Communicable diseases

1. Concepts, transmission and the public-health rationale

Communicable diseases arise through interactions among an infectious agent, a susceptible host and an enabling environment: the epidemiological triad. Agents include bacteria, viruses, parasites and fungi. Transmission may occur through respiratory particles, contaminated food or water, blood and sexual contact, vectors, direct contact or animal exposure. Tuberculosis predominantly spreads through the air, cholera through the faecal–oral route, and malaria through infected female Anopheles mosquitoes. Effective control requires identifying the transmission mechanism rather than treating all infections alike.

The chain of infection consists of an agent, reservoir, portal of exit, mode of transmission, portal of entry and susceptible host. Prevention interrupts one or more links through vaccination, ventilation, safe water, sanitation, vector control, protective equipment or prompt treatment. Endemicity means a disease's usual presence in a population; an outbreak or epidemic represents occurrence above expected levels. A pandemic extends across countries or continents, but the term does not itself indicate severity.

Public intervention is essential because infection creates externalities: one person's delayed diagnosis can expose others. Individuals may also lack reliable information or the resources to protect themselves. Surveillance, laboratory networks and outbreak response therefore require collective financing. Disease control should integrate biomedical measures with healthier living and working conditions.

• Incidence measures new cases over a specified period; prevalence captures existing cases in a population.
• Isolation separates infected people; quarantine restricts exposed people who may become infectious.
• Eradication means permanent worldwide reduction to zero incidence of infection through deliberate efforts; smallpox is the classic example.

2. India's disease burden and unequal vulnerability

India faces persistent endemic infections alongside seasonal outbreaks and emerging threats. Tuberculosis remains a major cause of illness and death. According to WHO's Global Tuberculosis Report 2024, India accounted for approximately 26% of estimated global incident TB cases in 2023. Dengue creates recurrent urban and peri-urban pressures, while malaria risk is unevenly concentrated, including in several forested and tribal areas. Diarrhoeal diseases remain linked to unsafe water and sanitation failures.

Risk is socially distributed. Undernutrition increases vulnerability to active TB, overcrowded accommodation facilitates respiratory transmission, and unreliable water supply encourages household storage that can support mosquito breeding. Migrant workers may struggle to continue treatment across districts. Remote tribal communities encounter geographic barriers, while women may face restrictions on mobility and household healthcare spending. HIV, TB and leprosy-related stigma can discourage testing, disclosure and sustained care.

Climate variability, urban expansion and ecological disruption alter disease risks without determining outbreaks by themselves. Flooding can contaminate water and increase leptospirosis exposure; changing temperature and rainfall can affect vector ecology. Zoonotic threats such as Nipah underline the links among animal health, human activity and ecosystems. Prevention must therefore involve housing, labour, water, municipal and animal-health institutions, rather than burdening health departments alone.

• Measure inequalities by geography, income, gender, disability and social group, while protecting confidentiality.
• Distinguish rising notifications caused by better detection from a genuine increase in disease incidence.

3. Institutions, laws and major Indian programmes

States deliver most public-health services, while the Union supports national programmes, standards, financing and coordination. The National Centre for Disease Control supports surveillance and outbreak investigation. The Integrated Disease Surveillance Programme, launched in 2004, uses decentralised surveillance and response mechanisms. Its digital strengthening through the Integrated Health Information Platform supports more timely reporting, although completeness, laboratory confirmation and local response capacity remain decisive.

The National Tuberculosis Elimination Programme combines case detection, drug-susceptibility testing, treatment and patient support. Nikshay enables case-based monitoring, while nutritional assistance and community support seek to reduce treatment interruption. The National AIDS Control Programme combines targeted prevention, testing, free antiretroviral treatment and measures to reduce discrimination. The National Centre for Vector Borne Diseases Control coordinates programmes addressing diseases including malaria, dengue, chikungunya, Japanese encephalitis, kala-azar and lymphatic filariasis.

The Universal Immunisation Programme and Mission Indradhanush address vaccine-preventable diseases and immunisation gaps. The National Viral Hepatitis Control Programme supports prevention, diagnosis and treatment. Ayushman Arogya Mandirs can strengthen first-contact care, screening, referral and treatment follow-up. The Epidemic Diseases Act, 1897 provides epidemic-control powers, while the Disaster Management Act, 2005 was extensively used during COVID-19. The HIV and AIDS (Prevention and Control) Act, 2017 specifically protects rights and prohibits specified forms of discrimination.

• Article 47 directs the State to improve public health; judicial interpretation connects health protection with Article 21.
• The International Health Regulations (2005) provide a framework for surveillance, notification and coordinated responses to international health risks.

4. Implementation gaps and governance dilemmas

Fragmented care weakens control. Patients often move between informal providers, private clinics and public facilities before receiving a correct diagnosis. Under-reporting, uneven diagnostic access and weak referral systems obscure transmission. Shortages of epidemiologists, laboratory staff, nurses and field workers constrain district response. Hospital-centred expenditure cannot substitute for routine immunisation, environmental health, community outreach or dependable primary care.

Antimicrobial resistance complicates communicable-disease management. Inappropriate prescribing, non-prescription access, inadequate diagnostics, poor infection prevention and antimicrobial use across animal and environmental systems contribute to selection and spread of resistant organisms. Drug-resistant TB illustrates the resulting need for susceptibility testing, effective regimens and sustained support. Stewardship must improve access to appropriate medicines rather than simply restrict access for underserved patients.

Outbreak response also raises ethical questions. Movement restrictions, disclosure of patient identities and coercive enforcement can undermine livelihoods and trust. Measures should be lawful, necessary, proportionate, time-bound and reviewable. Risk communication must acknowledge uncertainty and counter misinformation without stigmatising communities. Digital surveillance requires purpose limitation, secure systems and restricted access. Transparent communication and material support make voluntary cooperation more achievable than punitive approaches alone.

• Insurance coverage for hospitalisation does not by itself ensure access to outpatient diagnostics, medicines or preventive services.
• Disease notifications and elimination claims require clear definitions, reliable denominators and independent verification.

5. Priorities for an equitable public-health strategy

India needs a prevention-oriented system built around strong district public-health capacity. Priorities include interoperable surveillance, quality-assured laboratories, trained rapid response teams and reliable supplies of vaccines, diagnostics and medicines. Private providers should be integrated through notification requirements, referral arrangements and quality standards. Community workers require adequate remuneration, training and protection. Financing should sustain preparedness between emergencies rather than surge only after outbreaks begin.

A One Health approach should connect human, animal and environmental surveillance, particularly for zoonoses and antimicrobial resistance. Local governments must address drainage, waste disposal, safe drinking water and vector breeding, with community participation. Social protection, nutrition support and portable treatment records can reduce the burdens of prolonged illness. Progress should be judged through reduced incidence and mortality, timely diagnosis, treatment completion, lower catastrophic expenditure and narrower inequalities—not merely the number of facilities or tests.

• Combine universal services with targeted outreach to high-risk and underserved populations.
• Treat trust, transparency and patient rights as operational foundations of disease control.

Previous year questions

No UPSC question has been asked directly on this micro-topic yet. Use the practice questions below.

Practice questions