Understanding Pollenosis


Understanding Pollenosis
Iltrct l'('. N{BChl} (trCI'), BSc (H<>rx>urs
MD (L:CT), tCP (SA),l)CH (SA),I'AAAAI (LtSA)
Pxrli:ssorand Head, AllergologvDiagnosticand Clinicalllescarclr['rrit
Lung Irrstitrrtc
('rtLt'.;Jxrrhtu r'.'P O Box 34560,Groote Schuur,71)37,S<xrtlrAlirca
1-el:+27 (0)21406-6889,Fzx: +27 0)21 ,1(Xj-(jlltlt|
. About 6 rnilli<>nSouth Africans suffer fi'om
\Mrich plants in South Africa are allergenicanrl r'l'hich
. Ongeveer6 miljoen SuidA1i'ikzurers
lv aanh<xrikrxrrs.
. Watter plantein Suid-Afiikais allergenies
en watter
is niei)
. Vcrstaansnrilineel- die induseerders
of them :re not?
van allelgiese
toest:rndesoos hooikoors, voortdurenrleallergicsc
Ljnderstand pollen the inducers of allergic<liseases
like hal'fever, allergic rhinitis, conjunctivitisand
cn asnlil.
,lA Fant Ptacr 2003;45(7):29-,74
hayfever was not causedby hay but by
the pollen of plants. Later Blackleyl
invented a clockwork device that
Pollens are important causal agents in
sensitisingallergic patients and indu- exposedsticky platesto pollen for a set
cing the symptoms of allergic diseases time andby attachinghis deviceto kites
such as hayfever, persistent allergic he could also assessthe distributionof
the pollen in the air abovethe ground.
rhinitis, conjunctivitisand asthma.
He alsoprovedthat pollen could induce
symptomsof hayfeverby inoculatinghis
own conjunctivaand mucusmembranes
Prehistoricpollen hasbeenidentifiedin
with pollen.
rocks millions of years old. Fifty
Although pollenosis was rare until
thousandyear old pollen recoveredfrom
the 20'hCenturyit is now recognisedas
the gravesitesof Neanderthalpeoplein
a post industrial revolution epidemic.
modern day Iraq, indicate that man has S e r i a l s t u d i e s i n S w i t z e r l a n dh a v e
been exposedto pollen since he was indicated that, while hayfever was
created. Howeveq it was only in the presentin 0.26% of the population in
l7'h Century that pollens were first
1926,by1958it wasup to 4.8%o
identifiedunder the microscope.
1993 up to 13.3o/o2.Similar increases
T h e f i r s t E u r o p e a n t o d e s c r i b e in prevalencehave beenreportedfrom
symptoms of seasonalallergy was
Scotland, Japan, the USA and also
r h o urban and rural gradientsworldwide.
L e o n a r d oB o t a l l o ( 1 5 1 9 - 1 5 9 7 )w
describeda constellationof symptoms
including headache,sneezingand an ALLERGENIC
itchy nose which he, in fact, termed
"nose catarrh".
Although there are 250,000 well
describedpollen producingplants,less
In l8l9 John Bostock, from Liverthan 100 are significant in terms of
pool, England, who had suffered from
pollen allergy. To be allergic, pollen
annual recurrent nasal and ocular
symptoms since the age of 8 years and grainsmust:
a. contain antigens able to elicit a
asthmalike synptoms from the age of
Specific IgE mediatedresponsein
16 years was the first to provide a
atopic subjects,
classicaldescriptionof hayfever.
I t w a s . h o w e v e r . J o h n E l l i o t s o n b. be producedin high quantities,
( 1 7 9 1 - 1 8 0 8w
) ho suggested
t h a t t h e c. be buoyant and carried for long
SA F'anrl'ract 2003;415(7)
distancesin the air,
d. be produced by plants that grow in
Pollen grains develop in the anthers
(male part of the plant) which are
located at the top of the filaments and
together these 2 parts are called the
"stamen". It is the wind pollinated
specieswhich are most relevantfrom
the allergologicalpoint of view. Plants
which are pollinated by insects (e.g.
orchids and roses) are endowed with
nectar insects and brightly coloured
petals to attract these insects are often
large and sticky and thus do not become
airborne and do not causesymptoms.
