5. Common Diseases and Epidemics

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CSS GSA — Paper 7, Part-I, Section II, Sub-topic 5: Common Diseases and Epidemics — Polio, Diarrhoea, Malaria, Hepatitis, Dengue: their causes and prevention

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Past-paper weightage: the single most-asked biology area. Hepatitis (2020, 2023, 2024, 2025), polio (2018, 2022), dengue (2016, 2026), vaccines/antibiotics (2016, 2019, 2022), TB (2024), diabetes (2023 Special), heart attack and drugs (2017), anaemia and pollen allergy (2015). MCQs on vectors, antibiotics and viruses appear almost every year.

1. Basic Terms

• Pathogen: germ that causes disease (virus, bacterium, protozoan, fungus, worm)
• Vector: carrier that spreads a pathogen (mosquito, fly)
• Communicable diseases spread from person to person (TB, hepatitis, COVID-19); non-communicable do not (diabetes, heart disease, cancer)
• Incubation period: time between infection and symptoms
• Perinatal transmission: mother to baby around birth (hepatitis B, HIV)

2. Quick Comparison of the Five Syllabus Diseases

3. Polio (Poliomyelitis)

• Cause: poliovirus (enterovirus) that attacks motor neurons of the spinal cord
• Spread: faecal-oral (dirty water and food), person to person; mostly children under 5
• Symptoms: most infections are asymptomatic (CDC estimates about 70% in children); some get fever, headache, vomiting, stiff neck; about 1 in 200 get irreversible paralysis (usually legs); breathing-muscle paralysis can kill
• Prevention: OPV (oral drops, live attenuated — cheap, gives gut immunity) and IPV (injection, killed — very safe); repeated campaigns; clean water
• Pakistan and Afghanistan are the only two countries where wild poliovirus is still endemic
• Barriers: insecurity in southern KP, vaccine refusal and misinformation, population movement, weak sanitation

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Pakistan case-count verification: The previous notes claimed “7 so far in 2026” and listed annual figures without a linked surveillance bulletin. These figures have not been verified in this review and should not be memorised as current statistics. Use a dated Pakistan Polio Programme or GPEI bulletin and distinguish wild poliovirus from vaccine-derived poliovirus. The syllabus answer can be completed without a live case count.

4. Diarrhoea

• Passing three or more loose stools a day; a leading killer of children under 5 because of dehydration
• Types: acute watery (cholera, rotavirus), bloody/dysentery (Shigella), persistent (14 days or longer)
• Causes: germs in unsafe water and food, poor sanitation, no hand-washing
• Treatment: ORS prepared with safe water according to the packet, continued feeding/breastfeeding, and clinician-directed zinc for children. Antibiotics are not routine: selected bacterial infections require diagnosis-based treatment. Severe dehydration needs urgent assessment. WHO
• Prevention: safe drinking water (the presence of E. coli shows faecal contamination), sanitation, hand-washing, breastfeeding, rotavirus vaccine

5. Malaria

• Cause: Plasmodium — P. vivax is commonest in Pakistan; P. falciparum is most deadly
• Vector: female Anopheles mosquito, bites at night
• Life cycle (simple): infected mosquito bite injects sporozoites → they multiply in the liver → enter red blood cells and burst them in cycles (fever can be periodic, but a regular cycle is not required for diagnosis) → mosquito picks up gametocytes when biting → sexual stage in the mosquito
• Symptoms: fever with chills and sweating, headache, anaemia
• Treatment principle: confirm malaria with microscopy or a rapid diagnostic test; treatment depends on species, severity and local resistance. ACTs are central for falciparum malaria. Medicines to clear relapsing liver stages require assessment, including G6PD status. WHO
• Prevention: insecticide-treated nets, indoor spraying, draining stagnant water; the WHO-recommended RTS,S and R21 vaccines for children in Africa

6. Hepatitis

• Hepatitis = inflammation of the liver (Greek hepar = liver, -itis = inflammation); mostly viral, also alcohol, drugs, autoimmune

• Symptoms: jaundice (yellow eyes and skin), dark urine, pale stools, tiredness, nausea, abdominal pain
• Pakistan: has one of the world's largest hepatitis C burdens; reuse of syringes and unsafe blood are major drivers

