Fever and Tropical Infections for NEET PG Medicine: Malaria, Dengue, Typhoid, Leptospirosis, Scrub Typhus, Fever of Unknown Origin

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🎯 Exam priority: High. Expect: the national malaria regimens and primaquine doses, severe malaria criteria, IV artesunate schedule, malaria in pregnancy, dengue warning signs and test timing, NSAIDs and platelets in dengue, typhoid week-by-week tests and complications, eschar in scrub typhus and the FUO definition.

CBME mapping: GM 4.1–4.20. Programme indicators and vector control are in Community Medicine; parasite biology in Microbiology; malaria pathology in Pathology article 7.

Malaria, dengue, typhoid, leptospirosis, scrub typhus and FUO. Drawn by TrackNation.

Malaria

• Test every suspected case immediately by microscopy and/or RDT.

• P. vivax forms dormant liver hypnozoites that cause relapse — hence 14 days of primaquine. P. falciparum can turn severe within 12–24 hours.

• Severe malaria (any one): impaired consciousness/coma, repeated convulsions, creatinine > 3 mg/dL, bilirubin > 3 mg/dL, Hb < 5 g/dL, pulmonary oedema/ARDS, glucose < 40 mg/dL, metabolic acidosis, shock (SBP < 80; < 50 in children), abnormal bleeding/DIC, haemoglobinuria, temperature > 42 °C, parasitaemia > 5%.

Dengue

• Three phases: febrile, critical (leakage; from about day 3–4 of fever, lasting 24–48 hours; commoner in secondary infection) and recovery. Do a tourniquet test and look for petechiae.

• Warning signs (admit): abdominal pain or tenderness, persistent vomiting, fluid accumulation (ascites, effusion), mucosal bleeding, lethargy or restlessness, liver > 2 cm, rising haematocrit with falling platelets.

• Tests: NS1 antigen for samples from day 1–5; IgM after day 5.

• Treatment: no specific antiviral; paracetamol and fluids; avoid aspirin and NSAIDs (mucosal bleeding). Prophylactic platelet transfusion does not prevent bleeding better than supportive care and causes adverse events.

Typhoid, Leptospirosis, Scrub Typhus, FUO

• Typhoid (S. Typhi; humans are the only host): prolonged fever, relative bradycardia, rose spots on chest and abdomen in week 2 (5–30%). Blood culture is positive in the first 2 weeks, stool culture in weeks 3–5; bone marrow culture is the most sensitive. The Widal test is only ~70% sensitive and non-specific. Complications: distal ileal perforation (1–2%) in week 3. Treatment: ceftriaxone, a fluoroquinolone or azithromycin.

• Leptospirosis: from urine of carrier animals (rats, dogs, cattle); conjunctival suffusion on day 3–4. Weil syndrome = icteric leptospirosis with jaundice and azotaemia. Doxycycline or penicillin.

• Scrub typhus (Orientia tsutsugamushi, mite-borne): an eschar at the chigger bite at fever onset; doxycycline.

• Classic FUO: temperature ≥ 38.3 °C for more than 3 weeks with no cause after 3 days in hospital or 3 outpatient visits.

Traps the Examiner Sets

• Primaquine: 14 days for vivax (0.25 mg/kg), single dose for falciparum (0.75 mg/kg) — never in pregnancy, infants, G6PD deficiency.

• North-east India uses artemether–lumefantrine, not AS+SP.

• Dengue: NS1 before day 5, IgM after.

• Typhoid week 1–2 blood culture; week 3 perforation.

• Fever + eschar → scrub typhus → doxycycline.

Memory Hooks & Shortcuts

Shortcuts to lock in this article's numbers and lists. Each one only re-packages facts proven above.

• 🧠 Vivax = 'V-for-Vacation in the liver' → 14 days primaquine — vivax

• 🧠 Falciparum = 'Fast and Fatal' (12–24 h) → artesunate — falciparum

• 🧠 Primaquine: no P-I-G (Pregnancy, Infants, G6PD) — primaquine contraindications

• 🧠 Dengue: 'NS1 till 5, IgM after 5' — dengue tests

• 🧠 Typhoid: Blood first (wk 1–2), Stool later (wk 3–5), Marrow most sensitive — typhoid test timing

• 🧠 Scrub typhus: Spot of black (eschar) → Doxy — scrub typhus

Rapid-Revision Cards

• Malaria first step

  Microscopy and/or RDT.

• Vivax treatment

  Chloroquine 3 d + primaquine 0.25 mg/kg × 14 d.

• Hypnozoites

  Vivax liver stage → relapse.

