They generate humoral immune response (found in blood).
T-lymphocytes − They help B-cells to produce antibodies. They generate cell -mediated immune response. This response helps the body to differentiate between ‘self’ and ‘non-self’ as occurs in case of graft rejection.

Difference between active immunity and passive immunity

Active Immunity

This is the naturally acquired immunity produced in the host body in response to an antigen.
Immunization and body naturally getting immune to a microbe that had caused infection previously are examples of active immunity.

Passive immunity

When ready-made antibodies are provided to an individual to protect against foreign agents
Colostrums present in mother’s milk contain IgA. Also, the foetus gets antibodies from mother through placenta.

How does vaccination help?

Vaccines are nothing but inactivated pathogens.
These inactivated pathogens when introduced in the body produce a primary immune response and antibodies are produced against the pathogen.
Memory B and T-cells are produced.
Now when the pathogen again attacks the person, memory B and T-cells generate a massive immune response and the pathogen is killed.

Problems of immune system

Allergies

Exaggerated immune response to certain antigens present in environment
Allergens − Substances in response to which allergy is produced
E.g., dust, pollen, etc.
Antibodies involved − IgE type
During allergic reactions, chemicals such as histamines and serotonins are released.
Symptoms − Sneezing, watery eyes, difficulty in breathing, etc.
Allergy test − Patient is injected with small doses of allergens to monitor his response.
Antihistamines, adrenalins, and steroids may be given so that the symptoms of allergy subside.

Autoimmunity

In autoimmunity, body generates immune response against its own cells.
Reasons − Genetic and other unknown reasons
Example − Rheumatoid arthritis is an autoimmune disease.

Human immune system

Lymphoid organs are of two types − primary lymphoid organs and secondary lymphoid organs.
Primary lymphoid organs consist of bone marrow and thymus. Here, immature lymphocytes are differentiated to form antigen-sensitive lymphocytes.

Bone marrow − Here, all blood cells including lymphocytes are produced.
Thymus − It is responsible for maturation of T-lymphocytes. This lobed organ is situated near the heart and keeps on reducing in size as the age increases.

Secondary lymphoid organs − Lymphocytes migrate here after attaining maturity. It includes spleen, lymph nodes tonsils, Peyer’s patches, and appendix.

Spleen − Large bean-shaped organ containing lymphocytes and phagocytes, which acts as a filter for blood
Lymph nodes − Located at different points throughout the immune system, they trap the antigens present in lymph or tissue fluid, and these antigens cause activation of lymphocytes and generation of immune response.

MALT (Mucosal-associated lymphoid tissue) − Lines major tracts (respiratory, digestive, urogenital, etc); constitutes 50% of lymphoid tissue in body

AIDS & Cancer

AIDS (Acquired Immuno Deficiency Syndrome)

Caused by HIV (Human Immunodeficiency Virus) [HIV is a retrovirus (RNA virus)]
Transmission of HIV occurs through:

Sexual contact with infected person
Sharing infected needles (as in case of intravenous drug abusers)
Transfusion of contaminated blood
Infected mother to child through placenta

Time lag between infection and appearance of symptoms − Few months to many years (5-10 years)

How does AIDS infection spread?

Virus enters the body of a person and enters macrophages.
Here, virus replicates (viral RNA reverse transcribes to viral DNA, which gets incorporated into hosts DNA and subsequently new viral particles are produced).

Macrophages become a virtual HIV factory.
Thereafter, HIV enters helper T-lymphocytes, replicates, and produces progenies.
As the progenies are released, they attack other T-lymphocytes.
Therefore, T-lymphocytes start decreasing in number and immune response of the person becomes weak.
Even infections which could be overcome easily start aggravating.

Diagnosis of AIDS − By ELISA (Enzyme Linked Immuno Sorbent Assay)
Treatment − No permanent cure; antiretroviral therapies can prolong the life of patient
Prevention of AIDS

Ensuring use of disposable syringes
Screeningblood from blood banks
Advocating safe sex
NACO (National AIDS Control Organization) and many NGOs are doing a lot to create awareness among people.

Cancer

The process of development of cancer is called oncogenic transformation.
Normal cells have the property of contact inhibition (stoppage of growth on coming in contact with other cells), but cancer cells lose this property.
As a result, cancer cells divide continuously to give rise to mass of cells (tumours).
Tumours are of 2 types − benign and malignant.
Benign tumours − Remain confined to their original location and do not spread
Malignant tumours− These exhibit metastasis i.e., the cells sloughed from such tumours reach distant sites and wherever they reach, new tumour is formed.
Malignant tumours actually represent cancer. The cells actively divide, grow, and starve the normal cells of vital nutrients.

Causes of cancer

Carcinogens − Physical, chemical, and biological agents that cause cancer Example - ionizing radiations (X-rays and gamma rays), non-ionizing radiations (UV)
Oncogenic (cancer-causing) viruses − They have viral oncogenes (cancer-causing genes).
Sometimes normal genes in our body called proto-oncogenes get converted into cellular oncogenes that cause cancer.

