Medical Entomology Cat Practice | MCQ Quiz | OmpathStudy Kenya

Question 1

A mosquito species that prefers to feed on humans indoors and rests inside houses after feeding would be classified as

Accepted Answer

Endophagic and endophilic — Endophagic refers to feeding indoors, while endophilic refers to resting indoors after blood meal digestion. This combination makes a vector particularly dangerous for indoor transmission of diseases like malaria.

Question 2

Which of the following best describes the strategy of zooprophylaxis in vector control?

Accepted Answer

Diverting vectors to feed on animals instead of humans — Zooprophylaxis involves diverting zoophilic vectors away from humans by providing alternative animal hosts, thereby reducing human-vector contact and disease transmission.

Question 3

The term "hemimetabolous" in reference to tick development means

Accepted Answer

Incomplete metamorphosis without pupal stage — Hemimetabolous development is incomplete metamorphosis proceeding through egg, nymph, and adult stages without a pupal stage. This is seen in ticks, bedbugs, and cockroaches.

Question 4

Nidicolous behavior in arthropod vectors refers to

Accepted Answer

Remaining close to the host's resting place — Nidicolous behavior means the vector stays near the host's home or resting area. Soft ticks (Argasidae) exhibit this behavior, while hard ticks (Ixodidae) are non-nidicolous and move away from the host's dwelling.

Question 5

Which characteristic distinguishes diurnal from nocturnal vectors?

Accepted Answer

Time of day when they are most active — Diurnal vectors are active during the day (e.g., Aedes aegypti), while nocturnal vectors are active at night (e.g., Anopheles mosquitoes, cockroaches). This affects control strategies and personal protection measures.

Question 6

A "questing behavior" in ticks refers to

Accepted Answer

Climbing vegetation and extending limbs to attach to passing hosts — Questing is the characteristic behavior of hard ticks where they climb up vegetation and extend their forelegs to attach to warm-blooded animals that pass by. This is how they locate and attach to potential hosts.

Question 7

In the context of vector-borne diseases, what does "mechanical transmission" mean?

Accepted Answer

The pathogen is physically carried by the vector without multiplication — Mechanical transmission occurs when a vector carries a pathogen on its body parts (e.g., legs, mouthparts) without the pathogen undergoing development or multiplication in the vector. Houseflies mechanically transmit many pathogens.

Question 8

The term "exophagic" describes a vector that

Accepted Answer

Feeds on blood outdoors — Exophagic means feeding outdoors. This is important for vector control because exophagic vectors are less affected by indoor residual spraying (IRS) compared to endophagic vectors.

Question 9

Trans-ovarial transmission in vectors refers to

Accepted Answer

Transmission from infected female to her offspring through eggs — Trans-ovarial (vertical) transmission occurs when an infected female vector passes the pathogen to her eggs, resulting in infected offspring. This is seen in soft ticks transmitting Borrelia (relapsing fever).

Question 10

Which of the following vectors exhibits incomplete metamorphosis?

Accepted Answer

Cockroaches — Cockroaches, ticks, and bedbugs undergo incomplete metamorphosis (egg → nymph → adult) without a pupal stage. Mosquitoes and houseflies undergo complete metamorphosis (egg → larva → pupa → adult). --- ## SECTION B: COCKROACHES & BEDBUGS (Questions 11-16)

Question 11

Which cockroach species is commonly known as the German cockroach?

Accepted Answer

Blattella germanica — Blattella germanica is the German cockroach, one of the most common household pest cockroaches worldwide. Periplaneta americana is the American cockroach, and Blatta orientalis is the Oriental cockroach.

Question 12

The primary medical importance of cockroaches includes all of the following EXCEPT

Accepted Answer

Biological vector of malaria — Cockroaches are NOT biological vectors of malaria. They are mechanical vectors that transmit bacteria like E. coli and cause allergies through inhalation of their body parts and feces. Malaria is transmitted by Anopheles mosquitoes.

Question 13

What is the rostrum count characteristic of bedbugs?

Accepted Answer

Five-segmented rostrum — Bedbugs (Cimicidae) have a five-segmented rostrum (proboscis) used for piercing skin and taking blood meals. This is a key morphological feature for identification.

Question 14

Bedbugs are primarily active during

Accepted Answer

Nighttime — Bedbugs are nocturnal feeders with an aversion to light. They hide in cracks and crevices during the day and emerge at night to feed on sleeping hosts.

