Communicable Diseases


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Prelims: General Science

Mains: Science and Technology- Developments and their Applications and Effects in Everyday Life.

A communicable disease spreads from person to person or from animal to person. Communicable diseases are sometimes referred to as "infectious" or "transmissible" diseases. These diseases constitute a significant global health concern, impacting individuals, communities, and nations alike.

Communicable diseases are caused by a diverse array of pathogens such as bacteria, viruses, fungi, and protozoa, and have the potential to transform into pandemics like Coronavirus (Covid-19).

Causes and Spread of Communicable Diseases

Communicable diseases are caused by pathogens such as bacteria, viruses, fungi, and protozoa that can be spread from one person to another. They can be transmitted through the following ways:

  • Direct contact: When a person comes into contact with the bodily fluids of an infected person, such as blood, saliva, urine, or faeces.
  • Indirect contact: When a person comes into contact with an object that has been contaminated with the bodily fluids of an infected person, such as a doorknob, light switch, or toy.
  • Airborne transmission: When a person breathes in infected droplets that have been released into the air when an infected person coughs or sneezes.
  • Vector-borne transmission: When a person is bitten by an infected insect or arthropod, such as a mosquito, tick, or flea.


  • Symptoms vary according to the disease. Some people will have no symptoms at all. They can, however, still spread the pathogen.
  • Some symptoms are caused by the pathogen directly damaging the body's cells. Others are caused by the immune system's response to the infection.
  • Some communicable diseases are mild, with symptoms lasting only a few days. Some, on the other hand, can be serious and even fatal. The severity of symptoms can vary depending on a person's overall health and immune function.

Communicable Diseases Caused by Bacteria

Bacteria are single-celled, microscopic organisms and can cause infections that harm the body.

Tuberculosis (TB)

- Caused by Mycobacterium tuberculosis.

- Transmission: Through the air from one person to another, sneeze or spit.

- Not spread by hand shaking, food or drink sharing food or drink or touching bed linens or toilet seats.

- Symptoms: Cough over 3 weeks, chest pain, fatigue, fever, sweating.

- Treatment: Vaccine: BCG and Antibiotics: Streptomycin

- Initiatives:

  • National Strategic Plan to end TB in India by 2025
  • Nikshay Portal: Online portal launched in 2012 for Drug-Resistant TB
  • TB Harega Desh Jeetega Campaign in 2022 by the Ministry of Health and Family Affairs
Leprosy (Hansen's disease)

- Caused by Mycobacterium leprae

- Transmission: Through droplets from the mouth and nose with close contact.

- Symptoms: Red skin patches, numbness, effect on peripheral nerves.

- Treatment: Curable with multidrug therapy (rifampicin, dapsone and clofazimine) and BCG (Bacillus Calmette-Guerin) vaccine.

Whooping cough (Pertussis)

- Caused by Bordetella pertussis

- Transmission: Through sneezes or coughs from one person to another.

- Symptoms: Cough, fever, Apnea and cyanosis in babies

Treatment: Diphtheria, tetanus, and pertussis (DTaP) vaccines


- Caused by Salmonella

- Symptoms: Fever, abdominal pain, diarrhoea, nausea and vomiting.

- Transmission: Through the food chain, person-to-person transmission through the faecal-oral route.

- Treatment: Treatable through electrolyte replacement and routine antimicrobial therapy.

Communicable Diseases Caused by Viruses

Viruses are microscopic pathogens that carry genetic material. They must enter the cells of other living beings to replicate. They use the cell's machinery to duplicate themselves once inside.


- Caused by the poliovirus, mainly affects children under 5 years of age

- Transmission: Mainly through the faecal-oral route, contaminated water or food, spread from person to person possible.

- Symptoms: Effect on the nervous system; can lead to paralysis

- Treatment: No cure, prevention through oral polio vaccine and inactivated polio vaccine

- India became polio-free in 2014.

Acquired immunodeficiency syndrome (AIDS)

- Caused by the Human Immunodeficiency Virus (HIV).

