'Super-spreaders' of hantavirus: the extreme precedent among humans of 2018

BarcelonaThe hantavirus outbreak aboard the luxury cruise ship MV Hondius –with eight confirmed cases, three of which have already died– was caused by the Andes strain, which is the only one that is also transmitted between humans with close contact. However, there is a precedent from 2018 of another outbreak in Argentina with 34 cases and 11 deaths following a birthday party where it was shown that super-spreading events can occur. These events happen when an infected person, due to a high viral load or high social activity, can transmit the virus to several people at once; a type of contagion that, it must be said, is very unusual with this type of virus. According to the conclusions of a study published in The New England Journal of Medicine six years ago, there were at least three people from that outbreak classified as super-spreaders because each infected more than four people.

Abdirahman Mohamud, head of the Department of Health Emergencies Alert and Response Operations of the World Health Organization (WHO), linked the current outbreak to the 2018 one this Thursday. "We then had a similar situation where a symptomatic person attended a social gathering, which led to many people becoming infected. The current case is similar, contagion in an enclosed space with close contact," he said at a press conference. At that time, the origin of the outbreak was traced to a party with about 100 people, among whom was what is known as the index patient, i.e., the first case of the outbreak. It was a person who became infected through an infected rodent and who presented symptoms, such as fever and general malaise, when they arrived at the party.

The index patient was at the party for an hour and a half and sat near five people who developed symptoms between 17 and 24 days after the event. The study indicates that one of these people, a man who had a very active social life, was likely the source of six more infections and ended up dying 16 days after falling ill. On the day of his funeral, his wife had symptoms and was in contact with ten people. These also developed symptoms between 14 and 40 days later, as the incubation period of the disease can be very long. Furthermore, there were twelve more infected individuals who had contact with at least one of the other affected individuals when they had symptoms. Researchers found that half of those affected were infected on the same day the person infecting them began to develop symptoms and that this was the only time they interacted.

Isolation and confinement

Therefore, the WHO insists that all possible measures are being applied on the ship to break the chains of contagion, such as the isolation of passengers in their cabins and the use of masks if they have to go out into shared spaces. "If we follow public health measures and apply the lessons learned in Argentina on contact tracing and isolation, we can break the chain of transmission," reasons Mohamud. In 2018, once eighteen cases were confirmed, health authorities imposed isolation on the infected and confinement of possible contacts, which helped to limit its spread.

At that time, the reproduction rate of the disease, that is, the number of people that each infected patient can infect, was 2.12. This means that for each case there were two secondary cases; a scenario that allowed for an explosive spread of the virus. With isolation and confinement measures, the virus's reproduction rate decreased to 0.96 and the transmission chains were cut. It should be taken into account that when there are no super-spreading events, experts assure that these types of viruses are not very contagious, which is why the WHO insists that it does not have the potential to cause an epidemic like COVID-19 did, for example.