Recent days have stirred uncomfortable memories of the pandemic years that most of us would rather forget. Screens are once again filled with images of healthcare workers in full protective gear, patients being rushed to hospitals, and close contacts placed under strict quarantine for days on end. News outlets are running daily coverage of a new viral threat, while health authorities around the world are issuing emergency briefings in rapid succession.
All of this is because of hantavirus, a pathogen virtually unknown to most people until recently, even though scientists have been studying it for decades. It crept overnight into our lives much the way it crept aboard the cruise ship MV Hondius, where, as of last Wednesday when this article was written, it had killed three people and infected eleven others, nine of whom were laboratory-confirmed cases, with three in intensive care.
Extended Quarantines
Dozens of other passengers aboard the vessel, representing 23 different nationalities including one Greek citizen, have since been evacuated and transported back to their home countries, where they are being held under strict protocols. The Greek passenger will spend a total of 42 days in an isolation unit at Attikon Hospital in Athens, as Greece is following the stringent guidelines set by the European Centre for Disease Prevention and Control (ECDC).
It is hardly surprising, then, that the public is alarmed. Everyone seems to be asking the same question: is hantavirus the new COVID-19? Are we heading back to the dark days of 2020? To address that burning question, along with many others surrounding this rodent-borne pathogen that is testing our already frayed nerves, Vima-Science spoke with one of the most qualified people to answer: Dr. Gianfranco Spiteri, head of emergency management at the ECDC and leader of its Global Epidemic Intelligence and Health Security unit. Dr. Spiteri was also one of the scientists who led COVID-19 surveillance in Europe during the pandemic.
Hantavirus Is Not COVID-19
From the outset, Dr. Spiteri made clear that hantavirus does not share the same ease of human-to-human transmission that characterized COVID-19. He was quick to add, however, that “this outbreak is concerning,” and proceeded to explain why.
“While people generally contract hantavirus through exposure to aerosols from the urine, feces, or saliva of infected rodents, this particular outbreak involves the Andes strain of the virus, which can be transmitted between people, though this is rare and requires prolonged close contact with an infected individual. And while human-to-human transmission is not common, this strain carries a high mortality rate, as it can cause a potentially fatal condition known as hantavirus pulmonary syndrome.”
Dr. Spiteri added to the list of concerns the fact that infected individuals can transmit the virus before showing any symptoms, and that the window for this is substantial. The incubation period ranges from two to eight weeks. Initial symptoms resemble the flu, including high fever, muscle aches, fatigue, and headaches, but in severe cases they can rapidly progress to a respiratory syndrome. “The long incubation period poses significant challenges to outbreak containment,” he said. The major sticking point, according to Dr. Spiteri, is that “there is no specific treatment for the infection, and no preventive vaccine exists for the Andes strain. Only symptomatic care can be offered.”
Sustained Spread Considered Unlikely
The challenges are real, yet Dr. Spiteri was reassuring about the risk to the broader European population. “The Andes strain, which is the only one for which human-to-human transmission has been documented, is primarily found in South America. The rodents that serve as its natural reservoir are not found in Europe, so further spread of the virus through animals is not expected.”
That brings us to the key question: could this outbreak spark an epidemic or even a pandemic? Dr. Spiteri’s response was that “the characteristics of this particular strain, which are quite different from those of COVID-19, make sustained community spread of the virus rather unlikely.”
That is what everyone hopes for, though we have all learned by now that viruses are unpredictable. WHO Director-General Tedros Adhanom Ghebreyesus touched on this a few days ago while speaking in Madrid: “We do not have signs that we are seeing the beginning of a larger hantavirus outbreak. But the situation can change, and given the long incubation period, it is possible we will see more cases in the coming weeks.” For now, the story remains unfinished, and, as viruses have made abundantly clear, they have no interest in our wishes.
Efforts to Develop a Vaccine and Treatments
Hantavirus is not a new pathogen, and several research groups had already been working on vaccines against it before the cruise ship outbreak.
An RNA Vaccine Against the Andes Strain
Jesse Erasmus, director of virology at the American company HDT Bio, told Vima-Science that his team is collaborating with the University of Texas at Austin to develop an RNA vaccine targeting the Andes strain. “Hantavirus is one of at least 12 viruses with pandemic potential for which we are developing vaccines in partnership with government agencies and academic institutions. We chose the Andes strain because it can spread between humans and is associated with high mortality.”
The candidate vaccine has so far been tested in mice with strong results, appearing to trigger an immune response without side effects such as myocarditis. It is built on a novel platform developed by the research team, one that could also serve as a basis for antibody-based therapies against the virus.
“We create harmless nanoparticles that mimic the virus, carrying on their surface the same glycoprotein structure found on real Andes strain viral particles. We recently published this structure in the journal Cell. Based on these particles, we developed an mRNA vaccine that prompts the body’s cells to temporarily produce those particles with the correctly arranged glycoproteins, effectively training the immune system to recognize the virus before it can cause infection.”
The team also developed a second candidate vaccine targeting a different viral protein, the nucleoprotein, and tested it in mice infected with hantavirus with comparably strong results. While these findings involve laboratory animals, the researchers say they are now designing the first human clinical trials. “If our vaccine ever receives approval, it would be intended primarily for individuals at high risk of hantavirus exposure, such as those living and working in affected regions,” Erasmus noted. “The RNA vaccine platform we have developed has already been tested in thousands of people across the US, India, and Brazil for other viruses, with no adverse events recorded.”
A British Vaccine Against the Hantaan Strain
Across the Atlantic, researchers at the University of Bath’s Department of Chemistry, led by Associate Professor Asel Sartbaeva, are developing their own mRNA vaccine targeting the Hantaan strain, which is found mainly in Asia and can cause hemorrhagic fever with renal syndrome, infecting roughly 100,000 to 200,000 people globally each year.
The vaccine incorporates Ensilication technology, developed by the group since 2010 and now commercialized through the university spin-off EnsiliTech. The technology allows the vaccine to be transported and stored in standard refrigerators rather than requiring ultra-cold storage at minus 80 degrees Celsius, by coating the vaccine with protective layers of silicon, a natural inorganic material.
The vaccine is still in preclinical development. “We recently conducted experiments in rodents and found that our vaccine produced a strong immune response with no side effects. The silicon coating also caused no problems; it is a biocompatible, biodegradable material that has already received approval for oral administration,” Dr. Sartbaeva explained. She added that the underlying approach is expected to be effective against the Andes strain as well.
Toward Antibody-Based Therapies
Further along in development is a vaccine created by virologist Jay Hooper of the US Army Medical Research Institute of Infectious Diseases (USAMRIID), which has already completed Phase 1 clinical trials and targets multiple hantavirus strains, including the Andes strain. The vaccine appears to stimulate the production of neutralizing antibodies, though it requires three doses to be effective. Dr. Hooper and his colleagues are also working on antibody-based therapies. By vaccinating genetically modified cattle that produce human antibodies, the researchers developed an antibody treatment called SAB-163, which has been shown to protect animal models against the Andes strain and three other types of hantavirus. The treatment has not yet been tested in humans.
Moderna, one of the two main developers of mRNA vaccines during the COVID-19 pandemic, had also already entered the hantavirus vaccine race before the cruise ship outbreak. Its research is at an early stage and is being conducted in animal models in collaboration with USAMRIID. In the wake of recent events, efforts on the research front are certain to intensify.
