Symptoms such as a rash, high fever, delirium, and eye pain can occur. Mumps also occurs in the respiratory tract and later the infection can spread throughout the body. Swelling of the glands can occur. Typhus is considered a vector-borne disease meaning an intermediate host is involved. Symptoms include fever, weakness, and hemorrhagic rash.
Smallpox is a virus that enters the respiratory tract.
The origin of disease in the New World and the Old World is very different. In the Old World, Europeans had already come in contact with various types of infectious disease and acquired immunity. The European s genes also became resistant overtime. Through natural selection the relative frequency of a gene appears to change over generations. For an example, people who have acquired resistant genes over generations are more likely to survive various types of diseases.