The US just had its first Zika death

Ana Rius, Puerto Rico's health secretary, just announced the first Zika-related death on the island.

According to the Associated Press, a 70-year-old man who had been infected with Zika died in February from a drop in blood platelets, the part of the blood that is responsible for forming clots.

It's still unclear if or how the two issues converged to be fatal; while a low-platelet count can be deadly on its own if untreated, Zika is rarely fatal in healthy adults.

Puerto Rico, a US territory, has seen more than 600 Zika cases of Zika. Seventy-three of those cases have been in pregnant women, which is of particular concern to health officials since the virus can cause severe birth defects like microcephaly, a condition in which babies being born with abnormally small heads. So far, 14 of the infected women have given birth to healthy babies, according to AP.

Another 16 Puerto Ricans are currently hospitalized with the virus; health officials say 4 may have developed Guillain-Barre Syndrome, a temporary condition that can cause paralysis, as a result.

Zika is a fairly new virus that's been spreading throughout South America and some US territories. While it's been documented among US travelers, local transmission has only been reported in US territories. So far, there's no rapid diagnostic test to detect Zika in a newly-infected person. And it has no cure.

Despite its severe potential consquences for babies, Zika is rarely deadly for healthy adults and typically only causes symptoms similar to those of having a cold or a fever.

Nevertheless, some scientists are concerned about Zika in North America, especially since only about 20% of infected people ever show symptoms. Peter Hotez, Dean of the National School of Tropical Medicine at Baylor College of Medicine and the Director of the Texas Children's Hospital Center for Vaccine Development, told NBC News in January that he was "very worried about Zika."

While a single tourist is unlikely to be the cause of an outbreak in the US, some American cities could be vulnerable to Zika's spread, he said.

As of April 18, 43 countries and territories have reported local transmission of the virus:

Though unlikely, there is some cause for concern of Zika spreading in the US, as the WHO has previously warned. The mosquitos that can spread Zika are prevalent in many American states and thrive in tropical climates. This is why experts like Hotez have warned of it popping up in areas in the US with wet lowlands, warm temperatures, and species of mosquito that can transmit the virus.

The first reported case of a traveler with Zika in the US was in Texas. Since then, travelers have tested positive for the Zika virus in New York, Los Angeles, and in several other countries outside the Americas.