What is a primary testing sample for Hendra?

Oral fluid is considered a primary testing sample for Hendra virus because it provides a non-invasive method for detecting the virus in the infected animals, particularly horses. The virus is often present in the oral secretions, which means sampling oral fluid can yield sufficient viral RNA for accurate testing. This method is advantageous for both animal welfare and practical considerations, as it avoids the complications associated with blood draws and other more invasive sampling techniques.

In the context of Hendra virus zoonotic potential, prompt and effective monitoring through oral fluid can help in identifying outbreaks early and implementing necessary public health measures. The other options, while potentially viable in some circumstances, are not the primary choice for initial testing in this specific context, as oral fluid sampling is preferred for its ease and effectiveness in detecting Hendra virus.