Question 15

Which disease is mechanically transmitted by bedbugs?

Accepted Answer

Anthrax (Bacillus anthracis) — Bedbugs can mechanically transmit Bacillus anthracis (anthrax). They are also associated with transmission of Borrelia (Lyme disease) and may transmit filarial nematodes.

Question 16

Boric acid powder works as a cockroach control agent primarily through

Accepted Answer

Contact and stomach poison causing dehydration — Boric acid acts as both a contact and stomach poison. It adheres to the cockroach's body, is ingested during grooming, and causes dehydration by damaging the exoskeleton and digestive system. --- ## SECTION C: FLIES - MUSCIDAE, FANIDAE & TABANIDAE (Questions 17-24)

Question 17

Which housefly species is known as the "stable fly" and is a painful biter?

Accepted Answer

Stomoxys calcitrans — Stomoxys calcitrans (stable fly) is a biting fly that takes blood meals and causes painful bites. Unlike the common housefly (Musca domestica), which only feeds on liquid organic matter, Stomoxys is a true biter.

Question 18

Houseflies (Musca domestica) are primarily important as

Accepted Answer

Mechanical vectors carrying pathogens on body parts — Houseflies are mechanical vectors that carry pathogens (bacteria, viruses, protozoa, helminth eggs) on their body parts, especially legs and mouthparts, contaminating food and surfaces without the pathogen multiplying in the fly.

Question 19

Obligate myiasis differs from facultative myiasis in that obligate myiasis

Accepted Answer

Requires living tissue to complete the larval life cycle — Obligate myiasis requires living tissue for larval development (e.g., screwworm flies). Facultative myiasis can occur in living or dead tissue. Accidental myiasis occurs when larvae are ingested by chance.

Question 20

In maggot therapy using Lucilia sericata, the larvae are used to

Accepted Answer

Debride dead and necrotic tissue from wounds — Sterile maggots of Lucilia sericata selectively feed on dead, necrotic tissue (debridement) while leaving healthy tissue intact. This cleans wounds and promotes healing, a practice called maggot debridement therapy.

Question 21

Horse flies (Tabanidae) are primarily active during

Accepted Answer

Daytime, especially in bright sunlight — Horse flies are diurnal (day-active) and prefer bright, sunny conditions. They are persistent biters and are attracted to movement and dark objects, making them particularly troublesome during daytime outdoor activities.

Question 22

Which genus of horse flies is attracted by smoke?

Accepted Answer

Chrysops — Chrysops (deer flies) are specifically noted to be attracted by smoke, unlike other Tabanidae genera. This is an unusual characteristic that can be important in certain environments.

Question 23

Horse flies are involved in the mechanical transmission of all EXCEPT

Accepted Answer

Bacillus anthracis (Anthrax) — Horse flies mechanically transmit anthrax, tularemia, and Lyme disease pathogens. Malaria is biologically transmitted by Anopheles mosquitoes, not mechanically by horse flies.

Question 24

UV light traps for housefly control work by

Accepted Answer

Attracting flies with UV light then electrocuting them — UV light traps (insectocutors) attract flies using ultraviolet light, which flies find attractive. When flies approach, they are electrocuted by an electric grid, providing a non-chemical control method. --- ## SECTION D: TICKS - IXODIDAE & ARGASIDAE (Questions 25-34)

Question 25

Hard ticks (Ixodidae) differ from soft ticks (Argasidae) in that hard ticks

Accepted Answer

Remain attached to hosts for longer periods (1-4 weeks) — Hard ticks attach to hosts for extended periods (1-4 weeks) to feed. Soft ticks feed quickly (minutes to hours) and drop off. Hard ticks are non-nidicolous (move away from host's home), while soft ticks are nidicolous.

Question 26

How many nymphal stages do hard ticks (Ixodidae) have?

Accepted Answer

One — Hard ticks have only ONE nymphal stage (egg → larva → nymph → adult). In contrast, soft ticks have multiple nymphal stages, usually 4-5 nymphal instars.

Question 27

Tick paralysis is caused by

Accepted Answer

Toxins in female tick saliva during prolonged feeding — Tick paralysis results from neurotoxins in female tick saliva that are pumped into the host during the long feeding period. It causes ascending paralysis starting from the legs and can lead to respiratory failure, especially in children.

