Infectious diseases are the result of an infection caused by the disease-causing biological agents that enter an organism's body tissue and multiply. The host tissue uses the immune system to fight against these agents and the toxins released by them. The pathogens that cause infectious diseases are viruses and similar agents such as prions and viroids, bacteria, fungi, parasites, and arthropods such as ticks and lice. Each infectious disease has its unique symptoms but the most common ones include fatigue, night sweats, chills, pains, coughing, fever, weight loss, a running nose and loss of appetite. They are treated with several medications like antibiotics, antivirals, and antifungals. This book presents researches and studies performed by experts across the globe. From theories to research, case studies related to all contemporary topics of relevance to this field have been included in this book. It will provide comprehensive knowledge to the readers.