As high-consequence pathogens can potentially infect subjects through airborne particles, aerobiology has been increasingly applied in pathogenesis research and medical countermeasure development. We present a detailed visual demonstration of aerobiology procedures during an aerosol challenge in nonhuman primates in an animal biosafety level 4 maximum containment environment.
Aerosol or inhalational studies of high-consequence pathogens have recently been increasing in number due to the perceived threat of intentional aerosol releases or unexpected natural aerosol transmission. Specific laboratories designed to perform these experiments require tremendous engineering controls to provide a safe and secure working environment and constant systems maintenance to sustain functionality. Class III biosafety cabinets, also referred to as gloveboxes, are gas-tight enclosures with non-opening windows. These cabinets are maintained under negative pressure by double high-efficiency-particulate-air (HEPA)-filtered exhaust systems and are the ideal primary containment for housing aerosolization equipment. A well planned workflow between staff members within high containment from, for instance, an animal biosafety level-4 (ABSL-4) suit laboratory to the ABSL-4 cabinet laboratory is a crucial component for successful experimentation. For smooth study execution, establishing a communication network, moving equipment and subjects, and setting up and placing equipment, requires staff members to meticulously plan procedures prior to study initiation. Here, we provide an overview and a visual representation of how aerobiology research is conducted at the National Institutes of Health, National Institute of Allergy and Infectious Diseases Integrated Research Facility at Fort Detrick, Maryland, USA, within an ABSL-4 environment.
Transmission of viruses generally occurs by direct or physical contact, but many important viral diseases (e.g., measles, chickenpox, influenza) are caused by pathogens that are transmitted by aerosol or respiratory droplets. Such pathogens have the potential to cause a pandemic with consequences ranging from widespread mild disease associated with loss of work (e.g., common cold) to rarer serious disease with high lethality (e.g., smallpox). High-consequence pathogens that spread naturally by aerosol or by intentional aerosol release (biological weapons) are of particular interest to aerobiology1. Humans may become rapidly infected with some of these pathogens by large respiratory droplets or small-particle nuclei and easily spread these pathogens to others through salivary secretions, coughing, and sneezing2. In the US biodefense community, high-consequence pathogens (e.g., filoviruses or other NIAID Category A-C Priority Pathogens and CDC Bioterrorism Agents) are the focus of aerosol research programs due to high lethality of associated infections3,4. Significant scientific strides within the aerobiology field have been made within the past decade due to technological advances in aerosol equipment and high containment facilities5,6. Research at the National Institutes of Health, National Institute of Allergy and Infectious Diseases (NIH/NIAID), Integrated Research Facility at Fort Detrick located in Frederick, MD, USA (IRF-Frederick) focuses on high-consequence emerging pathogens that require animal biosafety level 4 (ABSL-4) containment. The overall mission of the IRF-Frederick is to evaluate and facilitate the development of candidate vaccines and therapeutics (medical countermeasures).
Research with high-consequence pathogens at the IRF-Frederick is governed by stringent biosafety and animal care and use requirements. These requirements are outlined in the Biosafety in Microbiological and Biomedical Laboratories (BMBL) manual7 and the federal animal welfare regulations. These necessary requirements may restrict the type of research that can be performed and impact overall study design. As we previously described in this journal, all research conducted in an ABSL-4 environment requires particular caution, highly specialized training, and a robust and redundant facility infrastructure8,9.
Entry into the IRF-Frederick ABSL-4 suit laboratory requires donning a positive-pressure encapsulating suit8. Positive-pressure encapsulating suits are not required for entering the ABSL-4 cabinet laboratory. Donning a scrub suit, rubber or nitrile gloves, and close-toed shoes is appropriate when manipulating Risk Group 4 infectious material within a certified Class III biosafety Cabinet (BSC) in an ABSL-4 cabinet laboratory7.