Question 28

Which tick genus is classified as a one-host tick?

Accepted Answer

Boophilus — Boophilus is a one-host tick where all stages (larva, nymph, adult) feed on the same individual host. Hyalomma is a two-host tick, while many other genera are three-host ticks.

Question 29

The spirochete Borrelia burgdorferi, which causes Lyme disease, is transmitted by

Accepted Answer

Ticks — Borrelia burgdorferi, the causative agent of Lyme disease, is transmitted by ixodid (hard) ticks, particularly Ixodes species. The disease is characterized by erythema migrans (bull's-eye rash) and can affect multiple organ systems.

Question 30

Soft ticks (Argasidae) are described as nidicolous, meaning they

Accepted Answer

Stay close to the host's resting place — Nidicolous behavior means soft ticks remain in or near the host's dwelling (burrows, nests, houses). They make short feeding visits and quickly return to hiding places near the host, unlike hard ticks which move away.

Question 31

Trans-ovarial transmission in soft ticks is significant for which disease?

Accepted Answer

Tick-borne relapsing fever — Soft ticks transmit Borrelia species (spirochetes) causing tick-borne relapsing fever. The bacteria can be passed trans-ovarially from infected females to their eggs, making the next generation of ticks infectious from birth.

Question 32

The proper method for removing an attached tick involves

Accepted Answer

Applying petroleum jelly, waiting 3-5 minutes, then pulling slowly — The correct method is to apply petroleum jelly (Vaseline) on the tick, wait 3-5 minutes for it to release or suffocate, then pull slowly to avoid leaving mouthparts embedded in the skin, which can cause infection.

Question 33

Q fever, a zoonotic disease, is caused by which organism and transmitted by ticks?

Accepted Answer

Coxiella burnetii (bacterium) — Q fever is caused by the bacterium Coxiella burnetii and can be transmitted by ticks. It can also be transmitted through inhalation of contaminated aerosols from infected animals, particularly livestock.

Question 34

In cattle dipping for tick control, which insecticide is commonly used due to its persistence?

Accepted Answer

Deltamethrin — Deltamethrin, a Class II pyrethroid, is preferred for cattle dipping because of its persistence (long-lasting effectiveness). It remains effective on the animal's coat for extended periods, providing continued protection against ticks. --- ## SECTION E: CHEMICAL CONTROL - MODE OF ACTION (Questions 35-44)

Question 35

Pyrethroid insecticides work by

Accepted Answer

Keeping sodium channels open longer causing hyperexcitation — Pyrethroids target voltage-gated sodium channels (VGSCs) in nerve cells, preventing them from closing properly. This causes continuous sodium influx, leading to hyperexcitation, paralysis, and death of the insect.

Question 36

The primary target of organophosphate and carbamate insecticides is

Accepted Answer

Acetylcholinesterase enzyme — Both organophosphates and carbamates inhibit acetylcholinesterase (AChE), the enzyme that breaks down acetylcholine. This causes acetylcholine accumulation, leading to continuous nerve stimulation, hyperexcitation, and paralysis.

Question 37

DDT was banned in Kenya primarily because

Accepted Answer

It persists in the environment and bioaccumulates — DDT is a persistent organic pollutant that accumulates in the environment and food chain (bioaccumulation). Despite its effectiveness, its environmental persistence and potential long-term effects led to its ban in many countries, including Kenya.

Question 38

Rotenone's mode of action involves

Accepted Answer

Inhibiting Complex I of the electron transport chain — Rotenone inhibits Complex I in the mitochondrial electron transport chain, preventing electron flow and effectively shutting down cellular respiration. This depletes ATP production, leading to cell death and insect paralysis.

Question 39

Nicotine extracted from tobacco plants works as an insecticide by

Accepted Answer

Mimicking acetylcholine and causing continuous stimulation — Nicotine binds to nicotinic acetylcholine receptors, mimicking the action of acetylcholine. This causes continuous stimulation of the nervous system, leading to paralysis and convulsions in insects.

Question 40

Which insecticide class works by affecting the GABA-chloride channel complex?

Accepted Answer

Chlorinated alicyclics (organochlorines) — Chlorinated alicyclic compounds (like chlorinated camphor) interfere with the GABA-A receptor-chloride channel complex, blocking chloride ion flow and disrupting neuronal inhibition, causing hyperexcitation.

