Monkeypox virus under the electron microscope
Photo: dpa/RKI/Freya Kaulbars
Readers over 50 will often find an old, more or less elliptical scar on one of their upper arms. It is the visible sign of a vaccination against (human) smallpox, a once dangerous plague that must have appeared in ancient Egypt. However, thanks to worldwide vaccination campaigns, smallpox caused by the variola virus could be defeated in the 1970s. In 1980, the World Health Organization declared that smallpox for exterminated worldwide. Unlike most other smallpoxviruses, variola only circulated between humans. If and when the variola virus originally spread from the animal kingdom to humans and adapted to this new host can no longer be clarified after more than 3000 years. But such a transition is likely. Because practically all known orthopoxviruses have other mammals as a natural reservoir, often rodents, which do not become ill themselves. And the very helpful vaccine itself is based on a pathogen that also affects animals. Contrary to what the name vaccinia virus (from Latin vacca for cow) suggests, the vaccine virus is probably more closely related to the horsepox virus than to that of cowpox. Fortunately, the family relationship to the variola virus is not associated with a comparably serious illness. The vaccinia virus in the smallpox vaccines most recently used and still in storage today is weakened in the laboratory. Modern vaccines use the so-called Modified Vaccinia Ankara Virus (MVA), which is no longer able to reproduce in mammals.
Even though the vaccination is 40 years old in the best-case scenario, it probably still offers a pretty good level of protection. “We know from the times of the global vaccination campaign to eradicate human smallpox that a single vaccination with the reproductive live vaccine was sufficient for a very long-term protective effect,” says the virologist and veterinarian Gerd Sutter from the Ludwig Maximilian University in Munich. Even decades later, specific memory cells of the stimulated immune response prove. Sutter therefore assumes that vaccinated people have at least partial protection against monkeypox. However, the remaining protective effect is difficult to assess, since there is not enough data on the epidemiology of monkeypox, which occurs relatively rarely.
Older mostly protected
However, only the older Germans mentioned above would have this protection. Because the compulsory vaccination against smallpox, which has been in force since 1874, ended in the old FRG in 1976, in Austria in 1981 and in the GDR in 1982. The majority of children born later no longer have this vaccination protection. So far, that seemed irrelevant, because the 1970 first diagnosed in a human monkey pox, which is probably better known as squirrel pox after its probable host, occurred only very rarely. They were also hardly ever transmitted from person to person, but mostly after very close contact with infected animals. In addition, the course of the disease is usually relatively harmless. However, the current unusual accumulation of monkeypox cases in Western countries gives cause for concern, since many of the more than 300 cases confirmed worldwide have not contracted the infection either on trips to West Africa or through known animal contacts.
The head of the Standing Vaccination Commission (Stiko), Thomas Mertens, considers preventive vaccination of risk groups – such as people whose immune systems are weakened – against monkeypox to be useful under certain circumstances. “We are currently thinking about this,” Mertens told the “Rheinische Post”. However, the older smallpox vaccine would not be suitable for people with immune deficiencies because it contained viruses that could reproduce. According to estimates by the Viennese specialist in vaccination and travel medicine, Herwig Kollaritsch, around a quarter of the population would no longer be vaccinated with it because of contraindications. No side effects are to be expected with the modern vaccine. The MVA vaccine Imvanex from the German-Danish company Bavarian Nordic, which has been approved in the EU for adults against smallpox since 2013, is also approved in the USA against monkeypox. British health authorities have recently given more than 1,000 doses of it to contacts of people infected with monkeypox, according to the UK Health Security Agency. The epidemiologist Gérard Krause from the Helmholtz Center for Infection Research in Braunschweig says that these vaccinations can currently only be made on a case-by-case basis for special situations.
No adaptation to humans
According to virologist Thomas Mettenleiter, the current spread of the monkeypox virus probably has nothing to do with better adaptation to humans as the new host. But – according to the head of the Friedrich Loeffler Institute, which is responsible for animal diseases, to the news channel N-TV – the longer a pathogen circulates in a new population, the more likely it is that random genetic changes could lead to an adaptation. After all, the FLI does not currently expect that native animal species will become reservoir hosts. “It may be that a single pet like a cat is infected through direct contact with an affected person, but it currently seems rather unlikely that a chain of infections will actually start.”
In general, however, the number of infectious diseases transmitted by animals has increased in recent decades. An impression that the Munich virologist Sutter confirms. “We’ve seen this for 20 years, starting with the sudden conquest of North America by West Nile fever in 1999: plane, mosquito, arrival in New York – enough for it to spread across the North American continent within a few years .’ The reasons are complex. On the one hand, people are increasingly entering areas where they were not before. This means they come into contact with animals more often and open up a new host system for their pathogens. Added to this is climate change, which is bringing insects that transmit pathogens to other parts of the world. Also attitude and consumption of animals plays a role from Sutter’s point of view. In addition, there is a globalized one travel activitywhich can carry a pathogen halfway around the world in two days.
A joint research project by the Robert Koch Institute and the Max Planck Institute for Evolutionary Anthropology showed years ago that zoonoses are not a one-way street. It’s not just animal diseases that spread to humans, it also happens the other way around. According to Fabian Leendertz, founding director of the Helmholtz Institute for One Health in Greifswald, all respiratory diseases in great apes observed in the 2008 study were caused by viruses that were transmitted from humans to the animals.