How to study microbes that cause deadly diseases

You’ll undoubtedly have followed the horrific news stories about the West African Ebola virus epidemic as it progressed during 2014 to 2016. It was the largest outbreak of Ebola virus (Figure 1) on record, with over 28,000 cases and 11,000 deaths (WHO), which is more than all the other Ebola virus outbreaks combined.

Figure 1: Transmission electron microscope (TEM) image of Ebola virus

Ebola virus is transmitted via contact with infected bodily fluids including vomit, diarrhoea, and blood. Health-care workers treating infected patients and laboratory workers analysing infected samples are therefore particularly at risk of contracting the deadly Ebola virus disease (EVD). It is critical that containment measures are in place to prevent transmission of deadly pathogens such as Ebola in health-care and laboratory settings.

Containment measures

Microbiologists follow standard microbiological practices in the laboratory whether they’re working with a harmless soil microbe or a deadly pathogen. This includes not eating or drinking within the laboratory and regularly disinfecting working surfaces and washing hands before leaving. Aseptic technique is used to:

1. prevent contamination of the sample with microbes from the laboratory environment.

2. prevent contamination of the worker and work environment with microbes from the sample.

You’ll see microbiologists using aseptic technique in the practical demonstrations later this week.

Contaminated items must also be decontaminated before being washed or disposed of, to protect people handing the waste and to prevent the release of microbes from the laboratory into the environment. Decontamination can be achieved using an autoclave (Figure 2), which uses pressurised steam at high temperature (121°C) to kill microbes and destroy spores, or via incineration or chemical disinfectants.

Figure 2: Autoclave © By HelWol1982 CC BY-SA 4.0

It is important to wear the appropriate personal protective equipment (PPE) when conducting work in a microbiology lab, and a Howie style lab coat is the minimum requirement (modelled by Sinead in Figure 3). It is often necessary to perform work on samples containing pathogens in a biological safety cabinet (BSC). HEPA filters in the cabinet remove bacteria and viruses from the air as it exits the ventilated workspace inside, preventing pathogens from being released into the environment.

Figure 3: Microbiologist working in a safety cabinet © University of Reading

Biosafety levels

The specific containment measures required to reduce exposure of laboratory workers and the work environment (and ultimately the community) to potentially infectious microbes are determined by the biosafety level of the microbiological work being performed. There are four biosafety levels which relate to the likelihood of a microbe causing disease (infectivity), the potential disease severity, and how likely it would spread in the community (transmissibility), taking into consideration the available prevention / treatment methods and the type of work being performed (Table 1).

Table 1: Containment measures depend on the Biosafety level (BSL) of the microbes being investigated. Alternative text for table

When working with deadly pathogens, such as Ebola virus, microbiologists must take extra special precautions.

Figure 4: Microbiologists putting on positive pressure biosafety suits before entering the interior of a Biosafety Level 4 laboratory at the Centers for Disease Control and Prevention (CDC), USA. Fresh filtered, breathable air is pumped into the suit causing positive pressure which, in the event of a tear to the suit, adds extra protection against deadly pathogens by forcing air out of the suit (rather than sucking air and pathogens into the suit). © CDC/ Dr. Scott Smith, Photo credit: James Gathany

What must it feel like to work in a BSL4 lab, handling samples from Ebola patients? In the comment area below, discuss any films you’ve watched or any good books you’ve read about scientists wearing positive pressure suits to prevent the spread of infectious diseases.

Further reading

• Recognising the Biosafety levels on Centers for Disease Control and Prevention website

• Ebola Virus disease factsheet on WHO website