The FDA is worried about a growing, parasitic threat to the US blood supply

Tiny parasites normally spread by ticks are increasingly sneaking into the US blood supply.

Called Babesia, the blood-loving parasites rarely kill. Many people don't even have symptoms after an infection.

It's not harmless, though. Babesiosis - the disease caused by Babesia - can be lethal to those with weak immune systems, among others who often need blood transfusions.

What's more, there's "no way of knowing" how many infected people are donating blood, according to a major blood donation center Tech Insider contacted. There's also no large-scale, US government-approved way to test for Babesia in the 15.7 million blood donations transfused into 5 million Americans every year.

Those aren't the only Babesia-related issues troubling the Food and Drug Administration (FDA), which oversees the US blood industry. Tick-borne babesiosis infections are on the rise and, in lock-step, so are those linked to blood transfusions. Even though it's rare, babesiosis is the pathogen most often spread by blood transfusions, according to reports in The New England Journal of Medicine and Infectious Disease in Clinical Practice.

Thankfully, the FDA and other organizations are trying to do something about the growing threat.

A lurking danger

Almost all cases of babesiosis trace back to the bite of an infected deer tick, also called black-legged ticks. These are the same creepy crawlies responsible for the spread of Lyme disease - another tick-borne scourge experts have labeled an epidemic and a "public health fiasco."

Babesiosis isn't caused by bacteria or viruses. Rather, one-celled parasitic animals called sporozoans are responsible. And of the 100-or-so known species, Babesia microti are the sporozoans that most often infect humans.

Once inside a person's bloodstream, the microscopic creatures swim around until they find a red blood cell. They force their way inside, hijack the cell, and divide until it bursts. Then the sporozoans seek out new prey.

Red blood cells bursting with parasites are, of course, not good for you. Babesiosis typically causes headaches, chills, sweats, and a high fever within weeks or months of infection. (Except in an unknown fraction of people who don't - but more on this shortly.)

Like Lyme disease, babesiosis is pretty easy to treat if you're healthy. The prescription drugs azithromycin and atovaquone, which cost tens to a few hundred dollars per round, usually fight off a babesiosis infection in a matter of days.

However, even with treatment, as much as 20% of infections are fatal in a cluster of high-risk groups: infants, the elderly, people without a spleen, and those with weakened immune systems, including cancer patients on immunosuppressive drugs.

Unlike Lyme disease, which triggers a big rash in 60-75% of infections, babesiosis has no dead-giveaway signs. Weeks or months after infection by Babesia, you might think you have a stubborn flu or, with milder cases, a cold - perhaps not anything serious.

But 25% of infected adults and 50% of infected kids show no symptoms at all. Without treatment, such infections can last months or even years.

And therein lies the problem.

"There are tons of people out in [Long Island, New York] who've been infected but don't get sick," Debra Kessler, director of special donor services at the New York Blood Center, told Tech Insider. "They come in and donate blood because they feel fine."

Right now, the only thing specific to babesiosis that's preventing asymptomatic people from donating infected blood is a check box on a standard screening questionnaire.

Those unknowingly infected by Babesia are ticking the wrong box:

Tip of the 'bloodberg'

The Centers for Disease Control (CDC) logged 3,862 reported cases of babesiosis in the US from 2011-2013. About three-fourths of reported infections were in the elderly.

National data before 2011 is scant. That's because the CDC wasn't demanding it - it didn't deem babesiosis a "national notifiable condition," which all state health agencies should report annually, until 2011.

With the data the CDC has now, they can see babesiosis cases always spike during the summer.

That's because ticks flourish in forests and fields during warm periods, feasting upon hapless humans and other mammals.

Five high-risk states - Rhode Island, Massachusetts, Connecticut, New York, and New Jersey - are the biggest hotbeds for babesiosis. Together they account for more than 85% of cases.

Yet infections appear across the the Northeast and the Midwest, too, since both regions are crawling with black-legged ticks:

A few thousand cases in a few years, concentrated in a few states, might not seem like a lot. And against a backdrop of more than 300 million Americans, it isn't.

But the true scope of Babesia's grasp on the country is unknown, and the government as well as blood centers are quick to admit it.

First, the CDC relies on states to compile and report cases to the government. But states aren't required to participate - and not all of them do. (Lyme disease has a similar problem with vast underreporting; 10 times the reported cases likely exist.)

"So far 31 states have participated, and the disease has been reported from 36 states," Sanjai Kumar, who studies pathogens for the FDA, said during the agency's most recent blood safety committee meeting on May 13, 2015.