• Falciparum (most of India)

  AS+SP × 3 d + PQ 0.75 mg/kg day 2.

• Falciparum NE states

  Artemether–lumefantrine.

• Primaquine CI

  Pregnancy, infants, G6PD deficiency.

• Severe malaria labs

  Cr > 3, bili > 3, Hb < 5, glucose < 40, parasites > 5%.

• Severe malaria shock

  SBP < 80 (< 50 children).

• Severe malaria Rx

  IV artesunate 2.4 mg/kg at 0, 12, 24 h.

• Malaria in pregnancy

  T1 quinine; T2–T3 ACT.

• Dengue phases

  Febrile → critical (day 3–4, 24–48 h) → recovery.

• Dengue warning signs

  Pain, vomiting, fluid, bleeding, lethargy, liver > 2 cm, Hct ↑ platelets ↓.

• Dengue tests

  NS1 day 1–5; IgM after day 5.

• Dengue analgesic

  Paracetamol; no NSAIDs.

• Prophylactic platelets

  No benefit; adverse events.

• Typhoid signs

  Relative bradycardia; rose spots week 2.

• Typhoid tests

  Blood culture wk 1–2; stool wk 3–5; marrow most sensitive.

• Widal

  ~70% sensitive, non-specific.

• Typhoid perforation

  Distal ileum, week 3, 1–2%.

• Leptospirosis

  Rat urine; conjunctival suffusion; doxy/penicillin.

• Weil syndrome

  Jaundice + azotaemia.

• Scrub typhus

  Orientia; eschar; doxycycline.

• Classic FUO

  ≥ 38.3 °C > 3 weeks, no cause after 3 hospital days.

Sources

Facts in this article were checked against these documents.

• Guidelines for Diagnosis and Treatment of Malaria in India — National Vector Borne Disease Control Programme, MoHFW, 2014 (link)

• National Guidelines for Clinical Management of Dengue Fever — National Center for Vector Borne Diseases Control, MoHFW, 2023 (link)

• MSD Manual Professional: Malaria; Dengue; Typhoid Fever; Leptospirosis; Scrub Typhus; Fever of Unknown Origin — Merck & Co. (MSD Manuals), reviewed 2025–26 (link)

• Competency Based Undergraduate Curriculum, General Medicine (GM 4) — National Medical Commission, 2024

Test Yourself: Practice Questions

Thirty questions in NEET PG style, most of them clinical vignettes.

Practice Questions (NEET PG pattern)

Original questions written in the style of the exam: +4 for a correct answer, −1 for a wrong one. Every answer was checked against the sources listed above. NEET PG papers are not published by NBEMS, so these are not past-paper questions.

Q1. An adult in a malaria-endemic district has fever with chills. The first step under the national guidelines is

• (a) Widal test

• (b) immediate microscopy and/or RDT

• (c) start ACT without testing in all

• (d) chest X-ray

Q2. A man with smear-confirmed P. vivax malaria is treated with chloroquine. Primaquine is added at

• (a) 0.75 mg/kg single dose

• (b) not needed

• (c) 0.25 mg/kg daily for 14 days

• (d) 15 mg once weekly

Q3. Primaquine is given in vivax malaria to

• (a) kill gametocytes only

• (b) prevent anaemia

• (c) kill dormant liver hypnozoites that cause relapse

• (d) reduce fever

Q4. Primaquine is contraindicated in all EXCEPT

• (a) pregnant women

• (b) infants

• (c) adult men with normal G6PD

• (d) known G6PD deficiency

Q5. A patient in Madhya Pradesh has uncomplicated P. falciparum malaria. The national treatment is

• (a) chloroquine 3 days

• (b) quinine 7 days alone

• (c) primaquine 14 days alone

• (d) artesunate + sulfadoxine–pyrimethamine for 3 days plus single primaquine 0.75 mg/kg on day 2

Q6. In the north-eastern states, the ACT for falciparum malaria is

• (a) artemether–lumefantrine

• (b) artesunate + SP

• (c) chloroquine

• (d) mefloquine alone

Q7. A falciparum malaria patient becomes drowsy with creatinine 3.8 mg/dL. The drug of choice is

• (a) IV artesunate 2.4 mg/kg at 0, 12 and 24 hours, then daily

• (b) oral chloroquine

• (c) primaquine

• (d) oral ACT at home

Q8. Which value defines severe falciparum malaria?

