According To WHO, health is defined as
“ Health is a state of complete physical, mental and social well-being and not merely an absence of disease or physical fitness.
Health is a state of body when all the organs and systems are functionally properly and a perfect balance is maintained b/w the environment and body.
Any conditions which interferes with the normal functioning of the body and impairs the body is called disease.
Types of diseases
On the basis of their period of their occurrence.
These are inborn diseases which are present from birth and generally inherited.
Disease caused by gene mutation (colour blindness) and chromosomal mutation (Down Syndrome).
These occur only after birth and are non- inherited.
On the basis of their communication, acquired diseases are of 2 types:
- Communicable/ infectious
- Non- communicate/ Non- infections
These can be transmitted from an infected person to the healthy person by means of air, water, food and physical contact or vectors.
Depending upon the causative agent, communicable disease are of following types:
On the basis of their mode of transmission, communicable diseases are of two types:
Contagious diseases: (Direct contact)
- Bacterial Diseases: (Typhoid Pneumonia, Tuberculosis etc.)
- Viral Diseases: (Dengue, Polio, influenza, AIDs, measles etc.)
- Protozoan Diseases: (Malaria, amoebiasis, Kala azar, sleeping sickness etc).
- Helminths Diseases: (Ascariasis, Elephantiasis, Prichinosis etc.)
- Fungal Diseases: (Ringworm, athlete’s foot)
- Rickettsial Diseases: (Typhus fever, Trench fever etc.)
These communicable diseases can spread from infected people to healthy people by actual contact b/w them.eg. STDs, smallpox, chicken pox etc.
Non-contagious diseases: (Indirect contact)
These communicable diseases can spread from healthy people to infected people with food, air or water. Eg. Typhoid, Cholera or by microorganisms enters through host (eg. Malaria).
These do not spread from an infected person to a healthy person. These are of 4 types.
- Deficiency disease- Diabetes mellitus, Kwashiorkor (protein)
- Degenerative disease- eg. Cardiovascular Arthritis
- Cancerous diseases
- Allergies- Asthma, Hay fever
These are such microorganisms like bacteria, viruses and fungi which could cause disease in humans.
Means of Spread:
direct contact with an infected person (STDs), droplet infection (common cold), contact with soil (tetanus), animal bite (rabies) and transplacental transmission (syphilis).
Vector borne diseases (eg. Malaria), contaminated food and water (cholera), Air borne (influenza), Formite borne, uncleaned hand (ascariasis).
Prevention of diseases ( Prophylaxis):
There are 3 limitations of the treatment approach of infectious diseases.
- Body functions may never recover completely.
- Patient is bed- ridden for some time depending on the severity of disease.
- Infected people act as the source of spread of disease to even healthy person.
So, it is right to say that "Prevention is better than cure".
There are 2 ways of Prophylactic measures:
General prophylactic measure:
Specific prophylactic measures:
- Avoid overcrowding and providing hygienic living conditions.
- Providing safe drinking water.
- Proper sanitation of human foetus.
Vaccination and immunization.
Principle of Treatment:
There are two ways of treatment of infections diseases:
Symptom directed treatment
is directed to reduce the effect of diseases which are due to inflammation of certain body tissues.
Pathogen directed treatment
is directed to kill the microbes using certain chemical contibioties.
Some Important Protozoan Diseases
Amoebiasis: (Amoeboid dysentery)
Entamoeba histolytica (protozoa)
Direct and oral and sometimes by vectors (house- flies).
Ulceration, acute diarrhoea, abdominal pain, stools with excess mucus and blood clot.
Antibiotics like paramycin, erythromycin. Aureomycin and most effective metronidazole.
Site of effect:
Pathogen secretes cytolysin enzymes which damage intestinal mucosa.
Plasmodium- P. vivax, P. malariae, P-falciparum (malignant malaria).
Oral contact and by vector like female anopheles mosquito.
Fever, weakness, headache
Durg quinine (extracted from bark of Cinchona plant).
Life Cycle of Plasmodium
It is Digenetic (2 hosts):
- Man (secondary)
- Anopheles (primary)
Life cycle of plasmodium is Triphasic.
- It is the asexual phase of multiplication of parasites in the man.
- The sporozoites enter into the blood of man along with the drop of saliva, when a female anopheles bites him.
- Schizogony is divided into 2 phases:
- The sporozoites enter the liver cells, become rounded and feed on the cytoplasm and multiply to form large numbers of crypto merozoites.
- Some of the crypto merozoites enter into the fresh liver cells and repeat the process.
- The crypto merozoites enter the erythrocytes and feed on their haemoglobin, grow and undergo multiple fission to form merozoites. The haeme of the haemoglobin is converted into a toxic substance called haemozoin which is responsible for material attack.