- Destroys the WBC and infection-fighting CD4 cells of the immune system

- Symptoms: Loss of immune cells, weight loss, tiredness

- Transmission: Through sexual contact, blood, needles, mother to infant (cannot be transmitted through saliva or sweat)

- Treatment: No cure

- ELISA Test: Diagnosis test for HIV

Japanese encephalitis

- Caused by the bite of an infected mosquito with Flavi Virus

- Transmission: Spread to humans through bites from infected mosquitoes of Culex species

- Symptoms: Fever, headache, vomiting, disorientation, coma, and seizures

- Treatment: No cure for the disease, prevention through vaccination


- Caused by infection with one of the Ebola virus strains.

- Transmission: From person to person through direct or indirect contact with infected people’s blood, body fluids or secretions.

- Symptoms: Fever, fatigue, headache, muscle pain and chills.

- Treatment: Drug treatment through Inmazeb and Ansuvimab, prevention through vaccination (Vaccines: Ad5-EBOV and rVSV/Ad5)


- Caused by a variety of infectious hepatitis viruses

- Five strains: Hepatitis A, B, C, D and E

  • Hepatitis D infections only occur in people who have been infected with the Hepatitis B virus.
  • Hepatitis B and C can cause both acute and chronic disease.

- Transmission: Transmitted through direct or indirect contact such as sexual practice, faecal routes or ingestion of contaminated food and water.

- Symptoms: Fatigue, itching, dark-coloured urine, fever, malaise, diarrhoea, abdominal discomfort, and jaundice.

- Treatment: Prevention through vaccination, vaccines available for Hepatitis A, B and E, No vaccine for Hepatitis C

- National Viral Hepatitis Control Program: By 2030, eliminate viral hepatitis as a public health threat.

- Nobel Prize for Medicine or Physiology in 2020: For the discovery of the Hepatitis C virus


- Caused primarily by bites of Aedes mosquitoes (similar to dengue)

- Transmission: Through blood transfusion, sexual contact, and to babies from infected mother during pregnancy or childbirth.

- Effect: It can lead to neuropathy, Guillain-Barré syndrome, and myelitis.

- Symptoms: Fever, pain, headache, and conjunctivitis.

- Treatment: No specific treatment and no approved vaccine for prevention.


- Caused primarily by bites of Aedes mosquitoes (Same causes Zika).

- Transmission: Spread to humans by the bite of infected mosquitoes.

  • It cannot be transmitted from person to person directly. However, maternal transmission is possible. (Spain reported the first sexual transmission of Dengue).

- Symptoms: High fever, severe headache pain behind the eyes muscle and joint pains nausea vomiting swollen glands rash.

- Treatment: No specific treatment (vaccine in development)


- Caused by fruit bats (natural reservoir of virus)

- Transmission: Transmission from animals to humans, contaminated foods, direct transmission from human to human possible.

- Symptoms: Fever, headaches, myalgia, vomiting, can lead to acute respiratory infection and encephalitis

- Treatment: No specific treatment or vaccine is available either for people or animals.


- An acute respiratory infection caused by influenza viruses

- Four types: Influenza A, Influenza B, Influenza C and Influenza D.

  • Only influenza A viruses have been linked to the pandemic.
  • Influenza D viruses are primarily found in cattle.

- Transmission: Transmitted from person to person through cough or sneeze, droplets containing viruses.

- Symptoms: Fever, cough, body aches, sore throat and fatigue.

- Treatment: Treatment through the use of influenza drugs, and prevention through vaccination.


- Caused by monkeypox virus (a species of the genus Orthopoxvirus).

- Symptoms: Skin rash, fever, headache, pain, tiredness, and swollen lymph nodes.

- Transmission: Transmitted from animals to humans, transmission from person to person through direct physical contact with blood, bodily fluids, or mucosal lesions of an infected animal.

- Treatment: Early and supportive care, prevention through vaccination.

  • Vaccines and therapeutics developed for smallpox can be used in some circumstances.
Marburg virus disease (MVD)

- Caused by a genetically unique zoonotic Marburg virus of the filovirus family.

- Transmission: Human-to-human transmission through direct contact with the blood, bodily fluids or secretions of infected people, indirect contact through surfaces and materials contaminated with these fluids.

- Symptoms: Haemorrhagic fever, diarrhoea, severe pain, vomiting etc.

- Treatment: No approved vaccines or antiviral treatments.

Coronavirus (Covid-19)

- Caused by the SARS-CoV-2 coronavirus

- Symptoms: Fever, chills, headache, appetite loss, sore throat etc.

