Since last October, the United States has caught tens of thousands of children crossing the border with Mexico, most fleeing violence in Central America. Thousands continue to come into the country, and President Obama has called the influx an “urgent humanitarian situation,” asking Congress for $3.7 billion in funding to deal with the children and families that have arrived.

Complicating the problem are growing protests against the immigrants. “I’m protesting the invasion of the United States by people of foreign countries,” said one person at a recent demonstration in Oracle, Arizona. “This is about the sovereignty of our nation.” And at a similar one in Murietta, California, demonstrators held signs saying “illegals out!” and called for the U.S. government to “stop illegal immigration.”

But for as much as this anger is organic, growing from fear and anxiety, it’s also true that conservative media figures have stoked tensions with wild and dishonest rhetoric on the supposed threat of new arrivals. “Dengue fever, 50 to 100 million new cases a year of dengue fever worldwide. In Mexico, it is endemic. It’s a terrible disease, for anyone that’s had it,” said Fox News host Marc Siegel, who continued with a warning. “There’s no effective treatment of it. It’s now emerging in Texas because of the immigration crisis.” Likewise, on her radio show, Laura Ingraham declared, “The government spreads the illegal immigrants across the country, and the disease is spread across the country.”

Republican politicians have joined in as well. “Reports of illegal immigrants carrying deadly diseases such as swine flu, dengue fever, Ebola virus, and tuberculosis are particularly concerning,” wrote Georgia Rep. Phil Gingrey in a recent letter to the Centers for Disease Control and Prevention. His colleague, Texas Rep. Randy Weber, sounded a similar note in an interview with conservative pundit Frank Gaffney: “I heard on the radio this morning that there have been two confirmed cases of TB—tuberculosis—and either one or two confirmed cases of swine flu, H1N1. … We’re thinking these are diseases that we have eradicated in our country and our population isn’t ready for this, so for this to break out to be a pandemic would be unbelievable.” And Rep. Louie Gohmert—no stranger to the offensive outburst—told conservative publication Newsmax that “we don’t know what diseases they’re bringing in.”

But we do, and the reality is nowhere close to dire: While a handful of reports suggest there are incoming children with illnesses like measles and tuberculosis, the vast majority of these minors are healthy and vaccinated. Moreover, according to the Department of Homeland Security, border agents are required to screen “all incoming detainees to screen for any symptoms of contagious diseases of possible public health concern.” In short, the odds that migrant children would cause a general infection of anything are slim to none, right-wing claims notwithstanding.

These facts are easy to find, but it’s not a surprise that immigration opponents would claim otherwise. For as long as there have been immigrants to the United States, there has been scaremongering about their alleged disease and uncleanliness. What we’re hearing now, put simply, is an update on an old script.

“On the morning of 19 May 1900,” writes American University professor Alan M. Kraut in an essay titled “Foreign Bodies: The Perennial Negotiation over Health and Culture in a Nation of Immigrants,” “the Chinese community of San Francisco found itself under siege in the name of state and municipal security. It was not fear of bombs or terrorist attack that inspired officials to commit a wholesale violation of civil liberties that morning; it was fear of disease, specifically bubonic plague.”

That wasn’t the first quarantine of San Francisco’s Chinatown, and it wouldn’t be the last. Nor was it a surprise—local authorities long regarded Chinese immigrants as a threat to public health, a manifestation of long-standing nativist fears. To wit, notes Kraut, “The Irish were charged with bringing cholera to the United States in 1832. Later the Italians were stigmatized for polio. Tuberculosis was called the ‘Jewish disease.’ ” The entire discourse of 19th- and early 20th-century politics was saturated with attacks on immigrants as diseased intruders to the body politic. Indeed, this dialogue culminated, in 1891, to Congress, with revision of the 1882 Immigration Act to exclude “persons suffering from a loathsome or a dangerous contagious disease” from entry into the United States.

“Asians were portrayed as feeble and infested with hookworm, Mexicans as lousy, and eastern European Jews as vulnerable to trachoma, tuberculosis, and—a favorite ‘wastebasket’ diagnosis of nativists in the early 1900s—‘poor physique,’ ” write scholars Howard Markel and Alexandra Minna Stern in a 2002 paper on “the persistent association of immigrants and disease in American society.”

Vivid examples of this association aren’t hard to find. “[E]very ship from China brings hundreds of these syphilitic and leprous heathens,” writes one editor in an issue of Medico-Literary Journal. Likewise, wrote one columnist in an Oct. 3, 1907 edition of the Princeton Union, “[German immigrants] produce large and swarming hives of children who grow up dirty, ignorant, depraved, and utterly unfit for American citizenship.” And in a Dec. 1, 1906 edition of the Deseret Evening News, one writer complained of “runners” in southern and eastern Europe who “tell fairy tales about the prosperity of the many immigrants now in America and the opportunities we offer to aliens. It is by such means that paupers and diseased persons are induced to make the journey, only to find that they are shipped back upon landing.”

Mass participation in World War II changed American perspectives of European immigrants, and later, the Immigration and Nationality Act of 1965 ended national quotas and opened the doors to a huge numbers of immigrants from around the world. Still, the link between immigration and disease has persisted through the 20th century and into the 21st.

In the 1980s, for example, the influx of Haitian refugees merged with the AIDS crisis to produce a new wave of anti-immigrant discrimination. “When AIDS appeared suddenly in the 1980s,” writes Markel and Stern, “it was quickly conflated with deviant sexuality and several minority groups, ranging from gays and intravenous drug abusers to Haitians and Africans.” In 1983, the appearance of HIV among several Haitian detainees led the CDC to add the group to its list of “recognized vectors” for the virus, and in 1990—acting on potent AIDS stereotypes—it banned all Haitians from donating blood in the United States. What’s more, that same year, the Immigration and Naturalization Service began to detain and quarantine HIV-positive immigrants at the U.S. base at Guantánamo Bay, Cuba.

And in 1993, echoing earlier language against “paupers and diseased person,” Oklahoma Sen. Don Nickles introduced a bill prohibiting the entry of all HIV-positive immigrants on economic grounds, arguing that—if we didn’t—“it will almost be like an invitation for many people who carry this dreadful, deadly disease, to come into the country because we do have quality health care in this country … and jeopardize the lives of countless Americans and will cost U.S. taxpayers millions of dollars.”

Beyond the present situation, the most recent attacks on immigrants as carriers of disease came during the Bush administration. In 2005, an episode of Lou Dobbs Tonight falsely asserted, “We have some enormous problems with horrendous diseases that are being brought into America by illegal aliens,” including 7,000 cases of leprosy in the past three years. On his radio show, Bill O’Reilly agreed that immigrants were crossing the border with “tuberculosis, syphillis, and leprosy,” and in 2006, Pat Buchanan claimed “illegal aliens” were responsible for bedbug infestations in “26 states.” In reality, health officials attribute the growth in bedbugs to “widespread use of baits instead of insecticide sprays” for pest control.

Today, anti-immigrant protesters hold signs asking Washington to “Save our children from diseases,” while right-wing lawmakers fret about disease screening and spread fears of infection and contamination. In doing so, both draw from a long history of ugly nativism and prejudice dressed as concern for public health. And you don’t have to be a liberal, or support immigration reform, to see that it’s a disgrace.