"Tremendous infectious disease is pouring across the border," Trump said in a statement released on July 6, 2015. "The United States has become a dumping ground for Mexico and, in fact, for many other parts of the world."
This is the latest iteration of an old claim.
The CDC, on its website, acknowledges that there’s a risk, though it’s important to note that the risk doesn’t stem exclusively from undocumented immigrants. Indeed, they probably represent a distinct minority of border crossers. Approximately 300 million legal crossings take place from Mexico into the United States annually along the 1,969-mile border, and about 15 million Americans visit Mexico each year, according to CDC.
"The sheer number of people who live, work, and travel between the United States and Mexico has led to a sharing of culture and commerce, as well as the easy transportation of infectious diseases," CDC writes on its website. "The large movement of people across the United States and Mexico border has led to an increase in health issues, particularly infectious diseases such as tuberculosis."
For this reason, CDC and its Mexican counterpart have established a disease-surveillance infrastructure on the border.
In July 2014, when a surge of undocumented minors from Central America was heading toward the U.S.-Mexico border, a union that represents border patrol officers announced that an agent had been diagnosed with scabies while processing such migrants. Scabies is an itchy skin condition caused by a mite that is highly contagious, though also easily treated, according to the Mayo Clinic. It’s analogous to head lice.
A more serious risk -- if it materialized, which it hasn’t -- is tuberculosis. Tuberculosis is more common in other countries it is in the United States. But border officials are well aware of the threat and are on the lookout.
Thomas Fekete, the section chief for infectious diseases at the Temple University School of Medicine, agreed.
"When it comes to the health of immigrants, it is possible that undocumented folks have more health conditions that warrant concern, but I do not know of a scientific or quantitative assessment," Fekete said. "Workers are probably in decent health as the work itself is arduous. But there are some illnesses that occur more commonly in poor countries, such as tuberculosis, and some that occur more commonly because of farming or lifestyle issues, such as cysticercosis. But the notion that the Mexican government is orchestrating the movement of sick Mexicans to the U.S. is wacky."
He added, "Even if their health is in some ways worse than ours, we have the capacity to deal with this and produce minimum drag on our economy."