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In this article we will discuss how to prevent communicable diseases seen in humans.
1. Uses of Disinfectants and Antiseptics:
Disinfectant or germicide is a substance which destroys harmful microbes that can cause diseases. Disinfectants are suitable only to inanimate objects and used to clean floors, working surfaces such as sinks, kitchen table tops, crockery, surgical instruments, etc.
An antiseptic is a substance that inhibits or destroys the growth of microorganisms. Antiseptics are suitable for application to living tissues. A disinfectant in low or dilute concentrations can act as an antiseptic.
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Examples of disinfectants are as follows:
a. Phenol:
It is one of the most commonly used disinfectant and used along with detergents to clean the surfaces especially hospitals.
b. Ethanol and Isopropanol:
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These are used for storing boiled syringes. But alcohol destroys the bacilli bacteria and viruses but not fungal or bacterial spores.
c. Aldehydes:
Formaldehyde is used for disinfection and sterilisation of surfaces. But it irritates the skin and most commonly used as a preservative for dead organic material.
d. Detergents:
Detergents help in cleaning grease, bacteria and dust.
e. Dettol and Iodine:
These are disinfectant and in a milder form used as antiseptics.
f. Hypochlorites:
Calcium and sodium hypochlorite form hypochlorous acid with oxygen and rapidly kills microorganisms.
2. Methods of Sterilization:
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Sterilization is the removal of all kinds of life forms a non-living object.
The different methods used to sterilise solid and liquid materials are as follows:
a. Heat Treatment:
Heating in a dry oven or exposure to stem kills all kind of organisms. Pasteurization of milk is the sterilization technique used to kill microorganisms in milk. Tinned food is heat treated and stored for long periods of time. This kills the spores of clostridium botulinum. Heating at 250 degree Celsius for 200 minutes kills the spores.
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b. Steam Treatment:
Exposure to steam kills a number of organisms.
c. Radiation:
Short wavelength radiations such as UV light can kill microorganisms. X rays and gamma rays are also used to destroy microorganisms and are useful for sterilization. This can used to sterilize disposable syringes, scalpels, bandages, and some types of food.
3. Antibiotics:
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Antibiotics are chemicals produced by microorganism such as bacteria and fungi that are capable of destroying or inhibiting the growth of other microorganisms.
There are two types of antibiotics:
a. Biostatic and
b. Biocidal.
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a. Biostatic agents are those that inhibit the growth and multiplication of susceptible microorganisms. These include chloramphenicol, erythromycin, sulphonamides and tetracyclines. The microorganisms can continue its growth and multiplication once the agent is removed.
b. Biocidal agents are those that kill the microorganisms. Some examples are streptomycin, cephalosporins, penicillin, etc.
In 1928, Sir Alexander Fleming discovered penicillin that could kill Staphylococcus aureus. Antibiotics interfere with the metabolism of the microorganisms and inhibit its growth.
There are two classes of antibiotics:
a. Broad spectrum antibiotics and
b. Narrow antibiotics.
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a. Broad Spectrum Antibiotics:
These antibiotics are effective against a broad range of different bacteria. For example, tetracycline’s and chloramphenicol’s are effective against many gram positive and gram negative bacteria.
b. Narrow Spectrum Antibiotics:
These are effective against only a narrow range of bacteria.
One major problem that is observed in the use of antibiotics is the resistance to antibiotics. Resistance may develop in an organism by mutation or by transfer of resistance. Mutation can occur randomly and spontaneously in microorganisms. Once an organism becomes resistant against an antibiotic, the use of that particular antibiotic offers the organism a selective advantage over the non-resistant types.
This results in the rapid multiplication of the resistant type. Resistance may be transferred from one organism to another by conjugation, a form of sexual reproduction. Multiple-resistance is also seen when a bacterium is resistant to more than one type of antibiotic. Multiple resistant Staphylococcus aureus (MRSA) is a common problem seen in hospitals.
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Another growing concern is the presence of antibiotics in human food. Antibiotics are used to treat several infections in cattle. They are also used to encourage growth in young cattle. It is also used to control disease in plants and in food preservatives.
Because of these reasons, antibiotics occur in traces in human food, which is not good for health. It may lead to hypersensitive reactions and produce resistance in pathogenic organisms.
4. Immunisation Agents:
Vaccines are immuno-biological substances designed to provide specific protection against a specific disease. It stimulates the production of protective antibody and other immune mechanisms. Vaccines may be prepared from live modified organisms, inactivated or killed organisms, extracted cellular fractions, toxoids or combination of these. More recent preparations are subunit vaccines and recombinant vaccines.
a. Live Vaccines:
These are prepared from live, generally attenuated organisms. Attenuation is the process by which the virulence of the viruses or bacteria is weakened. These are more potent than the killed vaccines since the immune response produced is larger than that produced by the killed vaccine. Live vaccines should be administered to persons with immune deficiency diseases or to persons whose immune response is weak.
b. Killed Vaccines:
Organisms killed by heat or chemicals can also stimulate active immunity. They are usually safe but less effective than live vaccines. The duration of immunity following the use of inactivated vaccines varies form months to many years.
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c. Toxoids:
Certain organisms produce endotoxins, e.g. diphtheria and tetanus. The toxins produced by these organisms are detoxicated and used in the preparation of vaccines. The antibodies produced neutralise the toxic substance produced during an actual infection rather than acting upon the organisms.
d. Cellular Fractions:
Vaccines are also produced from cellular fractions of the infecting agent. For example, the meningococcal vaccine is prepared from the polysaccharide antigen of the cell wall, the pneumococcal vaccine is prepared from the polysaccharide found in the capsule of the organism. The efficiency and safety of the use of these vaccines is quite high.
e. Combination:
If more than one kind of immunising agent is used in a vaccine it is known as the mixed or combination vaccine. The aim of combined vaccine is to reduce costs and minimise the number of injections that needs to be administered.
Some examples of combination vaccines are:
DPT – Diphtheria-Pertussis-Tetanus
DT – Diphtheria – Tetanus
MMR – Measles – Mumps – Rubella
DPTP – DPT + Inactivated Polio
f. Subunit Vaccines:
If the exact antigenic determinants that stimulate immunity are known, it is possible to produce a vaccine based on a selected part of the microorganism. These are called subunit or a cellular vaccines. Examples of subunit antigens are the capsule of the pneumococcus, the protein surface antigen of anthrax and the surface receptors of hepatitis B virus.
Recombinant Vaccines:
The method of genetic engineering is very effective in designing vaccines for pathogens that are difficult or expensive to culture. This technology provides a means of isolating the genes that encode various microbial antigens, inserting them into plasmid vectors and cloning them in appropriate hosts.
