Human Diseases — Set 6

Correct Answer: A. Vitamin A

• **Vitamin A** = Vitamin A (retinol) is converted in the retina to retinal, which combines with opsin to form rhodopsin in rod photoreceptors; without adequate Vitamin A, rhodopsin regeneration is impaired, causing inability to see in dim light — night blindness (nyctalopia). • **Progression of deficiency** — if untreated, Vitamin A deficiency advances to xerophthalmia (dry eyes), Bitot's spots on conjunctiva, corneal ulceration, and eventually irreversible blindness. • Vitamin A deficiency is the leading preventable cause of childhood blindness globally, affecting millions of children under 5 in developing countries. • 💡 Option B (Vitamin C) is wrong because Vitamin C deficiency causes scurvy — bleeding gums, joint pain, and poor wound healing — not night blindness; Option C (Vitamin K) is wrong because Vitamin K deficiency impairs blood clotting; Option D (Vitamin B12) is wrong because B12 deficiency causes pernicious anaemia and neurological damage, not visual impairment.

Correct Answer: A. Cholera

• **Cholera** = caused by Vibrio cholerae, a comma-shaped bacterium that produces cholera toxin in the small intestine, triggering massive secretion of water and electrolytes into the gut lumen — causing profuse "rice-water" watery diarrhoea that can lead to fatal dehydration within hours. • **Transmission route** — cholera spreads through the faecal-oral route via drinking water or food contaminated with sewage; a single infected person can excrete up to 10¹² bacteria per day. • Cholera was responsible for seven global pandemics since 1817; the current (seventh) pandemic began in 1961 and continues in parts of Africa, Asia, and Latin America. • 💡 Option B (Influenza) is wrong because influenza is a viral (not bacterial) respiratory disease transmitted by airborne droplets, not water; Option C (Malaria) is wrong because malaria is a protozoan disease spread by Anopheles mosquito bites; Option D (Dengue) is wrong because dengue is a viral disease spread by Aedes aegypti mosquitoes.

Correct Answer: B. Protozoa

• **Protozoa** = Amoebiasis is caused by Entamoeba histolytica, a protozoan parasite transmitted via the faecal-oral route through contaminated food or water; it colonises the large intestine and can cause amoebic dysentery and, if it invades the bloodstream, amoebic liver abscess. • **Cyst vs trophozoite** — the infection cycle involves infective cysts (ingested in contaminated water) transforming into active trophozoites in the intestine that invade the gut wall, distinguishing it from the non-pathogenic Entamoeba dispar. • Amoebiasis affects ~50 million people worldwide annually and is the third leading parasitic cause of death after malaria and schistosomiasis. • 💡 Option A (Virus) is wrong because viral infections of the intestine are called viral gastroenteritis (e.g., Norovirus, Rotavirus); Option C (Bacteria) is wrong because bacterial intestinal infections include cholera (V. cholerae) and typhoid (Salmonella typhi); Option D (Fungus) is wrong because intestinal fungal infections are typically opportunistic candidiasis in immunocompromised patients.

Correct Answer: D. Proteins and Calories

• **Proteins and Calories** = Marasmus is the most severe form of protein-energy malnutrition (PEM) caused by a deficiency of both protein and total caloric intake, leading to extreme wasting — the child looks like a "bag of skin and bones" with no subcutaneous fat or muscle. • **Contrast with Kwashiorkor** — Kwashiorkor involves predominantly protein deficiency with some calories available (causing oedema), while Marasmus is total energy starvation affecting all macronutrients, causing extreme emaciation without oedema. • Marasmus most commonly occurs in the first year of life when breastfeeding is stopped too early and adequate weaning foods are unavailable. • 💡 Option A (Only Vitamins) is wrong because vitamin deficiencies cause specific diseases like scurvy or rickets, not the generalised wasting of marasmus; Option B (Only Minerals) is wrong because mineral deficiencies cause targeted disorders like goitre (iodine) or anaemia (iron); Option C (Only Proteins) is wrong because protein-only deficiency describes Kwashiorkor, not Marasmus, which requires both protein and calorie deprivation.

Correct Answer: A. Elephantiasis

• **Elephantiasis** = Lymphatic Filariasis (Elephantiasis) is caused by the parasitic nematode worm Wuchereria bancrofti, transmitted to humans through the bite of the female Culex mosquito; the larvae migrate to lymphatic vessels and lymph nodes, causing blockage and massive swelling of limbs and genitalia. • **Chronic vs acute** — repeated infections trigger immune-mediated lymphatic damage; the characteristic grotesque limb swelling (elephantiasis) develops over years of exposure in endemic areas. • Filariasis is targeted for global elimination by the WHO through mass drug administration (MDA) with albendazole and ivermectin or diethylcarbamazine (DEC). • 💡 Option B (Malaria) is wrong because malaria is transmitted by female Anopheles mosquitoes, not Culex; Option C (Dengue) is wrong because dengue is spread by Aedes aegypti (day-biting mosquito), not Culex; Option D (Yellow Fever) is wrong because Yellow Fever is a viral haemorrhagic fever transmitted by Aedes aegypti mosquitoes.

