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Sunday, 18 November 2018

November 18, 2018


Cholera is an infectious disease caused by a bacterium which infects the intestinal tract of humans. This tropical disease is widespread throughout south east Asia, India and parts of Africa.

Causative organism:

   The causative organism is a gram negative bacterium (vibrio cholerae or V. eltor). It is a comma shaped vibrio with a flagellum which propels its through water.

Mode of transmission:

  The bacteria are found in water contaminated by infected faeces from cholera patients. They enter out body when we take in contaminated food and water , or come in contact with the faeces, urine or oral secretions of an infected person. The disease can also be spread by the housefly.


    When the bacteria reach the intestines, they multiply rapidly and secrete an enzyme, mucinase, which digests  the mucus lining the membranes. The exposed intestinal wall becomes damaged by the endotoxins produced by the bacteria, resulting in severe diarrhoea, usually accompanied by acute abdominal pain and vomiting. The faeces are watery and full of bacteria. It is known as 'rice water stool' because of its appearance. Owing to the frequent and large quantities of water lost in the faeces, the patient becomes severely dehydrated, and if left untreated, death occurs in less than 24 hours in extreme cases.


   The main treatment is to prevent dehydration of the body. This is done by injecting large quantities of saline solution into the veins of the patient so that the water content of his cell is brought back to normal.


   Cholera can be controlled by vaccination, which however only gives a temporary protection of up to six months.

    The following methods can be used in the control of cholera.

• prosper sanitation and habits should be observed to prevent drinking water from becoming contaminated by infected urine and faeces.

• the cholera bacteria are easily killed by heat . therefore, drinking boiled water and eating thoroughly cooked food prevent infection.

• Cholera patients should be kept isolated in hospitals and their personal articles must be thoroughly disinfected.

• since the common housefly is the vector of the disease , measures should be adopted to discourage its breeding. Also , always keep cooked food covered.
November 18, 2018

Course of a Disease

When pathogens enter the body of a host, they do not produce the signs and symptoms of disease immediately. they have to fight the hosts defence mechanism and establish themselves in the host body first. there is an incubation period when the pathogens grow and multiply. Then the signs and symptoms of diseases appear. This is the disease period. The host is infectious during this stage. Finally, , the host may overcome the diseases. This sis the recovery period.

    Some disease like influenza and mumps have short incubation periods, while others like syphilis have long incubation periods.
November 18, 2018

How Pathogens cause Disease

Pathogens cause disease by the ways discussed. These microbial activities produce the signs and symptoms of a given disease. Symptoms of a disease are due to changes in the normal body functions. Pain , fever, headache, coughing, vomiting and paralysis are symptoms of a disease are the outward appearance of disease such as pallor, rash, swelling, oedema and diarrhoea.

November 18, 2018

Spread of Disease causing Micro organisms

Pathogenic micro organisms generally have a definite path by which they

• enter the body of a person , and 
• leave the body of an infected person to find new hosts.

These path of entry and exit from the host determine how these micro organisms are spread or transmitted to new hosts.

Pathogens can spread through

• air, I.e. air borne pathogens,
• water, I.e. water borne pathogens,
• food, I.e. food borne pathogens,
• direct skin contact, and 
• animals vectors.

Spread through air

  Many disease causing organisms are light or have light spores which can easily float in air. These air borne pathogens enter the body of a person in the air he breathes through the nose and mouth. They often affect the nose, throat, trachea, bronchi and lungs. They also leave the body of the infected persons in droplets in the air he breathes out, and when he sneezes, coughs and spits.  Disease like pneumonia, tuberculosis, influenza and mumps are caused by air borne pathogens.

Spread through Water

  Certain disease causing organisms are spread by drinking contaminated water. Thus, these water borne pathogens enter their new host through his mouth. They often affect their intestines of their host, causing diarrhoea. They leave the body of their host via his faeces. In places where sanitation and personal hygiene are poor, drinking water can easily become contaminated by such infected body wastes. Diseases like typhoid and cholera are caused mainly by water borne pathogens.

Note  some people can harbour pathogenic organism in their bodies without showing any signs of disease. These people are known as carriers. a carrier is a source of infection. For example, the faeces and urine of a person who is a carrier of water borne disease will be full of the pathogens causing that disease.

Spread through Food

   Pathogenic organisms can be spread by eating contained food. Like water borne pathogens, food borne pathogens enter and leave the body of their host via the  mouth, and in the faeces and urine, respectively. Food borne pathogens also tend to affect the intestines.

   Food becomes easily contaminated

• when handled by infected persons or carriers who have poor personal hygiene habits;

• by contaminated water;

• by animal vectors like flies.

Foods milk and ice cream are some of the most common sources of infection as pathogens can multiply rapidly in these foods. This is because they contain all the nutrients needed for microbial growth. Diseases like bacillary dysentery, amoebic dysentery, salmonella food poisoning and cholera are caused by food borne pathogens.

Spread through direct skin contact

    Certain pathogenic organisms are spread from one person to another by direct physical or skin contact. The diseases they cause are known as contagious diseases.

   Physical contact occurs in crowded places, when playing games, and during activities like kissing and sexual inter course. Suing the personal things of a person with a contagious disease can also cause infection.

   Contagious diseases usually affect the skin and mucous membranes. Leprosy, ringworm, yaws, syphilis  and gonorrhea are examples of contagious diseases.

Note :  scabies , a common contagious diseases, is caused by itch mites. The female mites burrow into skin and lay eggs. This causes severe itchiness in the affected parts.

Spread through animal vectors

   Animals , especially insects, can spread diseases causing organisms from person to person.
November 18, 2018

Harmful Effects of Micro organisms

The important types of diseases causing or pathogenic micro organisms in humans are viruses , bacteria, protozoa and fungi.

    Pathogenic micro organisms cause infectious or communicable diseases, I.e. diseases which can be spread from infected persons to healthy persons. This is because these pathogens are parasites. They have to find ways of spreading from one host to another
November 18, 2018

Biodegradation of Pollutants

Modern technology produces many organic substances that can not be degradation d and recycles in nature. These substances accumulate and pollute the environment. Scientists are trying to produce micro organisms that can degrade these pollutants.

    Petroleum is an important pollutant that is degraded poorly in nature. Hydrocarbon feeding bacteria are used to clean up areas like harbours that become frequently polluted with petroleum. Oil containing waste water from ships is also purified by these bacteria before the water is discharged into the sea.

   Scientists have produced petroleum digesting bacteria which are useful in getting rid of oil spills in the sea quickly.
November 18, 2018


Improving soil fertility

   In intensive crop cultivation, nitrate is one of the important plant nutrients in the soil that becomes used up. Scientists are developing various strains of nitrogen fixing bacteria like azotobacter and Rhizobium that can fix nitrogen more efficiently than the existing ones.

Biological control of pests

Chemical pesticides are unsatisfactory as they 

• pollute the environment,
• accumulate to toxic levels in the final consumer of a good chain,
• are non specific , killing both harmful pests and beneficial insects and spiders.

Now, where possible, biological agents are being used to control pests. several micro organisms have been produced to specifically attack insect pests. These pathogens may be added tot the crop in a powder. In one method, some of the male pest are inoculated with the pathogen and released into the pest population. They spread the pathogens to the females also become infected. Eventually, the pests die when the pathogens build up to lethal levels.