Human Diseases – Types, their cause and prevention: Science

Any person who Is free from illnesses and possesses good mental status is said to be healthy. A healthy person is always active and cheerful. It is truly said that a healthy mind resides in a healthy body.

Human Diseases - Types of Human Diseases


Human Diseases: The term ‘disease‘ means ‘not ease‘. In other words, we can say ‘the state or being uncomfortable. We feel uncomfortable when we suffer from diseases. Thus, a disease is an abnormal condition in which the body is not able to carry out all its functions properly. Fever, pain, cough, headache, loose motion, etc. are some common diseases. Our body gives some symptoms or indications when we are sick.

But there may be different ca uses for a particular disease. Hence, diseases are classified into two groups:

  1. Deficiency Diseases (Non-Communicable Diseases)
  2. Communicable Diseases

1. Deficiency Diseases

Some diseases are caused due to lack of some nutrients in our diets. These diseases are known as deficiency diseases. A person suffering from a deficiency disease can be cured by providing a balanced diet. These diseases do not spread from one person to another. So, they are also called non-communicable diseases.

Some deficiency diseases are discussed below:

  1. Night blindness is caused due to the lack of vitamin A. A person having this disease cannot see properly in dim light or at night. Milk, fish, eggs, carrots, tomatoes and papayas are some rich sources of vitamin A.
  2. Beriberi is caused due to the lack of vitamin B. It affects heart muscles and nerves of a person. The affected person feels extreme weakness. Milk, meat, eggs, nuts, cereals and green vegetables are some rich sources of vitamin B.
  3. Scurvy is caused due to the lack of vitamin C. The affected person has bleeding gums and swollen joints. Citrus fruits, Amla, tomatoes and leafy vegetables are some rich sources of vitamin C.
  4. Rickets is caused due to the lack of vitamin D. The affected person has weak and soft bones, which results in the bending of the backbone and bowing of the legs. Fish-liver oils are the major dietary source of vitamin D. Exposure to sunlight is very helpful as vitamin D is formed under the skin by the action of sunlight.
  5. Goitre is caused due to the lack of iodine in diet. The affected person has swelling in the thyroid glands. Iodised salt and seafood are rich sources of iodine.
  6. Anaemia is caused due to the lack of iron in diet. An anaemic person has a pale and tired look. Fish, green leafy vegetables, eggs and meat are some rich sources of iron.

Some other causes of non-communicable diseases:

  1. Pollution in air can cause respiratory diseases.
  2. Some bad habits like smoking, chewing tobacco and consumption of alcohol can cause cancer, etc.
  3. Eating too much junk food can cause heart diseases, diabetes, high blood pressure, etc.

2. Communicable Diseases

Some diseases spread from one person to another by very tiny organisms called microbes or germs. Microbes can only be seen under the microscope. When the microbes of a particular disease attack a healthy person, he/she suffers from the disease. The infected person may infect another healthy person and in this way, the disease spreads.

Thus, a disease which spreads from an infected person to a healthy person is known as a communicable disease.

Let us learn about different types of microbes, the diseases they spread and the modes of spreading of the diseases.


Bacteria cause diseases like tuberculosis and whooping cough. Modes of spreading of these diseases are sneezing, coughing  and sharing the things used by infected person. These are airborne diseases.

Bacteria are also present in contaminated food and water. Cholera and typhoid are some diseases caused by contaminated food and water. These are waterborne diseases.


  • By the bacteria, mycrobacterium tuberculosis, causes infection in lungs where it produces a toxin called tuberculin that causes high fever.
  • BCG (bacillus-calmette-guerin) vaccine gives considerable protection against TB.


  • Mainly from 2-5 yrs, but can also be in adults.
  • By the bacteria, corynebacterium diphtheriae.
  • It grows in the membranes of respiratory tract and blocks the respiratory passage resulting in difficult breathing.
  • Can ultimately lead to death due to choking.
  • Babies should be immunized within first 6 weeks of their birth using DPT (diphtheria, pertussis, and tetanus) vaccine. (Diphtheria, whooping cough and tetanus).

3. WHOOPING COUGH (or Pertussis)

  • By the bacteria, Bacillus Pertussis.
  • It begins with mild fever and an irritating cough that gradually becomes paroxysmal (whooping).
  • The children can be immunized by the use of DPT vaccine.


