IMMUNOLOGY

Detailed explanation-1: -The agents that cause disease fall into five groups: viruses, bacteria, fungi, protozoa, and helminths (worms). Protozoa and worms are usually grouped together as parasites, and are the subject of the discipline of parasitology, whereas viruses, bacteria, and fungi are the subject of microbiology.

Detailed explanation-2: -Infectious diseases are caused by pathogens, which include bacteria, fungi, protozoa, worms, viruses, and even infectious proteins called prions. Pathogens of all classes must have mechanisms for entering their host and for evading immediate destruction by the host immune system.

Detailed explanation-3: -Infectious diseases are caused by microorganisms such as viruses, bacteria, fungi or parasites and can spread between individuals.

Detailed explanation-4: -These include both acute and infectious diseases like the common cold, to chronic disease like AIDS. Apart from these acute diseases, viruses are also responsible for mumps, polio, rabies etc. Diseases caused by bacteria include diphtheria, typhoid, cholera etc.