Why Do We Fall ill?

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3 Infectious Diseases

Infectious agents
Microbes or microorganisms are small, unicellular organisms which cannot be seen with the naked eyes. While some microbes are useful in our day to day life others are harmful to our health. The harmful microorganisms are called pathogens like, bacteria, viruses, protozoa, and a few variations of worms. These agents enter the body directly or through some vector/agents like mosquitoes. They cause infectious chronic disease.

They invade the host cell, and disrupt or damage the normal cellular activities leading to diseases on a larger scale. Several diseases are caused by microbes

  • Viruses cause viral diseases that include both acute and infectious diseases like the common cold, to chronic disease like AIDS.  It is also responsible for mumps, polio, rabies etc.
  • Bacteria cause diseases like diphtheria, typhoid, cholera etc.
  • Protozoa cause diseases like malaria and sleeping sickness.
  • Worms like roundworms, tapeworms cause diseases like Ascariasis and Taeniasis respectively.

These infections have different source and means of transfer. Bacterias spread disease through different paths than viruses. Contaminated food and water are the main source of bacterial infection while air is the main carrier of viral diseases. Hence, bacterial and viral diseases are usually communicable. Direct physical contact i.e. blood transfusion, breastfeeding, sexual contact etc. are other means of transfer of pathogens.

Certain pathogenic diseases are organ or tissue-specific like, tuberculosis affects the lungs of the individuals while Jaundice causing viruses targets the liver. The depth or severity of infection depends on the amount and rate at which microbes spread.

Diseases Caused by Protozoa

1. Malaria

  • Malaria is caused by a protozoan parasite called plasmodium.
  • This disease spreads through the bite of the female Anopheles mosquito.


  • Headache, nausea, muscular pain and high fever are the main symptoms of malaria
  • Each malarial attack lasts from 6 to 10 hours It consists of 3 stages:
  • Cold stage, feeling of extreme cold and shivers;
  • Hot stage, i.e, high fever, causes faster respiration and increased rate of heart beat; and
  • Sweating stage, i.e, temperature of the body goes down to normal due to profuse sweating.


The only way to prevent malaria is to take precaution against mosquito bites.


In order to treat a person suffering from malaria, a drug named quinine, which is extracted from the bark of Cinchona tree is used

Diseases Caused by Viruses

1. Influenza

  • Influenza is commonly called flu and is caused by an influenza virus.
  • Influenza spreads mainly from person to person contact and by the droplet coughed out when an infected person sneezes, coughs or talks.


  • The most common symptoms of influenza disease are sudden onset of chills, discharge from the nose, sneezing fever, headache, muscular pains, inflammation of respiratory mucosa, coughing and general weakness.

2. Jaundice / Hepatitis

  • Jaundice or hepatitis is the disease of liver.
  • It causes inflammation of liver which affects digestion adversely.
  • Hepatitis is spread usually by good and water contaminated with hepatitis virus.


  • High fever, headache, fatigue, general weakness, and joint pains.
  • Loss of appetite (called anorexia) with a feeling of nausea and vomiting.
  • Appearance of irritating rashes on body.
  • Dark yellow urine.
  • Pale stools after 3 to 10 days of infection.


To avoid infection of hepatitis A, following preventive measures should be taken

  • Use chlorinated, boiled and ozonized water.
  • Proper cleaning of hands after handling bed and vessels of the infected patient.
  • Vaccination of Hepatitis-A.


  • Application of interferon injection on the advice of the doctor controls the disease.
  • It is essential that the infected person takes adequate rest to ensure early cure.
  • Jaundice patient should take high calorie diet such as juice of sugarcane, radish with gur (jiggery).
  • Consumption of protein and fat should be reduced.

3. Rabies (Hydrophobia)

  • The bite of a rabid dog (mad dog) and some other rabid mammals such as monkeys, cats or rabbits may cause rabies.
  • It is the disease caused by a virus called rabies.


  • The symptoms of rabies include severe headache, high temperature, painful contraction of muscles of throat and chest (due to which there is difficulty in swallowing).
  • The patient feels restless, does excessive salivation, has a choking feeling and finds difficulty in the intake of even liquid food.
  • As the patient develops a fear of water, the disease is also called hydrophobia.