Climatic factorsplay a very important role in the production and dispersal
of pollen. Some pollen producing
grasses,such as perennialrye, have a
worldwide distribution whereas others
are regional. For example,Ragweedis
widespread in the Americas, but is not
a problem in Africa.
Similarly many of the treesinducing
pollenosisin Europe(e.g.Birch, Alder)
are not a problem in South Africa. In
Japan, Cedar is an important pollen.
Although Acacia speciesoccur widely
in Africa, the pollen producedby
African Acacia specieshas not been
found to be highly allergenic.
The size of the pollen determines
whetheror not it will producesymptoms
or not. Pollen grains needto be smaller
than 50 microns to be carried by the
The main allergy producing pollens
are derived from the grasses(Poaceae).
In South Africa, weeds are an uncommon causeof allergic symptoms,but in
certain areas,trees are fairly important
causes of symptoms (e.g. Johannesburg). Pollen grains greater than l0
microns are too large to penetrate the
medium size and small airways and thus
may cause rhinitis but not asthma.
However, larger pollen grains can break
up into submicronic particles in rainy
and damp conditions following rupture
ofthe granulesupon hydration. These
small particles typically cause asthma
during thunderstorms3.
Pollen grain allergens may also be
transferredby physical contact to other
small airborne particles such as diesel
exhaust, which penetrate to small
The grass family (Poaceae or
Graminae)comprisesover 600 genera
and 10,000species.Grasspollinates 23 weeks earlier at sea level than in
mountainous regions. Atmospheric
levels of grasspollen peak within l-2
months of the start of the flowering
season.In SouthAfrica the grasspollen
flowering seasonsareoften 8-10 months
The most important of the weeds,
inducing pollenosisare the Compositae
which hasover 20,000speciesincluding
and the Urticaceae.
the Chenopodiaceae
Parietaria(Urticaceae)are particularly
important in the Mediterranean areas
(e.g.in SouthernItaly).
Cape Pincushion
Figure 2: King Protea Cynaroides
Figure3: Confettibus
Figure4: Kikuyu grassspecimen
With the development of volumetric
samplers,it has beenpossible to obtain
dataon the numbersand levels ofpollen
grains in the atmosphere worldwide.
Usually pollen is collected on a transparentplastic tape,mounted on a drum,
and coveredwith a thin layer of adhesive
substance(e.g. Vaseline and Paraffin)
about 2mm./hourfor 7 days. Pollen is
then identified under a light microscope
and quantified.
The numberofpollen grains counted
on each sample is expressedas a daily
averagein pollen grainsper cubic meter
of air basedon a known rate of airflow
through the pollen trap. There are also
other types of samplerswhich could be
usedfor shortersamplingperiods(e.g.
l-3 hours) which could be fitted with a
series of glass fibre filters of different
pore sizes which can fractionate the
pollen in size classes.
To determinethe allergenconcentration in different particle size fractions,
immunochemical methods such as IgG
s u b c l a s sR A S T i n h i b i t i o n , E L I S A ,
immunoblotting or chemic luminance
may be used.
In South Africa pollen monitoring
has been conductedin several of the
major cities during the past20 yearsand
recently reviewed5.
At presentactiveongoingmonitoring
of pollen in the South African atmosphere is only being conducted in a
handful of localized sites. However,
botanical data obtained from the
flowering calendars of major grass,
weed and tree species are a useful
practical guide for patients who suffer
from the pollenosis (e.g. hayfever,
persistentor intermittentrhinitis, asthma
and rhinoconjunctivitis) asto when they
are likely to be symptomatic, in the
absenceof actual day-to-day pollen
monitoring data. Pollen calendarsfor
the relevant speciesarepublished in the
ALLSA Hand Book of Allergy6.
Usually pollen countsof more than 50
grains per cubic meter indicate
significant risk to allergy sufferers,but
patient sensitivity is extremely variable
and many patients suffer at lower counts.
More local studiesare needed.
There is a wide biodiversity in climatic
conditions and pollenosis in South
Africa. It is estimated that about 6
million SouthAfricans suffer from pollenosis. Pollen profiles may be typical
of Mediterranean,subtropical,savanna,
grassland,semi-desertand arid regions.
South Africa is home to 957 (10%) of
the known grassspeciesworldwide.
