Of the 1,301 mosquito-borne cases recorded in the U.S., 97 percent of them are in Puerto Rico, neither a state nor a sovereign nation, but whose people are, nonetheless, U.S. citizens. As of early June, the start of Puerto Rico's long, hot and rainy summer, there are 1,259 recorded cases on the island, though some health officials believe the true number may be more than 80,000. ... unlike Ebola, which causes gruesome symptoms often followed by death, Zika is somewhat of a stealth virus. Most people infected will have no symptoms. Some may come down with conjunctivitis or break out in a skin rash, or experience muscle or joint pain or run a fever. Within a week or so, all of the symptoms, if they even emerged, are gone. In a certain number of cases, however, this may only be the beginning. ... the CDC estimates that it could cost $10 million to care for one microcephalic child. Zika, which seems to be particularly drawn to neurological tissue, may also cause swelling of the brain or spinal cord in adults, and has been linked to Guillain-Barré syndrome, an autoimmune neurological condition that can cause severe, if usually temporary, paralysis. ... But the scariest aspect of Zika is how little scientists actually know about it. ... Zika was first discovered in 1947 in the Zika Forest of Uganda, where researchers were studying the impact of mosquito-borne viruses on rhesus monkeys. Over the next 60 years, there were only 14 documented cases of Zika in humans, mainly in Africa and parts of southern Asia. ... given the prevalence of a host of factors, ranging from effective sanitation to the ubiquity of window screens and air conditioning, this kind of outbreak anywhere in the continental U.S., and much of Europe, for that matter, is unlikely.