Which of the following is not listed as a type of pathogen?

• A. Bacteria
• B. Rickettsiae
• C. Algal
• D. Fungi

Answer: (C)

Pathogens are typically categorized into bacteria, rickettsiae, fungi, viruses, protozoa, and prions. Algae, while some species can produce toxins or cause illness, are not included as a standard pathogen type in this taxonomy. So “Algal” doesn’t belong to the conventional list of pathogen types, making it the best answer. The other options—bacteria, rickettsiae, and fungi—are recognized pathogen categories, whereas algae are photosynthetic organisms and not treated as a classic pathogen type in this context.