Cruise ship with hantavirus may have seen a rare occurrence: humans infecting humans

It appears that hantavirus — which is typically spread by exposure to rodent urine, feces or saliva and can be deadly — may have spread between passengers on a cruise ship that's anchored off the coast of Cape Verde.

"We do believe that there may be some human-to-human transmission that's happening among the really close contacts, the husband and wife, people who've shared cabins," said Maria Van Kerkhove, the director of epidemic and pandemic management at World Health Organization, speaking at a press conference on Tuesday.

"It's very, very surprising, and obviously a very rare occurrence," says Kari Debbink, a virologist at the Johns Hopkins Bloomberg School of Public Health. However, she adds, the evidence presented by the WHO is "compelling," although the risk to the general public remains very low.

There are two confirmed and five suspected hantavirus cases among the 147 passengers and crew members on the boat.

Three of the patients have died and one patient is in intensive care in South Africa, although Van Kerkhove said this patient is "improving." She added that two people on board the ship are being prepared for medical evacuation to the Netherlands, where they will receive treatment. A final suspected patient had a fever but is currently asymptomatic.

The rare but serious infection can cause hantavirus pulmonary syndrome in which initial flu-like symptoms — including fatigue, fever and muscle aches — give way to severe respiratory symptoms as the lungs fill with fluid. According to the Centers for Disease Control and Prevention, more than a third of patients who get respiratory symptoms "may die" from the condition.

Humans are typically infected when inhaling hantaviruses that have become airborne from rodent excretions. However, in a small number of case studies it appears the virus can be transmitted between people.

"There are like 20 to 30 different species of hantavirus worldwide that can cause human disease, and there is only one [of those] species — the Andes Virus, which is found in Argentina and Chile — that has been implicated in human-to-human transmission," explains Dr. Emily Abdoler, a clinical associate professor of medicine at the University of Michigan. "One of the first clues that emerged is that this ship disembarked from Argentina."

The next clue is based on the timing between when a person is exposed to the virus and becomes sick — which can be anywhere between one and eight weeks." The first person to become sick — a man who traveled in Argentina before joining — got ill within the first week of the cruise and died shortly after. The other patients became sick a couple weeks later. Van Kerkhove said "our assumption is [the first patients] were infected off the boat and then joined the cruise.