Title : Asthma and occupational exposures
Occupational exposures may cause new-onset asthma in a healthy subject, aggravate pre-existing asthma in a symptomatic individual or reactivate asthma in an asymptomatic individual. All these disorders are covered by the term work-related asthma (WRA) or work-attributable asthma, i.e. asthma caused or aggravated by workplace agents or conditions. WRA significantly contributes to the overall burden of asthma, i.e. up to 30% of all adult asthma cases are caused or aggravated by workplace agents or conditions. On the other side, WRA is a heterogeneous entity that includes three subtypes, i.e. immunologic occupational asthma (OA), irritant-induced asthma (IIA) and work-exacerbated asthma (WEA).
OA encompasses immunologic OA and IIA (non-immunologic OA), i.e. WRA subtypes resulting from an inciting agent or condition only found at the workplace.
Immunologic OA is a form of WRA which develops after a sensitization to certain occupational agent that leads to chronic allergic inflammation of the airways. Up to now, 350 to 400 occupational agents that may cause immunologic OA are identified and they are divided into high-molecular-weight (HMW) and low-molecular-weight (LMW) agents. HMW agents, i.e. large molecules, proteins or glycopeptides, are complete sensitizing antigens, while LMW agents are incomplete antigens (haptens) that combine with a body protein to produce a sensitizing antigen.
Non-immunological type of OA (occupational IIA) is a form of OA caused by exposure to respiratory irritants. There is a number of irritants that may cause IIA, majority of which are related to certain workplaces. The rapid onset of asthma within a few hours after a single exposure to very high levels of irritant substances, i.e. reactive airways dysfunction syndrome (RADS) or acute-onset IIA, is the best characterized phenotype of IIA. Non-RADS-IIA also referred to as not-so-sudden-IIA and sub-acute IIA is the IIA phenotype that occurs following repeated moderate-to-high level exposures of respiratory irritants over a days or weeks, or even months. Still controversial is the IIA phenotype caused by chronic lower level of exposure to respiratory irritants (low-dose RADS).
Work-exacerbated asthma (WEA) is a form of WRA defined as a worsening of asthma due to condition at work, i.e. a pre-existing or concurrent asthma aggravated or reactivated by work agents and conditions. WEA can result by variety of occupational triggers, such as respiratory irritants and allergens, physical factors, behavioral states, etc.
As in the case of other workplace related disorders, the development of WRA is a matter of prevention. Activities and measures targeted to elimination or reduction of harmful workplace exposures, as well as to early detection and early intervention in the course of the lung damage, can significantly reduce the burden caused by WRA