- It is the phase of sexual reproduction.
- In it merozoites enter into fresh RBC and form two types of gametocytes, micro and macro.
- These gametocytes are sucked by female anopheles.
- In the stomach of anopheles, gametocytes form 2 types of gametes – sperm and ova.
- Fertilization occurs in the stomach of the mosquito and zygote is formed.
- As sexual reproduction occurs in mosquito it is the primary host, while man acts as secondary host.
- It is the phase of asexual reproduction.
- zygote changes into oocyst in the wall of stomach, feeds and undergoes multiple fissions to form large no. of sporozoites.
- Oocyst ruptures and sporozoites are released.
- Most of the sporozoites enter the salivary gland and wait to be injected into another man.
Some Important Helminth Diseases
- Caused by: Helminthes; Ascaris lumbricoides
- Symptoms: internal bleeding, blockage of intestinal passage, anaemia, muscular pain.
- Epidemiology: contaminated vegetables, fruits, soil etc.
- Control (prophylaxis): Mixture of oil of chenopodium and tetrachloroethylene.
- Caused by: Wuchereria bancrofti and Wuchereria malayi
- Symptoms: Normally caused inflammation of organs, affects the lymph vessels of lower limbs, genital organs are also affected resulting in gross deformities.
- Epidemiology: female culex mosquito is the vector.
- Control: Anti-helminth drugs like Hetrazin and Diethylcarbamazine.
- Caused by: fungi belonging to the genera Microsporum, Trichophyton and Epidermophyton.
- Epidemiology: from soil or fomite borne or direct contact.
- Symptoms: dry and scaly lesions on skin, nails, scalp and itching.
- Control: Antibiotics
- Immunity or disease resistance is the ability of an organism to resist the development of a disease.
- The study of immunity is called immunology; while the infected person with no disease is known as immune.
- Immune system forms the third line of defense.
- Any foreign substance which when enters the body, is capable of stimulating an immune response is called an antigen.
- The protective chemicals produced by the body in response to antigens are known as antibodies.
- Antibodies are a class of bodies called immunoglobulins.
- Immunity is of two types:
(b) Acquired immunity
- It is a non-specific type of defense that is present at the time of birth.
- This is accomplished by providing different types of barriers to the entry of the foreign antigens into our body.
- It consists of following barriers:
They include skin and mucus coated epithelium of the respiratory tract, gastro- intestinal and urino-genital tract where the mucus helps in trapping microbes entering our body.
- Acidity of stomach
- Lysozyme in saliva
- Tear from eyes
All prevent microbial growth.
They include the following specialized cells, which phagocytose and destroy the microbes.
- Natural killer lymphocytes (NTC cells)
Interferons produced by viral infected cells protect the non- infected cells from viral infections.
Acquired immunity (Adaptive Immunity)
- Acquired immunity refers to the immunity, a person acquires after birth; either by contacting the disease or by vaccination.
- It is pathogen specific and is present only in vertebrates. It has the following characters:
It has the ability to distinguish many different foreign molecules.
When the immune system encounters a pathogen for the first time, it develops an immune response by which a pathogen is eliminated (primary response). It also retains some memory cells which evoke a heightened immune response in further encounters (secondary response).
Acquired immunity has 2 limbs
- Humoral/ Antibody mediated immunity
- Cell mediated immunity.
- It consists of the antibodies that are circulating in the body fluid (humor/plasma).
- The antibodies produced by B- lymphocytes in response to the antigens are collectively called immunoglobulins and are of various types i.e. IgA, IgD, IgE, IgM, IgG.
- Each antibody consists of four polypeptide chains. Two of the polypeptide chains are called heavy chains (H) while the other two are short and are called light chains (L), hence an antibody is represented as H2 L2.
Cell- mediated immunity:
Acquired immunity can also be classified into two types:
- It is mediated by T- lymphocytes. These are 2 groups of T- lymphocytes:
- Cyto - toxic/ killer- T-cells which kill the specific target cell by a variety of mechanisms.
- Helper T-cells which activate the specific B-cells to produce antibodies.
- T-lymphocytes are responsible for graft rejection.
Vaccination and Immunisation
- The principle of vaccination and immunisation is based on the property called memory of the immune system.
- The vaccines generate antibodies that neutralize the toxin/pathogen and also produce memory B-cell and T-cell which recognize the pathogen in subsequent encounters and produce antibodies. This type of immunization is called active immunization.
- If a quick immune is needed as in tetanus infection, preformed antibodies or antitoxin injected into the patient. This type of immunization is called passive immunisation .
- Recombinant DNA technology has allowed the production of antigenic polypeptides of pathogens in other microbes like yeast and bacteria. Eg. Hepatitis-B vaccine is produced using yeast cells.
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