Select the incorrect set of “the typical Vector – Disease caused – Type of Pathogen”.
- (1)Aedes – Chikungunya – Bacteria
- (2)Culex – Lymphatic Filariasis – Parasite
- (3)Anopheles – Malaria – Parasite
- (4)Aedes – Dengue – Virus
Answer
Why
Correct — option (1), Aedes – Chikungunya – Bacteria.
The stem asks for the incorrect set. Option (1) gets the vector and the disease right but the pathogen type wrong: chikungunya is caused by a virus, the chikungunya virus, not by bacteria.
The World Health Organization's table of vector-borne diseases lists chikungunya under the Aedes mosquito with the pathogen type "virus".
The same table supports the other three sets. It lists lymphatic filariasis under Culex as a parasite, malaria under Anopheles as a parasite, and dengue under Aedes as a virus.
So only option (1) contains an error, and it sits in the third part of the set.
The idea to remember: Aedes spreads the dengue, chikungunya, Zika and yellow fever viruses; Anopheles spreads the malaria parasite.
Why the others are wrong
- (2)Culex – Lymphatic Filariasis – Parasite — This set is correct, so it is not the answer. Lymphatic filariasis is caused by parasitic filarial worms, and WHO lists Culex among its vectors, along with Anopheles and Aedes.
The worms damage the lymphatic system. Over time this can cause lymphoedema and elephantiasis, the gross swelling of limbs.
- (3)Anopheles – Malaria – Parasite — This set is correct, so it is not the answer. Malaria is caused by Plasmodium, a protozoan parasite, and spreads through the bites of infected female Anopheles mosquitoes.
Several Plasmodium species infect humans; Plasmodium falciparum causes the most severe, malignant form of the disease.
- (4)Aedes – Dengue – Virus — This set is correct, so it is not the answer. Dengue is caused by the dengue virus and spread mainly by Aedes aegypti, with Aedes albopictus as a secondary vector.
Aedes aegypti breeds in water stored in containers around homes and bites mostly during the day. WHO's prevention advice includes covering, emptying and cleaning domestic water-storage containers every week.
Concept
A vector is a living organism, often a blood-sucking insect, that carries a pathogen between hosts. WHO describes vector-borne diseases as human illnesses caused by parasites, viruses and bacteria that are transmitted by vectors.
A vector–disease–pathogen set joins three separate facts: which insect spreads the disease, what the disease is, and what kind of organism causes it. Any one of the three can be wrong.
Mosquito genera carry different diseases. Aedes spreads viruses such as dengue, chikungunya and Zika; Anopheles spreads the malaria parasite; Culex spreads Japanese encephalitis virus and filarial worms.
RPSC's 2024 syllabus lists "Health care; Infectious, Non-Infectious and Zoonotic diseases" under Science & Technology. Vector-borne diseases belong to the infectious group.
In India, the National Center for Vector Borne Diseases Control lists six diseases: malaria, dengue, filaria, kala-azar, Japanese encephalitis and chikungunya.
WHO's table of vector-borne diseases sorts pathogens as viruses, bacteria and parasites. "Parasite" there covers protozoa such as Plasmodium and worms such as filarial nematodes.
Key facts
- WHO lists chikungunya, dengue, Zika, yellow fever and Rift Valley fever as viral diseases spread by Aedes mosquitoes.
- Malaria is caused by Plasmodium parasites and spread through the bites of infected female Anopheles mosquitoes.
- WHO lists Aedes, Anopheles and Culex mosquitoes as vectors of lymphatic filariasis, a parasitic disease.
- Japanese encephalitis and West Nile fever are viral diseases that WHO lists under Culex mosquitoes.
- WHO lists leishmaniasis, a parasitic disease, and sandfly fever, a viral disease, under sandflies.
Based on WHO's table of vector-borne diseases. Only the chikungunya set in the question has a wrong pathogen type.
Study next
Common traps
- A set can have the right vector and the right disease but the wrong pathogen type, as option (1) does. Check all three parts separately.
- Lymphatic filariasis has more than one mosquito vector: WHO lists Culex, Anopheles and Aedes. A set pairing it with any of these is not wrong on the vector.
- In WHO's table, "parasite" is used for protozoa and worms. Viruses and bacteria also live off hosts, so read the label in the narrow sense the set uses.
A question can list vector–disease–pathogen sets and ask which is incorrect, ask which disease is not bacterial or not viral, match diseases with their vectors, or ask which Plasmodium species causes the severe form of malaria.
Related PYQs
UnlockIAS will link similar questions from RAS Pre 2023 and 2021 here once those papers are published on this site.
Practice
- practice — not a real PYQ
Which one of the following diseases is spread by Culex mosquitoes and caused by a virus?
- (a)Dengue
- (b)Japanese encephalitis
- (c)Malaria
- (d)Kala-azar
Answer(2) — Japanese encephalitis is a viral disease spread by Culex mosquitoes. Option (1), dengue, is viral but spread by Aedes; option (3), malaria, is a parasitic disease spread by Anopheles; option (4), kala-azar, is a parasitic disease spread by sandflies. - practice — not a real PYQ
Select the correct pair of "Disease – Type of Pathogen".
- (a)Malaria – Virus
- (b)Dengue – Bacteria
- (c)Lymphatic filariasis – Parasite
- (d)Chikungunya – Parasite
Answer(3) — Lymphatic filariasis is caused by parasitic filarial worms. Option (1) is wrong because malaria is caused by the Plasmodium parasite; options (2) and (4) are wrong because dengue and chikungunya are both caused by viruses.