Although the Cape has over 2,622
different species in one of the richest
floral kingdoms of the world, the
indigenous African flowers (e.g.
Fynbos) (fig1,2,3) are not allergenic
to any degree.
SA Fiun Pract 2003:45(7)
Pollens causing symptoms in South
Africa include indigenousgrasspollens
suchasEragroslr, Buffalo and Kikuyu?
as well as to Bermuda and Rye grasses,
which are well known grass pollens
It is interestingthat in rural Africans
pollen allergy is extremely rare. However, when rural Africans move to
informal settlementsin peri urban areas
and adopt a more Western Style of
living, they rapidly acquire pollen
An important effect of cultivation of
an African grass on its clinical
allergenicity has recently been alluded
to1. In the rural areas Kikuyu grass
grows tall (fig 5) and is propagatedby
rhizomatouspropagation. In the urban
environment this handy grass is cut
regularly for domestic lawns, sports
fields or golf cowses,particularly in the
Gauteng area, and abundant pollen is
producedin the mornings.
Figure 5: Tall uncultivated Kikuyu
grass (Pennisetum Clandestinum)
Table I
r e.g.EragrostisCurvula r
(BoerLove grass) |
L - - -
- - - - - - J
Figure 6: Shorto cultivated male
Kikuyu grass showing anthers
I e.g.Pennisetumr
r (Kikuyu grass) |
! - - - - - - - - - J
Allergenic grasspollens in SouthAfrica
belongto 3 main subfamilies: Pooideae,
Chloridoideae and Panicoideae(Table
1). Important speciesfor testing for
allergenicity include Lolium (Rye),
eragrostis(Boer Love Grass),cynodon
dactylon (Bermuda),zeamays (Maize),
pennisetum (Kikuyu grass) and
stenotaphrum secundaturn (Buffalo
grass) (fig 7).
Figure 7: Buffalo grass (stenotaphrum secundatum), widespread
along the East Coast of Southern
Interestinglyin the Cape,mainly female
Kikuyu strandsare found, a reason for
less allergenicity of this grass in the
Cape when compared to Gauteng and
along the East Coastwhere male plants
are abundant. Often male plants are
introducedwhen cultivating large areas
(e.9. golf courses) (ng O leading to
more allergenicity than occurs in
domestic gardens.
Preliminary studiesin the UCT Allergology Unit by Prescott and Potter have
shown that grassessuchasKikuyu have
both cross reactivity as well as unique
IgE binding proteinsT.
Not all abundantpollen producing
grassesare highly allergenic. Cadman
et al5 have reported extremely high
levels of pollen production by thatch
grass(hyparrhenia hirta) in the Gauteng
area,but his grasspollen appearsnot to
be an important cause of allergy
An abundantpollen producer which
is indeedhighly allergenic,is eragrostis
curvula which is an indigenousAfrican
s p e c i e sw h i c h h a s b e e n s h o w n b y
immuno absorption experiments and
RAST inhibition experiments in the
Allergology Unit at the University of
CapeTown to possessa number of cross
reacting elementsfrom the other major
allergenic grass pollen producing
speciesin South Africa.
Eighty per cent of pollen allergy
sufferersin South Africa are sensitive
to Bermuda grasspollens.
Flowers from the Compositaeand
chrysanthemums induce allergenic
symptoms on a more limited scale in
South Africa. English plantain does,
however, occur quite extensively in the
Cape and is an important cause of
symptoms. It is, however, unusual for
patients to complain of allergy
syrnptomswhen viewing the spectacular
Namaqualand spring flower displays.
These flowers often include succulents
but a numberof thesefloweringspecies
belong to the Compositae.
The only true African tree species
which appear to be allergenic are the
Acacias,but to a very limited extent. Inhousestudiesof allergenicityofAcacia
pollen at the University of Cape Town
Allergology Unit have identified only
weak IgE binding elements in Acacia
pollens to date.
The pollenosis from the alien Port
Jackson tree imported from Australia
(fig 8) and the colourful Jacaranda,
especially in the Pretoria area,appears
to be overestimated. Thesetreespollinate at the peak of the grass pollen
seasonand it is believed that patients
often falsely attributetheir symptomsto
SA Fa-rnPlact 2003;45(7)
( .l , l )
Figure8: Port JacksonTree
these pollens as they are the pollens
which are "visible". It is, however,the
invisible airborne grass pollens which
arethe more importantallergensin most
o f t h e s e c a s e sa n d t h i s i s u s u a l l y
confirmedby specific allergy testingfor
the grass pollen specific IgE in such
In a recent survey of South African
Olympic athletes, it was found that
Plane pollen allergy was present in
about l5o/oof the athletes,followed by
Oak pollen a11ergy8.
