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Communicable Disease – Disease Caused by Viruses, Bacteria ,Protozoa, Fungi Ringworm

Diseases caused by Viruses : 

Following are some of the important viral diseases in man:
  • Chicken Pox 
  • Measles 
  • Poliomyelitis 
  • Rabies
  • Small Pox 
  • Trachoma 
  • Influenza

Chicken Pox 

Causal Organism: 
Varialla-Zoster Mode of spread:

  • 1. By direct contact with diseased person. 
  • 2. By indirect contact i.e., by clothings, bed and other articles used by patient might spread the diseases to a healthy person.


  • Occurrence of moderate fever in the beginning. 
  • Appearance of rashes or eruptions within 24 hours from the time of infection. 
  • These rashes pass through several stages. 
  • Appearance of crusts or scabs finally.  
  • These crusts or scabs fall off within 14 days after the rash begins.

Prevention and control:

  • The patient suffering from this disease should be isolated from public places until all crusts or scabs are fallen off. 
  • Bed and clothing of patient should be kept clean. 
  • Calamine lotion should be applied on the rashes.

Measles or Rubeola

Causal organism: 
Myxovirus Mode of spread:

  • 1. By direct contact with patient. 
  • 2. By coughing or sneezing.

Symptoms : Since the incubation period of this virus is 10 days, therefore first symptom appears after 10 days.

The symptoms are: 

  • Fever, dry cough and running nose. Inflammation of the respiratory mucous membrane. 
  • Loss of appetite. Pink or red rashes or eruption appear on the face, neck and trunk. 
  • These rashes last for 4-7 days and the marks of dark pigmentation left thereafter disappear after a few days. Vomitting. 
  • Eyes become sensitive to light. Contract pneumonia as a secondary infection.

Prevention and Control :

  • Passive immunity can be attained by injecting of gamma globulin. 
  • This immunity thus developed lasts for only three to four weeks. Isolation of patient and personal hygiene are important to prevent the spread of infection. 
  • Use of glycerine or carbolized oil prevents its further spread.

Poliomyelitis or Polio-Causal organism

Entero- virus Mode of spread:

  • 1. By contaminated food and water. 
  • 2. By intestinal discharge of diseased person. 
  • 3. Insects and flies play an important role in the transmission of viruses.

Site of infection : The virus enters the intestine through contaminated food. It multiplies in the intestine through contaminated food. It multiplies in the intestine from where it reaches the nervous system through the blood stream i.e., circulatory system. In the spinal cord it causes inflammation of motor cells which control the movement of voluntary muscles. In the absence of nervous control, the muscles wither away and get paralysed.

  • The initial symptoms of the disease are occurrence of fever and stiffness of neck. 
  • Due to stiffness of neck, the head cannot bend forward and downward. Skeletal muscles get weakened and paralysed. 
  • Movement of limbs becomes weak and finally stops as the muscles fail to contract.

Prevention and Control :

  • 1. Poliomyelitis vaccine is quite safe and effective against this disease.
  • 2.All children should be immunised in the beginningof infancy to ensure complete safety against thedisease.
  • 3.The immunity can be maintained if booster doseis given every few years. Other viral diseases areRabies, Small Pox, Trachoma, Influenza etc.

Diseases Caused by Bacteria:Following are some of the important Bacterial diseases in man.

Cholera – Causal organism 

Vibrio choleraeMode of spread:

  • 1.By contaminated food and water.
  • 2.By inhalation of droplets expelled by diseasedperson through coughing, speaking, sneezing orsputum.
  • 3.Flies are the main carrier of these bacteria andspread the disease.
  • 4.Epidemic of cholera usually occur during fairsand after flood and other such natural calamities.

Symptoms :Since the incubation period of this bacteria is 2-3 days, therefore symptoms will appear after 2-3 daysof infection.
The various symptoms of this disease are:

  • 1.Vomitting and acute diarrhoea with rice waterstools resulting in dehydration and loss ofminerals from body. In acute cases death mayalso occur.
  • 2.Muscular cramps.
  • 3.Suppression of urine.

Typhoid – Causal OrganismSalmonella Typhiod

Mode of spread:
  • 1.By contaminated food and water.
  • 2.By faeces and urine of the patient.
  • 3.By direct contact with patient.Symptoms :Since the incubation period of the bacteria is 10-14  days  therefore symptoms of disease will appearafter 10-14 days of infection. 

Various symptoms ofdisease are:

  • 1.High fever.
  • 2.Slow pulse.
  • 3.Tender and distended abdomen.
  • 4.Eruption of rose coloured rashes on body.
  • 5.Diarrhoea with water-green stools.