7. Dengue

• Cause: dengue virus (DENV), family Flaviviridae; four serotypes (DENV-1 to 4)
• Vector: female Aedes aegypti (also Ae. albopictus) — black-and-white striped, bites in daytime (early morning, late afternoon), breeds in clean standing water (tyres, pots, coolers, flower vases)
• Transmission cycle: mosquito bites an infected person during the viraemic phase → virus multiplies in the mosquito's gut and reaches its salivary glands in about 8–12 days (extrinsic incubation) → mosquito can remain infectious for life; transmission is possible, not guaranteed at every bite → in humans symptoms start after 4–10 days. No spread by ordinary casual contact; rare maternal, blood-product and transplant transmission can occur. CDC
• Symptoms: sudden high fever, severe headache, pain behind the eyes, joint and muscle pain ("breakbone fever"), rash
• Severe dengue (dengue haemorrhagic fever/shock syndrome): falling platelets, bleeding, plasma leakage; more likely on a second infection with a different serotype
• Care principle: supportive care and appropriate fluids; paracetamol rather than aspirin/ibuprofen. Severe abdominal pain, persistent vomiting, bleeding or shock signs require urgent care. Severe dengue is not defined by platelet count alone. WHO
• Prevention: destroy breeding sites, cover water containers, nets, repellents, full sleeves, fumigation; vaccines (Dengvaxia, Qdenga) exist in some countries
• Pakistan: major outbreaks in Lahore 2011 and later years in Punjab, Sindh and KP, peaking after the monsoon (September–November)

8. Other Diseases Asked in Past Papers

8.1 Tuberculosis

• Mycobacterium tuberculosis; airborne droplets; cough over 3 weeks, fever, night sweats, weight loss, blood in sputum
• Multi-drug antibiotic therapy; regimen and duration depend on drug susceptibility and eligibility. BCG mainly protects children against severe TB. WHO

8.2 Diabetes mellitus

• Chronic high blood sugar because the pancreas makes too little insulin or the body does not respond to it
• Type 1: autoimmune destruction of β-cells; usually young; needs insulin
• Type 2 (about 90%): insulin resistance; linked to obesity, inactivity, age, family history
• Gestational: during pregnancy
• Symptoms: thirst, frequent urination, tiredness, slow healing; complications: heart, kidney, eye and nerve damage
• Pakistan has one of the highest adult diabetes rates in the world

8.3 Heart attack (myocardial infarction)

• Coronary artery blocked by atherosclerosis plus a clot; heart muscle dies
• Risk factors: high LDL, high blood pressure, smoking, diabetes, obesity, inactivity, stress, family history

8.4 Others

• Tetanus ("lockjaw"): Clostridium tetani toxin; prevented by tetanus toxoid
• Anaemia: low haemoglobin, mostly from iron deficiency
• Typhoid: Salmonella typhi, faecal-oral; Pakistan has faced an extensively drug-resistant (XDR) typhoid outbreak since 2016 (Sindh), now prevented with the typhoid conjugate vaccine
• COVID-19: SARS-CoV-2 virus; spreads through infectious respiratory particles, including aerosols
• Silicosis: lung scarring from inhaled silica dust (stone, cement, glass workers)

9. Vaccines vs Antibiotics

• Vaccine types: live attenuated (OPV, MMR, BCG), inactivated (IPV, hepatitis A), subunit/conjugate (hepatitis B, typhoid conjugate), toxoid (tetanus), mRNA/DNA (some COVID-19 vaccines)
• Antibiotic resistance: unnecessary or inappropriate antibiotic exposure selects resistant bacteria. Use the prescribed drug, dose and duration; changing a course without clinical advice can cause treatment failure. Resistance develops in microbes, not in the patient's body

10. Drug Abuse vs Drug Addiction

11. MCQ Traps

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• Malaria = female Anopheles (night), parasite; dengue = female Aedes (day), virus
• Only female mosquitoes bite (they need blood for eggs)
• Hepatitis A, E = faecal-oral; B, C, D = blood; B is a DNA virus; no vaccine for C
• Antibiotics kill bacteria, never viruses (COVID-19, flu, dengue are viral)
• Spanish flu 1918 = H1N1; tetanus = lockjaw
• Endemic = usual presence; epidemic = excess above expectation; pandemic = widespread international epidemic. These are not compulsory stages or measures of severity.

12. Self-Test Questions

1. Give the cause, vector, life cycle and prevention of dengue.
2. Describe polio: symptoms, spread, prevention and vaccines.
3. What is hepatitis? Give its types, causes, prevention and cure.
4. Write a note on diarrhoea and its treatment.
5. What causes malaria and how is it treated?
6. Differentiate vaccines and antibiotics; why is antibiotic misuse dangerous?
7. Explain diabetes, its causes and types.

13. CSS Exam Perspective

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• Most repeated: hepatitis (almost yearly), polio, dengue, vaccines vs antibiotics
• Syllabus coverage priority: malaria and diarrhoea have no dedicated long question in the saved collection; prepare both regardless of past frequency. This is not a prediction.
• Likely angles: dengue life cycle and Aedes, polio in Pakistan, antimicrobial resistance, epidemic vs pandemic
• Tip: use one fixed frame for every disease — cause → spread → symptoms → prevention → treatment → Pakistan angle

Syllabus completion — causes, prevention and epidemic reasoning

Prevention must match the transmission route

References: WHO polio, WHO hepatitis B, WHO hepatitis C.

