NEET Biology Human Health And Disease Notes - Diseases Caused by Bacteria

Notes - Diseases Caused by Bacteria

Category : NEET

Diseases Caused by Bacteria


Diseases Caused by Bacteria : The human diseases caused by bacteria include cholera, pneumonia, typhoid, tetanus, diphtheria, whooping cough, tuberculosis, plague, leprosy, syphilis, gonorrhoea, diarrhoea and anthrax.

Bacterial diseases and their pathogens

Disease Causative Bacterium

(1)   Cholera

(2)   Pneumonia

(3)   Typhoid

(4)   Tetanus

(5)   Diphtheria

(6)   Whooping cough

(7)   Tuberculosis

(8)   Plague

(9)   Leprosy

(10) Syphilis

(11) Gonorrhoea

(12) Diarrhoeal Diseases

(13) Anthrax

Vibrio comma (Vibrio cholerae)

Diplococcus pneumoniae

Salmonella typhi

Clostridium tetani

Corynebacterium diphtheriae

Bordetella pertussis

Mycobacterium tuberculosis

Pasteurella pestis

Mycobacterium leprae

Treponema pallidium

Neisseria gonorrhoeae

Escherichia coli, Shigella dysenteriae, Campylobacter, Salmonella

Bacillus anthracis



(1) Cholera : Cholera is an acute diarrhoeal disease. It is caused by a comma-shaped, motile bacterium called Vibrio comma or Vibrio cholerae. The organisms live in the intestine. Infection occurs with contaminated food and water. Incubation period varies from a few hours to 2-3 days. The symptoms of the disease are sudden onset of severe diarrhoea and vomiting. The stools are watery and give rice-water appearance. If the disease is not checked early, it leads to dehydration, loss of minerals, muscular cramps, suppression of urine and death. Rapid replacement of fluid and electrolytes is needed by oral rehydration therapy. Cholera epidemics are common in out country during fairs and floods and other natural calamities when water supply and sanitation go out of a gear. Preventive measures include proper community sanitation, personal  cleanliness, and taking boiled water and heated food. Cholera vaccine is useful during epidemic and visit to a fair. It, however, provides immunity for a short period, about 6 months. Visits to cholera affected places and families should be avoided. Vibrio cholerae first Isolate by Robert Koch in 1883.


(2) Pneumonia : Pneumonia is a serious disease of the lungs. Lymph and mucus collect in the alveoli and bronchioles. With the result, the lungs do not get sufficient air to support life. The disease is caused by a bacterium Diplococcus pneumoniae. It usually follows lowered body resistance due to exposure or infection of some other disease such as influenza. Infection spreads by sputum of the patient. Incubation period is just 1-3 days. Pneumonia commonly occurs in old people.

(3) Typhoid : Typhoid is characterized by constant fever. It is caused by a rod-like, motile bacterium named Salmonella typhi. The organisms live in the intestine and cause lesions in the intestinal wall. The disease spreads by contaminated food and water. Intestinal discharges of the patient contain the parasites. Incubation period varies from 1-3 weeks, average 2 weeks. Preventive measures include proper community sanitation, screening of water supply and food from contamination by flies, and personal cleanliness. Natural calamities like floods and hurricanes may cause epidemic of the disease. Typhoid vaccine provides immunity for about three years. Georges Fernand I. Widal (1896) devised the Widal Test for Diagnosis of Typhoid.


(4) Tetanus (Lockjaw) : Tetanus is a major endemic recurring in a locality disease in our country. It is responsible for a high mortality of infants and their mothers. It is caused by anaerobic bacillus Clostridium tetani. The bacillus enters the body through wounds and burns, and also by use of improperly sterilized surgical instruments. Incubation period varies from four days to three weeks. Tetanus results in painful muscular spasms and paralysis, which usually begins with jaw and neck muscles. This has led to the name ?lockjaw?. The disease is often fatal.

Tetanus organisms live in the intestine of horses and other animals without doing any harm. The spores are, therefore, abundant in the soil manured with animal dung. They are also present in the road and street dust because the animals pass out dung as they move about. Spores may survive for 60 or more years in the contaminated soil. On entering the body by way of wounds, the spores release active bacteria. The latter multiply and secrete a powerful toxin tetanospasmin into the tissue, and blood carries it to the central nervous system. The toxin brings about tetanus.

It is advisable to have tetanus toxoid injection in case of an injury in a road accident or a cut contaminated with street dust or animal dung. This will prevent tetanus. All of us should have toxoid immunization as a safe preventive measure against this dangerous disease. Tetanus toxoid gives active immunity. Anti tetanus serum (A.T.S.) produces passive immunity. It is now a practice to immunize the infants against diphtheria, whooping cough (pertussis) and tetanus simultaneously by DPT or triple vaccine.


