Which organism is a blood-sucking ectoparasite associated with human infestation?

• A. Plasmodium falciparum
• B. Pediculus humanus/Phthirus pubis
• C. Cimex lectularius
• D. Rickettsia prowazekii

Answer: (B)

Blood-sucking ectoparasites that infest humans are the organisms that live on the outside of the body and feed on blood. The classic human infestation caused by this behavior is pediculosis, the condition of lice infestation. Pediculus humanus (body louse) and Phthirus pubis (crab louse) attach to hair or clothing and bite to take blood meals, leading to itching and possible secondary infections. This direct blood-feeding on the surface of the body is what makes them quintessential ectoparasites.

The other options don’t fit as the best answer in this context. Plasmodium falciparum is a protozoan parasite that lives inside red blood cells and is transmitted by mosquitoes, not an external blood-feeding parasite. Cimex lectularius, the bed bug, also feeds on blood and causes bites, but the term most associated with infestation in exams is pediculosis due to lice. Rickettsia prowazekii is a bacterium carried by lice and causing disease, not an ectoparasite itself.

So the organism that best matches a blood-sucking ectoparasite associated with human infestation is the lice: Pediculus humanus/Phthirus pubis.