How can Anopheles larvae be told apart from Culex larvae in a water sample?

They lie parallel to the surface and lack a siphon

They are comma-shaped with two breathing trumpets

They pierce plant roots with a sharp siphon

They hang head-down from a long breathing siphon

In the coastal wetlands of Kerala, control of Mansonia mosquitoes, the vectors of Brugia malayi, depends on removing water plants such as Pistia because Mansonia larvae:

Obtain air by piercing the roots of these plants

Are sheltered there from larvivorous fish

Feed only on algae growing on these plants

Need the shade of the leaves to develop

A 48-year-old farmer from Pathanamthitta has had high fever, headache and myalgia for 6 days. There is a painless black-crusted ulcer in his groin with tender regional lymph nodes. Weil-Felix test: OX-K 1:320, OX-19 negative, OX-2 negative. Platelets 90,000/µL. The vector and the best preventive measure are:

Larval trombiculid mites; clearing scrub and using repellents

Hard ticks; removing ticks from cattle and dogs

Body lice; delousing clothes and bedding

Rat fleas; rodent control with insecticide dusting

How does a person usually acquire epidemic typhus from the human body louse?

By scratching infected louse faeces into the skin

By crushing the louse and releasing its body fluid

By regurgitation from the louse's blocked foregut

By injection of rickettsiae in the louse's saliva

Medical entomology

8 Kerala MSc MLT Entrance practice questions on Medical entomology, part of Microbiology. The first 8 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
How can Anopheles larvae be told apart from Culex larvae in a water sample?
1. AThey lie parallel to the surface and lack a siphon
2. BThey are comma-shaped with two breathing trumpets
3. CThey pierce plant roots with a sharp siphon
4. DThey hang head-down from a long breathing siphon
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Answer: A · They lie parallel to the surface and lack a siphon
Anopheles larvae have no respiratory siphon; they breathe through spiracles on the back and lie horizontally just under the surface, held by palmate hairs. Culex and Aedes larvae have a siphon and hang at an angle, head down, from the surface film. Mansonia larvae pierce the roots of aquatic plants with a modified siphon to obtain air. These differences guide larval surveys and the choice of control measures.
- B: A comma shape with breathing trumpets describes mosquito pupae, not larvae.
- C: Piercing plant roots with the siphon is typical of Mansonia larvae.
- D: Hanging head-down from a siphon describes Culex and Aedes larvae.
Question 2 · Medium
In the coastal wetlands of Kerala, control of Mansonia mosquitoes, the vectors of Brugia malayi, depends on removing water plants such as Pistia because Mansonia larvae:
1. AObtain air by piercing the roots of these plants
2. BAre sheltered there from larvivorous fish
3. CFeed only on algae growing on these plants
4. DNeed the shade of the leaves to develop
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Answer: A · Obtain air by piercing the roots of these plants
Mansonia larvae and pupae do not come to the surface to breathe; they insert their sharp siphon or trumpets into the air-filled roots of water plants such as Pistia, water hyacinth and Salvinia. Removing these plants by hand or with herbicides therefore cuts off the oxygen supply of the immature stages. Surface larvicidal oils work poorly against them because they rarely surface. Mansonia annulifera and M. uniformis transmit Brugia malayi in the wetlands of Kerala.
- B: Fish are not the reason; plant removal works by cutting off the larvae's air supply.
- C: Mansonia larvae are filter feeders; the plants matter as an air supply, not as food.
- D: Shade is not the key need; the larvae depend on the roots for air.
Question 3 · Easy
Which disease does the oriental rat flea, Xenopsylla cheopis, classically transmit?
1. APlague
2. BRelapsing fever
3. CScrub typhus
4. DEpidemic typhus
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Answer: A · Plague
Yersinia pestis multiplies in the flea's proventriculus and blocks it, so the hungry 'blocked' flea bites repeatedly and regurgitates bacilli into the bite wound. When rats die in an epizootic, their fleas move to people and bubonic plague follows; a fall of dead rats in a locality is a warning sign. X. cheopis also transmits murine (endemic) typhus. Control combines insecticide against fleas with rodent control, in that order.
- B: Epidemic relapsing fever is louse-borne and endemic relapsing fever is tick-borne.
- C: Scrub typhus is spread by larval trombiculid mites (chiggers).
