Which of the following best explains why symptoms of protozoan and helminthic diseases occur in infected individuals?

• A. The direct damage caused by the parasites to host tissues
• B. The production of toxins by the parasites
• C. The replication of bacteria within host cells
• D. The host's immune response to viral antigens

Answer: (A)

Verified step by step guidance

1. Identify the type of pathogens involved in the question: protozoans and helminths, which are eukaryotic parasites, not bacteria or viruses.
2. Understand that protozoan and helminthic diseases cause symptoms primarily through physical interactions with host tissues rather than through bacterial replication or viral antigen responses.
3. Recognize that unlike some bacteria, protozoans and helminths typically do not produce toxins as their main pathogenic mechanism.
4. Consider that the symptoms arise mainly because these parasites directly damage host tissues by feeding on cells, migrating through tissues, or causing mechanical injury.
5. Conclude that the best explanation for symptoms is the direct damage caused by the parasites to host tissues, rather than toxin production, bacterial replication, or immune responses to viral antigens.