Leading infectious disease researchers are alarmed at the U.S.’s “concerning” response to the hantavirus outbreak that has killed three people who were traveling on a Dutch cruise ship.

“A lot of the things you would like to see, we haven’t seen,” Carlos del Rio, the former president of the Infectious Diseases Society of America, told reporters Thursday morning at a briefing hosted by the organization.

During past international outbreaks, experts from the U.S. Centers for Disease Control and Prevention have played a key role in assisting the World Health Organization. That doesn’t appear to be happening this time, del Rio, whose past organization is not involved in the response, said.

“Many, many days ago, we would have seen a team from CDC deployed to the area, and we haven’t seen that,” del Rio said.

Jeanne Marrazzo, CEO of the IDSA and former head of the National Institutes of Allergy and Infectious Diseases, said the CDC would typically send a message about the outbreak to the health community via the Health Alert Network. That hasn’t yet occurred.

“This, to me, not overstating it, is a travesty,” Marrazzo said.

The CDC said the Department of State is leading the U.S. response to the outbreak, including “direct contact with passengers, diplomatic coordination, and engagement with domestic and international health authorities,” according to a Wednesday statement.

The U.S. withdrew from the WHO in January, in compliance with an executive order President Donald Trump issued last year that said the WHO demanded “unfairly onerous” amounts of funding from the U.S.

Typically the WHO would have asked the CDC to deploy a team to the outbreak location to provide technical assistance, do epidemiological tracing, interview patients and obtain samples – “to do many of the things that are necessary in order to really investigate the outbreak,” Del Rio said.

Marrazzo said that the NIH would also normally mobilize researchers and public health experts to determine the best treatments for such an outbreak.

“Maybe that stuff is happening, but it does not give me a lot of assurance or reassurance that we’re not hearing about any of it. It’s very, very concerning,” Marrazzo said.

A spokesperson for the Department of State said via email the administration is “closely tracking reports of the suspected hantavirus outbreak on a cruise ship in the Atlantic Ocean and are in close contact with the cruise ship and U.S. and international health authorities.”

“We stand ready to provide consular assistance to any affected Americans,” the spokesperson said.

The CDC and NIH did not immediately respond to requests for further details on how they are responding to the outbreak.

The ongoing hantavirus outbreak began on a Dutch cruise ship that had been traveling across South America. A total of seven confirmed or suspected cases have been reported by the WHO as of Thursday morning. Three passengers, a Dutch couple and a German passenger, have died.

Hantavirus is a rare but severe disease that can be deadly. Humans usually contract it from rodents like wild mice, but the strain of hantavirus detected in the ongoing outbreak has been known to transmit from human to human on rare occasions.

The CDC’s Wednesday statement said the Trump administration is “closely monitoring the situation with U.S. travelers onboard the M/V Hondius cruise ship with confirmed hantavirus.”

The company operating the cruise ship said in a Wednesday statement that 29 passengers left the ship after the first death and returned to their countries of origin, including six U.S. passengers. Those passengers returned to Arizona, Georgia and California, NBC News reported, and none were showing symptoms of the virus. The ship is currently sailing to the Canary Islands for the medical assessment and disembarkation of the approximately 150 people still on board.

There is limited evidence that transmission may have occurred outside of the cruise ship. A flight attendant who was on the same flight as one of the passengers who later died has been hospitalized with symptoms.

Both del Rio and Marrazzo emphasized that they thought it unlikely for hantavirus to become a pandemic like COVID-19, but said that the current outbreak was an opportunity to learn about the virus — and to take stock of the U.S.’s capacity to respond to a disease threat.

“Research to help us develop vaccines and develop treatments is urgently needed,” del Rio said. The Trump administration has cut millions of dollars’ worth of vaccine funding since last year.

The IDSA experts also emphasized the relative dearth of communication from the CDC and other public health agencies — including at their own briefing.

“Believe me, we would love to have had someone from CDC here,” Marrazzo said.

Correction: This story has been updated to accurately reflect the past employment of Carlos del Rio and Jeanne Marrazzo. Marrazzo was the former head of the National Institutes of Allergy and Infectious Diseases. Del Rio was the former president of the Infectious Diseases Society of America.