While Congress continues to debate President Obama's proposal to spend $1.8 billion to fight the Zika virus, an unpleasant reality is beginning to surface. That figure could be insignificant compared to the total long-term cost if Zika runs rampant across the country this summer.

The warning signs are already here. The first "Zika baby" born in the continental U.S. at a Hackensack, New Jersey, hospital was diagnosed with a deformed head. There are 341 confirmed cases of Zika among pregnant women in the U.S. and its territories, according to the Centers for Disease Control and Prevention (CDC).

"The economic cost of Zika could be very high," said Dr. Peter Hotez, microbiologist at Texas Children's Hospital and dean of the National School of Tropical Medicine at Baylor College of Medicine.

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Hotez will go before a closed session of the U.S. Senate on the morning of June 8 along with other top U.S. health officials to present the findings of their study of Zika, which focuses on the U.S. Gulf Coast. He said he couldn't be more specific about the potential impact of the disease until his congressional testimony.

No one, including the CDC, health insurers or those with the best handle on it, such as the Kaiser Family Foundation, seems prepared to go out on a limb and offer an estimate on the cost -- which could end up being abominably high ... or absurdly low.

This caution is admirable, but not helpful, when you consider what's at stake. Insurance companies estimate costs on the basis of past experience, and while Zika isn't a new virus, its probable connection with the birth defect microcephaly in newborns (abnormally small heads) has only recently come to light. Although the epidemic is now centered in Brazil, it's spreading around the world as the virus "hitchhikes" on migrating mosquitoes, travelers and possibly infected blood banks.

Brazil expects 2,500 cases of microcephaly this year, according to the World Health Organization (WHO). And with the active transmission of the virus throughout at least 62 countries and territories, including the Southern U.S. and Puerto Rico, carrying with it the danger of microcephaly for pregnant women, it's not surprising that Health and Human Services Secretary Sylvia Burwell warned that Zika "has the significant potential to affect ... the health of Americans."

But no one can predict how fast or far it will spread here. How many women in the first four to five months of pregnancy will be bitten by infected mosquitoes or be infected by sexual partners? Research has yet to show how long the virus remains in the body or whether the patient develops immunities after an initial bite.

Due to the lag between conception and birth, and since summer is the worst season for mosquitoes, many of these cases won't become known until fall or winter, when "clusters" could suddenly appear, particularly in areas that lack early detection of symptoms. Fetal abnormalities generally are detected six months after the initial infection, according to WHO.

Could these mosquitoes be largely wiped out by spraying? Right now there's no way to tell. CDC Director Dr. Thomas Frieden described this mosquito as "a sneaky cockroach" that can lay its eggs in a bottle cap and is a blood "sipper" that likes to bite multiple people, making it the ideal transmission vehicle.

A vaccine isn't an option until 2017 at the earliest, and it would probably be rushed with minimal testing. It's also possible that giving a vaccine to pregnant women might do more harm than good.

But two things are predictable. Without immediate forceful action, the Aedes aegypti mosquito -- which carries Zika and other dangerous viruses such as dengue fever, chikungunya and yellow fever -- will bite a lot of people, many of them poor and without window screens or access to full-time air conditioning.

In Puerto Rico, a likely hot spot for Zika this summer, estimates are that nearly a million people could be bitten and get the virus, many of them women who won't even know it before giving birth to a microcephalic child, depending on the quality of their medical care. If the mosquito and Zika epidemic aren't wiped out, one estimate is that 80 percent of the island could be vulnerable.

Avoiding pregnancy until the epidemic is over is one answer, but an estimated 20 percent of those who become pregnant there are high school girls. Preventing pregnancy in this group could prove harder than stopping Zika.

Children born with microcephaly, which has no cure, will require long-term care if they survive. Some microcephalics can live normal lives, but most suffer from severe disabilities. And while some could die early on from complications, a vast majority will need care throughout their lives.

In insurance lingo, this is referred to as a "long-tail" loss because the extent of the damage isn't known and is paid out over many years. For example, children with Down syndrome can live well into their 60s.

During a recent webinar for the Kaiser Family Foundation, the CDC's Frieden said the lifetime cost of care for a microcephalic child would be somewhere between $1 million and $10 million. Some of it would be borne by parents and relatives, but most of it would require the intervention of either private insurance or the public health care system. Many of these children would probably be institutionalized for at least part of their lives.

So here's the speculative -- and very speculative at that -- math. The Center for American Progress estimates that 2 million women in the U.S. will get pregnant this summer and fall, with nearly half of them living in areas potentially at risk of Zika. It's important to note that the public policy group's analysis isn't based on the actual prevalence of Zika around the country, while even if the virus spreads only a fraction of women are likely to be infected.

Still, if even just one in 10 gets Zika, the CDC estimates that up to 13 percent of their unborn offspring could develop microcephaly. If just 13,000 babies are born in the U.S. with this disability or to women who migrated here for better medical treatment, the cost of keeping them alive and providing for their lifetime care could range from $13 billion to as much as $130 billion.

But the saddest part of the equation is the much larger number of microcephalic children born abroad who will never have the money or resources to be kept alive.