  • It is important to clean the wound with carbolic soap and clear water immediately after the dog bite.
  • An antiseptic medicine (e.g., Savlon, Dettol) should be applied to the wound caused by dog bite.
  • A doctor should be immediately consulted for application of anti-rabies vaccine to the infected patient.
  • Immunization of stray dogs and cats should be compulsorily done. Even the pet dogs should be vaccinated with anti-rabies vaccine.
  • A rabid animal shows excessive salivation and tries to seek isolation after bite. Such an animal should be killed.


  • Rabies can be treated with Pasteur’s treatment (discovered by Louis Pasteur).
  • In this course, 14 vaccines were given to the patient.
  • At present, 5 anti-rabies vaccines are prescribed at an interval of 0-3-7-14-30 day of dog bite.


  • AIDS is caused by virus called retrovirus (a RNA virus) known as Human Immunodeficiency Virus (HIV).
  • These viruses attacks white blood cells (WBCs) and weakens the human body’s immunity or self – defense mechanism.
  • Thus, the patients suffering from AIDS become prone to many other infectious diseases.

AIDS spread because of following reasons:

  • This disease is usually spread through unprotected sexual contact with an infected person carrying AIDS virus.
  • It also spreads through the transfusion of blood contaminated with an AIDS virus.
  • The AIDS disease also spreads through the use of infected needles for injections.
  • AIDS also spreads by infected mother as she can transmit the virus to her child during pregnancy or during birth.


Some important symptoms of AIDS are as follows:

  • Swollen lymph nodes; regular fever; sweating at night and weight loss.
  • AIDS virus causes severe damage to brain and may lead to loss of memory, inability to speak and loss of clear thinking.

Prevention and control

  • It is important that people are educated about AIDS
  • Disposable syringes and needles should be used for injection.
  • Sexual contact with unknown people should be avoided.
  • People belonging to high risk groups should refrain from donating blood.
  • Sterilized needles should be provided to drug addicts.
  • Before receiving blood for transfusion, it is essential to ensure that the blood has been screened for HIV.
  • Common razor at the barber’s shop should not be used.

5. Polio

  • Poliomyelitis or polio is a disease of the nervous system caused by virus, called polio virus.
  • The virus enters the body through the food and water and reaches the intestine. From the intestine, it enters the central nervous system (brain and spinal cord) via blood stream and lymphatic systems. Here, the virus destroys the motor nerve cells of spinal cord that are responsible for the muscular control.
  • Polio is a kind of paralysis and mostly affects the legs.
  • Children between the age of 6 months and 3 years are mostly prone to this infection.


  • Sore throat and headache are early symptoms of polio disease.
  • If the infection persists, the patient suffers from high temperature, vomiting muscular pain, stiffness in the neck, tingling sensation in limbs and ultimately paralysis.


  • In the beginning of polio virus attack, complete rest and physiotherapy is helpful.
  • Exercising of legs is done to reduce the paralytic effect.
  • It is important to maintain hygiene by proper sanitary disposal of waste to prevent polio.
  • Nowadays Oral polio vaccine (OPV) is given orally to the children as per National Immunisation Schedule in India.

Pulse polio Immunisation programme (PPIP)

  • The pulse polio immunisation programme forms the largest single day public health project.
  • It was first conducted in December 1995, in an attempt to eradicate polio from our country.
  • This programme uses oral polio vaccines or OPV.
  • As per the National Immunisation Schedule (NIS), a dose of 3 drops (0.5 ml) is given orally to children.
  • This vaccine consists of milder forms of polio viral particles. These particles in the vaccine starts living in the intestine of the human body.
  • And this leads to production of protective molecules (antibodies) in the intestine and the blood.
  • From 1999-2000, this programme covers mass immunisation of target groups on 4 occasions (4 NIDS or National Immunisation Days).
  • Since the incidence of poliomyelitis in India has decreased dramatically, India recorded 4,791 cases of polio in 1994; 2,489 in 1997; 1600 in 2002; 225 in 2003 and 135 in 2004.

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