The virus research into bats
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- A leaf-nosed bat in flight. Specimens from Ghana are among those being investigated by the researchers in Bonn. Source: Florian Gloza-Rausch/University of Bonn
09.05.2012 -
They live in seclusion, and are the stuff of myth and legend – in earlier times they were associated with witches and the undead. More recently, bats were generally regarded as innocuous creatures. Since the SARS epidemic in 2002/03, however, the animals, which are protected in Germany, are also seen as reservoirs for zoonotic diseases - previously unknown animal viruses that can spread to humans. In the meantime, the habitats and routes of transmission are the subject of numerous research projects. One of them is the cooperative project 'SARS: Ecology and Pathogenesis', funded by the Federal Ministry of Research (BMBF) within the framework of the National Research Platform for Zoonoses.
Severe acute respiratory syndrome (SARS) is a typical example of a zoonosis, a disease that has featured in many headlines in recent years. The avian and swine influenza viruses, as well as the tropical Ebola virus and the EHEC bacteria, are all germs that have jumped the species barrier from animals to humans, and they've all brought disaster in their wake. Because the pathogens were previously unknown, they posed a particular problem to the human immune system, ultimately threatening a pandemic.
To combat this risk, the BMBF is funding research into viruses that spans multiple diseases, and which sees human and veterinary medicine working closely together. In 2009, the National Research Platform for Zoonoses was established to promote integration between various stakeholders and individual projects. From 2007 to 2010, research associations studying zoonotic diseases were funded to the tune of €24.6 million; about €28 million has been earmarked up to 2013. Among the funded research approaches are also a three-year cooperative project 'Ecology and Pathogenesis of SARS', coordinated by Bonn's Institute of Virology.
The objective: a broadband vaccine
The research being conducted into the SARS pathogen includes two exemplary approaches that are shared by all zoonoses. Firstly the study of their habitats, and secondly the clarification of the transmission to humans. "If we succeed in understanding the process of host change, then our fundamental understanding of the emergence of new epidemics also improves," says Christian Drosten, head of Bonn's Institute of Virology and coordinator of the project. In 2003, Drosten identified the SARS virus together with tropical medicine expert Stephan Günther. Since then, both have continued to investigate the occurrence of these previously unknown viruses, as well as possible remedies for the human immune system. Such viruses are occurring more frequently, among other reasons because their natural habitat is being destroyed, explains Drosten. "Typically, many different microbes live in small quantities – comprising 'specialists' and 'generalists' – in a host population. But if one narrows the size of the biotope, it's the generalists that remain and multiply, and these are the potential pandemic viruses."
Broad-spectrum antibiotics against bacteria that are simultaneously effective against numerous bacterial pathogens have existed for a long time. To date, no such products have been possible for viruses. "All currently available antiviral drugs have directly targeted the pathogens," says Drosten. "Because the pathogens differ greatly, these compounds can only be effective against specific viruses." Viruses are very versatile, meaning that what works with one pathogen is useless for another, and by the time a vaccine is found, the virus has mutated.
In the case of bats, the scientists do not regard the mass killing of host animals such as the culling of poultry during the bird flu epidemic as a sensible or meaningful response. "Bats live in seclusion," says Drosten, "and moreover it would be catastrophic from an ecological perspective. The world can possibly live without breeding chickens, but it can by no means live without bats."
Removing the docking point from the viruses
The research network is therefore concentrating on the mechanisms of the immune system. For a virus to multiply in the body of an animal or a human, it must first dock to a cell envelope protein. Using an automated high-throughput method, the researchers have thus systematically tested different protein-virus combinations as potential targets for inhibitors, and have finally found the protein that provides SARS with access to the human body.
"This concerns a signal path that controls the immune system," reports Drosten. "We have found an approach for inhibiting one of the proteins in this pathway, by which means viral replication is suppressed." The practical side effect: When the signal is interrupted, whole virus families are excluded. Other signalling pathways compensate for the vital functions of the host cell. The researchers have published their insights in the journal PLoS Pathogens (2011, online prepublication).
To date, the results have only been demonstrated in cell cultures. "It will take years before we know whether these results can be transferred to human therapy," says Drosten. Nevertheless, Drosten and his colleagues regard the new testing method as important first successes. The SARS Research Network brings together the virology expertise of two veterinary- and four medical university facilities. Drosten is convinced that "this could not have been achieved by any of the participating teams on their own."
Author: Cornelia Kästner
