Researchers know very little about how long the Andes version of the hantavirus can remain in human hosts

By Adam Kovac edited by Claire Cameron

The deadly hantavirus behind a cruise outbreak that’s sickened at least a dozen people and killed three of them may be transmissible through numerous bodily fluids ranging from saliva to breast milk to semen, but how long it remains transmissible after a person is infected is a mystery.

At a press conference on Friday, World Health Organization (WHO) officials said numerous studies are in progress on the Andes type of the hantavirus, which began spreading among passengers and crew onboard the MV Hondius in April. Among those investigations is an attempt to clarify how long people with the virus remain infectious, said Maria Van Kerkhove, who leads the WHO’s emerging diseases and zoonosis unit. The WHO is setting up a natural history study that will examine the virus’s “life cycle” in human hosts, she said—that knowledge is particularly important, given there are no hantavirus-specific treatments yet available.

“Essentially what this study will do is to look at regular sampling of individuals who are in quarantine to look at, one, ‘Are they infected?’ but two, ‘Are they infectious?’” she said.

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Establishing the latter can be tricky. The virus’s RNA can remain detectable in human bodily fluids long after the risk of infecting another person is over. At least one case study indicates that viral RNA can persist in human bodily fluids for years after infection. In this case, a 55-year-old Swiss man who traveled from Ecuador to Chile in 2016 began showing symptoms of the hantavirus after he returned home; he tested positive for the Andes type. In a follow-up exam conducted six years after the infection, vestiges of the virus’s RNA were found in the man’s semen.

Viral RNA in bodily fluids after infection isn't necessarily a sign of danger, however, says David Safronetz, chief of special pathogens at Canada’s Public Health Agency. “Just because the RNA is present doesn’t mean that that individual is actively infectious,” he says. “The virus could be inside the immune cells within the body that killed it, but we’re still able to detect the genomic materials.”

The presence of the virus in semen hints at the possibility that it may be capable of sexual transmission, but Safronetz says that is difficult to say conclusively. Based on previous outbreaks of the Andes type, hantavirus is believed to require extended close contact to be transmitted from one person to another—the kind of closeness that might come from living in close proximity or having sex. But some outbreaks, such as the current cruise ship conflagration, suggest the virus may not require such prolonged close contact to spread in some cases. The prevailing scientific theory, which has not been definitively proved, is that the Andes hantavirus likely spreads from person to person through aerosolized droplets of saliva and other oral fluids that carry high viral load.

Many viruses can persist in semen for years, says Steven Bradfute, an immunologist at the University of New Mexico, and whether the pathogen remains infectious can vary from virus to virus.

“There are certain sites in your body, like semen or the eye, called immune privileged sites,” he says. “Sometimes there’s not as much clearance of pathogens from those areas, but we don’t know if that means it’s infectious or just [represents] the RNA.”

For people who do test test positive for hantavirus RNA, further blood tests can determine whether they are still infectious, he adds. Bradfute says there have been no documented cases of someone being infected by a person who was discharged from a health care facility after they recovered from a case of Andes type hantavirus.

The WHO insists there is no danger to the public from the hantavirus outbreak, and Safronetz notes that everyone who has displayed any symptoms or who was on the cruise ship or in contact with any of the ships passengers is under some form of close monitoring and undergoing regular testing. In the case of the cruise ship passengers, many won’t leave quarantine until at least 42 days after their last exposure to the virus. The odds that any of them may be contagious after that point is virtually nil, Safronetz says.

“If you take a sample at day 45, and these individuals are still negative for Andes virus, then the likelihood that they were actually even exposed in the first place is very low,” he says. “In fact, it’s probably negligible, because the virus would have done something by that point. That’s just based on 30 years of epidemiological experience.”