Woodhall Stopford*

Common occupational and environmental biological hazards include microorganisms (viruses, rickettsia, chlamydiae, bacteria, fungi, and parasites), allergens of biological origin (e.g., the aeroallergenic fungi and animal dander), and the by-products of microbial growth (e.g., the endotoxins and mycotoxins). Because of their invisible and frequently undetectable nature, biohazards are considered “silent hazards.” Among the occupations associated with biohazards are the healthcare industry, agriculture, science and technology, livestock management, fish and shellfish processing, forestry, waste management, and recreation management.

Microorganisms are found everywhere in nature. They inhabit all environmental niches from the polar icecap to the tropics and deserts. Microorganisms are intimately associated with all living species. Many forms are present as the normal flora of the skin and body orifices, whereas others may cause disease. Most of the microorganisms found on earth, including most of the human and animal pathogens, belong to the mesophilic species, which survive best at ambient temperatures of 20–400°C. Microorganisms that require elevated temperatures for growth belong to the thermophilic species and those that thrive at lower temperatures belong to the psychrophilic species.

The human host is constantly exposed by a variety of routes to biological materials, including living microbes ...

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