Preface

With a surface area of 100 m² and a capacity of some 6 L, approximately 10% of which is exchanged during each of the15 breaths taken every minute, the lungs are the most likely portal for systemic intoxication by airborne pathogens and toxins. Pathogens are disease-producing microorganisms. Bacteria, mycoplasma, rickettsia, fungi and viruses are among the naturally occurring pathogens. Toxins are poisons produced through the metabolic activities of living organisms. They are organic chemical compounds such as proteins, polypeptides and alkaloids that come from a variety of biological sources.

In Chapter 1, Henderson and Salem discuss the relationships between the structure and historical development the atmosphere of and the presence of airborne microbial life. They address the questions of contributions from the atmosphere to the origin and evolution of microbial life and whether the atmosphere can be considered as the true habitat for airborne microorganisms. These are indeed relevant questions considering the diverse array of airborne microbes identified in collaborative research by the University of Colorado Denver and the North Carolina State University. The study reported more than 110 000 bacterial species and more than 55 000 fungal species in dust samples collected from 1200 homes representing locations in all 50 states. The average dust sample contained 4700 bacterial species and 1400 fungal species.¹  Some of these microbes could be carried on airborne dusts of terrestrial origin and/or in airborne mists of aquatic origin. At present, it is undecided if the atmosphere is a habitat for microbes or merely a conduit for their dispersal.

Airborne bacteria are responsible for diseases such as anthrax (Bacillus anthracis), diphtheria (Corynebacterium), legionellosis (Legionella pneumophila), meningitis (Neisseria species), pneumonia (Mycoplasma pneumoniae, Streptococcus species), tuberculosis (Mycobacterium tuberculosis) and whooping cough (Bordetella pertussis). Chickenpox (varicella zoster virus) and smallpox (variola major virus), influenza (influenza virus), measles (morbillivirus) and German measles (rubellavirus) and mumps (rubulavirus) are among the diseases of viral origin communicable by airborne transport. Psittacosis (Chlamydia psittaci), aspergillosis (Aspergillus fumigatus, A. flavus, A. niger), histoplasmosis (Histoplasma capsulatum) and coccidioidomycosis (Coccidioides immitis) are examples of infections in humans initiated by the inhalation of fungal spores and their deposition in the alveoli. In addition to infections with microbial pathogens, some of their airborne metabolic by products are toxic. Some examples of such toxins are aflatoxin, a hepatotoxin of fungal origin (Aspergillus flavus, A. parasiticus), botulinum toxin, a neurotoxin of bacterial origin (Clostridium botulinum) and ricin, a cellular toxin extracted from the caster oil bean (Ricinus communis).

The recent outbreak of measles demonstrates the importance of immunization in providing effective protection against this viral disease.²  Measles is only one of the two dozen or so vaccine-preventable diseases. During the 225 years since Jenner “vaccinated” 8-year-old James Phipps with exudate taken from a cowpox lesion on the hand of dairy maid Sarah Nelms,³  routine vaccination against smallpox has virtually eliminated this disease from human infection. However, Vora et al.⁴  reported the infection of three unvaccinated Georgian dairy men with an orthopoxvirus as recently as 2013. In Chapter 2, Ibrahim and Meyer describe animal models, pathogenesis, vaccine and drug studies for smallpox and the other orthopoxviruses. Smallpox is a human disease. Each of the animal models was able to mimic some features of the human disease and collectively the mousepox, rabbitpox and monkeypox models contributed significantly to understanding the pathogenesis of the disease and to developing new generations of vaccines.

Recent media reports^5–7  on the unintentional shipment of live anthrax spores from the Dugway Proving Ground to as many a 68 external institutions on 22 May 2015 are reminders of the continuing need for planning, developing and implementing emergency response strategies. Hamilton et al.⁸  have presented an analysis of post-attack strategies for mitigating risks associated with reoccupying areas contaminated with Bacillus anthracis. In Chapter 3, Falk and Eisenkraft evaluate the inhalation hazard and the dose–response relationships for anthrax, which is another vaccine-preventable disease. They focus on their relevance to risk analysis and response planning and on their relevance to the mitigation of biological terrorism and biological warfare attacks. The review by Shah et al. in Chapter 7 considers the aerodynamics of anthrax particles, their mechanisms of infection at the molecular level and the manifestations of infection at the clinical level, in addition to diagnosis and treatment of the inhalational, cutaneous, gastrointestinal and injectional forms of the disease. Timely and relevant considerations of anthrax protection, detection and decontamination are included in this chapter.