Second, most people don't know they have babesiosis, if they have symptoms at all. So it's unknown how many people are undiagnosed.

Hence, babesiosis is the parasitic disease most often spread by transfusions.

Back in 1994, it was found that about one in 601 tested blood transfusions in Connecticut - one of the highest-risk states - resulted in a babesiosis infection. But with "expanding areas of transmission and infections" in recent years, an FDA representative told Tech Insider in a statement, this threat is increasing.

The raw numbers make the threat seem almost vanishingly small, with about 90 reported cases in a span of 5 years. But the actual scope of the problem is almost impossible to pin down.

"I like to refer to the tip of the 'blood-berg,'" said Barbara Herwaldt, who studies parasitic diseases for the CDC, during the recent committee meeting. "Undoubtedly, the cases that have been recognized represent a fraction of those that have occurred, but the sizes of the relative fractions ... aren't known," Herwaldt said.

Also, blood donations - and generous donors - don't recognize state borders. People travel, and blood centers ship units to places in need.

"It's nationwide because the donors from non-endemic areas travel to endemic areas and acquire infection," Kumar said during the recent FDA blood products meeting. "Donors who normally reside in endemic areas may donate elsewhere."

'No way of knowing'

Babesiosis was, for a long time, only a problem known to domesticated animals. Historical records tell us today that the first known human cases dates back to 1910 in France, but it wasn't until 1957 that researchers first described it in a Croatian farmer.

Babesia soon made its way to Nantucket Island (and North America) in the late 1960s.

Since then, human populations have exploded in tick-infested regions, and so have the number of disease-carrying ticks. We've pushed disease-carrying ticks into new habitats through human-accelerated climate change. We've expanded prime tick habitat in the form of more suburban communities near forests and grassy fields. We've pushed out or eradicated predators that used to keep deer, mice, and other reservoirs for Babesia in check.

In effect, we've increased our exposure to ticks and their ability to infect us.

Beyond preventing tick bites, the easiest way to confront this growing threat to the blood supply is to screen blood donors for Babesia with a diagnostic test. Donated blood is already tested for HIV, Hepatitis B, syphilis, and other diseases.

The good news is that if someone infected with Babesia donates blood, there are some promising tests. An expert can also identify the parasite using an old-school method: examining suspect blood under a microscope.

The bad news is that looking at tens of millions of units of donated blood under a microscope every year isn't feasible (nor very sensitive), and the FDA has yet to approve a large-scale test the blood industry can use.

In effect, Kessler told Tech Insider in an email, "[w]e have no way of knowing how many people may be infected and donating."

FDA approval of a diagnostic test isn't a bureaucratic formality. It mandates strong scientific evidence to show a test actually works, see how reliable it is, and single out its shortcomings - including the rate of misleading false-positive and false-negative results.

Two medical companies - IGeneX and Imugen - are each developing two types of tests to detect babesiosis. One type looks for Babesia microbes directly by detecting their DNA in a person's blood. The other test looks for antibodies that a person's body generates to fight Babesia.

The FDA refused to discuss either company's products, since that would be against the law. Yet both manufacturers shared results with the FDA in May 2015 - and those results suggest the tests are upwards of 97% reliable and thousands of times more sensitive than current methods, the blood-under-a-microscope method. Kessler said "licensure should come in the next year" for both types of tests, but didn't indicate the manufacturer.

Should the new tests work as well as manufacturers claim and get approved, the FDA has a plan to conservatively prevent 95% of future blood-transfused cases of babesiosis. They'd do this by mandating antibody screening for blood donors in all 50 states, plus Babesia DNA testing in the five high-risk states.

But the FDA isn't stopping with diagnostic tests.

This month it unveiled two critical (if unassuming) tools to detect risks to the blood supply in real-time: an email survey system, plus a unified database to shared anonymized blood donor information with the government.

Here's the debut email my wife received in August, since she's a frequent blood donor (if you can donate blood, you should - and regularly - since it saves lives):

An email survey and shared database might sound obvious or even laughable as tools to fight infectious diseases.

But Mark Walderhaug, a microbiologist and babesiosis researcher at the FDA, says nothing like it has ever existed between major US blood centers and the government.

"It's giving us timely, accurate data regarding risks to blood safety," Walderhaug told Tech Insider. "We could only guess at those before."

Learn to protect yourself from tick-borne diseases with resources from the FDA and CDC, and learn about the value of donating blood at the American Red Cross.