Which statement about Avian Influenza H/N types is true?

• A. There are at least 16 different H types (H1-H16) and 9 different N types (N1-N9).
• B. There are only two H types and three N types.
• C. H types do not pair with N types.
• D. All H-N combinations cause disease in humans.

Answer: (A)

H and N describe the two main surface proteins of influenza A viruses, hemagglutinin and neuraminidase, and each unique pairing defines a distinct avian influenza subtype. There are many of these subtypes circulating in birds, with identified H types ranging up to at least H16 and N types up to N9. That breadth explains why this statement is true: the diversity of H and N subtypes is wide, so “at least 16 H types and 9 N types” reflects the real variety seen in avian influenza. It’s also useful to remember that only some of these subtypes have jumped to humans, and not all H–N combinations cause human illness. The other choices are not correct because they underestimate the diversity, misstate how H and N pair, or claim that every H–N combination causes disease in humans.