On the Dutch cruise ship “MV Hondius” several people fell ill with a hantavirus infection and three people died. The ship was on its way home from Argentina to Europe when the disease broke out. But how do the hantaviruses, which are normally only found in rodents, get onto the ship and how threatening is the situation for the remaining passengers? Virologists explain the background.
Hantaviruses and infections with these viral pathogens are not uncommon, because these single-stranded RNA viruses occur worldwide – including in Germany. Typically, the viruses use various species of rodents as reservoir hosts. Depending on the region and host species, different strains of the virus have evolved. The name “Hantavirus” is derived from the Korean river Hantan-gang, where several thousand soldiers fell ill with a severe hemorrhagic fever during the Korean War in the early 1950s. The hantavirus was later found to be the cause.
What happened on the cruise ship?
The Dutch cruise ship “MV Hondius” with 88 passengers and crew on board set off from Ushuaia in southern Argentina across the Atlantic towards the Cape Verde Islands off West Africa around three weeks ago. On April 10, a passenger became seriously ill and was diagnosed with a hantavirus infection, according to the World Health Organization. Three people on board have now died and one is receiving intensive care.
The cruise ship is currently moored in front of the port of the Cape Verde capital Praia. According to the WHO, it is not yet clear whether the dead and the remaining suspected cases are actually infected with the hantavirus. “Virological confirmation and sequencing will be crucial,” explains virologist Jonas Schmidt-Chanasit from the Bernhard Nocht Institute for Tropical Medicine (BNITM) in Hamburg. “This is an extraordinary infection event that you would not expect in this form on a cruise ship.”
How are hantaviruses transmitted?
“Hantaviruses are usually transmitted by infected rodents,” explains Schmidt-Chanasit. “Humans are typically infected by inhaling pathogen-containing dust that is contaminated with the urine, feces or saliva of infected rodents, or through direct contact with such excretions. Humans are a false or final host for most hantaviruses, so that no relevant human-to-human transmission occurs.”
In the case of the hantavirus infections on the cruise ship, however, it could also be the Andes virus, which is widespread in South America: “Human-to-human transmission through close contact has been described for this hantavirus. Since the ship came from southern Argentina, this possibility must be taken seriously in terms of differential diagnosis,” says Schmidt-Chanasit.
What are the consequences of a hantavirus infection?
Depending on the virus type, hantaviruses can cause various diseases. The incubation period is usually between two and four weeks, but can also last up to eight weeks. However, most hantavirus infections have no symptoms or only cause non-specific flu-like symptoms. But there are also severe cases that cause two different clinical pictures. In hemorrhagic fever with renal syndrome (HFRS), those affected develop a high fever with chills, pain and often tiny bleeding in the mucous membranes and skin. After a week, coagulation disorders and severe kidney inflammation follow. Dialysis is necessary in around ten percent of cases.
The second form of severe hantavirus disease primarily affects the heart and lungs. Hantavirus-induced (cardio)pulmonary syndrome (HPS/HCPS) also begins with a high fever, then after about a week cough and worsening shortness of breath occur. In 25 to 40 percent of cases, this form is fatal. However, the two severe forms are rare. “Although these are life-threatening, most hantavirus infections do not progress to this stage of the disease and are more likely to occur in people with previous illnesses,” explains virologist Liam Brierley from the University of Glasgow.
According to the researcher, it is still unclear which form of the disease and which hantavirus viruses affected the people on the cruise ship.
How could the passengers have become infected?
“Basically there are two possible scenarios,” explains Schmidt-Chanasit. “Firstly, one or more people could have already been infected in Argentina or in the South American exposure area and brought the virus on board. If it was the Andes virus, further transmission on board would then be conceivable in the event of close contact.” Because of the relatively long incubation period, it could also be that other passengers have already become infected but are not yet showing any symptoms.
“Secondly, an infection through rodents on board or through contaminated food, storage areas, cabins, surfaces or dust would also be conceivable – for example if mice or rats have colonized the ship or storage areas,” the virologist continued. “Both possibilities must be clarified through epidemiological investigation, environmental inspection, rodent control and virological diagnostics.”
What should happen now?
According to the experts, two measures are now important. First, all passengers and crew members should be medically examined and asked about symptoms, exposures and close contacts. This makes it possible to determine whether more people are affected by the infection. On the other hand, it should be determined which type of hantavirus is involved in all sick people. “This allows us to clarify whether it is the Andes virus or another hantavirus,” says Schmidt-Chanasit.
If it is the Andes virus that can be transmitted from person to person, all affected patients would have to be isolated and treated under quarantine conditions. “If the Andes virus is confirmed or highly probable, sick people should be isolated and close contacts should be actively monitored, and medical staff should work with appropriate personal protective equipment,” says Schmidt-Chanasit. “If the Hantavirus species is unclear and a severe respiratory illness occurs after a stay in southern Argentina, I would initially proceed as a precaution until the Andes virus has been ruled out.”
How can Hantavirus disease be treated?
Similar to many viral infections, there are no specific medications against Hantavirus. Instead, therapy aims to relieve patients’ symptoms and stabilize them. “The treatment is primarily supportive medicine: close monitoring, administration of oxygen, intensive medical care in the event of respiratory insufficiency or shock,” explains Schmidt-Chanasit. In severe cases, patients can also be ventilated.
Source: Robert Koch Institute, Science Media Center Germany