Tuberculosis – Causal organism : MycobacteriumtuberculosisTuberculosis is most common in crowded cityslums. Bacterium which causes tuberculosis can infectany organ of body but the most favourite site is lung.It can also attack lymph nodes, bones and joints.
Mode of spread:
  • 1.By inhalation of droplets of infected sputumexpelled by patient during coughing, sneezing orspeaking.
  • 2.By contaminated food, water or milk.
  • 3.By inoculation of bacteria into the skin or mucusmembrane.

  • 1.Constant fever.
  • 2.Pain in chest.
  • 3.Cough and blood in sputum.
  • 4.Loss in body weight.
  • 5.Gradual weakening of body.

Prevention and control:
1.Isolation of patient.
2.The B.C.G. vaccine against tuberculosis givesconsiderable protection against disease.

Leprosy – Causal organism

Microbacterium leprae

Mode of spread :By prolonged contact with diseased parts ofpatient.
  • 1.Appearance of light coloured patches on theskin.
  • 2.In acute cases the organs are deformed and partsof body are lost.
  • 3.Perpheral nerves are damaged therefore affectedorgan becomes senseless.
  • 4.Ulcers, nodules, scaly scabs and deformities oftoes and fingers may also be caused.


Causal organism : Neisseria meningit
Mode of spread:By coughing and sneezing the germs spread frominfected person to healthy person.
Symptoms :
  • 1.Sore throat, fever, severe headache.
  • 2.Vomitting.
  • 3.Difficulty in bending the head to forward due tostiffness of neck.
  • 4.Occasional appearance of red spots all over thebody surface.
  • 5.The clear cerebrospinal fluid becomes turbid dueto inflammation of meninges (membranes covering the brain and spinal cord) also called meningitis.


It is called veneral disease.
Mode of spread :
  • 1.Through intercourse with an infected man.
  • 2.They enter the body through any crack or cut inthe skin.
  • 3.Through contaminated objects.

Symptoms :
  • Occurrence of fever and skin eruptions. 
  • After 3-4 weeks of infection, the primary sore or pimple appears on external genitals (the penis in male and labia minora and majora in female) which gradually becomes big and hard and later on becomes more prominent. 
  • Enlargement of lymph nodes in groin takes place. 
  • After 2-3 months, white shiny patches appear inside the mouth. 
  • Eruption appears on the skin particularly on face, palms, soles and scalp. 
  • Destructive changes in the internal organs of the body take place even after many years. 
  • Cardio vascular system may be badly affected. 
  • The infection can pass from infected pregnant mother to developing foetus through placenta and may result in the premature death of the foetus.


Mode of spread :
through intercourse with infected man through indirect way like cloths, bedding.
Symptoms :

  • urine passes out with difficulty and there is an urge for frequent urination. 
  • infection may pass into foetus through placenta if the infected female is pregnant. 
  • eruptions appear on the skin. 

Other common diseases caused by bacteria are: Plague, Botulism, Pneumonia etc.
Diseases caused by ProtozoaAmoebic dysentry or Amoebiasis

Mode of spread : 
  • indirectly through flies which may pollute human food with cysts. 
  • through contaminated water, vegetables, fruits and other food stuffs. 


  • frequent loose stools or diarrhoea. 
  • the blood stained mucous passes along with stool.

Prevention and Control:
  • Proper disposal of faecal matter of the patient. 
  • Vegetables and fruits when used raw, should be thoroughly washed preferably with potassium permanganate.

Malaria  :  Plasmodium 

Mode of spread : By the bite of an infected female anopheles mosquito which acts as a carrier.

Symptoms :
  • sudden onset of fever and sensation of extreme cold. 
  • signs of shivering and intense headache also follow. 
  • fall in temperature is accompanied by profuse sweating. 
  • the symptoms are repeated after every fixed hours depending upon the species of Plasmodium.

Prevention and control :
  • Destruction of breeding places (stagnated water) of mosquito by spreading an oil film on the water. Use of mosquito nets. 
  • Use of mosquito repellents like odomos. 
  • Spraying of D.D.T. or malathion in residential areas and other places. 
  • Use of various drugs like Quinine, Atebrine, Isopenta-quine is quite effective in control of malaria. 
  • By fumigation i.e., certain chemicals are burnt so as to produce fumes that either kill mosquitoes or drive them away from their dwelling places.

Diseases caused by Fungi  –  Ringworm

Mode of spread : Ringworm of foot spreads on the skin peripherally and heals centrally and the pathogen gains entry through foot if the person moves bare-footed.

  • the early lesion which appears on body is ring like-with a scaly border. 
  • in case if the ringworm appears on nail, the free edges of nails become grey or brown, rough, dull and sometimes nails are shed.

Prevention and control :
  • Personal hygiene is the best method of prevention of disease. 
  • The infected body parts should be washed with dilute potassium permanganate and kept clean.

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