  • Caused by the bacteria Vibrio Comma.
  • It is transmitted through contaminated food and water.
  • Symptoms of disease are vomiting, acute diarrhoea and muscular cramps. Dehydration and loss of minerals are the other symptoms.


  • These are a group of intestinal infectious diseases including the food poisoning. All these have a common symptom of diarrhoea.
  • The pathogens responsible for these diseases are Escherichia coli, Shigella sp., Campylobactera and Salmonella.
  • Spreads through contaminated water, food, etc.

6. LEPROSY (or Hansen’s disease)

  • Caused by a rod-shaped bacterium Mycobacterium leprae.
  • It is a chronic infection of the skin and other tissues including nerves.
  • The symptoms include ulcers, nodules, scaly scabs, deformities of fingers and toes and wasting of body parts. The infected part of the body become senseless (benumbed).
  • The disease spreads only after a long and close contact with the patient (one of the least infectious of all infectious diseases).
  • Symptoms occurs after more than one year of the entry of bacteria into the body.


  • By a motile bacteria, clostridium tetani, found in soil, dust, water, etc.
  • The bacteria enter the body through injured surfaces. It takes about one-two weeks for bacteria to show first symptoms.
  • The disease is characterized by painful contraction of muscles usually of the neck and jaws followed by the paralysis of thoracic muscles. It is a disease of the C.N.S. (also called lock-jaw).
  • ATS (Anti-tetanus serum) is prescribed.


  • Caused by Streptococcus pneumoniae.
  • It is inflammatory disease of lungs.
  • It is characterised by sudden chill, chest pain, cough, rapid shallow breathing and high temperature.
  • In this the fluids collect in the  alveoli and bronchioles due to which the lungs do not get sufficient air to support life.


  • Caused by Salmonella typhi which is found in the intestine of humans.
  • Typhoid spreads through food, milk and water contaminated with intestinal discharges either directly or through flies and personal hygiene.
  • Main symptoms are high fever, headache, diarrhoea, gastrointestinal disorder like ulceration of intestine, etc.


  • Plague is primarily a disease of rat.
  • It is caused by rod shaped bacterium Pasteurella/Yersinea pestis which is an endoparasite of gut of rat flea, Xenopsylla cheopsis.
  • Rat flea is an ectoparasite of rat.
  • Its germs can also be transmitted from man by head louse and bed bug.
  • Plague is of 3 types:
    1. Bubonic Plague: It is a blood disease in which bacteria multiply in the blood stream and localise in the lymph nodes, especially those of armpits, neck and groin. It is characterised by high fever,weakness, enlargement of lymph nodes, haemorrhages which turn black. The patient dies thereafter. Hence, plague is also called black death.
    2. Pneumonic Plague: Characterised by haemorrhage of bronchi and lungs. It spreads from human to human (without rat flea) through droplets and fomites.
    3. Septicemic Plague: Characterised by anemia, fever, chill, etc., leading to death within 2 days.


  • It is an acute infectious disease caused by Bacillus anthracis.
  • It is most common in agricultural regions where it occurs in animals.
  • It most commonly Occurs in wild and domestic lower yertebrates (cattle, sheep, goat, camel and other herbivores).
  • But it can also occur in humans when they are exposed to infected animals or tissues from infected animals.
  • Anthrax infection can occur in three forms: cutaneous, inhalation and gastrointestinal.


  • By a bacteria, Neisseria gonorrhoeae.
  • It is transmitted through sexual contact (It is an infection of the mucous membrane of the urinogenital tract).
  • It may result in female sterility.


  • Also a sexual disease caused by a bacteria, Treponema Pilludum.
  • It is transmitted through sexual contacts.

Dental plaque is caused by bacteria Streptococcus mutants.


Viruses cause diseases like common coldmeasles and chicken pox. When a healthy person comes in comes in contact with the sneezing, coughing and clothing of an infected person, he/she too gets infected with the disease. These are airborne diseases.


  • Caused by a virus Paramyxo virus.
  • Characterized by painful swelling of the salivary glands (particularly the parotid gland) accompanied with high fever.
  • Due to this, the movement of the jaw becomes very difficult.
  • In adults, the gonads (both testes and ovaries) may also become inflammed.


