disease to other humans, particularly when caring for the sick or burying the dead. Population overgrowth, eating of livestock, and clearing of the land contributed to the outbreaks we ve had. SARS or severe acute respiratory syndrome is a 21st century disease from a type of coronavirus. It was originally in China and was found originally in bats but later infected civet cats. Civet cats were eaten in China, where it originated. The disease was passed in open live animal markets. Zika virus is another relatively new viral infection first isolated in rhesus monkeys back in 1947. It gets to humans through mosquito bites. While it has been around for a while, it has become more popularized by the birth defects it causes in pregnant women who get it. It is not infectious outside of mosquito bites.
DISEASE SUSCEPTIBILITY Infectious diseases are strongly influenced by genetics. Infections that reduce a human s reproductive potential will drive selection toward individuals that are more resistant to disease. Selection is more likely to be seen in diseases that have been around humans for a long period of time. Some pathogens cause sudden diseases but, if survived, have little consequences. Others have the risk of chronic infections and fertility impairment. Evolutionarily-speaking, malaria is one of the oldest human diseases. This was later followed by tuberculosis, smallpox, leprosy, cholera, and most recently, HIV disease. These diseases spread with migration patterns that have happened over time and many originated in Africa. Modern medical practices have significantly decreased the risk of all of these diseases. Doctors and researchers have studied the genetic susceptibility to certain infectious diseases. The goal is to identify better medications and vaccines that can reduce the incidence of disease. One recent finding, for example, is a genetic marker in some Europeans that result in a decreased risk off HIV disease. This led to new drugs to fight the disease. In addition, there are those that are resistant to malaria, who are being studied to find a vaccine against the disease. Doctors are also using genetics to target vaccines to children who would be most susceptible to the disease. The risk for disease susceptibility in infectious diseases is genetically-related. There are certain families that have a great risk of infectious diseases. Twin studies on identical and fraternal twins have been done looking at disease resistance. Several chronic infectious diseases, such as leprosy, tuberculosis, and chronic hepatitis B are controlled through inheritance. The difficulty
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