Missing syllabus practice: diarrhoea and malaria

These are syllabus-based practice questions, not newly attributed past-paper questions.

Diarrhoea—causes and prevention (five-mark outline): Define frequent loose stools; identify bacterial, viral and parasitic causes; explain faecal contamination; describe safe water, sanitation, food hygiene, handwashing and rotavirus vaccination; distinguish prevention from management. ORS replaces lost water/electrolytes rather than killing pathogens. Continued feeding supports recovery. WHO diarrhoeal disease.

Malaria—cause and prevention (five-mark outline): Identify Plasmodium and female Anopheles; outline mosquito → human liver → red cells → mosquito; connect red-cell infection to fever/anaemia; explain treated nets, indoor residual spraying and bite protection; mention diagnosis and appropriate treatment. Vaccines complement other control measures in eligible populations; they do not replace nets. WHO malaria.

Epidemics and outbreak control

An epidemic is disease occurrence above the expected level in a population and period. “Endemic” does not mean harmless, and “pandemic” describes geographic spread rather than individual severity.

A short outbreak-control answer should cover: confirm diagnosis → establish a case definition → identify affected people/place/time → investigate source and transmission → apply route-specific controls → communicate clearly → monitor whether cases fall. Examples: water/sanitation measures for faecal–oral outbreaks; vector control for dengue; vaccination and surveillance for polio. Isolation is not a universal solution for every disease.

Strengthen the saved-paper answers

• Polio, 2018/2022: distinguish OPV (live oral) and IPV (inactivated injection); include transmission, prevention and lack of a curative treatment.
• Hepatitis, 2020/2023/2024/2025: use A–E comparisons rather than giving every type the same transmission route; B may be suppressed with treatment, while C can often be cured with direct-acting antivirals and has no effective vaccine.
• Dengue, 2016/2026: distinguish pathogen from vector and human incubation from mosquito extrinsic incubation. For the life-cycle question, explain virus acquisition, replication in mosquito tissues and transmission at a later bite.
• Vaccines/antibiotics, 2015/2016/2019/2022: vaccines train immunity; antibiotics act against susceptible bacteria. Resistance evolves and spreads in microbes, not because a person's body becomes “used to” antibiotics.
• Keep TB, diabetes, cardiovascular disease, allergy, anaemia and substance-use questions as past-paper extensions; they do not replace the five expressly named diseases.

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14. Past-Paper Long Questions — Exam-Ready Answers

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These are exam-ready study answers for the questions recorded in this page. Year labels and wording follow the saved collection; they have not all been authenticated against original papers. Coverage splits are suggested planning guides, not official FPSC marking schemes. Use the marks printed on your paper. For combined questions without an explicit sub-split, divide space according to the tasks asked.

• CSS 2026 Q4(c): Dengue—agent, transmission, life cycle and role of Aedes. (5 marks)

  Suggested coverage: agent/transmission 1; cycle 2; vector contribution 2.

  Model answer

  Dengue is caused by dengue virus, which has four principal serotypes, DENV-1 to DENV-4. Its main vectors are infected female Aedes aegypti mosquitoes; Ae. albopictus also transmits it.

  Human–mosquito cycle: An infected mosquito introduces virus in saliva during a bite. Virus replicates in human cells and enters the bloodstream. Another mosquito feeding during viraemia acquires it. Virus replicates in the mosquito’s midgut, disseminates and reaches its salivary glands. At subsequent bites, the mosquito can infect another person. Viral replication inside cells involves entry, RNA translation and replication, assembly and release.

  Vector contribution: Aedes breeds in water-holding containers near homes, often feeds during daylight and may bite several people. Its close association with humans sustains urban transmission. Dry-resistant eggs help populations persist between wet periods.

  Diagram: viraemic person → feeding mosquito → midgut replication → salivary glands → next human. The mosquito’s egg–larva–pupa–adult development is distinct from the viral transmission cycle.

  CDC dengue transmission.

• CSS 2025 Q3(c), 2023 Q3(d), 2020 Q5(a): Hepatitis—types, causes, prevention and cure. (5-mark topic variants)

  Suggested coverage: definition 0.5; types/routes 2; prevention 1.5; treatment 1.

  Model answer

  Hepatitis is inflammation of the liver. Causes include viruses, alcohol, medicines and autoimmune disease; viral hepatitis has five major types.

  Type	Principal route / distinguishing feature
  A	Faecal–oral; contaminated food/water; usually acute
  B	Blood, sexual exposure and mother-to-child; may become chronic
  C	Mainly infected blood; often chronic
  D	Requires hepatitis B infection; chiefly blood/body-fluid exposure
  E	Commonly contaminated water; foodborne zoonotic transmission also occurs

  Possible symptoms include fatigue, nausea, abdominal discomfort, dark urine and jaundice; infection may be asymptomatic. Chronic B and C can lead to cirrhosis and liver cancer.

