(a) (i) 1. Enumerate five agents of malaria in humans. 2. Describe in brief rapid diagnostic test (RDT) used for malaria and its…

(a)(i) Malaria: agents, rapid diagnostic test and vaccines (5 + 3 + 2 = 10 marks)

1. Five agents of human malaria. These are protozoa of the genus Plasmodium, spread by the female Anopheles mosquito:

• Plasmodium falciparum, which causes the most severe (malignant tertian) malaria.
• Plasmodium vivax, benign tertian malaria, with relapses from hypnozoites.
• Plasmodium ovale, a mild tertian malaria that also relapses.
• Plasmodium malariae, quartan malaria.
• Plasmodium knowlesi, a zoonotic parasite of macaques in South-East Asia (a 24-hour cycle, which can cause severe disease).

2. Rapid diagnostic test (RDT). It is an immunochromatographic (lateral-flow) test on a drop of finger-prick blood, which detects parasite antigens with monoclonal antibodies on a nitrocellulose strip. A coloured line appears in 15–20 minutes.

• Target antigens: histidine-rich protein-2 (HRP-2), specific to P. falciparum; parasite lactate dehydrogenase (pLDH), either pan-specific or specific to P. vivax; and aldolase (pan-malarial). In India the bivalent RDT (HRP-2 for P. falciparum and pLDH for P. vivax) is used.
• Advantages: rapid results (within 20 minutes), no microscope, electricity or trained microscopist needed, simple to perform, so it is suitable for remote and peripheral areas. It can detect P. falciparum even when the parasites are sequestered, and gives a species result. It is stable in field conditions and is used for early treatment.
• Limitations: it cannot quantify parasite density, HRP-2 stays positive for weeks after cure, and false negatives occur with HRP-2 gene deletion, so microscopy remains the reference.

3. Malaria vaccines. Two vaccines against P. falciparum are recommended by the WHO for children in endemic areas: RTS,S/AS01 (Mosquirix), recommended in 2021, and R21/Matrix-M, recommended in 2023. Both target the circumsporozoite protein of the sporozoite and are given as four doses to young children, and they give partial protection. They do not protect against P. vivax.

(a)(ii) Antibody-dependent enhancement in severe dengue; laboratory diagnosis (10 marks)

Antibody-dependent enhancement (ADE). Dengue has four serotypes (DENV-1 to DENV-4). Infection by one serotype gives lifelong immunity to that serotype only, and only short protection against the others. The severe forms (dengue haemorrhagic fever and dengue shock syndrome) occur mainly in a second infection by a different serotype, or in an infant with maternal antibody.

• The antibodies of the first infection cross-react with the new serotype but are poorly neutralising at low concentrations.
• They bind the virus, and the virus-antibody complexes attach to the Fcγ receptors of monocytes and macrophages, which take up the virus by receptor-mediated uptake. This gives a much higher rate of infection of these cells and a higher viral load.
• The cross-reactive memory T cells (original antigenic sin) respond with a large release of cytokines (TNF-α, IL-6, IL-8, IFN-γ), with complement activation and NS1 antigen effects.
• The result is endothelial dysfunction with plasma leakage, haemoconcentration (haematocrit rise of 20% or more), thrombocytopenia, bleeding and shock. This explains why severe disease appears around days 3–7, when the fever falls and viraemia is decreasing.

Laboratory diagnosis, by day of illness.

• Days 1–5 (febrile phase): detection of the virus and its products: NS1 antigen (ELISA or rapid card), RT-PCR for viral RNA (also for serotyping), and virus isolation in C6/36 mosquito cell lines (mainly for research).
• From day 5 onwards (convalescent phase): antibody detection: IgM capture ELISA (MAC-ELISA), which is positive from day 4–5 and persists 2–3 months; and IgG, which rises in paired sera four-fold or more, and is high early in a secondary infection.
• Supportive tests: leukopenia, falling platelets (below 100,000/mm³), a rising haematocrit, and a positive tourniquet test.

(b)(i) Injury, mechanical injuries and concealed punctured wound (3 + 3 + 4 = 10 marks)

Definition. Under Section 2(14) of the Bharatiya Nyaya Sanhita, 2023 (Section 44 of the old IPC), "injury" means any harm whatever illegally caused to any person, in body, mind, reputation or property.

Mechanical injuries. Injuries caused by mechanical force are classified as:

• Abrasions (scratch, graze, pressure and impact abrasions).
• Contusions (bruises).
• Lacerations.
• Incised wounds (including chop wounds).
• Punctured (stab) wounds, penetrating or perforating.
• Firearm wounds.
• Injuries of bones and joints (fractures and dislocations) are also included in some classifications.

Concealed punctured wound. A punctured wound made by a thin, sharp-pointed instrument (a needle, hatpin, knitting needle, ice pick, stiletto or thin knife) may leave only a tiny external opening, which is hidden in a natural site or is easily overlooked, although a deep organ is injured.

