To cause a human pandemic, the H5N1 avian flu virus would have to a. spread to primates such as chimpanzees. b. develop into a virus with a different host range. c. become capable of human-to-human transmission. d. become much more pathogenic.

Verified step by step guidance

1. Identify the key factor for a virus to cause a human pandemic: The virus must be able to spread efficiently among humans.
2. Analyze the options: Option c, 'become capable of human-to-human transmission,' directly addresses the requirement for efficient spread among humans.
3. Understand virus transmission: Human-to-human transmission means that the virus can spread through respiratory droplets, contact, or other means directly between people, without needing an intermediate host.
4. Compare with other options: Options a, b, and d do not specifically address the ability of the virus to spread between humans. While changing host range or becoming more pathogenic might affect transmission, they do not guarantee human-to-human spread.
5. The most critical change that would allow H5N1 avian flu virus to cause a human pandemic is for it to become capable of human-to-human transmission.

Key Concepts

Host Range

Host range refers to the spectrum of hosts that a virus can infect. For a virus like H5N1 to cause a human pandemic, it must adapt to infect humans effectively, which may involve changes in its genetic makeup to target human cells specifically.

Human-to-Human Transmission

Human-to-human transmission is the ability of a virus to spread from one person to another. For H5N1 to cause a pandemic, it must acquire the capability to transmit efficiently between humans, as opposed to primarily spreading through contact with infected birds.

Pathogenicity

Pathogenicity refers to the ability of a virus to cause disease. While H5N1 is already highly pathogenic in birds, for it to become a significant threat to humans, it would need to not only spread effectively but also maintain or enhance its virulence in human hosts.