The word “infection” literary means “invasion of the body by harmful organisms (pathogens), like bacteria, fungi, protozoa, rickettsiae or viruses. The infective agent may transmit from one to another through droplet (during coughing, sneezing etc.), by direct contact (kissing, sexual intercourse etc.), by animal or insect vectors, by ingestion of contaminated food or drink, from an infected mother to the fetus during pregnancy or birth. An infectious organism is that which causes infection after entering into the body of a human/ animal or otherwise. The modern science, specially with the invention of microscope has identified a good number of infective organisms. Since identification these organisms are studied in detail with special reference to their structure, genetic character, mode of transmission, target organ, signs symptoms etc. Different branches for study on different types of such organisms are now working in their respective fields and trying to know them in detail with the aim to prevent their effect on the human beings / animals. Interesting facts about them are being explored day by day by the scientists of the respective fields.
Ayurveda, the science of life existing since time immemorial, is basically based on the ancient samhitas, viz , Charaka Samhita, Susruta Samhita , Ashtanga Sangraha and Ashtanga Hridaya . In these Samhita literatures concept of infection and infectious organisms are not found directly. But there are some descriptions that direct to the knowledge of the ancient Ayurvedic scholars on the concept of invasion of the external agents that manifest some typical signs and symptoms. As described, they are not visible by the naked eye and even not treatable with only application of medicine. It is considered to be beneficial for the modern society to discuss on the concepts of the external agents that can cause disease of peculiar character described by the pioneers of the medical science, Ayurveda. Some more systematic, scientific study on the concepts is also considered to be initiated