Vector-borne diseases and medical entomology

43 NEET-PG practice questions on Vector-borne diseases and medical entomology, part of Community Medicine. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Medium

   Despite two rounds of DDT indoor residual spraying with good coverage, malaria cases keep rising in a tribal block of Chhattisgarh, and most are P. falciparum. WHO tube susceptibility tests show that Anopheles culicifacies survives exposure to DDT and malathion but dies after exposure to synthetic pyrethroids. What should the district malaria officer do next?

   1. AStop IRS and rely on outdoor fogging
   2. BSwitch IRS to a synthetic pyrethroid
   3. CChange to malathion spraying
   4. DRepeat DDT at double the dose

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   Answer: B · Switch IRS to a synthetic pyrethroid

   Rising cases despite spraying, with documented resistance to DDT and malathion, mean the vector is no longer controlled by these insecticides. The next round should use an insecticide to which the vector is susceptible, here a synthetic pyrethroid, along with long-lasting insecticidal nets, early diagnosis and complete treatment. Key point: Choose the IRS insecticide by vector susceptibility; resistance calls for a switch of class.

   • A: Space spraying gives only temporary adult kill and is not a substitute for IRS.
   • C: The vector is also resistant to malathion.
   • D: Doubling the dose does not overcome established resistance.

2. Question 2 · Medium

   On day 2 of fever, a medical student in a Chennai hostel has severe retro-orbital headache, myalgia, a flushed face and mild nausea; BP 116/76 mmHg, no bleeding and no abdominal pain. Haemoglobin 13.8 g/dL, WBC 3,400/mm3, platelets 1.6 lakh/mm3. Three hostel mates had confirmed dengue last week. Which test best confirms the diagnosis today?

   1. AIgM capture ELISA
   2. BHess tourniquet test
   3. CIgG ELISA
   4. DNS1 antigen ELISA

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   Answer: D · NS1 antigen ELISA

   In the first five days of dengue, the virus and its non-structural protein NS1 circulate in blood, so NS1 antigen ELISA (or RT-PCR) confirms early infection. IgM antibodies appear after about day 5, so IgM capture ELISA is the test from the second week. The programme confirms dengue by ELISA-based tests rather than rapid kits. Key point: Dengue: NS1 antigen in days 1-5; IgM capture ELISA after day 5.

   • A: IgM is often negative before day 5.
   • B: The tourniquet test indicates capillary fragility and is not confirmatory.
   • C: IgG indicates past or secondary infection and does not confirm current dengue.

3. Question 3 · Easy

   In a dengue-hit town in Kerala, the municipal health officer asks every household to empty, scrub and dry desert coolers, flower vases, refrigerator drip trays, overhead tanks and discarded tyres once every week, and announces Sunday as the dry day. Ward volunteers check compliance. This weekly measure works mainly because Aedes aegypti does what?

   1. ARests outdoors in vegetation by day
   2. BFlies several kilometres from where it breeds
   3. CBreeds in dirty, polluted drains
   4. DBreeds in clean water in man-made containers

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   Answer: D · Breeds in clean water in man-made containers

   Aedes aegypti is a domestic container breeder that lays eggs singly on the inner walls of water-holding containers. Development from egg to adult takes about a week, so emptying and drying containers once a week breaks the cycle; scrubbing removes eggs that survive drying for months. It bites by day, rests indoors and has a short flight range of about 100 metres. Key point: A weekly dry day breaks the Aedes cycle: a container breeder taking about a week from egg to adult.

   • A: Aedes aegypti rests indoors in dark corners.
   • B: Its flight range is short, about 100 metres.
   • C: Dirty polluted water is the breeding site of Culex quinquefasciatus.

4. Question 4 · Medium

   At a PHC in Alappuzha, a woman with stage 2 lymphoedema of the left leg from filariasis has had three attacks of painful red swelling with fever this year; between attacks there are small cracks between her toes. Besides treating each attack, which measure most reduces further attacks?

   1. ADEC courses every three months
   2. BDaily washing of the limb and care of entry lesions
   3. CMonthly benzathine penicillin injections
   4. DLymphovenous surgery of the limb

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   Answer: B · Daily washing of the limb and care of entry lesions

   Acute attacks (acute dermatolymphangioadenitis) are bacterial infections entering through cracks, fungal lesions and wounds in the swollen skin. The morbidity management and disability prevention package teaches daily washing and drying of the limb, care of entry lesions with antifungal cream, elevation, exercise and footwear, which sharply reduces attacks and slows progression. DEC does not reverse established lymphoedema. Key point: Lymphoedema care: limb hygiene and entry-lesion care prevent acute attacks.

   • A: DEC does not reverse lymphoedema or prevent bacterial attacks.
   • C: Penicillin prophylaxis is a second-line add-on, not the main measure.
   • D: Surgery is rarely needed and does not replace limb hygiene.

