Pock formation on chorioallantoic membrane (CAM): Which virus classically produces visible lesions (pocks) on the CAM of embryonated eggs used in diagnostic virology?

Introduction / Context:The chorioallantoic membrane (CAM) of embryonated eggs has long been used to culture viruses and visualize pock lesions. Recognizing which viruses yield characteristic CAM pocks is a staple of classical diagnostic virology.

Given Data / Assumptions:

• CAM inoculation can reveal discrete, opaque “pocks.”
• Poxviruses (e.g., vaccinia, variola) produce prominent, countable pocks.
• Some herpesviruses can produce focal lesions, but the classic teaching example for CAM pocks is vaccinia.

Concept / Approach:Poxviruses replicate in the cytoplasm and form large virions; upon CAM inoculation, vaccinia yields conspicuous pocks used for titration. While herpes simplex can produce lesions in certain systems, “pocks on CAM” traditionally points to vaccinia/variola in basic exam questions. Herpes B is a zoonotic primate virus and is not the standard CAM reference.

Step-by-Step Solution:Recall hallmark: CAM pock assay is a classic for poxviruses.Identify vaccinia virus as the standard laboratory poxvirus used for pock formation and titration.Select Vaccinia virus as the best single answer.

Verification / Alternative check:Historic smallpox vaccine production and lab titrations used vaccinia on CAM to count pocks.

Why Other Options Are Wrong:Herpes simplex may cause lesions, but the archetypal CAM pock reference is vaccinia; Herpes B is not used classically for CAM pock titration in basic coursework; “all of these” overgeneralizes.

Common Pitfalls:Assuming any virus that forms lesions in tissues will generate classic CAM pocks; conflating “lesion” with “pock” in exam wording.

Final Answer:Vaccinia virus