(5) Diphtheria : Diphtheria is a serious disease of 2-5 years old children. It may attack adults also. It tends to occur in an epidemic form. It is caused by a rod-shaped bacterium named Corynebacterium diphtheriae. It commonly attacks the mucous membrane of nose, throat and tonsils. A semisolid material oozes from the affected region and forms a tough membrane over it. It may block the air passage.  An acute case may need throat surgery. The bacteria may invade the heart, causing fatal heart blockade. The disease spreads by discharges from the affected regions (droplet infection). Incubation period is 2-5 days. Diphtheria antitoxin rids the victim of infection fully if given within 24 hours of the appearance of the symptoms. The symptoms include high fever, sore throat, difficulty in breathing due to choking. After 24 hour the antitoxin is not effective. Babies should be immunised with DPT vaccine within the first six weeks of birth.


(6) Whooping Cough (Pertussis) : Whooping cough is primarily a disease of children. It is usually not serious in older children, but is often fatal in infants. It affects the respiratory tract. It is caused by a bacterium Bordetella pertussis. It spreads by discharges from the throat of infected person (droplet infection) and direct contact. Incubation period is 10-16 days. Fever, severe coughing, vomiting and characteristic gasping ?whoop? (loud, crowing inspiration) are common symptoms. Infants strangle from accumulation of mucus. Whooping cough vaccine (DPT) can immunize the infants.


(7) Tuberculosis : Tuberculosis, commonly called T.B., is a very serious disease. About half a million people die of this disease each year in our country. It is especially common among poor people living in dingy, ill-ventilated, congested localities of big cities. It is caused by a rod-shaped bacterium named Mycobacterium tuberculosis. Tuberculosis (TB) or ?consumption? is a bacterial disease caused by Mycobacterium tuberculosis. It commonly affects the lungs, where small tubercles are formed but may attack any part of the body, including the brain. Infection spreads by sputum from the person suffering from the disease (droplet infection). Incubation period is quite variable. The bacteria damage tissues and release a toxin named tuberculin which produces the disease. Symptoms of pulmonary tuberculosis are fever, cough, blood-containing sputum, pain in the chest and loss of weight. Contrary to common belief, tuberculosis is curable. Treatment in early stages of the disease yields best results. It includes rest, good diet, drugs, surgery, health education and rehabilitation. BCG vaccine gives considerable protection against tuberculosis, but it should be used as a supplemental measure rather than to replace other measure of control. World T.B. Day is celebrated on 24 March.


(8) Plague : Plague is essentially a disease of the rats, and is one of nature?s methods of periodically reducing the rat population. Man is affected incidentally. The disease is caused by a rod-shaped, nonmotile bacillus, Pasteurella pestis. It is carried from rat to rat by rat fleas, chiefly, Xenopsylla cheopis. The rat fleas leave the rats that die of plague, and bite human beings, thus infecting them with the disease. Death of the rats in a house may indicate the onset of plague. Plague is normally not spread from man to man. The incubation period of plague is 2-6 days. The disease is characterized by high fever, prostration (extreme weakness), and painful bubo (enlargement) of lymph nodes, generally in the groin or armpit. Plague has high mortality. A plague epidemic in Europe in 1348 reduced the population to one-third. Plague reached India in 1895 with ships from Hong Kong. Bubonic plague is caused by yersinia pestis (formerly pasteurella pestis) wayson stain test is used for susceptilbility of plague. Bubonic plague is basically a blood disease.

Preventive measures include killing the rats, having rat-proof ships and houses, killing the rat fleas when plague outbreak is suspected and immunization with plague vaccine.


(9) Leprosy (Hansen?s Disease) : Leprosy is a chronic infectious disease, endemic in warmer climates. It is caused by a bacillus named Mycobacteriun leprae, which was discovered by Hansen. It primarily affects the skin, mucous membrane and peripheral nerves, but may affect internal organs also. Its symptoms include hypopigmented skin patches, partial or total loss of sensation in the affected areas, lesions, ulcers, nodules, scales, deformity of fingers and toes, wasting of body parts, and thickened nerves. Infection occurs by prolonged and close contact with the leprosy patients. Babies isolated from leper parents early in life grow into normal healthy individuals. The bacilli leave the body in nasal discharge, from the throat during coughing, sneezing and even speaking, and through broken skin lesions. Incubation period is not exactly known. It is commonly between 2 to 5 years, but may vary from a few months to 30 or 40 years. Some 10.7 million people suffer from leprosy in Asia and Africa (WHO report). Leprosy has a special position among the communicable diseases because of the long duration of the disease, the frequency of disabilities and the social stigma it carries. It is a curable disease and the public should be educated about it and about the rehabilitation of the cured patients in society.