  • Caused by the virus, rubella virus, 10-12 days incubation period.
  • At the end of this period, the buccal and respiratory passage (mucous membranes) show signs of inflammation.
  • There is a loss of appetite and eruption occurs on the skin.


  • Caused by vericella-zoster virus.
  • It is highly contagious.
  • It is generally in children less than 10 yrs.


  • Caused by the smallest known virus, enterovirus.
  • The virus occurs only in man and it enters the body through contaminated food and water.
  • It multiplies in the cells of intestinal wall and then the infection spreads through the blood stream and lymphatic system.
  • The virus mainly attacks the C.N.S. and destroy the cells of the dorsal horn of spinal cord.
  • This results in the atrophy of the muscles of arms and legs as these muscles do not get the nerve impulses.
  • It usually leads to paralysis.


  • Influenza is an acute respiratory tract infection caused by influenza virus.
  • Influenza viruses are classified within the family Orthomyxoviridae.
  • It spreads mainly from person to person by droplet infection or droplet nuclei created by sneezing, coughing or talking.
  • Influenza causes inflammation or upper respiratory tract, nose, throat and eyes.


  • Caused by rhinovirus (rhino means nose) which belongs to picornavirus group.
  • The viruses are transmitted through droplet-nuclei, pharyngeal and nasal secretions.
  • Symptoms include headache, watery eyes, sneezing, excessive nasal secretions and cough.

7. RABIES (Hydrophobia)

  • Caused by RNA virus called Rabies virus.
  • The virus is neutrotrophic, i.e., damages motor neurons of brain.
  • Rabies affects all warm blooded animals and is exclusively transmitted by the bites of  carnivores.
  • It leads to encephalitis, fear of water (hence called hydrophobia), high fever, severe headache, spasm of throat and chest leading to death.
  • Vaccine against rabies was developed by Louis Pasteur.


  • Hepatitis is the viral infection of liver.
  • It is accompanied by loss of appetite, nausea, whitish stool, but orange brown urine and jaundice which occur due to bilirubin released from damaged liver cells.
  • Hepatitis is of two types:
    1. Hepatitis A (epidemic jaundice): Caused by hepatitis A virus (HAV). It is transmitted from person to person by faecal-oral route. It is benign and usually not fatal.
    2. Hepatitis B (Serum hepatitis): Caused by hepatitis B virus (HBV). It is transmitted by transfusion of contaminated blood and blood products. It may be chronic and is fatal.


  • It is an acute tropical frequently epidemic viral disease of humans which is caused by RNA containing dengue virus.
  • It is transmitted by the bite of female tiger mosquito Aides aegpti during day time.
  • Two types of dengue fever are:
  • Classical dengue fever: More severe in adults and characterised by mild conjunctivitis, high fever, backache, retro-orbital pain (pain behind the eye ball), etc.
  • Dengue haemorrhagic fever: Fatal form with nausea, headache, vomitting, abdominal pain, etc.

Disease by mosquitoes - DENGUE FEVER


  • Caused by arbovirus.
  • It is a haemorrhagic disease transmitted by the infected Aides aegypti.
  • Symptoms are headache, fever, vomitting, rupture of veins in kidneys, spleen, liver, etc.
  • In severe cases, the skin of the sufferer becomes yellow from jaundice, hence the name yellow fever.


Protozoa cause diseases like diarrhoea and amoebic dysentery. When a healthy person consumes contaminated food and water, he/she gets infected. Houseflies are common transmitters of these diseases. When they sit on garbage, microbes get stuck to their hairy legs. When they sit on uncovered food, microbes contaminate the food.

Similarly, protozoa of malaria and dengue spread through the bites of mosquitoes When a mosquito, carrying malaria-causing protozoa, bites a healthy person, it injects these protozoa into his/her blood and causes malaria. Diseases that are caused by the bites of infected vectors such as mosquitoes and flies are called vector-borne diseases.


By a protozoan, Plasmodium. There are several species of Plasmodium ith different periods of incubation:

Plasmodium Vivax

  • Causes benign tertiary malaria.
  • Incubation period is 13-15 days.
  • Fever recurrs after every 48 hours.

Plasmodium Malariae

  • Causes quartan malaria.
  • Incubation period is 28-30 days.
  • Fever recurrs after every 72 hours.