Other causesoftree
pollenosis in the Gauteng and Mpumalangaareasincludethe Cypress,Willow,
Ulmus and in the CoastalareasofNatal
Moracea (Mulberry) speciesproduce
the most abundanttree pollen in the
spring. Tree pollens usually cause
symptoms in well defined peaks
between August and November, and
symptomsare usually short lived.
Although the reeds(Arundinoideae)
are abundant pollen producers and
widely distributedin SouthAfrica, their
role in the induction of clinical
symptomshas not been established.
A wealth of information is available on
the pollen production of the various
grass,tree and weed speciesin South
Africa. Pollen calendarsof the allergenic pollenshavealso beenpublishedand
are useful guides to patients as to when
they can expectsymptoms.
Strong allergenicity of indigenous
pollens has been confirmed for
Eragrostis, Kikuyu, Buffalo and weaker
allergenicity for Acacia and Themeda
Ongoing research is important to
identify and characterizethe important
allergensboth for clinical sensitivity
testingand for recommendingimmunotherapy.
Pollen monitoring in the atmosphere
has an important role in the care of
pollen sensitivepatients.In the USA and
in Europe pollen seasonsare extremely
well defined and reproducible, particularly for tree pollens (e.g. Birch),
ragweed and panetaria.
In the Southernhemisphere(e.g.
RSA, Australia, Argentina) pollen
monitoring poses a more difficult
challengeasthe grasspollen seasonsare
typically long (8-10 months). In South
Africa thereareat least5 distinct biomes
and a wide variability in the Burkard
sporetrap data obtained,even when the
sites are in close proximity.
This field needsto be developedand
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further refined in the future. Until this
occurs patients and doctors will continue to rely on pollen calendarsobtained
from botanists and specific IgE test to
guide both pharmacotherapyand immunotherapy in the foreseeablefuture.D
I wish to thank Mrs. Lindi Terblanche
for excellent secretarialassistanceand
Mrs. Ruth Prescott for her work on the
pollen collection and allergen
characterization of the indigenous
grasses in the Allergology Unit,
University of Cape Town.
I also wish to thank Mrs. Dilys
Berman of Red CrossAllergy Clinic for
providing an excellent continuouslocal
pollen monitoring service during the
past 20 yearsin the CapeTown area.
Pleaserefer to the CPD
Questionnaire on page 71.
Ed. E. Simons. Seasonalallergicrhinitis and
pollen in "Ancestors of allergy". Global
Communications Ltd. Publishers N.Y.
(USA) Chapter 9;78-84
2. Ed. D Amato, G Bonini, S Bousquet,S
Durham, TAE Platts-Mills. Pollenosis 2000.
A global approach.
3. SuphiogluC,SingM,TaylorP. Mechanisms
of grass pollen induced asthma. Lancet
1992: 339: 569-5'12
4. Knox RB, Suphioglu C, Taylor P. Major
grass pollen Lol pl binds to diesel exhaust
particles. Clin Exp Allergy 1997;27: 246-
Potter PC, Cadman A. Pollen allergy in
South Africa. Clin Exp Allergt 1996;26:
Ed. Potter PC. ALLSA Handbook of Allergy,
2'd Edition 2002; 162-169
Potter PC. Pollenosisin South Africa 2000
Ed. D Amato, S Bonini, J Bousquet, S
Durham, TAE. Platts-Mills. JCI Editions,
Naples 2001, 15: 117-120
Potter PC, Mather S, Lockey P, Ainslie G.
IgE specific IgE immune responsesto an
African grass, Kikuyu (Pennisetum
Clandestinum). Clin Exp Allergt 1993:23:
5 81- s 8 6
Hawarden D, Baker S, Toerien A, Prescott
R, Leaver R, Potter PC. Aeroallergy in
South African Olympic Athletes. S Afr Med
Journal 2002; 42(5): 855-856
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SA Fanr Pract2003;45(7)