As hantavirus conjures up memories of the COVID-19 global pandemic, some Coloradans remember when the virus was discovered in their home state.

Colorado remains the state with the second-highest number of reported hantavirus cases, with cases recorded in nearly every county and at least 132 infected since 1993, when it was discovered in the Four Corners.

Hantavirus has many strains, and the Andes strain, which recently infected passengers on a luxury cruise ship sailing from Argentina to Cape Verde, is not the same as the virus’ typical form in the Centennial State.

Colorado’s strain, called the Sin Nombre virus, comes from deer mice droppings, and while it cannot be transmitted between humans like the Andes strain, the virus has wreaked havoc in the state for more than three decades.

Since 1993, there has been one hantavirus outbreak with dozens of unrelated surges in cases, resulting in the death of 47 Coloradans, said Hope Shuler, a Colorado Department of Public Health and Environment (CDPHE) spokesperson.

While the likelihood of a hantavirus pandemic is “extremely low,” according to the Centers for Disease Control and Prevention (CDC), Colorado is no stranger to the rodent-born virus.

Hanta-history

Hantavirus wasn’t known to infect humans until the 1993 outbreak in the Four Corners region killed 14 people, according to the CDC.

The Sin Nombre virus, which means the “virus without a name” in Spanish, stumped medical professionals as they navigated the outbreak, which killed 14 of the 18 people infected (78%), the American Society for Microbiology wrote. Five of the 14 were Coloradans.

Once the cause of deaths was uncovered, surveillance of hantavirus in the United States began, Shuler said.

No other official outbreaks have been reported in Colorado since 1993, but the state has recorded the second-most U.S. cases behind New Mexico.

Since monitoring began, Colorado has had several “spikes” in cases, but no outbreaks, as they were all unrelated. Notably, in 2000, seven cases were reported that led to two deaths; in 2005, 11 cases were reported with one death; and in 2016, 11 cases were reported with three deaths, according to the CDC.

Historically, the areas with the most cases are Weld, La Plata, Saguache and Alamosa counties, but for the most part, the cases were unrelated and can pop up around the state and, more broadly, North America.

Notably, Teller, El Paso, Elbert and Douglass counties have all recorded at least one case of the virus, according to data by the CDPHE.

After all, “rodents migrate,” said Michelle Bannon, senior medical director of infection prevention at UC Health Memorial.

Contracting Sin Nombre

Deer mice are not Colorado-specific rodents — they are a common genus across North America. However, they carry diseases that other mice, like the common house mouse, do not.

Contracting the Sin Nombre hantavirus can happen after inhaling fumes from deer mice’s droppings, usually through breathing in enclosed areas inhabited by unwelcome rodents, Bannon said.

“Especially when you are cleaning out a space, like an old storage closet, you just never know,” Bannon said. “And so it’s smart when you’re in those areas, not just for hantavirus, to make sure that you’re wearing a mask and that you open windows to have good air circulation; you can try to limit how much of the stuff you’re inhaling.”

Fortunately for U.S. residents, the Sin Nombre virus does not transmit between people.

“Sin Nombre hantavirus has not been shown to transmit person-to-person. Sin Nombre virus is transmitted in the urine and feces of infected deer mice, and people are most commonly infected when they breathe in aerosolized virus,” Shuler said.

Fatalities

Most of the fatalities from the Sin Nombre hantavirus occurred after the virus caused Hantavirus Pulmonary Syndrome.

“Hantavirus Pulmonary Syndrome is like a pneumonia,” Bannon said. “And so viruses in general … when it gets into the lungs, your immune system kicks in and says, ‘I have an intruder.’ If there is an intruder, it’s going to attack. And there is always the potential for collateral damage.”

When the immune system attacks Hantavirus Pulmonary Syndrome, fluid leaks into the lungs, and the more fluid, the less oxygen, Bannon explained.

“Often, individuals end up needing to be mechanically ventilated,” she said.

On the cruise

While deer mice cause the Sin Nombre hantavirus, the Andes strain of the hantavirus comes from long-tailed pygmy rice rats, which are native to South America, specifically, Argentina and Chile.

Unlike the Sin Nombre hantavirus, the Andes strain can be contracted through human contact. It may have ended up on the Dutch MV Hondius cruise after a couple went bird watching in a landfill.

The Associated Press reported that the Argentine government suspects that the Dutch couple who died from the virus on the cruise contracted it during a bird-watching outing in Ushuaia, Argentina. One of the stops was at a landfill that may have been infested by the pygmy rats, but Ushuaia officials rejected this claim, ABC News reported.

Bannon emphasized that while the cruise news is frightening, the chance of the Andes hantavirus turning into a pandemic is incredibly low.

“Don’t go canceling any travel plans unless you needed an excuse because you didn’t want to go in the first place,” Bannon said. “This is not going to be an issue.”