aSuccessful public health campaigns and medical advances have enabled the United States to conquer a range of disfiguring and damaging diseases. Polio, which paralyzed thousands of Americans annually, was wiped out by widespread vaccinations. In 1999 the nation’s last hospital for lepers closed its doors in Louisiana. A global campaign eradicated smallpox, while lethal tuberculosis, the “consumption” that stalked characters in decades of literature, seemed beaten by antibiotics. Measles outbreaks still occur from time to time, but they are small, local, and easily contained.

Recently, however, some of these forgotten but still formidable infectious diseases have begun to reappear in the U.S. For two years running, polio has been detected in some New York water samples, and this fall, leprosy re-emerged in Florida, where cases of malaria have also been recorded.

Health officials say they are not sure why these and other infectious diseases are resurfacing. One distinct possibility, which officials are loath to discuss, is that the millions of migrants who have crossed into the country in recent years could be bringing the scourges with them, since many are from countries where such rare diseases persist and vaccination programs are not robust.

“The recent polio and leprosy cases are almost certainly imports to the U.S.,” said Dr. Jay Bhattacharya, a physician and scientist at Stanford University, one of the most outspoken critics of official COVID-19 narratives in the last pandemic that later proved flawed.