How does a virus cause disease?

Viruses are like hijackers. They invade living, normal cells and use those cells to multiply and produce other viruses like themselves. This can kill, damage, or change the cells and make you sick. Different viruses attack certain cells in your body such as your liver, respiratory system, or blood.

Explanation:

Viruses tend to target specific tissues (cells) in the host.

For example, the influenza virus has a predilection for the respiratory tract, hepatitis viruses target the liver, polio virus targets the motor neurons of the spinal cord and rotavirus multiplies in the gut. Symptoms of a viral infection may be subtle and nonspecific or specific and suggestive of the causative agent.

Dengue virus, Ross river virus, measles and rubella infections are associated with fever and a widespread red rash, chicken pox and herpes simplex viruses are associated with blistering, often localized, rashes; and hepatitis viruses cause liver damage and jaundice.

Bacteria tend to be less tissue-specific and non-discriminatory than viruses and can cause a variety of infections once they have invaded the host.

These bacterial infections are often manifested by the presence of pus wherever the bacteria settle, and systemic symptoms such as fevers, chills, pain, swelling and loss of function occur when bacteria invade and multiply.