- Transmission: Transmission from human to human through close contacts.

- Treatment: Isolation and preventive care, vaccination (Covishiled, Covaxin etc).

Communicable Diseases Caused by Protozoa

Protozoa are unicellular microscopic eukaryotes with a relatively complex internal structure and metabolic activities. Following are the diseases caused by Protozoa:


- Caused by a plasmodium parasite (P. falciparum and P. vivax)

- Transmission: Transmission to people via the bites of infected female Anopheles mosquitoes.

  • However, it does not spread from person to person but transmission through blood transfusion and contaminated needles is possible.

- Symptoms: Fever, cold, headache, fatigue, seizures, and difficulty breathing, effects on RBCs.

- Treatment: Prevention through vaccination, vector control, and preventive chemotherapies.

Kala-azar (Leishmaniasis)

- Caused by protozoan Leishmania parasites.

- Transmission: Transmitted via bites of infected female phlebotomine sandflies.

- Symptoms: Fever, anaemia, weight loss, and enlargement of the liver and spleen.

- Treatment: Treatable and curable, however no specific vaccines.


- Caused by a parasite called Entamoeba histolytica.

- Commonly found in people living in tropical areas with poor sanitary conditions.

African sleeping sickness (Trypanosomiasis)

- Caused by protozoans of the genus Trypanosoma.

- Endemic in sub-Saharan Africa

- Transmission: Spread to humans by bites of tsetse flies (glossina), mother-to-child transmission, transmission through sexual contact.

- Antitrypanosomal treatment

Communicable Diseases Caused by Fungi

Fungi are organisms that include yeasts, moulds, and mushrooms. The following are the diseases caused by fungi:


- Caused by Aspergillus, a type of fungus living indoors and outdoors.

- Symptoms: Cough, shortness of breath, can lead to lung infections

- Treatment through fungal medication


- Caused by a yeast called Candid

- It can cause infections in the bloodstream or internal organs.

Athlete’s foot

- Caused by a variety of different fungi

- Symptoms: Skin fissures or scales between toes that can be red and itchy

- Prevention through hygiene


- A circular rash caused by fungus.

- Symptoms: Itchy skin, ring-shaped rash, red, scaly, cracked skin, hair loss

- Transmission: Through close contact with an infected person such as sharing towels, bedding, or other personal items

PYQs on Communicable Diseases

Question 1: Which of the following statements is not correct? (UPSC Prelims 2019)

  1. Hepatitis B virus is transmitted much like HIV.
  2. Hepatitis B, unlike Hepatitis C, does not have a vaccine.
  3. Globally, the number of people infected with Hepatitis B and C viruses are several times more than those infected with HIV.
  4. Some of those infected with Hepatitis B and C viruses do not show the symptoms for many years.

Answer: (b)

Question 1: Consider the following statements: (UPSC Prelims 2017)

  1. In tropical regions, Zika virus disease is transmitted by the same mosquito that transmits dengue.
  2. Sexual transmission of Zika virus disease is possible.

Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2

Answer: (c)

Question 2: Which of the following diseases can be transmitted from one person to another through tattooing? (UPSC Prelims 2013)

  1. Chikungunya
  2. Hepatitis B

Select the correct answer using the codes given below:

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

Answer: (b)

FAQs on Communicable Diseases

What are communicable diseases?

Communicable diseases, also known as infectious diseases, are illnesses caused by pathogens such as bacteria, viruses, fungi, and protozoa that can be transmitted from one person or animal to another.

What is the difference between communicable and non-communicable diseases?

Non-communicable diseases are not easily spread from one person to another, whereas communicable diseases can be easily spread between humans.

How do communicable diseases spread?

They can spread through direct contact involves contact with bodily fluids, while indirect contact occurs through contaminated objects, airborne transmission happens when infected droplets are inhaled, and vector-borne transmission occurs through insect or arthropod bites.

What are the 5 most communicable diseases?

Following communicable diseases are the five most common globally: Hepatitis B, Malaria, Hepatitis C, Dengue and Tuberculosis.

Can fungi cause communicable diseases?

Yes, fungi can cause communicable diseases, such as Aspergillosis, Candidiasis, Athlete's foot, and Ringworm.