All four pairs are correctly matched! Pair 1 ✓ — Kala-azar (Visceral Leishmaniasis) is caused by Leishmania donovani, transmitted by the phlebotomine sandfly. India (Bihar, Jharkhand, WB, UP) accounts for a large share of global cases. Near-eliminated in India (633 blocks achieved <1/10,000 target). Pair 2 ✓ — Malaria in India is predominantly P. vivax (also P. falciparum — more deadly). P. vivax has a dormant liver stage (hypnozoites) that can relapse months-years later — requires Primaquine for radical cure. P. falciparum causes cerebral malaria, the most deadly form. Pair 3 ✓ — African Sleeping Sickness is caused by Trypanosoma brucei, transmitted by the tsetse fly in sub-Saharan Africa. T. brucei gambiense (West/Central Africa — chronic) and T. brucei rhodesiense (East Africa — acute). Not present in India. Pair 4 ✓ — Lymphatic Filariasis (Elephantiasis) is caused by Wuchereria bancrofti (>90% of cases) and Brugia malayi. Transmitted by Culex mosquito. Causes lymphatic blockage → gross swelling of limbs (elephantiasis). India has 40% of global burden. MDA programme: DEC + Albendazole. Answer: (c).

Statement 1 ✗ — Classic UPSC trap: TB does NOT spread through contaminated food or water. TB is spread ONLY through the AIR — when an infected person coughs, sneezes, or spits, they release droplet nuclei containing M. tuberculosis. The droplets can remain suspended in the air for hours. TB is NOT spread by sharing food, water, handshakes, or touching toilet seats. This distinction is very frequently tested. Statement 2 ✗ — BCG (Bacillus Calmette-Guérin) vaccine does NOT protect against all forms of TB. It provides good protection against severe forms of childhood TB (TB meningitis, miliary TB) but gives variable and often inadequate protection against pulmonary TB (the most common adult form) — which is why TB continues to spread despite BCG. Statement 3 ✓ — India has set an ambitious target to End TB by 2025 — five years before the WHO's global End TB Strategy target of 2030. NTEP (National TB Elimination Programme), TB Harega Desh Jeetega campaign, Nikshay Portal (for drug-resistant TB), and Nikshay Poshan Yojana (nutritional support) are key initiatives. Statement 4 ✓ — MDR-TB (Multi-Drug Resistant TB) is defined as TB resistant to at least Isoniazid AND Rifampicin — the two most powerful first-line anti-TB drugs. XDR-TB (Extensively Drug Resistant) = MDR-TB + resistance to any fluoroquinolone + at least one second-line injectable. Answer: (c).

Statement 1 ✓ — Aedes aegypti (and Aedes albopictus — tiger mosquito) transmits multiple arboviruses: Dengue (DENV 1-4), Zika virus, Chikungunya virus, and Yellow fever virus. Distinctive features: has white/silver striping, bites during daytime, breeds in clean stagnant water (flower pots, tyres, coolers, containers). Statement 2 ✓ — Only female mosquitoes (of all species) bite humans — they need blood protein for egg production. Male mosquitoes feed only on nectar. In Anopheles: only the female carries and transmits Plasmodium parasites. Bites predominantly between dusk and dawn. Rests with its body at an angle to the surface (distinguishes from Culex which rests parallel). Statement 3 ✗ — Important trap: Dengue CANNOT spread directly from person to person. The virus requires an Aedes mosquito as an intermediate vector — a human cannot infect another human directly. Exception: very rare maternal transmission (mother to baby during pregnancy). Spain reported the first confirmed sexual transmission in 2024 — but this is extremely rare, not a standard route. Statement 4 ✓ — Culex mosquito transmits: Japanese Encephalitis (JE — with pigs and birds as amplifying hosts), Lymphatic Filariasis (Wuchereria bancrofti), and West Nile Virus. Culex bites at night, breeds in stagnant/dirty water (drains, puddles). Answer: (b).

Statement 1 ✓ — OPV (Oral Polio Vaccine = Sabin vaccine) uses live attenuated (weakened) poliovirus — given orally. IPV (Inactivated Polio Vaccine = Salk vaccine) uses killed virus — injected. OPV is preferred for mass immunisation (cheap, easy, creates gut immunity, can spread vaccine virus to contacts — "herd vaccination"). IPV is safer for immunocompromised individuals but more expensive. India uses both: IPV for primary schedule + OPV for Pulse Polio campaigns. Statement 2 ✓ — Hepatitis B vaccine is produced using recombinant DNA technology — the gene for HBsAg (Hepatitis B surface antigen) is inserted into yeast cells, which produce the antigen protein. This is then purified and used as the vaccine. It was one of the first commercial vaccines produced using rDNA technology (1986). Given at birth under UIP in India. Statement 3 ✗ — This is a key factual error. BCG (Bacillus Calmette-Guérin — live attenuated Mycobacterium bovis) provides GOOD protection against severe childhood forms (TB meningitis, miliary TB) but POOR and VARIABLE protection against pulmonary (lung) TB — which is the most common and transmissible form. This is why TB persists globally despite widespread BCG vaccination. Statement 4 ✓ — R21/Matrix-M malaria vaccine received WHO prequalification and recommendation in October 2023. It is the second malaria vaccine to receive WHO approval (after RTS,S/AS01 — Mosquirix in 2021). R21 showed >75% efficacy in African children. No malaria vaccine has been deployed in India's UIP yet. Answer: (b).

Statement 1 ✓ — HIV is indeed a Retrovirus (Family: Retroviridae, Genus: Lentivirus). It carries its genetic material as RNA. Inside the host cell (CD4+ T cell, macrophage, dendritic cell), the enzyme reverse transcriptase converts the viral RNA into DNA — which is then integrated into the host's chromosome (as a "provirus") by the enzyme integrase. The host cell then produces new viral particles. This RNA→DNA process is the reverse of the normal cellular DNA→RNA flow — hence "retrovirus." ART drugs target different steps: Reverse Transcriptase Inhibitors (RTIs), Protease Inhibitors (PIs), Integrase Inhibitors. Statement 2 ✗ — Critically important fact: HIV is NOT transmitted through saliva, sweat, tears, casual contact, handshaking, hugging, sharing food/water, or mosquito bites. HIV transmission requires: sexual contact (vaginal/anal/oral), blood/blood products (transfusions, shared needles, needle-stick injuries), or vertical transmission (mother to child during pregnancy, childbirth, or breastfeeding). This misconception causes enormous social stigma against HIV-positive people — UPSC tests awareness of this. Statement 3 ✗ — ART (Antiretroviral Therapy) CANNOT cure HIV. ART suppresses the viral load to undetectable levels, prevents AIDS progression, protects the immune system, and prevents transmission (U=U: Undetectable = Untransmittable). However, HIV remains integrated in "latent reservoirs" (resting CD4 cells) — permanently. If ART is stopped, the virus rebounds. There is currently no cure for HIV. A small number of people have been functionally cured through bone marrow transplants (Timothy Ray Brown - "Berlin patient"), but this is not scalable. Statement 4 ✓ — India achieved an 84% reduction in mother-to-child HIV transmission (2010–2024), compared to the global reduction of 56.5% — India's progress outpaced the global average. Through the PPTCT (Prevention of Parent-to-Child Transmission) programme. Answer: (c).