Malaria — Epidemiology & Control

Malaria is a protozoan disease caused by Plasmodium species transmitted by the bite of an infective female Anopheles mosquito. For NEET PG, the highest-yield zone is Community Medicine / Epidemiology — species differences (especially relapse in vivax and ovale), vector bionomics, programme indicators like the Annual Parasite Incidence (API), NVBDCP/NCVBDC strategy, spray thresholds, and chloroquine-resistant P. falciparum. Clinical management overlaps with Medicine but the exam loves the public-health angle.

Causative organisms & classification

Five Plasmodium species infect humans. In India, P. vivax historically dominated (~60–65% of cases) and P. falciparum is the most dangerous (responsible for nearly all malaria deaths and cerebral malaria); the falciparum share has been rising, especially in the North-East, Odisha, Chhattisgarh, and Jharkhand.

Species	Relapse?	Incubation (days)	Periodicity of fever	Key clinical/epidemiological note
P. vivax	Yes (hypnozoites)	12–17	Tertian (48 h) — benign tertian	Commonest in India; Duffy-antigen dependent (rare in West Africa)
P. falciparum	No	9–14	Malignant tertian (36–48 h, often irregular)	Cerebral malaria, blackwater fever, deaths; chloroquine resistance
P. ovale	Yes (hypnozoites)	16–18	Tertian (48 h)	West Africa; mildest; relapses
P. malariae	No (but recrudescence)	18–40	Quartan (72 h)	Quartan malarial nephropathy; long latency
P. knowlesi	No	~9–12	Quotidian (24 h)	Simian/zoonotic; SE Asia (Malaysia, Borneo); can be severe

High-yield: Only P. vivax and P. ovale form hypnozoites (dormant liver stages) and therefore cause true relapse. P. falciparum and P. malariae do NOT relapse — P. malariae shows recrudescence (persistence of low-grade erythrocytic parasitaemia), not relapse.

Life cycle (epidemiological essentials)

The parasite has two hosts. Man is the intermediate host (asexual cycle = schizogony) and the female Anopheles is the definitive host (sexual cycle = sporogony, because the parasite completes its sexual reproduction in the mosquito).

Sporozoite (mosquito bite) → liver (exo-erythrocytic schizogony) → merozoites → RBC (erythrocytic schizogony, causes fever) → gametocytes → taken up by mosquito → sporogony → sporozoites in salivary gland.

• Pre-patent period = time from infection to first detectable parasites in blood.
• Incubation period = time from infective bite to first symptoms (see table; falciparum shortest).
• Extrinsic incubation period = time for sporogony within the mosquito (≈10–14 days; shorter at higher temperature, optimum 20–30 °C). The mosquito remains infective for life once sporozoites reach the salivary glands.
• Gametocytes are the only transmissible (infective-to-mosquito) form; in falciparum they appear later (~day 8–11 of illness), which is why a treated patient may still infect mosquitoes — hence gametocytocidal drugs (primaquine single dose) matter for transmission control.

High-yield: Man is the intermediate host; mosquito is the definitive host. This reversal (we usually think of humans as definitive) is a favourite MCQ trap.

The vector — Anopheles bionomics

Malaria in India is transmitted by several Anopheles species; key vectors and their breeding preferences are heavily tested.

Vector	Region / habitat	Breeding habit
An. culicifacies	Rural plains; chief rural vector of India	Clean ground/rain pools, irrigation channels, rice fields
An. stephensi	Urban vector	Wells, overhead tanks, cisterns, domestic containers
An. fluviatilis	Hills, foothills, terraced agriculture	Slow-flowing streams, seepage
An. minimus	North-East India	Slow streams with vegetation
An. dirus	North-East / forest	Forest pools, animal footprints
An. sundaicus	Coastal (Andaman)	Brackish/coastal water
An. fluviatilis & minimus	most efficient vectors	high man-biting habit

Key vector concepts:

• Anthropophilic (prefers human blood) vectors transmit more efficiently than zoophilic ones.
• Endophilic (rests indoors) vectors are amenable to indoor residual spraying (IRS); exophilic vectors are not.
• Anopheline larvae lie parallel to the water surface (no siphon tube) — distinguishing them from Culex/Aedes larvae which hang at an angle. Eggs are laid singly with lateral floats (vs Culex egg rafts, Aedes single eggs without floats).
• Vectorial capacity depends on vector density, man-biting habit, longevity, and the extrinsic incubation period.

High-yield: An. culicifacies = main rural vector; An. stephensi = urban vector (also the invasive vector now spreading malaria in African cities). An. minimus and An. fluviatilis = most efficient vectors.

Epidemiological determinants

• Agent factors: species, drug resistance, gametocyte load.
• Host factors: all ages susceptible; some genetic resistance — sickle-cell trait, G6PD deficiency, thalassaemia, Duffy-negativity (protects against P. vivax), and HbF in neonates. Pregnancy and non-immune travellers are high-risk.
• Environmental factors: temperature (optimum 20–30 °C; transmission stops <16 °C), humidity (>60% favours mosquito longevity), rainfall (creates breeding sites; transmission usually peaks after the monsoon), and altitude (rare above ~2000–2500 m).

