Opinion article by Prof Felicity Burt, Principal Medical Scientist in the Pathogen Research Laboratory within the Division of Virology, National Health Laboratory Service and the University of the Free State

A cruise ship is currently docked off Cabo Verde awaiting investigations regarding an outbreak of hantavirus affecting the passengers. While we wait for the outcome of further testing and confirmation of the strain of hantavirus causing the outbreak, and the extent of the outbreak, we can reflect on what is known about hantaviruses. Understanding how hantaviruses are transmitted to humans can allay fears concerning the potential for spread of the virus. 

Hantavirus is the name given to the members of a large family of viruses that are carried primarily by rodents and transmitted to humans via aerosols from infected rodent urine, faeces and saliva, and less frequently from rodent bites. 

History of the virus

Prior to 1993 the story of hantaviruses was relatively easy to describe. A handful of viruses, each associated with a specific rodent host, and each associated with disease presenting with fever, varying degrees of kidney failure and in some instances haemorrhaging and fatalities. Although disease caused by these viruses had been described for decades, it was only in the late 1970s that an illness common among soldiers during the Korean War, and aptly named Korean haemorrhagic fever, was found to be associated with an infectious agent carried by rodents. In 1981, the first hantavirus was isolated from rodent tissues and named Hantaan virus after the Hantan River, which flows from North to South Korea. At this time, disease caused by hantaviruses had only been confirmed in Asia and Europe. 

The picture changed after a cluster of human cases, all previously healthy individuals, presented with acute respiratory distress syndrome and a high fatality rate, in the Four Corners region of the US. A race between American researchers to confirm the aetiologic agent and isolate the virus ensued, with a novel hantavirus being confirmed as the culprit. No previous hantavirus had caused a respiratory illness with significant fatalities. The naming of the virus became a political issue and the proposed names, Four Corners virus and Meurto Canyon virus among others, were rejected with concerns of social stigma affecting the region. Sin Nombre virus was finally adopted as the name, translating to “without a name virus”. Active surveillance of rodents identified additional hantaviruses in multiple locations throughout both North and South America and more than 20 viral species have been detected. Hosts have expanded beyond rodents to include bats, shrews and even fish, however to date, only rodent borne hantaviruses have been transmitted to humans and caused disease.

Low risk of spread of a hantavirus infection

Returning to the current situation, hantavirus infections in humans have been described previously. The type of disease and severity depends on which hantavirus the patient has contracted. New World hantaviruses, such as Sin Nombre virus and Andes virus, are found in North and South America respectively, and are associated with an acute respiratory disease, referred to as hantavirus cardiopulmonary syndrome (HCPS). The fatality rate associated with HCPS can be as high as 50%. Old World hantaviruses, such as Hantaan virus and Puumala virus, are found in Asia and Europe and cause haemorrhagic fever with renal syndrome (HFRS) and a fatality rate from <1 to 15%. Limited human-to-human transmission has been documented on rare occasions for Andes virus, found in Argentina, and requires extremely close contact. 

The Andes virus has now been confirmed as the cause of the outbreak on the cruise ship. Andes virus has been associated with person-to-person transmission, however, this occurrence is rare and has only been documented in a small number of outbreaks. In each instance spread was facilitated by extremely close contact of individuals living in confined households or attending a crowded social event. In all instances the interhuman transmission was limited and spread of the virus contained. 

In general, humans are considered dead-end hosts of the virus. Human cases occur more commonly in rural settings where there is opportunity for closer contact with rodent populations, and the residents are exposed to rodent urine and faeces in homes, fields, forests or rodent-infested buildings. Outbreaks are influenced by ecological and environmental factors that impact on rodent populations and activities. 

Further epidemiological investigations and genome data will assist with understanding the transmission of the virus among infected individuals in this outbreak.

Prof Vasu Reddy, Deputy Vice-Chancellor: Research, Innovation and Postgraduate Studies, notes: “Research on zoonotic diseases (when carried from animals to humans) like hantavirus reminds us that responsible societal futures are built on scientific understanding, not speculation and fear. At the University of the Free State, translating health research into public insight is central to acting responsibly in an interconnected world.”

He adds: “Universities have a critical role in shaping responsible futures by ensuring science informs both policy and public trust. Prof Burt’s insights are a powerful reminder of why trusted science matters. They help build public confidence by replacing uncertainty with understanding. I must acknowledge that I had no idea such a virus existed until recent headlines, and her ideas are enlightening.”