- D: Epidemic typhus is spread by the body louse, Pediculus humanus corporis.
Question 4 · Hard
A 48-year-old farmer from Pathanamthitta has had high fever, headache and myalgia for 6 days. There is a painless black-crusted ulcer in his groin with tender regional lymph nodes. Weil-Felix test: OX-K 1:320, OX-19 negative, OX-2 negative. Platelets 90,000/µL. The vector and the best preventive measure are:
1. ALarval trombiculid mites; clearing scrub and using repellents
2. BHard ticks; removing ticks from cattle and dogs
3. CBody lice; delousing clothes and bedding
4. DRat fleas; rodent control with insecticide dusting
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Answer: A · Larval trombiculid mites; clearing scrub and using repellents
A black eschar with regional lymphadenopathy and fever, and a Weil-Felix reaction only with Proteus OX-K, point to scrub typhus caused by Orientia tsutsugamushi; IgM ELISA is now preferred for confirmation. It is transmitted by the larval stage (chigger) of trombiculid mites such as Leptotrombidium deliense, which live in scrub and grassy areas. Prevention relies on clearing vegetation around homes, protective clothing, mite repellents and acaricide treatment of infested ground. Tick-borne spotted fevers react with OX-19 and OX-2, and louse- and flea-borne typhus react with OX-19.
- B: Hard ticks transmit spotted fevers, which react with OX-19 and OX-2, not OX-K alone.
- C: Body lice transmit epidemic typhus, which reacts with OX-19 and does not cause an eschar.
- D: Rat fleas transmit plague and murine typhus; murine typhus reacts with OX-19.
Question 5 · Medium
How does a person usually acquire epidemic typhus from the human body louse?
1. ABy crushing the louse and releasing its body fluid
2. BBy regurgitation from the louse's blocked foregut
3. CBy scratching infected louse faeces into the skin
4. DBy injection of rickettsiae in the louse's saliva
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Answer: C · By scratching infected louse faeces into the skin
Rickettsia prowazekii multiplies in the gut cells of Pediculus humanus corporis and is passed in large numbers in its faeces. The bite itches, and scratching rubs the infected faeces into the abrasion; dried faeces can also infect through the conjunctiva or by inhalation. The louse itself dies of the infection, so there is no passage to its eggs. Delousing of clothes and bedding with insecticide dusting is therefore the main control in outbreaks.
- A: Crushing the louse to release its body fluid is how louse-borne relapsing fever (Borrelia recurrentis) is acquired.
- B: Regurgitation from a blocked foregut is how the rat flea transmits plague.
- D: The louse saliva does not carry the rickettsiae; spread is faecal.
Question 6 · Medium
Anti-larval work against dengue and chikungunya concentrates on emptying and covering domestic water containers because Aedes aegypti:
1. ABreeds in polluted drains, septic tanks and cesspits
2. BBreeds in clean water held in artificial containers
3. CBreeds attached to the roots of floating water plants
4. DBreeds in paddy fields and large irrigation channels
Answer and explanation in LearnFree account
Question 7 · Easy
Visceral leishmaniasis (kala-azar) in India is transmitted by the bite of:
1. AThe mosquito Anopheles culicifacies
2. BThe tsetse fly Glossina palpalis
3. CThe mosquito Culex quinquefasciatus
4. DThe sandfly Phlebotomus argentipes
Answer and explanation in LearnFree account
Question 8 · Hard
In March, a 45-year-old man who collects firewood in a forest in Wayanad develops sudden high fever, severe headache, myalgia and bleeding from the gums. Villagers report several monkeys found dead in the forest over the past month. Platelets are 60,000/µL and the total WBC count is 2,800/µL. Malaria antigen and dengue NS1 tests are negative. Which vector most likely transmitted his infection?
1. AThe mosquito Culex tritaeniorhynchus
2. BThe mosquito Aedes albopictus
3. CThe soft tick Ornithodoros moubata
4. DThe hard tick Haemaphysalis spinigera
Answer and explanation in LearnFree account

Medical entomology

How can Anopheles larvae be told apart from Culex larvae in a water sample?

In the coastal wetlands of Kerala, control of Mansonia mosquitoes, the vectors of Brugia malayi, depends on removing water plants such as Pistia because Mansonia larvae:

Which disease does the oriental rat flea, Xenopsylla cheopis, classically transmit?

How does a person usually acquire epidemic typhus from the human body louse?

Anti-larval work against dengue and chikungunya concentrates on emptying and covering domestic water containers because Aedes aegypti:

Visceral leishmaniasis (kala-azar) in India is transmitted by the bite of: