People who oppose immigration often argue that migrants bring disease with them, and that they then become a burden to health systems in their new countries because they’re so sick.

But that's not true, a team of experts argued in a new report released Wednesday.

In fact, they point out that immigrants make up a significant portion of the healthcare work forces in their new homelands.

"There is no evidence to show that migrants are spreading disease," said Dr. Paul Spiegel, who directs the Center for Humanitarian Health at Johns Hopkins School of Public Health. "That is a false argument that is used to keep migrants out," Spiegel told NBC News.

"Contrary to the current political narrative portraying migrants as disease carriers who are a blight on society, migrants are an essential part of economic stability in the U.S.," added Terry McGovern, who heads Columbia University’s Department of Population and Family Health.

McGovern and Spiegel were among 24 commissioners who worked on a two-year project to analyze whether migration spreads disease and to look into the effects that migrants have on health. The final study, published in the Lancet medical journal, finds that migration benefits economies. It also finds that people are using myths to fight migration.

"In too many countries, the issue of migration is used to divide societies and advance a populist agenda," said Lancet editor Richard Horton.

"With one billion people on the move today, growing populations in many regions of the world, and the rising aspirations of a new generation of young people, migration is not going away. Migrants commonly contribute more to the economy than they cost, and how we shape their health and well-being today will impact our societies for generations to come."

About a quarter of the one billion migrants are moving from one country to another. The rest are moving internally, the report found.

The two-year study found that international migrants are less likely than people in their host countries to die of heart disease, cancer, respiratory diseases and other ills. The exceptions are hepatitis, tuberculosis and HIV. But the study also found these infections are generally only spread within the affected immigrant communities and not to the wider population.

Conditions in refugee camps and detention centers can lead to undervaccination and the spread of infectious disease, Spiegel noted. "It’s not migrants or migration itself that is spreading disease. It may be the situations that they are in and the lack of access to basic care that may exacerbate the situation," he said.

As for fears that immigrants will outbreed their hosts, the study found that, in six European countries, fertility rates among migrant women were lower than among native-born residents.

And several reports have found that immigrants make up a substantial portion of the healthcare workforce, including in the United States. A report published Tuesday in the Journal of the American Medical Association found that 16 percent of healthcare workers in the U.S. were born somewhere else, including 29 percent of physicians, 16 percent of registered, nurses 20 percent of pharmacists, 24 percent of dentists and 23 percent of nursing, psychiatric and home health aides.

In Britain, 37 percent of doctors were educated in another country. "Rather than being a burden, migrants are more likely to bolster services by providing medical care, teaching children, caring for older people, and supporting understaffed services," the Lancet, which sponsored the report with University College London, said in a statement.

Nonetheless, migrants are often mistreated because of unfounded fears, the report found.

For instance, the Trump administration has proposed barriers to make it harder for immigrants already in the U.S. legally to get visas or green cards if they use Medicaid, food stamps or public housing. Medical groups including the American Medical Association have spoken out against the policy, saying it will end up costing taxpayers more as people fail to get early health care and end up getting sicker than they otherwise would.

"Forgoing care can exacerbate medical conditions leading to sicker patients and a higher reliance on hospital emergency departments. In turn, this could drive up costs for all purchasers of care," American Hospital Association president Rick Pollack said in a statement.

Research has already found that many immigrants are afraid to sign up for public benefits because of fear they will be deported — even if they are in the U.S. legally.

Other policies can worsen mental health and have long-term repercussions.

"The separation of migrant children from their parents creates long term psychological damage — and is a cruel and unnecessary aspect of U.S. policy," Columbia’s McGovern said. "The criminalization and detention of migrants seeking internationally protected refuge violates international law, and puts them at greater risk of ill health."

It makes better sense for host countries to take care of immigrants and asylum seekers, Spiegel said.

"Migration is occurring and will be occurring no matter what," he said.

"Racism and prejudice should be confronted with a zero tolerance approach," the report recommends. "Public leaders and elected officials have a political, social, and legal responsibility to oppose xenophobia and racism that fuels prejudice and exclusion of migrant populations."