When an outbreak of Andes hantavirus on a Dutch cruise ship sickened 13 passengers and crew members and caused three deaths this spring, a coordinated, multinational public health response helped contain the outbreak and kept the risk to the general population low.
A report compiled by researchers from the Centre for Infectious Disease Control in the Netherlands and other international agencies details the public health response involving medical evacuations, international contact tracing, quarantine, and laboratory monitoring across several continents.
The findings were published last week in Eurosurveillance.
The first case turns deadly
Investigators believe the outbreak began when one passenger was exposed to rodents infected with Andes virus (ANDV) in South America before boarding the Dutch ship MV Hondius.
“The most likely cause of infection of the primary case (Case 1) is through zoonotic transmission from inhaling aerosolised ANDV from the urine, faeces or saliva of infected rodents,” write the researchers. “Given the symptom onset and travel history, exposure probably occurred in South America in the weeks before embarkation on the MV Hondius.”
On April 1, the vessel set sail from Ushuaia, Argentina, with 121 passengers and 61 crew members for a several-week voyage to Cape Verde, a small island country 350 miles off the coast of West Africa. En route to Cape Verde, the ship made stops in South Georgia, Cooper Island, Tristan da Cunha, Gough Island, Saint Helena, and Ascension Island.
The most likely cause of infection of the primary case (Case 1) is through zoonotic transmission from inhaling aerosolised ANDV from the urine, faeces or saliva of infected rodents.
The ship stayed in Saint Helena from April 22 to 24, where 32 passengers disembarked, including the wife of the first patient, who became case 2. The body of case 1 was also removed from the ship in Saint Helena.
The vessel reached the capital of Cape Verde on May 3, one day after British and Dutch authorities notified the World Health Organization and the European Centre for Disease Prevention and Control (ECDC) of a cluster of severe respiratory illnesses onboard. Testing confirmed it was Andes virus, a type of hantavirus that can cause severe respiratory disease in people.
Experts believe the 12 confirmed cases and one probable case on the ship resulted from person-to-person transmission. Unlike other hantaviruses, ANDV can spread between people. No rodents were detected on the vessel.
Routine screening identified two cases before symptoms developed. Three people died, which translates to a case-fatality rate of 23%.
The public health response
The Andes virus has a long incubation period, up to 42 days, which meant the possibility of continued disease spread after passengers left the ship. Following the precautionary principle, the ECDC classified everyone onboard as high-risk contacts and recommended six weeks of quarantine from their last potential exposure to the virus, as well as active monitoring.
The response involved medical teams boarding the vessel in Cape Verde, medically evacuating passengers with symptoms, and coordinating repatriation flights to Canada, France, Ireland, Spain, the Netherlands, the United Kingdom, the United States, and Turkey.
Health officials also tracked people who had disembarked earlier at remote islands, as well as airline passengers, airport workers, and healthcare workers who may have been exposed.
Following up with 188 high-risk contacts
In total, investigators identified 188 high-risk contacts across seven countries. “All these contacts are quarantined, monitored daily, and tested weekly,” write the researchers.
On June 10, 12 healthcare and laboratory workers who handled clinical waste from a confirmed case-patient had their quarantines lifted.
One June 18, quarantine was lifted for the 61 passengers and crew members quarantined in the Netherlands, and the 42-day monitoring period for people exposed on planes ended. On June 21, the quarantine period for American passengers ended.
The last person being monitored is expected to complete quarantine on July 2.
As of June 18, all 13 cases remained confined to people who had been on the ship, and no community transmission had been detected. The authors say the threat of ongoing community transmission is unlikely.
“This outbreak highlights the need for preparedness protocols for expedition and cruise vessels, including early recognition of syndromic clusters, rapid international notification with complete information sharing on cruise ship passengers and crew and any flight contacts, as well as collaboration, implementation of onboard infection prevention and control measures, timely medical evacuation, structured risk communication, coordinated repatriation and follow-up,” the authors said.
