Toxicology of Industrial Compounds

11
Occupational Asthma Induced by Chemical
Agents
C.A.C.PICKERING
Wythenshawe Hospital Manchester
Introduction
Occupational asthma may be defined as variable airways narrowing
causally related to exposure in the working environment to airborne dust,
gases, vapours or fumes (Newman Taylor, 1980). This definition includes,
therefore, both immunological and nonimmunological causes of asthma in
the workplace. Immunological causes of asthma in general demonstrate a
latent period between exposure and the development of symptoms. Once
sensitisation has occurred airway responses may be seen at very low levels
of exposure. Both high and low molecular weight agents may cause
sensitisation. Irritantinduced occupational asthma characteristically follows
within 24 h of a usually, single, high level exposure to an irritant substance
and has been named reactive airways dysfunction syndrome (Brooks et al.,
1985).
The number of chemical agents causing occupational asthma is
extensive. As new, highly reactive, chemicals are developed these numbers
are likely to grow. Low molecular weight chemicals may act as haptens,
reacting with body protein to form a complete antigen to which specific
antibodies are formed.
The incidence of occupational asthma in most countries is not known
with any great accuracy, there are considerable variations in reporting
systems between countries. Since many individuals with occupational
asthma change jobs without a specific diagnosis being established, the
published figures of incidence will be significant underestimates of the true
incidences. In Japan (Kobayashi et al., 1973), the prevalence of
occupational asthma amongst adult male asthmatics is said to be about
15%. In the UK a new reporting system has recently been established—
Surveillance of Work-related and Occupational Respiratory Disease Project
(SWORD). Newly diagnosed cases of workrelated respiratory disease are
reported monthly by consultant chest and occupational physicians.
Between 1989 and 1991, 631 cases of chemically induced occupational
asthma were reported, of these 53% were associated with exposure to