This has no alternate host

The correct option is Ascaris lumbricoides.

To understand why this is the correct answer, let's break down the concepts of host lifecycles in parasites:
1. Monogenetic Parasites: These are parasites that complete their entire lifecycle within a single host. They do not require an intermediate or alternate host to develop or transmit to another primary host.
2. Digenetic Parasites: These parasites require two (or more) different host species to complete their lifecycle. Typically, they have a primary host (where sexual reproduction occurs) and an intermediate/secondary/alternate host (where asexual development or larval stages occur).

Let's evaluate each option to determine if they require an alternate host:
- Plasmodium vivax: This is a digenetic parasite. It requires two hosts: female Anopheles mosquitoes (where sexual reproduction occurs) and humans (where asexual reproduction occurs). Thus, it has an alternate host.
- Tape worm (e.g., Taenia solium): This is digenetic. It requires humans as the primary host and pigs (or cattle) as the intermediate/alternate host to complete its lifecycle.
- Fasciola hepatica (Sheep liver fluke): This is digenetic. Its lifecycle involves sheep (or humans) as the primary host and freshwater snails as the intermediate/alternate host.
- Ascaris lumbricoides (Giant roundworm): This is a monogenetic parasite. It completes its entire lifecycle in a single host, which is the human. Infection occurs directly through the ingestion of embryonated eggs from contaminated soil, food, or water. There is no intermediate or alternate host involved in its lifecycle.

Therefore, Ascaris lumbricoides is the only parasite among the options that has no alternate host.