The assessment of biohazards in the workplace has been concentrated on agricultural workers, health-care workers and laboratory personnel, who are at considerable risk of adverse health effects. A detailed compilation of biohazards by Dutkiewicz et al. (1988) shows how widespread the risks can be to workers in many other occupations as well (table 1).

Dutkiewicz et al. (1988) further taxonomically classified the micro-organisms and plants (table 2), as well as animals (table 3), which might possibly present biohazards in work settings.

Table 1. Occupational settings with potential exposure of workers to biological agents

Source: Dutkiewicz et al. 1988.

Micro-organisms

Micro-organisms are a large and diverse group of organisms that exist as single cells or cell clusters (Brock and Madigan 1988). Microbial cells are thus distinct from the cells of animals and plants, which are unable to live alone in nature but can exist only as parts of multicellular organisms.

Very few areas on the surface of this planet do not support microbial life, because micro-organisms have an astounding range of metabolic and energy-yielding abilities and many can exist under conditions that are lethal to other life forms.

Four broad classes of micro-organisms that can interact with humans are bacteria, fungi, viruses and protozoa. They are hazardous to workers due to their wide distribution in the working environment. The most important micro-organisms of occupational hazard are listed in tables 2 and 3.

There are three major sources of such microbes:

1. those arising from microbial decomposition of various substrates associated with particular occupations (e.g., mouldy hay leading to hypersensitivity pneumonitis)
2. those associated with certain types of environments (e.g., bacteria in water supplies)
3. those stemming from infective individuals harbouring a particular pathogen (e.g., tuberculosis).

Ambient air may be contaminated with or carry significant levels of a variety of potentially harmful micro-organisms (Burrell 1991). Modern buildings, especially those designed for commercial and administrative purposes, constitute a unique ecological niche with their own biochemical environment, fauna and flora (Sterling et al. 1991). The potential adverse effects on workers are described elsewhere in this Encyclopaedia.

Water has been recognized as an important vehicle for extra-intestinal infection. A variety of pathogens are acquired through occupational, recreational and even therapeutic contact with water (Pitlik et al. 1987). The nature of non-enteric water-borne disease is often determined by the ecology of aquatic pathogens. Such infections are of basically two types: superficial, involving damaged or previously intact mucosae and skin; and systemic, often serious infections that may occur in the setting of depressed immunity. A broad spectrum of aquatic organisms, including viruses, bacteria, fungi, algae and parasites may invade the host through such extra-intestinal routes as the conjunctivae, respiratory mucosae, skin and genitalia.

Although zoonotic spread of infectious disease continues to occur in laboratory animals used in biomedical research, reported outbreaks have been minimized with the advent of rigorous veterinary and husbandry procedures, the use of commercially reared animals and the institution of appropriate personnel health programmes (Fox and Lipman 1991). Maintaining animals in modern facilities with appropriate safeguards against the introduction of vermin and biological vectors is also important in preventing zoonotic disease in personnel. Nevertheless, established zoonotic agents, newly discovered micro-organisms or new animal species not previously recognized as carriers of zoonotic micro-organisms are encountered, and the potential for spread of infectious disease from animals to humans still exists.

Active dialogue between veterinarians and physicians regarding the potential of zoonotic disease, the species of animals that are involved, and the methods of diagnosis, is an indispensable component of a successful preventive health programme.

Table 2. Viruses, bacteria, fungi and plants: Known biohazards in the workplace

¹ Infection-zoonosis: Causes infection or invasion usually contracted from vertebrate animals (zoonosis).
² (e) Endotoxin.
³ (m) Mycotoxin.

Source: Dutkiewicz et al. 1988.

Some Occupational Settings with Biohazards

Medical and laboratory staff and other health-care workers, including related professions, are exposed to infection by micro-organisms if the appropriate preventive measures are not taken. Hospital workers are exposed to many biological hazards, including human immunodeficiency virus (HIV), hepatitis B, herpes viruses, rubella and tuberculosis (Hewitt 1993).

Work in the agricultural sector is associated with a wide variety of occupational hazards. Exposure to organic dust, and to airborne micro-organisms and their toxins, may lead to respiratory disorders (Zejda et al. 1993). These include chronic bronchitis, asthma, hypersensitivity pneumonitis, organic dust toxic syndrome and chronic obstructive pulmonary disease. Dutkiewicz and his colleagues (1988) studied samples of silage for the identification of potential agents causing symptoms of organic and toxic syndrome. Very high levels of total aerobic bacteria and fungi were found. Aspergillus fumigatus predominated among the fungi, whereas bacillus and gram-negative organisms (Pseudomonas, Alcaligenes, Citrobacter and Klebsiella species) and actinomycetes prevailed among the bacteria. These results show that contact with aerosolized silage carries the risk of exposure to high concentrations of micro-organisms, of which A. fumigatus and endotoxin-producing bacteria are the most probable disease agents.

Short-term exposures to certain wood dusts may result in asthma, conjunctivitis, rhinitis or allergic dermatitis. Some thermophilic micro-organisms found in wood are human pathogens, and inhalation of ascomycete spores from stored wood chips has been implicated in human illnesses (Jacjels 1985).

