For example, dogs can give people rabies, which destroys nerve cells. Certain viruses can cause cancer in animals. These viruses do not destroy all the cells they infect. Some of the infected cells have their chemical makeup altered, which causes them to behave abnormally. These altered cells reproduce in an uncontrolled manner, forming masses of tissue called tumors.
Cancerous tumors invade and damage surrounding healthy tissue.
Researchers have discovered a similarity between some viruses that cause cancer in animals and certain viruses that infect human beings. Virus diseases in plants. Viruses infect all kinds of plants and can cause serious damage to crops. Plant cells have tough walls that a virus cannot penetrate. But insects penetrate the cell walls while feeding on a plant and thus enable viruses to enter.