AIDS, MERS, SARS, avian flu, swine flu, Hendra, Lujo, Marburg, Lassa, Nipah, Crimean-Congo hemorrhagic fever, Ebola — in the past decades, barely a year has passed without a new pathogen being discovered that can cause serious illness in humans.

According to the World Health Organization (WHO), hitherto unknown viruses and a string of new infectious diseases that are transmissible from animals to humans (zoonoses) could become a global threat to health.

Special laboratories are needed to identify the respective pathogens as quickly and reliably as possible and to develop methods for diagnostics, therapy and vaccine production. Rapid and reliable diagnostics under high-security conditions are also absolutely essential when a bioterrorist attack is suspected.

Four biosafety levels

The respective pathogens are divided into four biosafety levels (BSL) or pathogen/protection levels. 

At the lowest level of biosafety, precautions may consist in regular hand-washing and minimal protective equipment. At higher biosafety levels, stricter requirements are stipulated that the premises, equipment and work procedures must fulfill when handling these pathogens. 

Biosafety Level 3 (BSL-3) is commonly used for research and diagnostic work involving various microbes that can be transmitted by aerosols and/or cause severe disease. Surprising as it might seem, the coronaviruses SARS-COV-1, MERS-CoV and the new SARS-COV-2 are currently classified only as BSL-3. 

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Biosafety Level 4 (BSL-4) is the highest level of biosafety precautions. It is appropriate for work with agents that could easily be aerosol-transmitted within the laboratory and cause severe to fatal diseases in humans, and for which there are no available vaccines or treatments.

These include a number of viruses such as the Ebola virus, the Marburg virus, the Lassa virus and the virus that causes Crimean-Congo hemorrhagic fever. Other pathogens handled at BSL-4 include the Nipah virus, the Hendra virus and some flaviviruses. 

Worldwide research in a few laboratories

Because of the complex protective measures involved, there are only around 50 high-security laboratories working at BSL-4 worldwide. Around a dozen of them are in the US, followed by the United Kingdom with almost 10 and Germany with four. 

There are two high-security BSL-4 laboratories in the People's Republic of China, including the Wuhan Institute of Virology of the Chinese Academy of Sciences, which made the headlines as a possible source of the novel coronavirus SARS CoV-2. 

Read more: Did coronavirus really originate in a Chinese laboratory?

How safe is a BSL-4 Laboratory?

BSL-4 laboratories are designed to diagnose and investigate life-threatening pathogens without endangering the staff or the population at large. 

For this reason, such high-security laboratories are physically and organizationally separated from surrounding buildings in such a way that unauthorized persons cannot even get near the facilities. There are also strict access controls, video surveillance and other security measures. BSL-4 laboratories are completely independent, airtight units with their own air, power and water supplies, specially secured against technical faults.

Multilevel safety systems prevent pathogens from escaping into the environment. For one thing, the air pressure in the laboratory is negative, so that if a leak were to occur, the air would be unable to escape. In addition, the air flowing in and out is filtered through a multilevel system (HEPA filter) to ensure that it is pure, and all waste products and wastewater are completely inactivated. 

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All walls, ceilings and floors of a BSL-4 Laboratory are lined with a waterproof, easy-to-clean material, and the surfaces must be resistant to acids, alkalis and solvents as well as disinfectants. Scientists enter and leave the laboratory through a series of airlock security doors. The doors are mutually interlocked so that the air always flows toward the laboratory when the doors are opened and closed.

Even if an aircraft were to crash into such a BSL-4 laboratory or a bomb were to explode near or in one, there would be no danger, according to the Robert Koch-Institute,  Germany's federal disease control and prevention agency. This is because the very heat-sensitive viruses would be completely inactivated by the heat generated during such an event. The institute also points out that the pathogens all occur naturally in certain regions of the world and that terrorists could more easily obtain them there. 

Who works in the laboratories?

Access to the laboratory is restricted to a small number of selected, specially qualified staff, and is strictly monitored.

They wear inflatable full-body protective suits with their own air supply. To protect the hands, two to three pairs of gloves must be worn on top of each other, with the outer pair being tightly attached to the cuffs of the suit.

Since the work in the full-body protective suit, which weighs around 10 kilograms (22 pounds), is very stressful both physically and psychologically, the daily working time for each scientist is around three hours. 

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Only those pathogens that are actually needed for the research work are stored in the laboratories, and only in very small quantities.

Contaminated blood, tissue or sputum samples are processed in so-called safety workbenches under a glass cover; the laboratory technicians have to place their hands into the fixed gloves of the safety workbench to reach through to the substances.

Four-eyes principle

At the end of the work session, the working materials are put under lock and key. All objects used are decontaminated in an autoclave cleaning system at high heat and pressure. Laboratory waste or waste water is "inactivated," i.e., viruses that may be adhering to it or contained in it are killed.

Before leaving the laboratory, employees must first shower in their protective suits with highly diluted peracetic acid or similar antimicrobial agents to disinfect themselves. Afterward, the employees undress and shower again.

Since there are no measuring instruments for virus contamination, two employees usually work together, checking their suits for damage and helping each other to dress and undress. This process takes between 15 and 30 minutes.