At the IRF-Frederick, aerosol equipment is engineered, assembled, and maintained in two hermetically sealed, stainless steel, air-tight, negative-pressure Class III BSCs, Figure 1. The IRF-Frederick Aerobiology Core employs an automated aerosol management Platform (AAMP) to control and monitor aerosol experimentation within these BSCs, Figure 2. A previous publication outlined the specific functions of the Class III BSCs at the IRF-Frederick and the connection to the suit laboratory via a pass-through port5. The procedure of preparing the Class III BSC prior to experimentation is specific to the IRF. Other Class III BSCs used at other institutions function similarly to the Class III BSC in use at the IRF, but may have different mechanisms for transport, access, or docking.
To further understand how high-consequence pathogens remain infectious and spread through aerosol transmission, safe aerobiological experimentation must be conducted in these Class III BSCs according to a specific workflow procedure. Researchers have been carefully and thoroughly trained to ensure this workflow is followed in a safe and consistent manner. Prior to nonhuman primate (NHP) aerosol challenge, several aerosol characterization or sham aerosol runs are performed to test the stability and viability of an agent when in aerosol form. The aerosol characterization process mimics the actual aerosol challenge, and the researcher evaluates the variables associated with aerosol studies.
Another part of the workflow is to record physical manipulations, administration or anesthetics or other agents, or routine procedures on charts for each NHP. These subject charts are analyzed thoroughly to ensure procedural consistency and standardization. Subjects are anesthetized prior to aerosol exposure. Example anesthetics include tiletamine/zolazepam, ketamine/acepromazine, and ketamine. Anesthetics are chosen based on minimizing respiratory suppression and promotion of controlled, steady-state breathing. Additional anesthesia supplies are maintained in the animal procedure rooms and transported on the transfer cart with the NHP to the aerobiology ABSL-4 cabinet laboratory.
Within the ABSL-4 suit laboratory, NHPs undergo plethysmography via one of two methods (i.e., head-out plethysmography, respiratory inductive plethysmography [RIP]) to determine inspiratory tidal volume and breathing rate changes10-12. These derived parameters are used for accurate calculation of the estimated inhaled dose of the pathogen immediately prior to or during an aerosol exposure. Head-out plethysmography uses a long, cylindrical chamber that houses the NHP13. The pressure drop created when an animal is in the cylinder is captured by a pneumotachograph, relayed to the amplifier, processed by the alternating current/direct current converter, and integrated into the software to derive the above pulmonary parameters. RIP uses sensors made of inductive coiled copper wires that are embedded in elastic bands around the subject's chest and abdomen11,12. An inductive-capacitor generates a magnetic field in the sensor. Breathing changes the magnetic field, and the resulting voltage changes are relayed from a transmitter next to the elastic band to a receiver in the computer via short-wavelength ultra-high frequency radio waves. Dedicated software determines breathing rate and tidal volume from total thoracic displacement.
The minute volume (MV) obtained through plethysmography is used in the calculation of the estimated inhaled dose (D). In generating and sampling an aerosol, the aerosol concentration (AC) is calculated by multiplying the biosampler concentration (BC) by the volume of media (V) and dividing by result of multiplying the flow rate of the biosampler (FL) by the exposure time (T). The simplified formula is represented as AC = BC x V ÷ FL x T. In turn, for the actual aerosol challenge in NHPs, D is calculated by multiplying AC by MV and the exposure duration (time = T). The simplified formula is represented as D = AC x MV x T.
The purpose of this article is to visually demonstrate the entire aerosol challenge procedure using NHPs from two viewpoints, the ABSL-4 suit laboratory side and the ABSL-4 cabinet laboratory side. Although these procedures may be general in nature for several practices mentioned, they are specific to the IRF-Frederick Aerobiology Core and represent the actual practices used at this institution. This article focuses on the biosafety procedures needed to safely perform an aerosol challenge, not the actual aerosol challenge itself. In these procedures, we are using a dummy subject to show biosafety practices, due to the risk associated with anesthetizing an NHP. However, the process of performing an aerosol challenge is written in a general way because the procedure is the same regardless of high-consequence pathogen used. We aim to enhance knowledge and understanding of scientists about the rigors of conducting aerosol studies of high consequence pathogens under maximum containment conditions.