• (a) temperature 39 °C

• (b) Hb 9 g/dL

• (c) plasma glucose < 40 mg/dL

• (d) creatinine 1.4 mg/dL

Q9. Parasitaemia defining severe malaria is more than

• (a) 50%

• (b) 0.1%

• (c) 1%

• (d) 5% of red cells

Q10. A woman in the first trimester has falciparum malaria. Per the national guidelines, treat with

• (a) quinine

• (b) ACT

• (c) chloroquine plus primaquine

• (d) primaquine

Q11. Severe complications of P. falciparum can develop within

• (a) 12–24 hours

• (b) only after relapse

• (c) 2 months

• (d) 2 weeks

Q12. A dengue patient on day 4 of fever develops right upper quadrant pain, persistent vomiting and a rising haematocrit with falling platelets. The next step is

• (a) give prophylactic platelets

• (b) start antibiotics only

• (c) admit — these are warning signs

• (d) send home on NSAIDs

Q13. The critical (plasma leakage) phase of dengue usually begins

• (a) after the 3rd or 4th day of fever and lasts 24–48 hours

• (b) on day 1

• (c) after 3 weeks

• (d) only after recovery

Q14. A patient's sample is collected on day 3 of fever for dengue. The test the laboratory should perform is

• (a) IgM ELISA

• (b) NS1 antigen

• (c) paired IgG

• (d) Widal

Q15. For fever and body ache in dengue, the recommended drug is

• (a) aspirin

• (b) ibuprofen

• (c) paracetamol

• (d) diclofenac

Q16. A dengue patient has platelets of 18,000/µL without significant bleeding. Per national guidance, prophylactic platelet transfusion

• (a) should be given daily

• (b) is not superior to supportive care and has adverse events

• (c) is mandatory

• (d) prevents all bleeding

Q17. Severe plasma leakage in dengue is more common in

• (a) first infection in healthy adults only

• (b) secondary (repeat) dengue infection

• (c) infants only

• (d) vaccinated people only

Q18. A patient has 10 days of fever, relative bradycardia and pink blanching spots on the abdomen in the second week. The likely diagnosis is

• (a) typhoid fever

• (b) leptospirosis

• (c) dengue

• (d) malaria

Q19. In suspected typhoid in the first week of illness, the investigation of choice is

• (a) stool culture

• (b) urine culture

• (c) Widal test

• (d) blood culture

Q20. The most sensitive culture in typhoid fever, useful when blood cultures are negative, is

• (a) bone marrow culture

• (b) throat swab

• (c) urine culture

• (d) CSF culture

Q21. The Widal test in typhoid is

• (a) the gold standard

• (b) positive in week 1 always

• (c) 100% specific

• (d) only about 70% sensitive and lacks specificity

Q22. A typhoid patient in the third week develops an acute abdomen. The usual site of perforation is

• (a) stomach

• (b) distal ileum

• (c) sigmoid colon

• (d) duodenum

Q23. Drugs used to treat typhoid include

• (a) ceftriaxone, a fluoroquinolone or azithromycin

• (b) doxycycline only

• (c) penicillin G

• (d) metronidazole

Q24. The reservoir of Salmonella Typhi is

• (a) pigs

• (b) poultry

• (c) rats

• (d) humans only

Q25. A farmer exposed to water contaminated by rat urine has fever, severe muscle aches and conjunctival suffusion on day 4. The likely diagnosis is

• (a) typhoid

• (b) conjunctivitis

• (c) leptospirosis

• (d) dengue

Q26. Leptospirosis with jaundice and renal failure is called

• (a) Reiter syndrome

• (b) Weil syndrome

• (c) Felty syndrome

• (d) Waterhouse-Friderichsen syndrome

Q27. A patient develops an eschar at the site of a chigger (mite) bite as fever begins. The likely diagnosis and drug are

• (a) anthrax — penicillin

• (b) plague — streptomycin

• (c) leishmaniasis — amphotericin

• (d) scrub typhus — doxycycline

Q28. Scrub typhus is caused by

• (a) Orientia tsutsugamushi

• (b) Rickettsia prowazekii

• (c) Coxiella burnetii

• (d) Leptospira interrogans

Q29. Classic fever of unknown origin requires fever ≥ 38.3 °C for more than

• (a) 1 week

• (b) 3 months

• (c) 3 days

• (d) 3 weeks without a cause after 3 days in hospital or 3 outpatient visits

Q30. In severe malaria, parenteral artesunate should preferably be given

• (a) rectally always

• (b) intravenously rather than intramuscularly

• (c) orally

• (d) subcutaneously

Active Recall

From memory: give the national regimens for vivax and falciparum malaria, primaquine doses and contraindications, severe malaria criteria and IV artesunate schedule; describe dengue phases, warning signs, test timing and supportive care; give typhoid tests by week and complications; and describe leptospirosis, scrub typhus and classic FUO.