The Aerobiology Pathway

Figure 2.4
Aerial infra-red photograph
of potato late
blight (Phytophthora
infestans), disease gradients
from primary
foci in a potato crop
(Lacey, J. et al., 1997).
ming less steep. Gregory explained that area sources of disease usually have shallower
disease gradients than point sources because lateral diluting eddies would themselves
contain spores rather than being spore-free (Gregory, (1976).
5.2. Health hazards
Many airborne fungal, actinomycete and bacterial spores are capable of causing disease
in man and animals by direct infection (living tissue is invaded by the microbe), by toxicoses
(ingestion of toxic metabolites of microbes), or by allergy (sensitivity to microbial
proteins and polysaccharides). Respiratory allergy in man may develop immediately as
in hay fever or asthma, or it can be delayed as in Farmer’s Lung. Potential sources of
hazardous airborne spores are many stored products including hay, straw, grain, wood
chips and composts. Spore laden dust is also released into the air in many ways including
distributing hay to animals, spreading out bedding and moving stored grain.
Pollen and spores are nearly always present in air but their number and type depend
on the time of day, weather, season and local source. Indoors the diversity of airborne
particles is usually lower than outdoors, and numbers of particles lower, unless there is a
source of contamination within the building. The use of the cascade impactor and
Andersen sampler together enable the different size fractions of the air spora to be
monitored for both visual counts and the number of viable units. Fig. 2.5 is a very simplified
diagram showing how far spores of different sizes can penetrate into the lungs
and the resulting type of illness that can follow in susceptible people (Lacey, J., et al.,
1972).
24 THE AIR SPORA