shutterstock Americans are not immune to Zika.

While it may not be the most widespread Zika conspiracy theory on the internet, it's certainly among the weirdest.

The fact-checking website Snopes revealed last Wednesday that at least a few people falsely believe Americans are immune to Zika virus, as these tweets demonstrate:

@SpeakerRyan @WashTimes Say NO to more Obama requested FAKE #Zika virus funding. American immune systems are immune to it. Virus isn't new — Chad (@FlyOSUBuckeye1) May 22, 2016

@ABC dont spread propaganda about a non-existent threat to Americans Fake Zika war is a terrorist tactice — Barbara Adams (@SheSellsBoise) May 26, 2016

Such claims are completely unfounded, according to Derek Gatherer, a lecturer at Lancaster University in the U.K. who studies virus genetics. Asked if there is any scientific evidence that Americans might be immune to Zika virus, he replied, "None whatsoever."

But Zika conspiracy theorist Chad, above, is right about one thing: The virus isn't new. It was discovered in rhesus monkeys in the Ugandan forest in 1947, and is common in Africa and Asia. And some people do have Zika antibodies that indicate they're likely immune to the virus -- they just aren't Americans.

“If people haven’t been immunized or vaccinated against Zika but they have antibodies to Zika, it means that the virus must have gotten into them at one time or another in their lives,” Ahmed Kalebi, CEO of Lancet Laboratories in East Africa, told Newsweek.

In Kenya, scientists have encountered individuals with Zika antibodies -- likely because of continued exposure to the virus. In Uganda, a different subspecies of mosquito carries the virus, but doesn't tend to bite humans. In fact, there have only been two confirmed cases of people getting sick from Zika in Uganda over seven decades, according to the BBC, though many people in Uganda haven't been tested.

However, since Zika has only recently been detected in North and South America, people in the Western Hemisphere do not have immunity to it.

"There's no evidence that I'm aware of that Americans would be immune to Zika," infectious disease expert David Calfee concluded during a Facebook Livestream with The Huffington Post on Thursday. "A number of Americans have traveled to Zika-affected areas and have gotten infected."

Denis Balibouse/Reuters A display about Zika prevention at the 69th World Health Assembly at the United Nations European headquarters in Geneva on May 23, 2016.

Why Conspiracy Theories Are So Appealing

Humans fear uncertainty.

"The world is a big, scary, strange, random place," said Eric Oliver, a political science professor at the University of Chicago who studies conspiracy theories. "People like to put some order and make some sense of it."

"It’s easier for us to fabricate a monster we can identify than accept that there are some unknowns out there," he added.

Health issues are a particularly popular source of conspiracy theories, since illness affects everyone and involves uncertainty. Indeed, in a survey Oliver conducted that was published in The Journal of the American Medical Association in 2014, nearly half of Americans believe in at least one medical conspiracy theory -- such as the debunked claim that there's a link between vaccines and autism or that the U.S. Food and Drug Administration is withholding a natural cancer cure because of its ties to Big Pharma.

Such misguided beliefs can have practical consequences. Earlier this year, a review funded by the National Institutes of Health found that rising measles and whooping cough rates in the U.S. correlated with a refusal to get vaccines.

For Oliver, the fracture in American society isn't between liberals and conservatives; it's between rationalists and intuitionists. Rationalists base their world views on science and reason, while "intuitionists tend to follow their gut," Oliver said. "The ideas of the Enlightenment don’t hold a lot of utility for them."

Vaccine avoidance certainly fits this formula. Vaccination itself is counterintuitive: It involves inserting a foreign pathogen into one's body to avoid future illness. For parents of children with autism, it may be easier to believe that a vaccine -- rather than an unknowable constellation of genetic, environmental and lifestyle factors -- caused their child's disorder.

Jorge Cabrera/Reuters Test tubes with blood samples from patients who have been tested for Zika at the maternity ward of the Hospital Escuela in Tegucigalpa, Honduras, on April 15, 2016.

Zika Truthers Aren't Likely To Be Convinced By Research

The sticky thing about individuals who buy into conspiracy theories is that they don't trust experts or research -- the main tools we have to debunk what's not true.

One danger on the internet is confirmation bias: People tend to consume and focus on information that confirms the views they already hold. These days, there's a blog or a Reddit thread that confirms just about any alternative viewpoint you could cook up.

There's also what's know as the "backfire effect," which two political scientists documented in 2006. When people are confronted with accurate information that debunks their beliefs, they don't usually change their minds. Instead, they dig in their heels and develop an even stronger belief in the veracity of their discredited opinion.

To bridge the gap, Oliver suggests trying to empathize, rather than rationalize, with conspiracy theorists.