Measures of malaria burden (programme indicators)

Indicator	Formula / meaning
Annual Parasite Incidence (API)	(Confirmed +ve slides in 1 yr ÷ Population under surveillance) × 1000
Annual Blood Examination Rate (ABER)	(Blood slides examined ÷ Population) × 100 — index of operational efficiency (target ≥10%)
Slide Positivity Rate (SPR)	(+ve slides ÷ total slides examined) × 100
Slide Falciparum Rate (SFR)	(Pf +ve slides ÷ total slides examined) × 100
Annual Falciparum Incidence (AFI)	Pf cases ÷ population × 1000

High-yield: API is the key indicator used to stratify areas and decide spray operations. The classic threshold: API ≥ 2 (per 1000 population) is the cut-off historically used to identify high-risk areas for indoor residual spraying under modified plan of operation. ABER is a quality/effort indicator (should be ≥10%).

Prevention & control — the four pillars

Control attacks the agent, the vector, and the human host. Approach: Early diagnosis & complete treatment → Integrated vector management → Supportive measures (surveillance, BCC) → Sentinel surveillance & monitoring.

1. Anti-parasite measures (case management)

• Early diagnosis and complete treatment is the cornerstone — clears the reservoir and prevents transmission and severe disease.
• Diagnosis confirmed before treatment wherever feasible (test, treat, track).

2. Anti-vector measures (Integrated Vector Management)

1. Indoor Residual Spraying (IRS) — DDT, malathion, or synthetic pyrethroids; targets endophilic vectors. Sprayed when API ≥ 2 and Pf proportion is significant.
2. Insecticide-treated nets (ITNs) / Long-Lasting Insecticidal Nets (LLINs) — pyrethroid-impregnated; reduce man–vector contact; major programme push.
3. Larval control — anti-larval measures: larvicides (temephos, organophosphates), larvivorous fish (Gambusia affinis, Poecilia reticulata = guppy), source reduction, intermittent irrigation.
4. Environmental/source reduction & engineering measures.
5. Personal protection — repellents, full-sleeves, screening, mosquito nets.

3. Anti-larval & biological measures

• Gambusia and Poecilia fish, Bacillus thuringiensis israelensis (Bti) and B. sphaericus biolarvicides.

4. Chemoprophylaxis

• Not for the general population; for travellers, non-immune visitors, and pregnant women in endemic zones.
• Short-term (<6 weeks): Doxycycline 100 mg OD (started 2 days before, continued throughout and 4 weeks after).
• Long-term: Mefloquine weekly (after expert advice), started 2 weeks before.

Diagnosis & investigation of choice

Method	Notes
Peripheral smear (thick + thin)	Gold standard. Thick film = screening/parasite density; thin film = species identification.
Rapid Diagnostic Test (RDT)	Detects HRP-2 (Pf-specific) and pLDH/aldolase (pan-species). Bivalent kits used in the programme; useful where microscopy unavailable.
QBC (Quantitative Buffy Coat)	Acridine-orange fluorescence; sensitive but cannot speciate well.
PCR	Most sensitive; research/mixed/low-density infections.

High-yield: Peripheral blood smear is the diagnostic gold standard; HRP-2 based RDT is specific for P. falciparum. The programme uses bivalent RDTs (Pf + Pv) at field level.

Management / drug of choice (current NVBDCP/NCVBDC guidance)

• Uncomplicated P. vivax: Chloroquine 25 mg base/kg over 3 days + Primaquine 0.25 mg/kg/day × 14 days (radical cure to kill hypnozoites and prevent relapse).
• Uncomplicated P. falciparum: ACT — Artemisinin-based Combination Therapy.
  • In North-East India: ACT-AL (Artemether–Lumefantrine).
  • In rest of India: Artesunate + Sulfadoxine–Pyrimethamine (AS+SP) × 3 days + single-dose Primaquine (0.75 mg/kg) as a gametocytocidal agent on day 2.
• Severe/complicated malaria (any species): IV Artesunate is the drug of choice (replaced IV quinine). Followed by full oral ACT once the patient can take orally.

High-yield: Radical cure of vivax = chloroquine + 14-day primaquine (anti-relapse). In falciparum, primaquine is a single dose and acts as a gametocytocide (transmission blocking), NOT for relapse.

Primaquine caution: Causes haemolysis in G6PD deficiency — screen or use with caution; contraindicated in pregnancy and infants <1 year.

National programme — NVBDCP / NCVBDC

• The programme is now under the National Center for Vector Borne Diseases Control (NCVBDC), earlier the National Vector Borne Disease Control Programme (NVBDCP) — covers malaria, dengue, chikungunya, filariasis, kala-azar, and Japanese encephalitis.
• Goal: malaria elimination by 2030, aligned with the National Framework for Malaria Elimination (NFME 2016–2030) and the National Strategic Plan.
• Category stratification of districts/states (Categories 0–3) by API to phase elimination:
  • Category 0 — prevention of re-introduction (zero indigenous cases).
  • Category 1 — API < 1 (elimination phase).
  • Category 2 — API 1 to < 2.
  • Category 3 — API ≥ 2 (intensified control phase).