  Prevention: Safe water, sanitation and food hygiene reduce A/E transmission. Screened blood, sterile injection equipment and safer sex reduce blood/body-fluid transmission. Vaccines prevent A and B; B vaccination also prevents D by preventing B.

  Treatment: A and many E infections resolve with supportive care. Chronic B can be suppressed with antivirals; modern antivirals cure most C infections. Treatment is type-specific; “rest cures every hepatitis” is incorrect.

  CDC hepatitis overview, WHO hepatitis.

• CSS 2024 Q2(a): What are tuberculosis and hepatitis? Explain briefly. (5 marks)

  Suggested coverage: balanced coverage of the two diseases; approximately 2.5 each is a planning guide.

  Model answer

  Tuberculosis: TB is an infectious disease caused mainly by Mycobacterium tuberculosis. It usually affects the lungs and spreads through the air from people with infectious pulmonary TB. Symptoms include a persistent cough, fever, night sweats and weight loss. Diagnosis uses clinical assessment and appropriate microbiological tests. Treatment combines several antibiotics selected according to susceptibility and clinical eligibility. Early diagnosis, effective treatment, ventilation and respiratory protection reduce spread; BCG particularly protects children against severe TB.

  Hepatitis: Hepatitis means liver inflammation, commonly due to viruses A–E. A/E commonly spread through contaminated food or water; B spreads through blood, sex and birth exposure; C is mainly bloodborne; D requires B. Symptoms may include jaundice, dark urine and fatigue. Prevention combines sanitation, safe injections, screened blood and A/B vaccination. Many acute cases receive supportive care; chronic B is suppressible and most C is curable with antivirals.

  Key distinction: TB is a bacterial infection, whereas viral hepatitis is caused by viruses and cannot be treated with routine antibacterial drugs.

  WHO TB, NIH viral hepatitis.

• CSS 2023 Special Q5(a): Explain diabetes, its causes and classification. (5 marks)

  Suggested coverage: definition/mechanism 1; classification and causes 3; consequences 1.

  Model answer

  Diabetes mellitus is a metabolic disorder characterised by persistent high blood glucose caused by inadequate insulin secretion, impaired insulin action, or both. Insulin normally promotes glucose uptake and storage.

  Type	Main mechanism and causes
  Type 1	Autoimmune destruction of pancreatic beta cells produces severe insulin deficiency; genetic susceptibility and environmental factors contribute
  Type 2	Insulin resistance with progressive beta-cell dysfunction; risk involves genetics, excess adiposity, inactivity and ageing
  Gestational	Diabetes diagnosed during pregnancy in someone without previously recognised diabetes; pregnancy-related insulin resistance contributes
  Other specific types	Monogenic disorders, pancreatic disease or certain medicines, among other causes

  Common symptoms include frequent urination, excessive thirst, fatigue and unexplained weight loss, although type 2 may initially be silent. Persistently high glucose can damage blood vessels, kidneys, nerves and eyes.

  Precision: Eating sugar alone is not a complete explanation of diabetes. Type 1 is not caused by poor lifestyle, and diabetes mellitus differs from diabetes insipidus.

  NIDDK diabetes types, NIDDK causes.

• CSS 2022 Q3(b), 2018 Q3(a): Polio—cause, spread, symptoms, prevention and vaccines. (5-mark topic variants)

  Suggested coverage: cause/spread 1; symptoms 1; vaccination and prevention 3.

  Model answer

  Poliomyelitis is a highly infectious disease caused by poliovirus. It multiplies in the intestine and can invade the nervous system, damaging motor neurons and causing paralysis.

  Spread and symptoms: Transmission is mainly faecal–oral through contaminated hands, food or water. Most infections cause no symptoms; symptomatic cases can involve fever, fatigue, headache, vomiting, neck stiffness and limb pain. About one in 200 infections causes irreversible paralysis. Respiratory-muscle involvement can be fatal.

  Vaccines: Oral polio vaccine (OPV) contains live attenuated virus and induces useful intestinal immunity. Inactivated polio vaccine (IPV) is injected and strongly protects against paralysis. Their use follows immunisation programmes; vaccination requires the recommended doses.

  Prevention: High routine coverage, supplementary campaigns, safe water, sanitation, hand hygiene and surveillance interrupt transmission. Reaching missed children is particularly important in eradication work.

  There is no cure that reverses established paralytic polio; prevention through immunisation is essential.

  WHO poliomyelitis.

• CSS 2022 Q3(a): Vaccination—types, side effects and effectiveness. (5-mark variant)

  Suggested coverage: immune mechanism 1; types/examples 2; effects and effectiveness 2.