Question 41

Ryanodine receptors, targeted by the botanical insecticide ryanodine, are

Accepted Answer

Calcium channels in sarcoplasmic reticulum — Ryanodine targets ryanodine receptors, which are calcium channels in the sarcoplasmic reticulum of muscle and nerve cells. It causes uncontrolled calcium release, leading to muscle overstimulation and paralysis.

Question 42

The LD50 classification for insecticides with a value of 51-500 is labeled

Accepted Answer

Blue (moderately toxi — The WHO classification uses color codes: Red (1-50, very toxic), Yellow (51-500, toxic), Blue (501-5000, moderately toxic), and Green ( 5000, low toxicity). This helps users understand the relative danger of pesticides.

Question 43

Sabadilla alkaloids (veratridine and cevadine) kill insects by

Accepted Answer

Binding to sodium channels preventing closure — Sabadilla alkaloids bind to voltage-sensitive sodium channels in insect nerve membranes, preventing them from closing. This causes continuous sodium influx and permanent depolarization, resulting in paralysis and death.

Question 44

Indoor Residual Spraying (IRS) is most effective against vectors that are

Accepted Answer

Endophagic and endophilic — IRS is most effective against endophagic (indoor feeding) and endophilic (indoor resting) vectors because they come into contact with insecticide-treated walls. Exophagic/exophilic vectors spend less time indoors and are less affected. --- ## SECTION F: BIOLOGICAL CONTROL & INTEGRATED MANAGEMENT (Questions 45-50)

Question 45

Gambusia affinis is used in biological control of mosquitoes by

Accepted Answer

Feeding on mosquito eggs and larvae — Gambusia affinis (mosquito fish) is an effective biological control agent that feeds on mosquito eggs and larvae in water bodies, reducing mosquito populations without chemical insecticides.

Question 46

The Sterile Insect Technique (SIT) controls vector populations by

Accepted Answer

Releasing sterilized males that mate unsuccessfully with wild females — SIT involves mass-rearing vectors, sterilizing males (usually with radiation), and releasing them. When sterile males mate with wild females, no offspring are produced, leading to population decline over generations.

Question 47

Wolbachia pipientis causes cytoplasmic incompatibility, which results in

Accepted Answer

Infected males mating with uninfected females producing non-viable eggs — When Wolbachia-infected males mate with uninfected females, the embryos die (cytoplasmic incompatibility). This reduces population and Wolbachia-infected mosquitoes have reduced vector competence for arboviruses.

Question 48

Bacillus thuringiensis israelensis (Bti) controls mosquito larvae through

Accepted Answer

Production of enterotoxins that paralyze and kill larvae — Bti produces crystal proteins (Cry toxins) that are toxic to mosquito larvae when ingested. The toxins damage the midgut epithelium, causing paralysis and death. It's specific to Diptera larvae and environmentally safe.

Question 49

Toxorhynchites (elephant mosquito) larvae are useful in biological control because they

Accepted Answer

Feed on other mosquito larvae — Toxorhynchites larvae are predaceous and feed on larvae of other mosquito species, including disease vectors like Anopheles and Aedes. Adults don't take blood meals, making them ideal biological control agents.

Question 50

The use of paratransgenic vectors in disease control involves

Accepted Answer

Modifying vector gut bacteria to express anti-parasite molecules — Paratransgenesis involves genetically modifying symbiotic bacteria (like Sodalis in tsetse flies) that live in vectors to produce molecules that block parasite development, making the vector refractory (unable to transmit disease). --- ## ANSWER KEY Section A (1-10): B, B, B, B, B, B, B, A, B, C Section B (11-16): B, C, B, C, B, B Section C (17-24): C, B, B, C, C, B, D, B Section D (25-34): C, B, C, C, B, B, B, C, C, B Section E (35-44): C, B, B, B, C, C, B, B, B, B Section F (45-50): C, B, B, B, B, B --- ## SCORING GUIDE - 45-50 correct: Excellent - Well prepared for exam - 40-44 correct: Very Good - Minor review needed - 35-39 correct: Good - Review weak areas - 30-34 correct: Fair - Significant review needed - Below 30: Review all material thoroughly --- End of Examination Review your notes thoroughly, focusing on areas where you scored lower. Pay special attention to modes of action, disease transmission mechanisms, and vector control strategies.

Medical Entomology Cat Practice | MCQ Quiz | OmpathStudy Kenya

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