MLT GlobeParasitology: Arthropods & vectors
17 Parasitology MCQs on Arthropods & vectors with answers and explanations.
A patient has intensely itchy burrows between the fingers. Which specimen is examined to confirm scabies?
Scraping a burrow and examining it in mineral oil or KOH reveals Sarcoptes scabiei mites, eggs or faecal pellets.
Hexapoda (insects) have three pairs of legs. Which of these is a hexapod?
Bed bugs are insects with six legs. Ticks and mites are arachnids with four pairs of legs in the adult stage.
The term 'infestation' is used for parasites that live on the host's surface. Which group does this describe?
Infestation refers to ectoparasites (lice, mites, ticks) on skin or hair; endoparasites inside the body cause infection.
House flies carry pathogens on their legs and mouthparts from faeces to food. Which disease category do they chiefly spread?
Musca domestica acts as a mechanical carrier of enteric bacteria, protozoan cysts and helminth eggs to food. It does not bite, so it cannot transmit blood-borne pathogens.
Chagas disease is spread when faeces of which blood-sucking insect contaminate the bite wound?
Triatomine bugs deposit T. cruzi trypomastigotes in faeces near the bite. Tsetse flies transmit African trypanosomiasis; sandflies, Leishmania.
The house fly undergoes complete metamorphosis. Which order of stages is correct?
Musca domestica develops egg to larva (maggot) to pupa to adult. A nymph stage occurs in incomplete metamorphosis (e.g. bugs, lice).
Which class of arthropods contains the majority of disease vectors (mosquitoes, sandflies, lice, fleas)?
Most vectors are insects. Arachnids (ticks, mites) are important too but fewer; crustaceans act mainly as intermediate hosts (e.g. copepods).
A parasite carried on an insect's body without undergoing development or multiplication is spread by a 'mechanical vector'. Which is a classic example?
House flies passively carry cysts, eggs and bacteria. Sandflies, mosquitoes and tsetse flies are biological vectors in which the parasite develops.
A patient has itchy burrows between the fingers. Which laboratory procedure best confirms scabies?
Sarcoptes scabiei lives in epidermal burrows, so scraping the burrow and examining it in oil or KOH shows mites, eggs or scybala. Blood and stool tests are not useful.
Myiasis of the skin is caused by infestation with:
Myiasis is tissue infestation by dipteran fly larvae. Scabies is caused by mites, and cercarial dermatitis by schistosome larvae.
An arthropod with three pairs of legs and a body in three parts belongs to class:
Insects (lice, fleas, mosquitoes) have head, thorax, abdomen and six legs. Adult arachnids such as ticks and mites have four pairs.
Ticks and mites belong to which phylum?
Ticks and mites are arachnids within the phylum Arthropoda, with jointed legs and an exoskeleton. Nematodes are roundworms.
Which arthropod transmits the greatest burden of human parasitic disease?
Mosquitoes spread malaria and lymphatic filariasis. Bees, ladybirds and spiders are not vectors.
Which infection is transmitted by the human body louse?
Body lice transmit Borrelia recurrentis (louse-borne relapsing fever), as well as epidemic typhus and trench fever. Leishmaniasis is sandfly-borne and malaria mosquito-borne.
Horse flies (Tabanus) are known to transmit which infection mechanically via contaminated mouthparts?
Tabanids can mechanically transmit Bacillus anthracis and Francisella tularensis. Leishmaniasis is spread by sandflies, malaria by Anopheles, and typhoid faeco-orally.
In the Old World, the sandfly genus that transmits kala-azar is:
Phlebotomus species transmit Leishmania in Asia, Africa and Europe, and Lutzomyia in the Americas. Simulium transmits onchocerciasis and Glossina transmits sleeping sickness.
Cutaneous leishmaniasis in the Americas is transmitted by sandflies of the genus:
New World sandflies belong to Lutzomyia, while Old World vectors are Phlebotomus. Glossina is the tsetse fly.