Correct Answer: D. Lungs

• **Lungs** = Pneumonia is an infection that inflames the air sacs (alveoli) in one or both lungs, which may fill with fluid or pus; this impairs gas exchange causing symptoms of cough with phlegm, fever, chills, and difficulty breathing. • **Causative agents** — Streptococcus pneumoniae is the most common bacterial cause; viral pneumonia (influenza, RSV, SARS-CoV-2) and fungal pneumonia (Pneumocystis jirovecii in immunocompromised patients) also occur frequently. • Pneumonia is the single largest infectious killer of children under 5 globally, accounting for 14% of all deaths in this age group according to UNICEF/WHO data. • 💡 Option A (Heart) is wrong because heart infections are called endocarditis (inner lining) or myocarditis (muscle), not pneumonia; Option B (Kidneys) is wrong because kidney infections are called pyelonephritis or nephritis; Option C (Liver) is wrong because liver infections are called hepatitis or liver abscess.

Correct Answer: A. Citrus Fruits

• **Citrus Fruits** = Scurvy is caused by Vitamin C (ascorbic acid) deficiency; citrus fruits such as lemons, limes, oranges, and grapefruits are the richest natural sources of Vitamin C and were historically used by British sailors to prevent and cure scurvy at sea. • **Why Vitamin C is essential** — ascorbic acid is a cofactor for prolyl hydroxylase and lysyl hydroxylase, enzymes needed to synthesise collagen; without it, collagen breakdown leads to bleeding gums, skin haemorrhages, joint pain, and impaired wound healing. • The word "scurvy" is the etymological root of "scurvy knave," and the discovery of citrus as a cure by James Lind in 1747 was one of the first controlled clinical trials in medical history. • 💡 Option B (Milk) is wrong because milk provides Vitamin D, calcium, and B vitamins but very little Vitamin C; Option C (Green Vegetables) is wrong as they do contain some Vitamin C but are not the most concentrated or fastest-acting source compared to citrus; Option D (Eggs) is wrong because eggs provide protein and fat-soluble vitamins but negligible Vitamin C.

Correct Answer: D. Infectious Diseases

• **Infectious Diseases** = vaccines work by introducing an antigen (weakened pathogen, killed pathogen, subunit, or mRNA encoding an antigen) to prime the immune system's memory cells so that on real exposure, a rapid and stronger protective response is mounted — this principle applies specifically to infectious diseases caused by pathogens. • **Mechanism** — vaccines stimulate both humoral immunity (B cells producing antibodies) and cellular immunity (cytotoxic T cells), conferring long-lasting protection without the individual suffering the actual disease. • Vaccines have eradicated smallpox, nearly eradicated polio, and dramatically reduced burden from diseases like measles, tetanus, diphtheria, and hepatitis B. • 💡 Option A (Deficiency Diseases) is wrong because deficiency diseases like scurvy or rickets result from lack of nutrients, which vaccines cannot address; Option B (Lifestyle Diseases) is wrong because lifestyle diseases like diabetes and heart disease are caused by diet/behaviour, not pathogens that vaccines can target; Option C (Genetic Diseases) is wrong because genetic disorders like haemophilia or sickle cell are inherited DNA-level conditions, entirely outside the scope of vaccine-induced immunity.

Correct Answer: D. Calcium

• **Calcium** = approximately 99% of the body's calcium is stored in bones and teeth in the form of hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂], the mineral crystal that gives bones their rigidity and compressive strength. • **Vitamin D link** — calcium absorption from the intestine depends on active Vitamin D (calcitriol); deficiency of either calcium or Vitamin D in children causes rickets, while in adults it causes osteomalacia; in older adults low calcium accelerates osteoporosis. • The recommended daily intake of calcium is 1000–1200 mg/day for adults; dairy products, leafy greens, sesame seeds, and fortified foods are major dietary sources. • 💡 Option A (Zinc) is wrong because zinc is essential for immune function, wound healing, and enzyme activity — not structural bone/tooth mineralisation; Option B (Iron) is wrong because iron is needed for haemoglobin synthesis and oxygen transport, not bone formation; Option C (Sodium) is wrong because sodium regulates fluid balance and nerve impulses, not bone or tooth strength.

Correct Answer: C. Viral

• **Viral** = Poliomyelitis (Polio) is caused by the Poliovirus, a non-enveloped, single-stranded RNA virus belonging to the genus Enterovirus in the family Picornaviridae; it enters the body via the faecal-oral route and can invade motor neurons of the spinal cord, causing irreversible paralysis. • **Three serotypes** — Poliovirus has three wild serotypes (PV1, PV2, PV3); PV2 was declared eradicated in 2015 and PV3 in 2019, with only PV1 remaining in a few countries. • Two vaccines exist: OPV (Oral Polio Vaccine — Sabin) used in India's Pulse Polio programme, and IPV (Inactivated Polio Vaccine — Salk); India was declared polio-free by WHO in 2014. • 💡 Option A (Protozoan) is wrong because protozoan diseases include malaria, amoebiasis, and sleeping sickness — none involve motor neuron paralysis from Poliovirus; Option B (Bacterial) is wrong because bacterial diseases are treated with antibiotics and include tuberculosis and cholera; Option D (Fungal) is wrong because fungal infections typically cause superficial skin diseases or systemic infections in immunocompromised patients, not polio-type paralysis.