(a) Malaria is caused by stagnant water, which can become a breeding ground for the mosquitoes that transmit this disease. Polio is caused by the poliovirus, a highly contagious virus specific to humans. Viruses, bacteria, a fungus, or (in rare cases) parasites or other organisms can cause pneumonia. Chickenpox (Chicken Pox), also known as Varicella, is a very contagious infection caused by the varicella zoster virus