Plasmodium Falciparum

  • Causes malignant tertiary malaria.
  • Incubation period is 12 days.
  • Affects brain and recurrs every 36 hours. It is usually fatal.

Plasmodium Ovale

  • Causes mild tertiary malaria.
  • Recurrs after every 48 hours.
  • Incubation period is 14 days.

Disease spreads by certain species of Anopheles mosquito (only female anopheles).

Life cycle of Plasmodium is completed in 2 hosts:

  1. Man : Primary Host
  2. Female Anopheles : Secondary Host

After incubation period, temperature of body rises with a feeling of chill, signs of headache and nausea. Then temperature falls (symptom: sweating). The above symptoms are repeated after every fixed hrs. depending upon the species.

  • Certain fishes like Cat fish, Gambusia and aquatic birds eat mosquito larvae.
  • Quinane, a product of Cinchona tree, is administered for Malaria.

2. KALA AZAR (Leishmaniasis)

  • Caused by Leishmania donovani.
  • It is spread by sandfy (Phlebotomus) and characterised by enlarged spleen and liver with high fever.
  • Kala Azar is also known as dum dum fever.


  • Caused by Giardia intestinalis (first parasitic protozoan known).
  • It inhabits upper part of small intestine (duodenum and jejunum).
  • Characterised by mild diarrhoea involving passage of pale, bulky, foul smelling and greasy stool.


  • Caused by different species of Trypanosoma.
  • Main disease is Gambian fever or West African sleeping sickness, the vector of which is Tse tse.

5. AMOEBIASIS (Amoebic dysentry or Enteritis)

  • Caused by Entamoeba histolytica.
  • Characterised by abdominal pain, alternating diarrhoea and constipation, stool with blood, mucous and mucous membrane pieces.



  • Caused by Ascaris lumbricoides (Vector: Cockroach and Flies).
  • Symptoms are weakness, anaemia, diarrhoea, vomitting, etc.


  • Caused by Wucheraria bancrofti. Transmitted by female Culex mosquito.
  • Also called Elephantiasis – due to enlargement of body parts like legs.
  • Symptoms include fever, proliferation of endothelial cells and deposition of metabolites in the walls of lymph vessels resulting in swelling of affected parts.


  • Caused by Taenia solium (or pork tapeworm).
  • Transmitted by pig.
  • Symptoms are abdominal pain, indigestion, vomitting, Constipation, anorexia (loss of
  • appetite), nervous disorder.



  • Caused by Microsporum. Spreads by unbathed cats, dogs or infected persons.
  • In this, sores’are formed which become reddish and contain blisters.

Some other fungal diseases with their causative agents are Aspergillosis (Aspergillus fumigatus), Meningitis (Cryptococcus neoformans), Dermatitis of beard and hair (Trichophyton verrucosum) and Athlete’s foot (Tinea pedis).


  • by VIRUSChickenpox, Measles, Polio, Rabies, Mumps, Influenza, Hepatitis, Herpes, AlDS, Trachoma (of Cornea).
  • by BACTERIACholera, Diphtheria, Tuberculosis, Leprosy, Tetanus, Typhoid, Plague, Whooping Cough, Sore Throat, Pneumonia, Gonorrhoea, Syphilis, Botulism.
  • by FUNGIRingworm, Athlete’s foot, Dhobie itch
  • by PROTOZOANSAmoebiasis, Malaria, Sleeping ick-ness, Kalazar, Diarhoea, Piarrhoea.
  • by HELMINTHES/WORMSFilaria, Tapeworm and Hookworm transmission.

Prevention of Communicable Diseases

The spread of infectious diseases can be controlled by :

  1. Following the rules of personal hygiene.
  2. Keeping surroundings clean.
  3. Using disinfectants to clean the house, bathrooms and toilets.
  4. Disposing of garbage to prevent mosquitoes, cockroaches and houseflies from breeding in that.
  5. Using boiled and filtered water for drinking purpose.
  6. Not eating uncovered food.
  7. Isolating an infected person from other persons till his recovery.
  8. Disinfecting the clothes and other articles used by an infected person.
  9. Vaccination, which protects us from many diseases like polio, chickenpox, etc.

Disease at a Glance

Human Disease- Types, Cause and Prevention

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