Which of the following is a common strategy for overcoming host defenses in parasitology?

Utilizing both vertical and horizontal transmission is a common strategy for overcoming host defenses in parasitology because it increases the chances of a parasite's survival and propagation. Vertical transmission refers to the transfer of parasites from parent to offspring, which can ensure that a sufficient number of parasites are present in the next generation, bypassing many host defenses that would otherwise intercept a new infection. Horizontal transmission, on the other hand, involves the spread of parasites from one individual to another, often through direct contact or intermediate vectors. This dual approach allows parasites to exploit different methods of transmission to establish and maintain their populations, enhancing their chances against the host’s immune responses.

The other options do not encapsulate effective strategies for overcoming host defenses in a comprehensive manner. Infecting only a specific age group may limit the parasite's potential host range, while staying dormant within the host can be effective for some but does not actively engage with host defenses. Exclusively relying on external vectors could also restrict the parasite’s transmission opportunities and does not provide a multilayered approach to overcoming host defenses.