America is already experiencing a Zika outbreak. The disease has already infected almost 20,000 American citizens and more than 1,500 pregnant women—with some estimates reaching as high as over 10,000 infected pregnant women. There have been dozens of hospitalizations and dozens of cases of the immune disorder Guillain-Barré, including at least one fatal case. Thirteen Zika-infected mothers have either aborted or miscarried fetuses, many of which exhibited the brain damage often associated with the disease. This year’s cases are just the beginning, and it looks like the virus could become endemic on American soil in the near future.

As Congress dithers over funding for Zika prevention on the mainland, the island commonwealth of Puerto Rico is at a stage well beyond the reach of a preemptive strike. As the virus still struggles to establish a beachhead among Aedes aegypti mosquitoes in southern Florida, it has found a home in the Caribbean heat and moisture of Puerto Rico. And that’s awful for an island still deep in the throes of an economic and humanitarian disaster, and for one that’s always struggled with an underfunded and undermanned health infrastructure. Though Puerto Rico’s unique tropical climate is an outlier compared with that of much of the continental United States, the underlying issues with its infrastructure provide examples of just how Zika could spread elsewhere in the country, too.

It’s been less than a year since the first reported case of Zika in Puerto Rico, but doctors in the territory are already at their breaking points. Zika infections themselves are not terribly taxing to health-care systems—symptoms usually resemble those of a cold or flu, if patients exhibit them at all—but the potential complications can stagger even well-funded health systems. Treatment for microcephalic infants and adults that develop neurological complications can cost millions per patient. Evidence from Brazil presented in an upcoming Centers for Disease Control and Prevention study indicates that the true burden of neurological disorders from Zika is underreported, and that in addition to a well-reported link to Guillain-Barré, the disease is associated with a rise in expensive hospitalizations from other neurological conditions, including encephalitis, myelitis, and encephalomyelitis. Additional services for child and maternal health—including screening and access to abortions—and contraceptive services simply add to the price tag. And with so little information available about Zika’s long-term effects, it’s impossible to know if hidden symptoms and costs don’t lurk down the road.

That’s all bad news, and especially bad news for Puerto Rico, which simply doesn’t have the resources to fight even the immediate effects of Zika. Since the decade-long economic crisis began, the commonwealth has hemorrhaged hundreds of thousands of people—usually healthy, younger people seeking work—in a steady mass migration to the mainland. In that flood of people were hundreds of Puerto Rico’s doctors, and perhaps over a thousand physicians have moved away since 2014. The result back on the island is devastating. Not only are the remaining people more likely to be those most vulnerable to Zika—children, elderly people, and poorer families and women—many would-be primary-care providers are gone.

Most of Puerto Rico’s residents are covered by public insurance, either Medicare for elderly individuals or Puerto Rico’s Medicaid program for low-income families. In theory, these insurance programs should help defray the costs of Zika for patients themselves and should also help keep the lights on in hospitals and doctor’s offices—which is still a real challenge in some places. Medicaid, especially, is a vital part of the public-health safety net for the most vulnerable people. As evidenced by federal policy in Flint and other public-health responses, Medicaid is a first line of defense for women and children against diseases that uniquely affect women and children.

Puerto Rico’s Medicaid program doesn’t fill that role well, however, because its federal funding is capped at levels that are much lower than the rates provided to states. The federal government provides a federal medical assistance percentage (FMAP) to states and territories for each Medicaid enrollee based on the average income in that area; and the federal minimum is 50 percent, meaning that the federal government will pay for at least half of all Medicaid patients’ costs. Puerto Rico is entitled to a 55 percent rate by those calculations, but federal spending there is currently statutorily capped at only 19 percent. That means that the struggling Puerto Rican government has to foot 81 percent of the medical bills for a huge chunk of people on the island—including the low-income women and families who face the most risk from Zika complications. Even before Zika became the burden that it is today, that completely arbitrary underfunding led to hospital blackouts and drug shortages across the island. Those conditions contributed to poor health that has been exacerbated by the advancing outbreak.

The Department of Health and Human Services and the Department of the Treasury recognize that this underfunding is a significant contributor to both the debt crisis consuming Puerto Rico and its inability to contain Zika. In a joint letter, secretaries Sylvia Mathews Burwell and Jacob Lew urged Congress to “remov[e] the cap on Puerto Rico’s Medicaid program and gradually increas[e] the federal support Puerto Rico receives through the federal Medicaid match.” Their letter describes how the health crisis in Puerto Rico is a real existential risk to people on the island, even after Congress passed the debt-relief bill PROMESA this summer—and that there is a real and present danger that Zika could cripple the entire health and economic infrastructure.

Whether or not lawmakers consider it a bailout, the clearest solution in Puerto Rico is a significant injection of federal funds and a bolstering of women’s health services on the island. A $1.1 billion Zika package—for studying the virus, vaccine development, education, and prevention—has been held up in Congress, in part, thanks to controversy over funding Planned Parenthood, though that organization in particular has been essential in providing the educational and contraceptive services necessary to prevent human-to-human Zika transmission. Yet even if it is passed without restrictions on Planned Parenthood, that funding still may not be enough for prevention on an island with clearly favorable year-round conditions for Zika, with a beleaguered health infrastructure, and with a health-insurance program that has been chronically underfunded. If the emergency bill is the end and not the start of public-health debate over Zika funding, Congress’s scramble to protect the mainland could very well come at the cost of Puerto Rico.

Puerto Rico’s situation is certainly unique, but the weaknesses in its system are also harbingers for possible problems across the warming American South. Southern states are the most likely spots for Zika to become endemic among local populations of Aedes aegypti mosquitoes, and they also tend to be the places with the worst health outcomes and most vulnerable populations to disease. Southern states also make up the majority of states that have not expanded Medicaid to all low-income adults under provisions in the Affordable Care Act, even with a 100 percent FMAP rate for newly eligible adults. Notably, Florida is among those states that have not expanded Medicaid, and significant populations of highly vulnerable low-income people across the state now lack any kind of affordable health coverage. If the virus does gain a foothold in the state, these people will be the most difficult to monitor and administer preventative services to, and the bills for complications among uninsured patients will tax the health-care system’s ability to handle Zika.

Ironically, many of the most vulnerable people in Florida are thousands of Puerto Ricans fleeing the conditions back home and seeking opportunities on the mainland. The only way to ensure their freedom and safety as American citizens is to treat the Puerto Rican outbreak as an American outbreak—and to change standard American policy on infectious diseases. As Puerto Rico illustrates—for diseases like Zika with strong socioeconomic, racial, and geographic components—well-funded and highly functioning health-care systems are necessary complements to vaccine development and public-health efforts like mosquito control. Ignoring the structural problems in Puerto Rico is a potential choice, but with Zika those problems may not stay isolated on the island for long.