(10) Sexually Transmitted Diseases (STD) : The sexually transmitted diseases, also called venereal diseases (VD), spread by sexual intercourse with infected persons. The major venereal diseases are syphilis and gonorrhoea. These are international diseases. There are about 50 million cases of syphilis and 150 million cases of gonorrhoea in the world. However, the reported cases are merely a fraction of the actual prevalence of thesee diseases. The venereal diseases constitute a major medical problem in India.

      Syphilis : Syphilis is caused by spirochaete bacterium, Treponema pallidium. It affects the mucous membranes in genital, rectal and oral regions, and causes lesions. Infection occurs by contact. Incubation period is about 3 weeks. The mothers may transmit the disease to their new-born babies. Syphilis is an easily curable disease. Syphilis is commonly known as ?French disease? or ?French pox? caused by a spirochete, Treponema pallidum.

      Gonorrhoea : Gonorrhoea is caused by a diplococcus bacterium, Neisseria gonorrhoeae. The victim feels burning sensation during urination. Incubation period is 2 to 5 days. The disease affects the mucous membrane of the uriogenital tract, and spreads by sexual contact. The infection may spread to other parts of the body and cause arthritis and female sterility. The children born to afflicted mothers often suffer from eye infection (gonococcal ophthalmia). Gonorrhoea is also easily curable.


(11) Diarrhoeal Diseases : These are a group of intestinal infections, including food poisoning. The prominent symptom of all such infections is diarrhoea. Infections spread through contaminated food, water, drinks, hands, clothes, bed sheets and utensils. The causative agents are mainly bacteria such as Escherichia coli, Shigella dysenteriae, Campylobacter and Salmonella. A protozoan Giardia intestinalis and some viruses also act as causative agents. Toxins released by E. coli cause mild diarrhoea (loose and frequent evacuation of bowels) to severe dehydration. Shigellosis caused by Salmonella. The protozoans Giardia intestinalis and Balantidium coli and some viruses also act as causative agents. Toxins released by E. coli cause mild diarrhoea (loose and frequent evacuation of bowels) to severe dehydration. Shigellosis caused by Shigella is characterised by frequent passage of stools with blood and mucus and abdominal cramps. All diarrhoeal diseases caused dehydration, which can be countered with oral rehydration therapy, i.e., intake of adequate fluid and electrolytes.

        Food infection should be distinguished from food poisoning. In food infection, food merely transfers bacteria into the body. In food poisoning, bacteria grow in food and release toxins. When such a food is taken, toxins are absorbed into the blood from the digestive tract. They affect the body quickly, causing gastrointestinal trouble and other effects. Clostridium botulinum is a Gram positive anaerobic bacillus responsible food poisoning known as botulism The bacilli release exotoxin to the environment, which is one of the most potent neurotoxic substance produced by microbs. Bubonic plaque is caused by yersinai pestis (formerly pasteurella pestis), a Gram-negative rod


Bacterial Disease in Human




Main Symptoms

Mode of Infection



Vibrio comma (V.cholerae)


Severe diarrhoea and vomiting

By contaminated food and water

2 to 3 days


Diplococcus pneumoniae


Difficulty in breathing

By patient?s sputum

1 to 3 days


Salmonella typhi


Constant fever

By contaminated food and water

1 to 3 weeks

Tetanus (Lockjaw)

Clostridium tetani


Painful muscular spasms and paralysis

Through wounds and burns

4 days to 3 weeks


Corynebacterium diphthriae

Mucous membrane of nose, throat & tonsils

Sore throat, difficulty in breathing

By oral & nasal discharges

2 to 5 days

Whooping cough (pertusis)

Bordetella pertussis

Respiratory tract

Severe coughing characteristic gasping ?whoop?

By throat discharges and contact

10 to 16 days


Mycobacterium tuberculosis


Cough, bloody sputum, chest pain

By patient?s sputum



Pasteurella pestis

Blood and lymph

Painful pubo of lymph nodes

By rat-flea bite

2 to 6 days


Mycobacterium leprae

Skin mucous membranes, peripheral nerves

Hypopigmented skin patches, ulcers, deformity of digits

Long and close contact with patients

2 to 5 years


Treponema pallidium

Oral, genital, rectal mucosa


By contact

3 weeks


Neisseria gonorrhoeae

Urinogenital mucosa

Burning sensation in micturition

By sexual contact

2 to 5 days

Diarrhoeal diseases

Shigella dysenteriae, Salmonella, Escherichia coli, Campylobacter



By contaminated food, water, hands, fomite



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