Infectious diseases are caused by various agents that can invade a host’s body and cause a variety of symptoms. Viruses, bacteria, fungi, and parasites are all examples of agents that cause disease. Some of these diseases are contagious, while others can be fatal. Vaccines are a great way to prevent or minimize the effects of infectious diseases.
Pneumococci, staphylococci, and streptococci are the most common causes of bacterial infections in humans. These microorganisms usually live in the mouth, nose, and upper respiratory tract, but they can become virulent and cause a number of serious health conditions. Pneumococcal infections, for example, cause lung inflammation that leads to solid segments in the lung.
Climate variability and climate change affect the transmission of infectious diseases. These diseases are spreading to new parts of the world as a result of warming temperatures and increased precipitation. Previously, they were only found in tropical areas. Today, they have reached temperate regions, where they are a serious threat to human health. In fact, a new coronavirus disease, called dengue fever, has been identified in more than 100 countries.
The effects of infectious diseases on humans have been devastating. Ancient populations in many parts of the world had high rates of mortality, with half of people dying before reaching sexual maturity and passing on their genes to the next generation. In late medieval Florence, Italy, one-third of babies died in infancy, and infections of the digestive system were the most common cause of death. As civilizations advanced and agriculture spread, the incidence of infectious diseases increased as well.