  Model answer

  Vaccination exposes the immune system to an antigen or instructions for making one, inducing protective immune responses and memory without requiring the full disease.

  Types with examples: Live attenuated vaccines include measles and OPV; inactivated vaccines include IPV. Subunit/recombinant vaccines include hepatitis B, conjugate vaccines include Hib, and toxoid vaccines include tetanus. Genetic platforms include mRNA and DNA vaccines.

  Side effects: Temporary injection-site pain, tiredness and fever may occur. Serious allergic reactions are rare. Risks and suitability depend on the particular vaccine and recipient.

  Effectiveness: Vaccines reduce the risk of infection, severe illness or transmission to varying degrees. Protection depends on the vaccine, correct dosing, time since vaccination and the pathogen. Some require boosters; no vaccine guarantees absolute protection. High coverage can reduce spread for diseases where vaccination interrupts transmission.

  Example: Smallpox eradication illustrates the population benefit of coordinated vaccination.

  CDC vaccine basics.

• CSS 2016 Q4(a): Vaccines and DNA vaccines. (5-mark variant; check original wording)

  Suggested coverage: general mechanism 1.5; DNA mechanism 2; benefits/limitations 1.5.

  Model answer

  A vaccine stimulates adaptive immunity by presenting antigens or genetic instructions for their production. Antigen recognition activates immune cells and creates memory, allowing a faster protective response upon later exposure.

  DNA vaccine mechanism:

  1. A manufactured plasmid contains a gene encoding a pathogen antigen.
  2. Delivery introduces the plasmid into some host cells.
  3. In the nucleus, the gene is transcribed into mRNA.
  4. Ribosomes translate the mRNA into antigen.
  5. Antigen presentation stimulates antibody and T-cell responses and immune memory.

  Potential benefits: No live pathogen is required, the platform is adaptable, and production and storage may offer practical advantages.

  Limitations: Efficient delivery and sufficient immune responses can be challenging. Safety, effectiveness, cost and approval must be evaluated for each product. DNA vaccines should not be described as automatically cheaper, completely risk-free or equivalent to mRNA vaccines.

  Diagram: plasmid DNA → host-cell transcription → mRNA → antigen → immune response.

• CSS 2019 Q3(d): Differentiate vaccines and antibiotics. (5-mark topic variant)

  Suggested coverage: definitions 1; four paired distinctions 3; resistance qualification 1.

  Model answer

  Vaccines prepare immune defences against a specific disease; antibiotics kill bacteria or inhibit bacterial growth.

  Feature	Vaccines	Antibiotics
  Main purpose	Prevention and immune preparation	Treatment of susceptible bacterial infections; selected preventive uses
  Mechanism	Antigen-specific immune responses and memory	Act on bacterial targets such as walls or ribosomes
  Target	Certain viral or bacterial diseases	Bacteria, not viruses
  Timing	Usually before exposure; some post-exposure uses	Usually during infection
  Duration	Protection may persist, sometimes needing boosters	Drug effect requires an appropriate regimen; does not itself create immune memory

  For example, hepatitis B vaccine prevents infection, while an appropriate antibiotic regimen treats bacterial TB. Antibiotics do not treat influenza or dengue. Resistance arises in microbes, not because the patient’s body becomes resistant.

  CDC antibiotic use.

• CSS 2019 Q5(c): Explain the danger of antibiotic misuse. (5-mark topic variant)

  Suggested coverage: misuse examples 1; selection and spread 2; consequences/prevention 2.

  Model answer

  Antibiotic misuse includes unnecessary treatment of viral illness, use without proper assessment, incorrect drug selection, and inappropriate dose or duration.

  Resistance mechanism: Bacterial populations may contain resistant variants or acquire resistance genes. Antibiotic exposure kills susceptible bacteria while resistant bacteria survive and multiply. Resistance genes may also spread between bacteria. Unnecessary or inappropriate exposure increases selection pressure.

  Consequences: Resistant infections become harder to treat, may require more toxic or expensive medicines, prolong illness and increase the risk of complications and death. Unnecessary antibiotics can also cause adverse effects and disturb normal microbiota.

  Prevention: Use antibiotics only when indicated and exactly as prescribed. Do not share them or use leftovers. Prescribers should select appropriate agents and durations, supported by testing when relevant. Infection prevention, vaccination and surveillance reduce the need for antibiotics.

  Precision: Resistance develops in bacteria; it is not immunity acquired by the patient.

  CDC antibiotic use.

• CSS 2015 Q7(b): Short notes on antibiotics and hormones. (Marks not separately verified)

  Suggested coverage: use only the space allocated to each note; the original mixed prompt also includes greenhouse effect.