Examples illustrative of specific working conditions follow:

1. The fungus Penicillium camemberti var. candidum is used in the production of some types of cheese. The high frequency of precipitating antibodies of this fungus in the workers’ blood samples, together with the clinical causes of the airway symptoms, indicate an aetiological relationship between airway symptoms and heavy exposure to this fungus (Dahl et al. 1994).
2. Micro-organisms (bacteria and fungi) and endotoxins are potential agents of occupational hazard in a potato processing plant (Dutkiewicz 1994). The presence of precipitins to microbial antigens was significantly correlated with the occurrence of the work-related respiratory and general symptoms that were found in 45.9% of the examined workers.
3. Museum and library personnel are exposed to moulds (e.g., Aspergillus, Pencillium) which, under certain conditions, contaminate books (Kolmodin-Hedman et al. 1986). Symptoms experienced are attacks of fever, chill, nausea and cough.
4. Ocular infections can result from the use of industrial microscope eyepieces on multiple shifts. Staphylococcus aureus has been identified among the micro-organism cultures (Olcerst 1987).

Prevention

An understanding of the principles of epidemiology and the spread of infectious disease is essential in the methods used in the control of the causing organism.

Preliminary and periodic medical examinations of workers should be carried out in order to detect biological occupational diseases. There are general principles for conducting medical examinations in order to detect adverse health effects of workplace exposure, including biological hazards. Specific procedures are to be found elsewhere in this Encyclopaedia. For example, in Sweden the Farmers’ Federation initiated a programme of preventive occupational health services for farmers (Hoglund 1990). The main goal of the Farmers’ Preventive Health Service (FPHS) is to prevent work-related injuries and illnesses and to provide clinical services to farmers for occupational medical problems.

For some infectious disease outbreaks, appropriate preventive measures may be difficult to put in place until the disease is identified. Outbreaks of the viral Crimean-Congo haemorrhagic fever (CCHF) which demonstrated this problem were reported among hospital staff in the United Arab Emirates (Dubai), Pakistan and South Africa (Van Eeden et al. 1985).

Table 3. Animals as a source of occupational hazards

¹ Infection-zoonosis: Causes infection or invasion contracted from vertebrate animals.
² Vector of pathogenic viruses, bacteria or parasites.
³ Toxic B produces toxin or venom transmitted by bite or sting.

Vertebrates: Snakes and Lizards

In hot and temperate zones, snakebites may constitute a definite hazard for certain categories of workers: agricultural workers, woodcutters, building and civil engineering workers, fishermen, mushroom gatherers, snake charmers, zoo attendants and laboratory workers employed in the preparation of antivenom serums. The vast majority of snakes are harmless to humans, although a number are capable of inflicting serious injury with their venomous bites; dangerous species are found among both the terrestrial snakes (Colubridae and Viperidae) and aquatic snakes (Hydrophiidae) (Rioux and Juminer 1983).

According to the World Health Organization (WHO 1995), snakebites are estimated to cause 30,000 deaths per year in Asia and about 1,000 deaths each in Africa and South America. More detailed statistics are available from certain countries. Over 63,000 snakebites and scorpion stings with over 300 deaths are reported yearly in Mexico. In Brazil, about 20,000 snakebites and 7,000 to 8,000 scorpion stings occur annually, with a case-fatality rate of 1.5% for snake bites and between 0.3% and 1% for scorpion stings. A study in Ouagadougou, Burkina Faso, showed 7.5 snakebites per 100,000 population in peri-urban areas and up to over 69 per 100,000 in more remote areas, where case-fatality rates reached 3%.

Snakebites are a problem also in developed parts of the world. Each year about 45,000 snakebites are reported in the United States, where the availability of health care has reduced the number of deaths to 9–15 per year. In Australia, where some of the world’s most venomous snakes exist, the annual number of snakebites is estimated at between 300 and 500, with an average of two deaths.

Environmental changes, particularly deforestation, may have caused the disappearance of many snake species in Brazil. However, the number of reported cases of snakebites did not decrease as other and sometimes more dangerous species proliferated in some of the deforested areas (WHO 1995).

Sauria (lizards)

There are only two species of venomous lizards, both members of the genus Heloderma: H. suspectum (Gila monster) and H. horridum (beaded lizard). Venom similar to that of the Viperidae penetrates wounds inflicted by the anterior curved teeth, but bites in humans are uncommon and recovery is generally rapid (Rioux and Juminer 1983).

Prevention

Snakes do not usually attack humans unless they feel menaced, are disturbed or are trodden on. In regions infested with venomous snakes, workers should wear foot and leg protection and be provided with monovalent or polyvalent antivenom serum. It is recommended that persons working in a danger area at a distance of over half-an-hour’s travel from the nearest first-aid post should carry an antivenom kit containing a sterilized syringe. However, it should be explained to workers that bites even from the most venomous snakes are seldom fatal, since the amount of venom injected is usually small. Certain snake charmers achieve immunization by repeated injections of venom, but no scientific method of human immunization has yet been developed (Rioux and Juminer 1983).

One of the most comprehensive standards regulating biological hazards in the workplace is European Directive No. 90/679. It defines biological agents as “micro-organisms, including those which have been genetically modified, cell cultures and human endoparasites, which may be able to provoke any infection, allergy or toxicity,” and classifies biological agents into four groups according to their level of risk of infection. The Directive covers the determination and assessment of risks and employers’ obligations in terms of the replacement or reduction of risks (through engineering control measures, industrial hygiene, collective and personal protection measures and so on), information (for workers, workers’ representatives and the competent authorities), health surveillance, vaccination and record-keeping. The Annexes provide detailed information on containment measures for different “containment levels” according to the nature of the activities, the assessment of risk to workers and the nature of the biological agent concerned.

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