5. Question 5 · Medium

   A mason from Koraput has his third episode of P. vivax malaria in a year, each confirmed by smear; each time he took only three days of chloroquine from a private clinic and felt well within a week. He has not travelled, and no one else in his house is ill. His G6PD test is normal. Which parasite stage was left untreated, explaining the repeated attacks?

   1. ASporozoites in the bloodstream
   2. BMerozoites inside red cells
   3. CGametocytes circulating in peripheral blood
   4. DDormant hypnozoites in hepatocytes

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   Answer: D · Dormant hypnozoites in hepatocytes

   Chloroquine kills the asexual blood stages and ends the attack, but P. vivax and P. ovale leave dormant liver forms (hypnozoites) that reactivate weeks to months later and cause relapses. Primaquine for 14 days, given after a normal G6PD test, kills hypnozoites (radical cure). Key point: Vivax relapses come from liver hypnozoites; radical cure needs 14 days of primaquine after G6PD testing.

   • A: Sporozoites leave the blood within minutes to enter the liver.
   • B: Blood-stage merozoites are killed by chloroquine.
   • C: Gametocytes cause transmission to mosquitoes, not relapse.

6. Question 6 · Hard

   In a filaria-endemic panchayat in Cherthala, Alappuzha, night blood smears from several people show sheathed microfilariae with two separate terminal nuclei at the tail tip. Ponds around the houses are covered by the floating water plant Pistia stratiotes. The panchayat sprayed mineral larvicidal oil on the ponds for three months, but mosquito larval counts did not fall. Many residents work in coir retting near the ponds, and mosquitoes bite at night both indoors and outdoors. Why did the oil fail, and what is the logical next measure?

   1. ALarvae resist oil; switch to temephos
   2. BLarvae breathe through plant roots; remove the Pistia
   3. CLarvae breed in drains; spray fenthion there
   4. DAdults rest outdoors; begin indoor spraying

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7. Question 7 · Easy

   Malaria cases are rising in a city ward full of construction sites, overhead water tanks and wells. Which vector most likely breeds there?

   1. AAnopheles culicifacies
   2. BAnopheles annularis
   3. CAnopheles sundaicus
   4. DAnopheles stephensi

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8. Question 8 · Easy

   Rat falls are reported from a grain-market town after floods. Which flea species is the classic vector of bubonic plague?

   1. ATunga penetrans
   2. BPulex irritans
   3. CCtenocephalides felis
   4. DXenopsylla cheopis

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9. Question 9 · Medium

   During a Zika virus outbreak in Thiruvananthapuram, a woman 10 weeks pregnant asks the PHC doctor how to protect her baby. Besides avoiding mosquito bites by day, what else should she be advised?

   1. ATake a Zika vaccine in the second trimester
   2. BUse condoms or avoid sex for the rest of the pregnancy
   3. CTake weekly chloroquine prophylaxis
   4. DAvoid breastfeeding after delivery

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10. Question 10 · Medium

    Which larvivorous fish is commonly released into wells and ornamental tanks for malaria control?

    1. ACatla catla
    2. BLabeo rohita
    3. CClarias batrachus
    4. DGambusia affinis

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11. Question 11 · Hard

    In the paediatric ward of a medical college in Gorakhpur during the monsoon, a boy of 9 is admitted with 6 days of fever, altered sensorium and one seizure. CSF: 30 cells/mm3, mostly lymphocytes, protein 60 mg/dL, glucose normal. JE IgM in CSF is negative and the malaria RDT is negative. A small black crusted lesion is found behind his left ear; platelets are 70,000/mm3 and liver enzymes are raised. He had been going to the fields with his father daily. There is no neck rigidity. Which empirical treatment should be added?

    1. AAcyclovir for herpes simplex encephalitis
    2. BCeftriaxone alone for bacterial meningitis
    3. CIV artesunate for cerebral malaria
    4. DDoxycycline or azithromycin for scrub typhus

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12. Question 12 · Medium

    Paris green dusted on the surface of rice fields kills anopheline larvae but has little effect on Culex larvae in the same area. Why?

    1. AAnopheline larvae have no siphon
    2. BCulex larvae breed only in clean water
    3. CCulex larvae have tougher cuticles
    4. DAnopheline larvae feed at the surface

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13. Question 13 · Medium

    In a plague surveillance unit in Beed district, fleas combed from trapped rats yield an average of 2.4 Xenopsylla cheopis per rat. What does this finding indicate?

    1. AFlea control is working well
    2. BA high risk of an outbreak if infection enters
    3. CThe rodent population is falling
    4. DPlague is already spreading among the human population

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14. Question 14 · Medium

    The morning after the filaria MDA round in a village of Purnia, a farm labourer reports fever, headache, body ache and a tender swelling along the spermatic cord. He took the tablets after dinner and has no rash or breathlessness. His brother, who took the same tablets, feels well. What is the most likely cause?

