The diseases Prelims asks: pathogen, vector, programme

Prelims and MainsCurrent affairs on this: Communicable diseases, animal health and One Health

A question on a communicable disease is nearly always a question about one of three things: what causes it, a virus, bacterium, protozoan or worm; how it travels, a mosquito, a sandfly, water, air or an animal; and what India has promised to do about it, with a date. The cause decides the treatment, since antibiotics act on bacteria and not on viruses, and the vector decides the control: the Aedes mosquito carries dengue, chikungunya and Zika and bites by day, the Anopheles that carries malaria bites at night. The programmes carry the dates: tuberculosis to be ended by 2025 against the world's 2030, malaria eliminated by 2030, kala azar and filariasis below their thresholds, leprosy eliminated as a public health problem since 2005, rabies deaths to zero by 2030. Eradication, as with smallpox in 1980, means the pathogen is gone; elimination means cases below a threshold in a place.

Pathogen, vector and programme: the diseases a question names

Disease	Pathogen	How it spreads	Programme and target
Malaria	Plasmodium, a protozoan	female Anopheles mosquito, night	National Framework for Malaria Elimination, elimination by 2030
Dengue	flavivirus, four serotypes	Aedes mosquito, day	vector control; no specific drug
Chikungunya, Zika	alphavirus; flavivirus	Aedes mosquito, day	vector control
Japanese encephalitis	flavivirus	Culex mosquito; pigs and water birds amplify	vaccine in the immunisation schedule in endemic districts
Kala azar	Leishmania donovani, a protozoan	sandfly	below one case per 10,000 at block level, reached 2023
Lymphatic filariasis	Wuchereria bancrofti, a worm	Culex mosquito	mass drug administration; elimination targeted
Tuberculosis	Mycobacterium tuberculosis, a bacterium	air	National Tuberculosis Elimination Programme, end by 2025
Leprosy	Mycobacterium leprae, a bacterium	prolonged close contact	eliminated as a public health problem 2005; multidrug therapy
Rabies	lyssavirus	dog bite	zero human deaths by 2030
Nipah	paramyxovirus	fruit bats, then people	outbreak response; no vaccine
Scrub typhus	Orientia tsutsugamushi, a bacterium	chigger mite	doxycycline; no vaccine

Same vector, same control: the *Aedes* diseases are fought at the water pot, the *Anopheles* disease at the bed net, the bacterial ones with a drug.Source: National Centre for Vector Borne Diseases Control; Ministry of Health and Family Welfare programme documents

The vectors and what each carries: Anopheles (malaria, night biting, rests indoors, so bed nets and indoor spraying work); Aedes aegypti and albopictus (dengue, chikungunya, Zika and yellow fever, day biting, breeds in clean stored water, so source reduction works); Culex (Japanese encephalitis and lymphatic filariasis, with pigs and water birds amplifying the encephalitis virus); the sandfly Phlebotomus (kala azar and Chandipura); the chigger mite (scrub typhus); the tick (Kyasanur Forest disease). Rabies, Nipah and leptospirosis have no insect vector: a dog, a fruit bat, a rat's urine.
The pathogen classes: viruses (dengue, Japanese encephalitis, Zika, Nipah, rabies, polio, measles, hepatitis, influenza, COVID 19), against which there are vaccines or nothing; bacteria (tuberculosis, leprosy, cholera, typhoid, scrub typhus, leptospirosis, shigellosis), against which antibiotics work until resistance takes them; protozoa (malaria's Plasmodium, kala azar's Leishmania, amoebic meningoencephalitis); worms (filariasis, soil transmitted helminths, answered by mass drug administration).
The programmes and their dates: the National Tuberculosis Elimination Programme, end tuberculosis by 2025, with Nikshay Poshan Yojana's nutrition support and the campaign on its own subject; the National Framework for Malaria Elimination, zero indigenous cases by 2027 and elimination by 2030; kala azar below one case per 10,000 at block level, reached in 2023 and awaiting the World Health Organization's validation; lymphatic filariasis by mass drug administration of two or three drugs; leprosy's programme on its own subject; the National Rabies Control Programme, zero human deaths by 2030; polio, of which India was certified free in 2014 and still vaccinates; measles and rubella elimination targeted for 2026.
How disease is watched and declared: the Integrated Disease Surveillance Programme collects weekly district reports, the surveillance subject sets out the networks; the World Health Organization declares a Public Health Emergency of International Concern under the International Health Regulations of 2005, as it did for COVID 19 in 2020 and mpox in 2022 and 2024, and polio has been one since 2014; the Pandemic Agreement of May 2025 and its unfinished annex on pathogen access are on their own subject.
One Health: most new human infections come from animals, so the National One Health Mission and the draft zoonoses action plan join human, animal and environmental health; the animal diseases a question names are lumpy skin disease and foot and mouth disease in cattle, African swine fever in pigs and avian influenza in poultry, none of which infects people except the last, rarely. Incidence counts new cases in a period; prevalence counts all cases at a time; the basic reproduction number is the cases one case causes in a population with no immunity.

Mains: India's disease targets run ahead of the world's, tuberculosis by five years, because the burden is India's, and the test of each is not the campaign but the last mile: a case found in a slum, a dog vaccinated in a village, a well kept clean, which is why elimination is a health system question before it is a medical one.

Further reading: Vector-borne diseases (WHO)