  Model answer

  Antibiotics: These medicines kill or inhibit susceptible bacteria by targeting processes such as cell-wall formation or protein synthesis. Penicillins are an example. Antibiotics do not act against viruses. Their selection depends on the infection and susceptibility; inappropriate use favours resistance.

  Hormones: Hormones are chemical messengers secreted by endocrine cells. They reach target cells, often through blood, and act through specific receptors. Insulin from pancreatic beta cells lowers blood glucose by supporting uptake and storage; thyroid hormones influence metabolic activity. Feedback mechanisms regulate secretion, helping maintain homeostasis.

  Exam scope: If the paper also asks for the greenhouse effect, answer that separately: atmospheric gases absorb and re-emit outgoing terrestrial infrared radiation, warming the surface and lower atmosphere. Increased greenhouse gases strengthen the natural effect. Do not allocate the entire mixed question’s marks to these two biology notes.

• CSS 2016 Q4(b): State the causative organism and vector of dengue and enlist prevention methods. (5 marks)

  Suggested coverage: agent/vector 1; practical prevention linked to transmission 4.

  Model answer

  Dengue is caused by dengue virus. Its principal vector is the infected female Aedes aegypti mosquito; Ae. albopictus can also transmit it.

  Prevention:

  • Empty, scrub or remove water-holding containers, tyres and discarded objects to destroy breeding sites.
  • Keep water-storage vessels tightly covered and maintain gutters and drains.
  • Use suitable repellents, long sleeves and window or door screens to reduce bites.
  • Protect daytime sleepers with nets, because Aedes commonly bites during daylight.
  • Prevent mosquitoes from biting infected people, reducing onward transmission.
  • Support surveillance, community clean-up and targeted larval/adult mosquito control by public-health services.

  Control should focus on sustained source reduction; fogging alone is temporary and does not remove eggs or breeding containers. Vaccination eligibility depends on the vaccine and local programme.

  Exam focus: This question asks prevention; a long account of symptoms and treatment would displace relevant points.

  CDC dengue prevention.

• CSS 2017 Q3(a): Explain common causes of heart attack. (5 marks)

  Suggested coverage: definition 1; direct mechanism 2; risk factors with explanation 2.

  Model answer

  A heart attack, or myocardial infarction, occurs when prolonged inadequate coronary blood supply causes death of heart muscle.

  Main mechanism: Atherosclerotic plaque develops in a coronary artery. If a plaque ruptures or erodes, platelets and clotting factors form a thrombus. The clot may obstruct blood flow, depriving myocardium of oxygen and nutrients. Coronary spasm and other mechanisms can also cause infarction.

  Major risk factors:

  • Elevated LDL cholesterol contributes to plaque formation.
  • Hypertension injures arterial walls and increases cardiac workload.
  • Smoking promotes vascular injury and thrombosis.
  • Diabetes accelerates vascular disease.
  • Physical inactivity and excess adiposity worsen metabolic risk.
  • Age and family history indicate non-modifiable susceptibility.

  Thus, distinguish the immediate cause—loss of coronary perfusion—from factors that increase its probability.

  Diagram cue: coronary artery → plaque rupture → clot → reduced oxygen → myocardial cell death.

• CSS 2017 Q3(b): Differentiate drug abuse and drug addiction. (5 marks)

  Suggested coverage: definitions 1; paired distinctions 3; dependence qualification/example 1.

  Model answer

  Drug abuse is older terminology for harmful or inappropriate substance use. Addiction is characterised by compulsive use despite harm and impaired control. Modern clinical assessment generally uses “substance use disorder.”

  Aspect	Harmful use / abuse	Addiction
  Pattern	Use causes risk or harm; may be episodic	Persistent compulsion and difficulty controlling use
  Control	Loss of control need not be established	Impaired control is central
  Priorities	Harm can occur without drug seeking dominating life	Substance use may displace responsibilities and relationships
  Continuation	May occur without a sustained compulsive pattern	Use continues despite adverse consequences

  Tolerance and withdrawal may occur, but neither alone defines addiction. Physical dependence can develop during appropriate prescribed treatment without compulsive misuse. Conversely, addiction can exist without prominent withdrawal.

  For example, a single episode of dangerous misuse is harmful but does not by itself establish addiction. Repeated compulsive use despite serious harm warrants assessment for a substance use disorder.

  NIDA prescription drug report.

• CSS 2015 Q9(a): Define anaemia and describe its causes and symptoms. (5-mark topic; verify printed marks)

  Suggested coverage: definition 1; causes 2; symptoms/mechanism 2.

  Model answer

  Anaemia is a haemoglobin concentration below the appropriate reference range for a person’s age and physiological state. It reduces the oxygen-carrying capacity of blood.