This protocol adheres to the following animal care guidelines. Animals were housed in a facility accredited by the Association for Assessment and Accreditation of Laboratory Animal Care International. All experimental procedures were approved by the National Institute of Allergy and Infectious Diseases, Division of Clinical Research, Animal Care and Use Committee and were in compliance with the Animal Welfare Act regulations, Public Health Service policy, and the Guide for the Care and Use of Laboratory Animals recommendations.
1. Aerobiology: Animal Biosafety Level 4 (ABSL-4) Suit Laboratory
2. Plethysmography: Animal Biosafety Level 4 (ABSL-4) Suit Laboratory
3. Nonhuman Primate Transport and Handling: Animal Biosafety Level 4 Suit Laboratory
4. Aerobiology: ABSL-4 Cabinet Laboratory
The Class III biosafety cabinet (BSC) is a hermetically sealed stainless steel cabinet containing an ABSL-4 environment under negative pressure within an ABSL-4 cabinet laboratory (Figure 1). Materials can be introduced into the BSC by staff working in the ABSL-4 cabinet laboratory through an under-cabinet-mounted stainless steel tank (commonly referred to as a "dunk tank" in ABSL-4 or BSL-4 settings) containing a 5% dual quaternary ammonium (n-alkyl dimethyl benzyl ammonium chloride, n-alkyl dimethyl ethyl benzyl ammonium chloride) disinfectant solution. Because the BSC is built into the wall separating the cabinet laboratory from an ABSL-4 suit laboratory, materials, animals, and viral pathogens can also be moved into the BSC from the ABSL-4 suit laboratory side using a transport cart and a Rapid Transfer Port (RTP). The contents within the BSC can be manipulated from the outside by researchers wearing various types of synthetic rubber gloves, specifically neoprene/chlorosulphonated polyethylene. Contents, excluding infectious samples, are removed from the BSC after sterilization through a double-door autoclave or disinfection via the dunk tank. By checking/verifying that the Class III BSC and bioaerosol equipment (Figure 2) is functioning properly, we maintain a safe and properly operational environment. Proper maintenance and use of the Class III BSC is integral to personal protection for the researcher. Following aerosol exposure, trash and equipment from the aerosol challenge to be sterilized are placed into the pass-through autoclave attached to the Class III BSC, Figure 3. Through strict adherence to these procedures and practices, no laboratory-acquired infections have been recorded during bioaerosol research at the IRF-Frederick.
Figure 1. Schematic Presentation of the Class III Biosafety Cabinet Setup at the IRF-Frederick. Presentation of the cabinet in static state (reproduced from 5). Please click here to view a larger version of this figure.
Figure 2. Aerosol Management Platform. Adapted from 5. Please click here to view a larger version of this figure.
Figure 3. Interlocking Double-door Autoclave Attached to the Class III BSC. A researcher is selecting a pre-programmed autoclave cycle to ensure the contents within the autoclave chamber are noninfectious when the outer door is eventually opened. The door located nearest to the researcher cannot be opened until a full sterilization cycle has been completed. Biological indicators inside the autoclave chamber will be analyzed to determine agent inactivation after the sterilization process (reproduced from 5). Please click here to view a larger version of this figure.
We outline the aerobiology procedures used at the IRF-Frederick for working with highly hazardous (Risk Group 4) pathogens. One purpose of visualizing the bioaerosol procedures is to emphasize the safety of staff when using a Class III BSC during experimentation with such pathogens to avoid laboratory-acquired infections. Class III BSCs maintain an inward directional airflow that exhausts into double HEPA filters to ensure that pathogens are contained within the laboratory (Figure 1).