Shannon Guess Richardson⁹  and Nicholas Helman¹⁰  attempted to use “ricin letters” as tools for assassinating a sitting president and a rival suitor, respectively. Both were captured, tried, found guilty and incarcerated. The Bulgarian defector Gregori Markov is thought to have been assassinated with a ricin-injecting umbrella during the cold war.¹¹  Pincus et al.¹²  have focused on the potential use of aerosolized ricin as a bioweapon for use against civilian and military personnel and they have reported on the clinical aspects of inhalation exposure to ricin. Henderson et al. present a detailed description of ricin toxicity at the molecular level in Chapter 5.

The Working Group on Civilian Biodefense¹³  developed consensus-based recommendations for measures to be taken by medical personnel and public health officers in the event that botulinum neurotoxin was used as a biological weapon against a human population. The 23 members of the Working Group, representing academic, government and private institutions, were experts in public health, emergency management and clinical medicine. They concluded that an aerosol- or food-borne botulinum neurotoxin weapon would cause acute systemic, descending flaccid paralysis with bulbar palsies such as diplopia, dysarthria, dysphonia and dysphagia that would typically present 12–72 h after exposure. Effective response to a deliberate release of botulinum toxin would depend on timely clinical diagnosis, case reporting and epidemiological investigation. Persons potentially exposed to botulinum neurotoxin should be closely observed and those with signs of botulism would require prompt treatment with antitoxin and supportive care that would include assisted ventilation for weeks of months. The treatment with antitoxin should not be delayed by microbiological evaluation. Park and Simpson¹⁴  reported that rats vaccinated with the heavy chain component of the botulinum neurotoxin were completely protected when exposed to doses up to several thousand times the LD₅₀. In Chapter 4, Adler and Franz review the consequences of exposure to botulinum neurotoxin by both the ingestion and inhalation routes. They cite the effectiveness of treatment with equine antitoxins in non-human primates exposed to botulinum neurotoxin by the inhalation route. Like Park and Simpson,¹⁴  Adler and Franz stress the need for initiating treatment promptly.

The threat of bioterrorism and pandemics has highlighted the urgency for rapid and reliable bioaerosol detection.^15,16  Early detection of airborne pathogens and toxins is essential for reducing contagion and initiating protective measures. In Chapter 6, Santarpia identifies the compositions of ambient biological aerosols, discusses the roles of bacteria, viruses and fungi and reviews methods for their measurement. In Chapter 8, Trebše et al. review the chemical, physiological, biochemical and immunochemical principles serving as the basis of methods for the detection of airborne pathogens and toxins and the applications of these principles to their detection and measurement.

Several aspects of particle physics were considered by Polymenakou¹⁷  in his review on bioaerosols. In Chapter 9, Corriveau discusses these aspects as they relate to the weaponization of biological agents. In Chapter 10, Kesavan et al. discuss the impacts of particle size, shape, density, surface area, mass and concentration on predicting the movements of bioaerosols. In Chapter 11, Bona and Katz include these parameters in their discussion of the models for air filtration, and also identify some of the airborne pathogens and toxins, compare air filtration devices and describe some applications of respiratory protection devices.

Aerial dispersion of pathogens is a potential route for the spread of infection. King et al.¹⁸  have combined computational fluid dynamics simulations of bioaerosol deposition with a probabilistic healthcare workers surface contact model to estimate pathogen accrual. In Chapter 12, McClellan et al. describe the Deposition And Response in the Respiratory Tract (DARRT) model, which accounts for variations in human response caused by differences in particle size, in particular, for coarse particles that may be present near an aerosol dissemination source and that may remain suspended long enough in an urban environment to expose large numbers of people. In Chapter 13, Reed et al. describe and discuss several reproducible exposure methods for producing standardized infections by inhaled viral and bacterial agents. In Chapter 14, Ingersoll and Williams present computer code for agent-based disease models in the mathematical programming language R allowing characterizations of the dynamics of infectious diseases in host communities.

The contents of these chapters are intended to provide information for the protection of human health from the harmful effects of airborne pathogens and toxins. Continued research and development will undoubtedly change some of these perspectives. This is especially true in the areas of detection and protection. Consequently, the work presented here is a starting point for further enhancement of the quality of life in all parts of Planet Earth.

Sidney A. Katz

Cherry Hill, NJ

Harry Salem

Edgewood, MD