  Causes:

  • Reduced production: Iron deficiency limits haemoglobin synthesis; vitamin B12 or folate deficiency impairs red-cell production. Kidney disease can reduce erythropoietin.
  • Blood loss: Heavy menstrual bleeding, gastrointestinal bleeding or injury can cause anaemia.
  • Increased destruction: Haemolytic disorders, including some inherited conditions such as sickle-cell disease and thalassaemia, shorten red-cell survival.

  Symptoms and signs: Fatigue, weakness, pallor, dizziness, breathlessness and palpitations result from reduced oxygen delivery and compensatory cardiovascular activity. Mild or slowly developing anaemia may produce few symptoms.

  Anaemia is not synonymous with iron deficiency. Management requires identifying its cause; iron is appropriate for iron deficiency rather than automatically for every anaemia.

• CSS 2015 Q7(a): What do you understand by pollen allergy? (5-mark topic; verify printed marks)

  Suggested coverage: definition/trigger 1; mechanism 2; manifestations and control 2.

  Model answer

  Pollen allergy is an inappropriate immune response to proteins in pollen from plants such as grasses, weeds and trees. It commonly causes seasonal allergic rhinitis, or hay fever.

  Mechanism: During sensitisation, the immune system produces pollen-specific IgE antibodies that attach to mast cells. On later exposure, the allergen cross-links this IgE, triggering release of histamine and other mediators. These produce inflammation of nasal and eye tissues.

  Manifestations: Sneezing, a runny or blocked nose, itchy nose and watery, itchy eyes are typical. Susceptible people may also develop asthma symptoms. Timing depends on local plants and pollen seasons.

  Control: Reduce exposure during high pollen periods, keep outdoor pollen out of living spaces where practical, and use appropriate clinician-guided allergy treatment. Selected patients benefit from allergen immunotherapy.

  Distinction: Pollen allergy is neither a contagious infection nor a reaction to every kind of pollen.

15. Past-Paper MCQ Quiz (FPSC)

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Real FPSC GSA MCQs on this topic, newest first. Answers and explanations are worked out.

1. (CSS 2026) A key indicator of drinking water microbiological safety is:

• (A) pH (B) Turbidity (C) Hardness (D) E. coli
• ✅ Answer: (D) E. coli — its detection indicates faecal contamination and potential pathogen exposure; it does not by itself prove the presence of cholera or typhoid organisms.

2. (CSS 2025) Perinatal transmission occurs when a pathogen is transmitted from:

• (A) Non-human to human (B) Infected to uninfected (C) Mother to infant (D) None of these
• ✅ Answer: (C) Mother to infant — "perinatal" means around the time of birth (hepatitis B, HIV).

3. (CSS 2025) Cement factory labourers are prone to:

• (A) Leukemia (B) Cytosilicosis (C) Bone marrow (D) None of these
• Transcription warning: (B) appears intended to refer to silicosis, but “cytosilicosis” is not the standard diagnosis. Silicosis is caused by inhaling respirable crystalline silica; risk depends on exposure, not merely a job title. Original wording/key is unverified. CDC silica.

4. (CSS 2022) COVID-19 is caused by:

• (A) Bacteria (B) Virus (C) Infection (D) None of these
• ✅ Answer: (B) Virus — SARS-CoV-2, a coronavirus; so antibiotics do not cure it.

5. (CSS 2022) Deficiency of iron in the human diet causes:

• (A) Hepatitis (B) Malaria (C) Anaemia (D) None of these
• ✅ Answer: (C) Anaemia — iron is needed to make haemoglobin.

6. (CSS 2021) Diseases that spread from one person to another are called:

• (A) Communicable (B) Degenerative (C) Non-communicable (D) None of these
• ✅ Answer: (A) Communicable — caused by germs that pass between people (TB, flu).

7. (CSS 2021) The Spanish influenza of 1918–19 was caused by which influenza virus?

• (A) H1N2 (B) H3N1 (C) H1N1 (D) None of these
• ✅ Answer: (C) H1N1 — the same subtype caused the 2009 swine-flu pandemic.

8. (CSS 2020) Aedes aegypti transmits:

• (A) Malaria (B) Dengue fever (C) Typhoid fever (D) None of these
• ✅ Answer: (B) Dengue fever — malaria is spread by Anopheles; typhoid by contaminated food and water.

9. (CSS 2018) How is dengue fever transmitted?

• (A) Bite of an infected mosquito (B) Bite of an infected male Aedes (C) Bite of an infected female Anopheles (D) Bite of an infected female Aedes
• ✅ Answer: (D) — only female mosquitoes bite, and the dengue vector is Aedes, not Anopheles.

10. (CSS 2018) Antibiotics are used to fight against:

• (A) Proteins (B) Viruses (C) Bacteria (D) None of these
• ✅ Answer: (C) Bacteria — they attack bacterial cell walls, ribosomes or enzymes, which viruses lack.