• Sites: scalp under the hair, axilla, umbilicus, skin folds, natural orifices (ear, nostril, mouth, anus, vagina), the anterior fontanelle, under the tongue, the back of the neck (into the medulla), between the ribs and the eyeball.
• Medico-legal importance: the wound may be missed at an external examination and the death be labelled natural. It can be fatal by internal haemorrhage, injury to the heart, brain or spinal cord, or by infection. It may be used in homicide, in infanticide (a needle through the fontanelle) and for poisoning-type concealment. Careful examination (shaving the scalp, examining orifices), radiography and a full dissection are needed to find the track.

(b)(ii) Identification (3 + 4 + 3 = 10 marks)

Identification. Identification is the determination of the individual identity of a person, living or dead, or of remains: the establishment that a person is the same as the one claimed. It may be complete (absolute individuality) or partial (only some features).

Primary characteristics. These are the basic, fixed and most reliable characteristics: the biological profile of age, sex, stature and race, and the permanent personal identifiers that are unique to an individual: fingerprints, dental records (odontology) and DNA profile. They do not change (or change in a predictable way) and give the highest certainty.

Secondary characteristics. These help to individualise but may be altered or are not unique: complexion, colour of hair and eyes, build, scars, moles, birthmarks, tattoos, deformities and anomalies, occupational marks, healed fractures and surgical implants, handwriting, voice and gait, and clothing and personal effects.

Surest test. DNA fingerprinting (DNA profiling) by STR analysis is the surest test.

• The DNA profile is unique to an individual (except monozygotic twins) and is the same in every nucleated cell for life.
• A minute sample of blood, semen, hair root, saliva, bone or tooth is enough, and DNA remains stable after death and in decomposed, burnt or skeletal remains, when fingerprints and features are lost.
• It can also establish relationships (paternity, maternity, and matching of a body with relatives), and it is accepted as expert evidence in court (Section 39, Bharatiya Sakshya Adhiniyam, 2023).
• Fingerprints are also unique, even in identical twins, but need earlier records and are destroyed by decomposition.

(c)(i) Management of complicated Plasmodium falciparum malaria (5 marks)

Severe (complicated) malaria is a medical emergency, defined by the presence of P. falciparum asexual parasites with one or more features such as cerebral malaria (coma), severe anaemia (Hb below 5 g/dL), acute kidney injury (creatinine above 3 mg/dL), pulmonary oedema or ARDS, hypoglycaemia (below 40 mg/dL), shock, spontaneous bleeding or DIC, metabolic acidosis, jaundice and hyperparasitaemia (above 5%). It should be treated in hospital, in a high-dependency or intensive-care unit.

• Specific treatment: intravenous artesunate 2.4 mg/kg at 0, 12 and 24 hours, then once daily. If it is not available, give artemether IM (3.2 mg/kg on day 1, then 1.6 mg/kg daily) or IV quinine (20 mg salt/kg loading dose over 4 hours, then 10 mg/kg every 8 hours), with doxycycline or clindamycin.
• Completion: parenteral treatment is given for at least 24 hours (and until the patient can take oral drugs); then a full 3-day course of an oral artemisinin combination therapy (ACT) is given (artesunate + sulfadoxine-pyrimethamine, or artemether-lumefantrine in the north-east). A single dose of primaquine is added for gametocyte clearance.
• Supportive care: airway and oxygen; anticonvulsants for fits (IV benzodiazepine); frequent blood glucose checks and dextrose for hypoglycaemia; antipyretics and tepid sponging; packed-cell transfusion for severe anaemia; dialysis for renal failure; ventilation for ARDS; broad-spectrum antibiotics if sepsis is suspected; and careful fluid balance.
• To avoid: fluid overload (risk of pulmonary oedema), and the routine use of corticosteroids, heparin, mannitol and dextran, which are harmful.

(c)(ii) Primaquine (5 marks)

Primaquine is an 8-aminoquinoline that acts on the tissue stages of the parasite (the hypnozoites and the gametocytes).

Therapeutic indications.

• Radical cure of P. vivax and P. ovale malaria, to kill the liver hypnozoites and prevent relapse: 0.25 mg/kg daily for 14 days (adult 15 mg), given with the blood-stage drug (chloroquine).
• Gametocidal action in P. falciparum malaria: a single dose (0.75 mg/kg in India; 0.25 mg/kg advised by the WHO) with the ACT, to stop transmission.
• Terminal and causal prophylaxis in travellers, and in Pneumocystis jirovecii pneumonia with clindamycin.

Adverse effects.

• Haemolysis in G6PD deficiency, the main toxicity, with haemoglobinuria and jaundice (so the G6PD status should be checked before use).
• Methaemoglobinaemia, nausea, vomiting, abdominal cramps (reduced by taking it with food), headache, and rarely leukopenia or agranulocytosis and QT prolongation.
• It is contraindicated in G6PD deficiency (or modified weekly dosing is used), in pregnancy, and in infants under 6 months.