    1. AAcute bacterial epididymitis
    2. BAllergy to albendazole
    3. CReaction to dying parasites
    4. DOverdose of DEC

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15. Question 15 · Medium

    Several children died of Japanese encephalitis in a district of eastern Uttar Pradesh last year, most during the monsoon and post-monsoon months. The district has large paddy areas, scattered piggeries and a limited budget. The district health officer must choose the measure that gives children the most lasting protection. Which should be prioritised?

    1. ABed nets for children under 5
    2. BVaccination of all pigs in the affected villages
    3. CMalathion fogging around houses
    4. DJE vaccination of children under the UIP

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16. Question 16 · Medium

    Human cases of Japanese encephalitis do not contribute to further spread of the virus, although pigs in the same village do. What is the main reason?

    1. ACulex mosquitoes never bite humans
    2. BViraemia in humans is low and short-lived
    3. CThe virus is destroyed in the human liver
    4. DHumans gain lifelong immunity from one bite

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17. Question 17 · Medium

    From a village in Muzaffarpur, a farmer has had fever on and off for 3 months, weight loss and darkening of the skin. The spleen is palpable 8 cm below the costal margin; Hb 7.8 g/dL, WBC 2,600/mm3, platelets 80,000/mm3. Malaria smears are negative. Which test should be done first at the PHC?

    1. ASplenic aspirate for LD bodies
    2. BBone marrow aspiration
    3. CrK39 rapid diagnostic test
    4. DLeishmanin skin test

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18. Question 18 · Medium

    During an outbreak investigation of malaria in a tribal block of Koraput, the entomology team collects larvae from a slow, clear stream beside the hamlet. Under the hand lens the larvae lie parallel to the water surface, have no respiratory siphon and carry palmate hairs on the abdominal segments. To which genus do they belong?

    1. ACulex
    2. BAnopheles
    3. CMansonia
    4. DArmigeres

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19. Question 19 · Hard

    A primigravida at 22 weeks from a tea garden in Dibrugarh is brought to the CHC with fever and chills for two days. Thick and thin smears show P. vivax only; she is conscious, Hb 10.2 g/dL, platelets 1.4 lakh/mm3, no jaundice and no vomiting. Her G6PD test is normal. The fetal heart rate is 148/min and she has no contractions. She worries about relapses because her husband had malaria again and again last year. She has not taken any medicine yet, and her husband works on the same estate. What is the most appropriate treatment plan?

    1. AIV artesunate as for severe malaria
    2. BChloroquine with 14-day primaquine now
    3. CArtemether-lumefantrine with primaquine now
    4. DChloroquine now; primaquine deferred until after delivery

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20. Question 20 · Medium

    Which larvicide can be safely added to stored drinking water in earthen pots and cement tanks to kill Aedes larvae?

    1. AMineral oil
    2. BTemephos
    3. CParis green
    4. DFenthion

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21. Question 21 · Easy

    A painless black eschar in the groin is noticed in a sugarcane worker from Vellore who has had 7 days of high fever, severe headache and tender regional lymph nodes. Pulse is 88/min despite a temperature of 39.6 °C; platelets 90,000/mm3 and AST 140 U/L. Malaria and dengue tests are negative. Which arthropod transmits the likely infection?

    1. AOriental rat flea
    2. BHard tick (Haemaphysalis spinigera)
    3. CHuman body louse
    4. DLarval trombiculid mite (chigger)

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22. Question 22 · Medium

    In malaria microscopy, why is a thick smear examined along with a thin smear?

    1. AIt shows parasite morphology better
    2. BIt is more sensitive for detecting parasites
    3. CIt preserves red cell outlines
    4. DIt identifies the infecting species more reliably

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23. Question 23 · Medium

    A rickshaw puller from Saran district has had fever for 6 weeks, weight loss and a large spleen; Hb 8.1 g/dL, WBC 3,000/mm3 and the rK39 test is positive. He is HIV-negative and has normal renal function. He is admitted to the district hospital. Which treatment is preferred under India's kala-azar elimination programme?

    1. ASingle-dose liposomal amphotericin B
    2. BSodium stibogluconate injections for 30 days
    3. CMiltefosine alone for 28 days
    4. DParomomycin alone for 21 days

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24. Question 24 · Hard

    After five annual rounds of mass drug administration with good coverage, a district in Uttar Pradesh does night blood surveys at sentinel and spot-check sites. The microfilaria rate is below 1% at every site. The district health society wants to stop MDA immediately and announce elimination. As the district vector-borne disease officer, what should be done next?

    1. ADo a transmission assessment survey in children
    2. BStop MDA and declare elimination at once
    3. CContinue MDA for five more rounds
    4. DRepeat night blood surveys monthly

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25. Question 25 · Medium

    During the annual mass drug administration (DEC plus albendazole) for lymphatic filariasis in a Bihar village, the drug distributor asks whom to exclude. Consider: 1. Pregnant women. 2. Children below 2 years. 3. Seriously ill persons. 4. People known to have microfilaraemia. Which groups should NOT be given the drugs?

    1. A2 and 3 only
    2. B1, 2, 3 and 4
    3. C1, 2 and 3 only
    4. D1, 3 and 4 only

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