Twentieth century science and technology complicated ideas about the relationship between immigrants and infectious diseases. Medical researchers have found cures or effective treatments for a wide variety of potentially deadly diseases. While Americans generally have access to these, many are beyond the reach of potential immigrants. At the same time, jet aircraft have made intercontinental travel swift and relatively cheap. Visitors and U.S. travelers abroad, as well as immigrants, can and do enter America as carriers of a wide variety of pathogens.
Those who enter a country illicitly, or choose to remain undocumented, often avoid public health screening and surveillance officials who might identify them as carriers and treat their conditions. Instead, such individuals threaten members of the communities in which they settle. By the end of the twentieth century, tuberculosis was making an alarming resurgence across the globe, especially in developing countries in Asia and Africa. The United States has one of the world’s lowest levels of incidence of the disease, but neighboring Mexico’s rate is ten times higher. TB presents a problem that is being echoed by other diseases: the natural evolution of drug-resistant varieties that threaten to make the American pharmaceutical arsenal obsolete.
Sexually transmitted diseases, including HIV/ AIDS, can be treated, but immigrant communities are often resistant to public health measures. The worldwide spread of HIV/AIDS means that immigrants from Africa or Haiti are not alone suspect. The incidences of forms of hepatitis, malaria, dengue fever, and even leprosy were on the rise across the United States during the early twenty-first century, with health practitioners often noting the prevalence of the foreign-born among their victims. Since many modern-day immigrants find work in agricultural and food preparation and service sectors, the possibilities are good for spreading diseases beyond local communities. The failure effectively to screen those who cross America’s borders also opens the door for incidences of bioterrorism, as it raises the potential for other types of terrorism as well.