Which of the following has no alternate host?
A. Tape worm
B. Ascaris lumbricoides
C. Plasmodium vivax
D. Fasciola hepatica
D. Fasciola hepatica
The correct answer is D. Fasciola hepatica. Fasciola hepatica, also known as the sheep liver fluke, does not have an alternate host. It is a parasitic flatworm that infects the liver of various mammals, including sheep and humans. Unlike other parasites mentioned, Fasciola hepatica has a direct life cycle and does not require an intermediate host for its lifecycle.
To determine which organism has no alternate host, we need to understand the concept of an alternate host. An alternate host is a host that harbors a parasite during a particular stage of its life cycle. Let's examine each option and see if they have alternate hosts.
A. Tape worm: Taeniasis, caused by tapeworm infection, has two hosts - the definitive host (usually humans) and the intermediate host (usually cattle or pigs). The definitive host is where the adult tapeworm lives and reproduces, while the intermediate host harbors the larval stage of the tapeworm. Therefore, the tapeworm (option A) does have an alternate host.
B. Ascaris lumbricoides: Ascaris lumbricoides is an intestinal roundworm that infects humans. It does not have an alternate host, as it completes its entire life cycle exclusively in humans. Therefore, the answer could be B.
C. Plasmodium vivax: Plasmodium vivax is the causative agent of malaria, which is transmitted to humans through the bite of infected Anopheles mosquitoes. In the mosquito, the Plasmodium undergoes several stages of development before it can be transmitted to another human. Therefore, mosquitoes act as alternate hosts for Plasmodium vivax. So, option C is not the correct answer.
D. Fasciola hepatica: Fasciola hepatica is a parasitic flatworm that infects livestock like sheep and cattle. Its life cycle involves multiple hosts, including snails as intermediate hosts and mammals (such as humans, sheep, or cattle) as definitive hosts. Therefore, Fasciola hepatica does have an alternate host.
Based on the above analysis, the correct answer is option B, Ascaris lumbricoides, as it does not have an alternate host in its life cycle.