Which specific virus, belonging to the herpesvirus family, is responsible for causing chickenpox (varicella) in humans, especially in children?

Introduction / Context:
Chickenpox, also known as varicella, is a common infectious disease of childhood characterized by fever and an itchy vesicular rash that appears in crops. Even though effective vaccines are now available, understanding the causative virus remains an important part of basic medical and general knowledge. This question checks whether you can correctly identify the virus responsible for chickenpox among several other medically important viruses.

Given Data / Assumptions:

• The disease in question is chickenpox, also called varicella.
• We have to select the correct virus that causes this illness.
• The options list different viruses that cause other diseases such as rubella and smallpox.
• We assume familiarity with common viral diseases taught at school level.

Concept / Approach:
Chickenpox is caused by the Varicella zoster virus, often abbreviated as VZV. This virus is a member of the herpesvirus family. Primary infection with VZV leads to chickenpox, especially in children. After recovery, the virus can remain dormant in nerve ganglia and may reactivate later in life to cause herpes zoster, commonly called shingles. Many students confuse chickenpox with smallpox and rubella, but these are caused by different viruses: Variola virus causes smallpox, and the rubella virus causes German measles. The key to solving this question is to match the disease name varicella with Varicella zoster virus.

Step-by-Step Solution:
Step 1: Identify the disease as chickenpox, also known by its medical name varicella. Step 2: Recall that the causative agent of chickenpox is Varicella zoster virus, a herpesvirus. Step 3: Note that rubella, rabies, smallpox, and hepatitis are distinct diseases caused by different viruses. Step 4: Compare the options and locate the one that explicitly mentions Varicella zoster virus and its link with chickenpox. Step 5: Select Varicella zoster virus as the correct causative agent of chickenpox.

Verification / Alternative check:
To double check, remember that vaccines are named after the pathogens and diseases they prevent. Many childhood immunization schedules include a combined MMR vaccine for measles, mumps, and rubella, and a separate varicella vaccine specifically targeting Varicella zoster virus. There is no vaccine named “smallpox for children” in current routine use, because smallpox has been eradicated. This vaccine based memory confirms that Varicella zoster virus is the correct agent for chickenpox and separates it clearly from rubella virus and Variola virus.

Why Other Options Are Wrong:
Rubella virus that causes German measles: This virus causes rubella, a mild rash illness, and is different from the virus that causes chickenpox. Rabies virus transmitted by bites of infected animals: This virus causes fatal encephalitis after animal bites and is unrelated to chickenpox. Variola virus that causes smallpox: This virus causes smallpox, a severe and now eradicated disease, not chickenpox. Hepatitis B virus that infects the liver: This virus causes liver infection and chronic hepatitis, not a generalized vesicular rash like chickenpox.

Common Pitfalls:
A frequent error is confusing chickenpox with smallpox because both have pox in their names and both involve skin lesions. However, smallpox was more severe and is caused by Variola virus, while chickenpox is relatively milder and caused by Varicella zoster virus. Another confusion is between rubella and other childhood rashes. Properly associating each disease name with its virus, such as measles with measles virus, rubella with rubella virus, and varicella with Varicella zoster virus, helps avoid such mistakes in exams and clinical reasoning questions.

Final Answer:
Hence, chickenpox in humans is caused by the Varicella zoster virus that causes chickenpox.