As the Class III BSC is the primary barrier in preventing potential pathogen exposure during bioaerosol studies, researchers are required to check the integrity of the Class III BSC and attached integrated gloves for leaks before and after each aerosol experiment. Although every effort is taken to eliminate risk to laboratory researchers, a breach of a Class III BSC integrated synthetic rubber glove may occur. Staff must be provided with both didactic and hands-on training on the proper Class III BSC emergency response procedures. Such procedures include evacuation from the ABSL-4 cabinet laboratory, securing a breach in containment to the Class III BSC, and donning of personal protective equipment when necessary. We have used other gloves of varying thickness in the past that are dependent on the fine motor skills required for the procedure. Regardless of the thickness, all gloves chosen are equally as protective when performing these procedures. Robust training, strict adherence to safety protocols, and engineering controls help to ensure employee safety when using Class III BSCs at the IRF-Frederick. The processes above are subject to change due to new methodologies or safety reevaluations based on improving the workflow.
While the aerobiological procedures presented here generally follow the BMBL recommendations7, these procedures are specific to the IRF-Frederick. Each ABSL-4/BSL-4 facility has different building design specifications that impact the exact methods of laboratory operation. Alternative procedures and techniques for using Class III BSC laboratories depend in part on the design and operation of these laboratories. In addition, varying government regulations in different countries may also have an effect on aerosol research procedures. Nevertheless, a general understanding of ABSL-4 aerosol procedures and the building monitoring systems that support the safety of laboratory researchers will help health administrators, who are contemplating the design of similar buildings, and outside collaborators involved in studies of high-consequence pathogens.
When designing bioaerosol protocols with outside collaborators, sufficient time should be allotted to perform even basic bioaerosol operations. Expectations of time frames for delivering results have to be adjusted by accepting the difficulties inherent with work in ABSL-4 Class III BSC laboratories. A generalized assumption is that any bioaerosol experiment performed at ABSL-2 (e.g., 2 hr) will require twice the amount of time to perform in ABSL-4 (e.g., 4 hr).
The authors have nothing to disclose.
The content of this publication does not necessarily reflect the views or policies of the US Department of Health and Human Services (DHHS) or of the institutions and companies affiliated with the authors. This work was funded in part through Battelle Memorial Institute’s prime contract with the US National Institute of Allergy and Infectious Diseases (NIAID) under Contract No. HHSN272200700016I. J.K.B., K.J., M.R.H., D.P., L.B., and J.W. performed this work as employees of Battelle Memorial Institute. Subcontractors to Battelle Memorial Institute who performed this work are: J.H.K., an employee of Tunnell Government Services, Inc.; and M.G.L., an employee of Lovelace Respiratory Research Institute.
Micro-Chem Plus | National Chemical Laboratories | 255 | |
Ethanol | Fisher | BP2818500 | |
Paraformaldehyde | Sigma-Aldrich | 441244 | |
Class III BSC | Germfree | DGB-10 | |
Integrated BSC gloves | Piercan | 10UY2032-9 | |
Aerosol Management Platform (AeroMP) | Biaera Technologies | NA | |
Head-out plethysmography | Buxco/Data Sciences International | NA | |
Respriatory inductive plethysmography | Data Sciences International | NA | |
Centered flow tangential aerosol generator (CenTAG) | CH Technologies | NA | |
Collison nebulizer | BGI Inc. | CN25 | |
Autoclave | Getinge | GEB 2404 AMB-2 | |
Sperian positive-pressure suit | Honeywell Safety Products | BSL 4-2 | |
Outer suit gloves (latex, Ansell Canners and Handlers) | Fisher | 19-019-601 | |
Outer suit gloves (nitrile/rubber, MAPA) | Fisher | 2MYU1 | |
Scrubs | Cintas | 60975/60976 | |
Socks | Cintas | 944 | |
Duct tape | Pack-N-Tape | 51131069695 | |
Towels | Cintas | 2720 | |
O-rings | O-ring warehouse | AS568-343 | |
Overshoes | Amazon | B0034KZE22 | |
Zip lube | Amazon | B000GKBEJA |