Diagnosing cancer

Biopsy and histopathological studies
Biopsy − Suspected tissue is cut into thin sections and examined microscopically
Radiography, CT scan (computed tomography), and MRI (Magnetic resonance imaging) are techniques of diagnosing cancers.
C T Scan − 3-D imaging of internals of an organ is generated by X-rays.
MRI Scan − Pathological and physiological changes in a living tissue are detected by using magnetic fields and non-ionising radiations.
Immunological and molecular biological diagnostic techniques can all be used to detect cancers.
Identifying certain genes, which make an individual susceptible to cancers, can help to prevent cancers.

Treatment of cancer

Radiotherapy − Tumour cells are irradiated to death. Also, proper care is taken for protecting surrounding normal tissues.
Chemotherapy − Drugs specific for particular tumours are used to kill cancer cells. They have side effects such as hair loss, anaemia, etc.
Immunotherapy− Biological response modifiers such as α- interferons are used. They activate the immune system of patient and helps in destroying the tumour.

Commonly Abused Drugs

Opioids (Heroin)

Source: Acetylation of morphine extracted from the latex of poppy plants (Papaver somniferum)
Consumed by: Snorting or injection
Properties: White, bitter and odourless
Mode of action: Binds to opioid receptors present in the CNS and GI tract
Effect: It is a depressant; slows down body functions

Cannabinoids

Source: Inflorescences of the plant Cannabis sativa
Consumed by: Inhalation or oral ingestion
Mode of action: Binds to cannabinoid receptors present in the brain
Effect: Affects the cardiovascular system

Cocaine

Source: Coca plant Erythroxylum coca, found in South America
Consumed by: Snorting
Mode of action: Interference with transfer of neurotransmitter, dopamine
Effect: Stimulates the CNS, producing a sense of euphoria and increased energy; excessive dosages cause hallucination

Drugs Normally Used as Medicines

Drugs like barbiturates, amphetamines, benzodiazepines, LSD (Lysergic acid diethyl amides) are used as medicines to help patients with mental illness and insomnia.
Morphine: It is a pain killer which is used for patients who have undergone surgery, but it is also abused.

Nicotine

Present in tobacco, which is smoked, chewed or snuffed
Mode of action: Stimulates the adrenal gland to release adrenaline and nor-adrenaline
Effect: Increases blood pressure and heart rate

Ill Effects of Smoking

Increased risk of diseases like bronchitis, emphysema, coronary heart disease, gastric ulcer and cancer (throat, lung and urinary bladder)
Increased carbon monoxide levels in blood, leading to oxygen deficiency

Alcohol / Drug Abuse

Causes of alcohol/ Drug Abuse

Alcohol / drug abuse normally starts in adolescence (period between 12-18 yrs − transition phase between childhood and adulthood).
Many adolescents are motivated towards drugs/ alcohol due to curiosity and experimentation.
Peer pressure, academic stress, unstable family structure further incline youth towards alcohol/ drug abuse.
Perception of consuming alcohol / drug being cool and progressive and use of alcohol/drug in television, movies, etc. further promote this habit.

Alcohol/ Drug Addiction

When a person uses alcohol/ drug repeatedly, he becomes addicted.
Addiction refers to psychological attachment to certain effects such as euphoria and temporary feeling of well-being associated with use of alcohol or drugs.
In addiction, tolerance level of receptors present in our body increases towards the drug.
This drives the person to use them even when they are not required or when they tend to harm his health / family life.
Subsequently, the user runs into a vicious circle of addiction and subsequent dependence.
Dependence leads to manifestation of withdrawal syndrome on discontinuation of use.
Withdrawal syndrome − Anxiety, nausea, sweating, shakiness, and sometimes may be lethal

Effects of Alcohol/ Drug Abuse

Immediate effect − Vandalism, violence, and reckless behaviour
Drop in academic performance, lack of interest in personal hygiene, rebellious behaviour, and change in eating and sleeping patterns, weight and appetite fluctuations
Mental, psychological, and financial loss not only to the user, but also to his family
Those who take drugs intravenously have a high risk of acquiring deadly diseases such as AIDS and hepatitis B.
Damage to nervous system and liver (cirrhosis)
Use of anabolic steroids by sportsperson have adverse effects:

In females − Increase of masculinity, aggressiveness, depression, abnormal menstrual cycle, facial hair growth, enlargement of clitoris, and deepening of voice
In males − Acne, aggressiveness, depression, reduction in size of testicles, decreased sperm production, enlargement of prostate gland, breast enlargement, premature baldness

Ultimately, prolonged use of alcohol/drugs leads to coma and death.

Preventing Alcohol/ Drug Abuse

It is better to prevent the inclination of an individual towards alcohol/ drugs right from adolescence. Some of the ways of prevention are:

Avoid peer pressure − Understand the unique personality and capabilities of a child
Education and counselling − A child must be taught to accept success and failure equally. Especially during adolescence, he must be inclined towards constructive activities such as music, yoga, sports, reading based on his interest.
Help from parents and peers − This includes proper guidance, advice, and trust to overcome problems such as stress and guilt.
Identifying danger signals − If any sign of symptom of alcohol / drug abuse is seen in the adolescent by family or friends, then it should not be ignored because prevention is better than cure.