11. (CSS 2018) Sometimes people do not finish their antibiotic pills. This can result in:

• (A) Some bacteria left un-killed (B) Production of more bacteria (C) Bacteria becoming sensitive (D) Bacteria becoming resistant to antibiotics
• Saved answer: (D), not an authenticated key. Inappropriate treatment can cause failure and select resistant bacteria, but several outcomes overlap in these options. Take antibiotics exactly as prescribed; neither stopping early nor extending treatment independently is sound advice. CDC antibiotic use.

12. (CSS 2017) The disease called lockjaw is:

• (A) Arthritis (B) Hypertrophy (C) Tetanus (D) None of these
• ✅ Answer: (C) Tetanus — the toxin of Clostridium tetani causes jaw-muscle spasm.

Figures — separate pathogen, vector and disease

Dengue transmission cycle

flowchart TD
 A["Human with dengue virus in blood"] -->|"blood meal"| B["Female Aedes acquires virus"]
 B --> C["Virus replicates in mosquito and reaches salivary glands"]
 C -->|"later infective bite"| D["Virus enters another human"]
 D --> E["Replication in human; possible viraemia"]
 E -->|"another mosquito feeds"| B

Two clocks: human symptom incubation is usually 4–10 days; mosquito extrinsic incubation is commonly around 8–12 days at 25–28°C and varies with temperature and other conditions. These are not identical periods. Source: WHO dengue.

Malaria transmission cycle

flowchart TD
 A["Infected female Anopheles"] -->|"sporozoites at bite"| B["Human liver"]
 B -->|"merozoites"| C["Red blood cells"]
 C --> D["Some parasites become gametocytes"]
 D -->|"taken up during a blood meal"| E["Mosquito gut: sexual reproduction"]
 E --> F["Sporozoites reach salivary glands"]
 F --> A

Remember: malaria involves a protozoan parasite; dengue involves a virus. The mosquito's own life stages—egg, larva, pupa, adult—are a separate life cycle from either pathogen's cycle. WHO malaria.

Polio and inheritance — corrected facts

• Most poliovirus infections are asymptomatic; CDC estimates approximately 70% in children, rather than the earlier unsupported 90%. CDC Pink Book.
• WHO's educational estimate is one in 200 infections leading to irreversible paralysis. State the denominator: infections, not all paralysed patients. WHO polio.
• Mother-to-child HIV transmission is an infection route, not genetic inheritance. A hereditary condition is passed through genetic material; congenital means present at birth and need not mean inherited. NIH HIV.
• Avoid undated Pakistan case totals. An annual count must identify year, reporting date, wild versus vaccine-derived poliovirus, and the surveillance source.

Additional 5-mark syllabus practice — complete answers

These expand the earlier practice outlines; they are not newly discovered past-paper questions.

Diarrhoea: causes, prevention and management

Suggested coverage: definition/causes 1.5; prevention 2; management distinction 1.5.

Diarrhoea is the passage of three or more loose or liquid stools daily, or more frequently than normal for the individual. Infectious causes include viruses, bacteria and parasites; contaminated food or water and poor hand hygiene facilitate faecal–oral transmission. Noninfectious causes also exist.

Prevention: Provide safe drinking water, adequate sanitation and hygienic disposal of faeces. Wash hands with soap, prepare and store food safely, support breastfeeding and use rotavirus vaccination according to the immunisation programme.

Management: Oral rehydration solution replaces lost water and electrolytes; it does not kill pathogens. Prepare it with safe water according to packet instructions. Continue appropriate feeding and breastfeeding; childhood zinc treatment follows clinical guidance. Severe dehydration requires urgent assessment and may require intravenous fluids. Antibiotics are reserved for selected indications.

Thus, preventing faecal contamination reduces infection, while rehydration prevents its major dangerous consequence.

WHO diarrhoeal disease.

Malaria: cause, transmission and prevention

Suggested coverage: cause/cycle 2; manifestations 1; prevention/control 2.

Malaria is caused by Plasmodium parasites, usually transmitted through bites of infected female Anopheles mosquitoes. Sporozoites enter human blood and infect liver cells. Parasites then enter red blood cells, multiply and rupture them, contributing to fever and anaemia. Some form gametocytes, which another mosquito takes up; sexual development in the mosquito eventually produces infective sporozoites.

Symptoms include fever, chills and headache; severe disease may cause life-threatening organ complications.

Prevention: Insecticide-treated nets, indoor residual spraying and suitable bite protection reduce exposure. Early parasite-based testing and appropriate treatment reduce disease and contribute to control. Vaccine programmes in eligible populations supplement other measures. Treatment depends on parasite species, severity and resistance.

Diagram: mosquito → human liver → red cells → gametocytes → mosquito.

WHO malaria.

Further medical references: NHLBI heart-attack causes, WHO anaemia.