Human Diseases and their Causative Agents (Part I)

By Saroj Singh|Updated : March 25th, 2020

This article is relevant for the UPSC CSE, UPSC EPFO and State Services.

The term "disease" refers to conditions that impair normal body function. Diseases can be caused by foreign agents – pathogens – such as viruses, bacteria and other parasites, entering the body or by an internal malfunction of the body itself. Infections and infectious diseases are a great burden on many societies, including the countries in the WHO European region.

Human Diseases and their Causative Agents (Part I)

Microorganisms that can cause disease are called pathogens.  An infection results when a pathogen invades and begins growing within a host. Because of the invasion and growth of a pathogen, tissue function is impaired. Our bodies have defence mechanisms to prevent infection and, should those mechanisms fail, to prevent disease after infection occurs. 

Diseases caused by Protozoa

  1. Malaria: It is a mosquito-borne infectious disease that affects humans and animals. Malaria is a protozoan infection of the red blood cells.

Symptoms: Usually begin ten to fifteen days after being bitten by an infected mosquito. It includes fever, tiredness, vomiting and headache. When severe, it can lead to yellow skin, seizures, coma or death.

Malignant malaria is pernicious malaria, caused by plasmodium falciparum

Curable: Can be treated. Quinine is an effective medicine used in the treatment of malaria from the bark of the cinchona tree.

Note: Organisms that transmit disease from one individual to another is called a vector. Mosquito here is a vector.

  1. Kala-ajar: Itis the most severe form of leishmaniasis and, without proper diagnosis and treatment, is associated with high fatality.  It is caused by protozoan parasites of the genus Leishmania.
  • Leishmaniasis is caused by the protozoan Leishmania parasites which are transmitted by the bite of infected female phlebotomine sandflies.

Symptoms: fever, weight loss, fatigue, anaemia and swelling of liver and spleen

Curable: Kala-azar is fatal if left untreated in over 95% of cases. 

 Diseases caused by Bacteria:

  1. Tetanus: It is caused by a bacterial toxin that affects your nervous system, leading to painful muscle contractions, particularly of your jaw and neck muscles.
  • Clostridium tetani spores, if deposited in a wound, the neurotoxin interferes with nerves that control muscle movement.
  • Tetanus can interfere with your ability to breathe and can threaten your life. Symptoms: The spasms can also affect the facial muscles. Tetanus is commonly known as "lockjaw."

Curable: There's no cure for tetanus. Treatment consists of wound care, medications to ease symptoms and supportive care.

  1. Typhoid: is a bacterial infection due to a Salmonella typhi.

Symptoms: vary from mild to severe, and usually begin 6 to 30 days after exposure. Weakness, abdominal pain, constipation, headaches and mild vomiting.

Curable: An only effective treatment for typhoid is antibiotics. The most used are ciprofloxacin (for non-pregnant adults) and ceftriaxone. Other than antibiotics, it is important to rehydrate by drinking adequate water.

  1. Tuberculosis: Tuberculosis (TB) is caused by bacteria (Mycobacterium tuberculosis) that most often affect the lungs. TB is spread from person to person through the air. When people with lung TB cough, sneeze or spit, they propel the TB germs into the air. A person needs to inhale only a few of these germs to become infected.

Alcohol use disorder and tobacco smoking increase the risk of TB disease 

Curable: Tuberculosis is curable and preventable.

  1. Diptheria: It is a highly contagious and potentially fatal infection that can affect the nose and throat, sometimes the skin. It is caused by the bacterium Corynebacterium diphtheria.

Symptoms:  sore throat, headache, nasal discharge, difficulty breathing and swallowing and swollen glands in the neck.

Curable: the disease is not only treatable but also preventable with a vaccine. The diphtheria vaccine is usually combined with vaccines for tetanus and whooping cough (pertussis).

  1. Leprosy: also known as Hansen’s disease (HD), is a long-term infection caused by Mycobacterium leprae.
  • Can damage nerves, respiratory tract, skin, and eyes.

Symptoms: Nerve damage may result in a lack of ability to feel pain, which can lead to the loss of parts of a person's extremities from repeated injuries or infection due to unnoticed wounds.

  • An infected person may also experience muscle weakness and poor eyesight.

Curable: Leprosy is curable and treatment in the early stages can prevent disability.

Click here to know more about the 'Major Viral infections and their outbreak in India' and for 'Diseases and its affected area'

Some of the emerging diseases caused by viruses and other microorganisms can be studied in subsequent posts.

Que. Consider the following pairs:

         Vector                                 Disease

  1. Anopheles Mosquito Japanese encephalitis
  2. Sand-flies                        Kala Azar
  3. Aedes mosquito Rift Valley fever

Which of the pairs given above is/are correctly matched?

A. 1 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2 and 3

To attempt more such questions  CLICK HERE 

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