Strategy element	Tool
Surveillance	Active & passive case detection; fortnightly visits by ASHA/health worker
Diagnosis	Microscopy + bivalent RDT
Treatment	ACT (drug-of-choice by region) + primaquine
Vector control	IRS (API≥2), LLINs, larvivorous fish, source reduction
Monitoring	API, ABER, SPR, SFR

High-yield: Elimination categories are defined by API. API ≥ 2 = Category 3 (intensified control); API < 1 = Category 1 (elimination phase). India targets malaria elimination by 2030.

Drug resistance

• Chloroquine-resistant P. falciparum is now widespread in India — the reason ACT replaced chloroquine for falciparum. P. vivax still largely chloroquine-sensitive in India (so CQ retained for vivax).
• Sulfadoxine–pyrimethamine resistance is emerging in the North-East, prompting the switch there to Artemether–Lumefantrine.
• Artemisinin resistance (delayed parasite clearance, kelch13 mutations) is documented in the Greater Mekong Subregion and being monitored in India/Africa — a major global threat.

High-yield: Chloroquine resistance in P. falciparum drove the ACT policy; SP resistance in the North-East drove the regional switch to Artemether–Lumefantrine. Artemisinin resistance is linked to kelch13 mutations (Southeast Asia/Mekong).

Complications (mainly P. falciparum)

• Cerebral malaria — diffuse symmetric encephalopathy, coma (highest fatality).
• Severe anaemia, hypoglycaemia (worsened by quinine), metabolic acidosis.
• Acute kidney injury / blackwater fever (massive intravascular haemolysis, haemoglobinuria — "Coca-Cola" urine).
• ARDS/pulmonary oedema, DIC, algid malaria (shock), splenic rupture (more with vivax).
• Quartan malarial nephropathy — immune-complex nephrotic syndrome with P. malariae.
• Tropical splenomegaly syndrome (hyper-reactive malarial splenomegaly).

Key differentials

Fever with chills/rigors and splenomegaly: dengue, typhoid (enteric fever), leptospirosis, scrub typhus, kala-azar (visceral leishmaniasis), brucellosis, amoebic liver abscess, and viral hepatitis. In endemic settings any acute undifferentiated fever should be tested for malaria. Dengue (thrombocytopenia + no parasitaemia), scrub typhus (eschar), and leptospirosis (conjunctival suffusion, myalgia, jaundice + AKI) are the common NEET PG distractors.

Recently asked / exam angle

• API threshold for spray operations — API ≥ 2 triggers IRS / Category 3 classification.
• Relapse vs recrudescence — relapse only in vivax & ovale (hypnozoites); recrudescence in malariae & falciparum (no hypnozoites).
• Definitive host of malaria = mosquito (sexual cycle/sporogony).
• Chief rural vector = An. culicifacies; urban vector = An. stephensi.
• Drug of choice for severe malaria = IV Artesunate (not quinine anymore).
• Radical cure of vivax = chloroquine + 14-day primaquine; falciparum primaquine = single dose, gametocytocidal.
• ABER target ≥10%; ABER reflects operational efficiency, API reflects burden.
• Larvivorous fish = Gambusia and Poecilia (guppy).
• Malaria elimination target year for India = 2030 (NFME 2016–2030).
• Duffy-negative individuals are resistant to P. vivax.
• Anopheline larvae lie parallel to water surface (no siphon); eggs single with floats.

Mnemonic — relapsers "vivO": Vivax + Ovale relapse (hypnozoites). And "falciparum = fatal, no relapse". Mnemonic — vectors: "Culi-ci-facies = Countryside (rural); Steph-en-si = Streets/City (urban)."

Rapid revision

1. P. vivax is commonest in India; P. falciparum causes most deaths and cerebral malaria.
2. Hypnozoites (relapse) only in vivax & ovale; treat relapse with primaquine × 14 days.
3. P. malariae → quartan fever (72 h) + quartan malarial nephropathy; shows recrudescence.
4. Mosquito = definitive host (sporogony); man = intermediate host (schizogony).
5. An. culicifacies = main rural vector; An. stephensi = urban vector (breeds in wells/tanks).
6. API = (confirmed positive slides ÷ population) × 1000; API ≥ 2 → IRS / Category 3.
7. ABER ≥10% = operational efficiency; SPR and SFR measure positivity.
8. Smear = gold standard dx; HRP-2 RDT is P. falciparum-specific.
9. Severe malaria → IV Artesunate; falciparum (most of India) → AS+SP; North-East → Artemether–Lumefantrine.
10. Primaquine → haemolysis in G6PD deficiency; avoid in pregnancy/infants.
11. Chloroquine-resistant Pf is widespread → ACT policy; kelch13 = artemisinin resistance.
12. India aims to eliminate malaria by 2030 under NCVBDC / NFME 2016–2030; larvivorous fish = Gambusia & Poecilia.