Our southern border is leaking like a sieve, with thousands of illegal immigrants, including unaccompanied children, streaming into Texas and other border states. Texas Governor Rick Perry, in the thick of the border surge, calls it a “national disaster.” But it’s more than humans crossing the border. Along with many of the immigrants are hitchhikers of a much smaller variety, namely bacteria and other microorganisms that may cause far greater problems than the human toll of the border tsunami.

A whistleblower from Immigration and Customs Enforcement (ICE) characterized the flow of illegal immigrants across the border as, “bringing with it tuberculosis and other communicable diseases.” ICE isn’t screening for infectious diseases, instead relying on self-reporting. Immigrants are not detained for further health screening, “unless they tell us they’re sick,” according to the ICE agent.

Symptoms of TB, according to the CDC, include a persistent cough, weakness, fatigue, weight loss, and night sweats. Most everyone crossing the Mexican desert, hiding from authorities, with limited food and water, for weeks on end will have these symptoms. So who gets screened? Everyone or no one? Likely the latter, based on the sheer volume of immigrants.

Preventing the spread of TB, according to the Mayo Clinic, means staying home, avoiding closed spaces without ventilation, and covering the mouth when coughing or sneezing. The holding areas for the immigrants are quite the opposite, conducive for spreading infectious diseases. Holding facilities in Brownsville Texas are characterized by “the pungent odor that comes with keeping people in close quarters.” Sounds like ideal conditions for spreading a communicable disease.

Even if ICE agents could spot potential TB carriers, how many are they missing? “On a good day, we catch approximately 30 to 40 percent of all crossers while the rest simply get away,” according to the ICE agent. US Customs and Border Protection estimates over 50,000 apprehensions of unaccompanied children across the southwest border over the past nine months. It’s safe to assume three to four times as many are not apprehended, not to mention many more adults.

Once across the U.S. border, immigrant children are being sent to New York City, California, and other states. What a perfect way to disseminate an infectious disease, especially since the children will again be living in close quarters in makeshift detention centers, coughing and sneezing on each other.

The discussion so far has been about standard TB that is treatable by a variety of medications. What about “multi-drug resistant TB” or even worse, “extensively drug-resistant TB”? Both, according to the CDC, are much more difficult to treat.

One third of the world’s population are infected with TB,” per the CDC. Last year, “64% of all TB cases and 91% of multidrug–resistant TB cases in the United States occurred among people born in other countries.” And Latin American slums are described by USAID as “a breeding ground for tuberculosis.” Guess which “other countries” most of those crossing our southern border are coming from.

It’s not only TB crossing the border. Other infectious diseases such as scabies, MRSA staph infections, hepatitis, and chicken pox are being brought into the U.S. Scientific American warns of tropical diseases, “endemic in warmer, wetter and poorer areas of the world, often closer to the equator,” such as schistosomiasis, Chagas disease, dengue, and Chikungunya making their way to the U.S. as, “immigration may become a greater disease pipeline.”

Standard legal immigration into the U.S., as according to the U.S. State Department, requires a,“medical examination (that) will include a medical history review, physical examination, chest X-ray and blood tests for syphilis.” So what about illegal immigration? This is like closing your car windows to keep out the rain, but leaving the sunroof wide open.

While this public health crisis looms, little is being done to stop it. Senator Charles Schumer is concerned about World Cup soccer attendees bringing back the Chikungunya virus to the U.S. A reasonable concern from the Senator since, “the virus (can) spread among people from all nations of the world who are together.” What about immigrants from many nations stuck together in crowded detention facilities? And all impoverished, unlike those who are healthy and well nourished with the means to travel to the World Cup. Chikungunya virus “is not a fatal infection; it’s just a miserable infection,” said Dr. William Schaffner, chairman of Vanderbilt University’s Department of Preventive Medicine. But TB and some of the other tropical diseases are fatal, and against all public health common sense, are being welcomed into the U.S.

Dr. Joondeph is a retina surgeon at Colorado Retina Associates and serves on the faculty of Rocky Vista University School of Medicine. The views expressed here are purely his own, and not those of Rocky Vista UniversityTwitter @retinaldoctor.