Ragweed (Ambrosia) progression and its health risks: will Switzerland resist this invasion?

12 Pages·2005·0.93 MB·English

Review article SWISS MED WKLY 2005;135:538–548 · www.smw.ch 538
Peer reviewed article
Ragweed (Ambrosia) progression
and its health risks:
will Switzerland resist this invasion?
P. Taramarcaza, C. Lambeletb,e, B. Clotc,e, C. Keimerd,e, C. Hausera,e
a Service of Allergology and Immunology, University Hospital of Geneva and Medical School,
Geneva, Switzerland
b Conservatoire et Jardin botaniques de la Ville de Genève, Geneva, Switzerland
c MétéoSuisse, Biométéorologie et environnement, Station aérologique, Payerne, Switzerland
d Service de l’agriculture, station phytosanitaire, Geneva, Switzerland
e Geneva Ambrosia Group, Geneva, Switzerland
Summary
The purpose of this article is to alert physicians the southern part of the canton of Tessin, aside
for the environmental and health threats of Am- from minor foci registered all over Switzerland.
brosia artemisiifolia(common ragweed) in Switzer- The routes of ragweed invasion are presented and
land. Switzerland borders several heavily ragweed discussed. Current measures of ragweed contain-
colonised areas. Up to 12% of the population suf- ment and needs for the future are presented. The
fers from allergies (hay fever, asthma) to ragweed urge for these measures at an early stage of rag-
pollen in these areas. Switzerland is beginning to weed spread is underlined by the impracticability
be invaded by this plant. Currently, the ragweed of eradication in highly colonised areas. The costs
pollen counts are still low but can reach local peaks of preventing ragweed spread in Switzerland are
that induce symptoms in allergic individuals. Rag- likely to be several magnitudes lower than the
weed allergy, however, is still rare in Switzerland. treatment of a significant percentage of the Swiss
Because the amount of ragweed pollen was in- population for ragweed pollen allergy. Because
creasing in the last few years, identification and areas can change from low to heavy ragweed
surveillance of ragweed plant foci was started. colonisation within a few years, the current win-
Colonisation is currently systematically monitored dow of opportunity to prevent further colonisation
in Geneva and southern Tessin. Major accumula- by ragweed should not be missed.
tion of ragweed foci have been detected in the
canton of Geneva, the western shore of the lake of Key words: Ambrosia; allergy; health risk; allergic
Geneva belonging to the canton of Vaud, and in rhinits; asthma; Switzerland
Introduction
Allergic rhinitis and asthma commonly coex- ago. In the future this may lead to new cases of rag-
ist and are high-prevalence and high-cost diseases weed allergies. In heavily infested areas of neigh-
throughout the world. Two large Swiss cross-sec- bouring countries such as France and Italy, up to
tional studies performed last decade have evaluated 12% of the population suffers from allergies (pri-
the prevalence of rhinitis and asthma at respec- marily hay fever and asthma) to ragweed pollen.
tively 11.1% and 6.8% in adults [1] and 17% and We therefore risk a burst in the prevalence, the
9% in children [2]. The regular increase in the severity and the duration of asthma and rhinitis
prevalence of asthma and allergic rhinitis since 40 during the late summer/early autumn months
years may have come to an end in the adolescent causing additional health care costs.
subpopulation as demonstrated recently [3]. This The purpose of this article is to alert physicians
trend has not been confirmed in adults were the for the environmental and health threats of Am-
prevalence of both conditions seems to continue to brosia artemisiifolia(common ragweed) in Switzer-
No financial rise. A low-grade ragweed colonisation has started land.
support declared.
in some areas of Switzerland more than a decade
SSWWIISSSS MMEEDD WWKKLLYY 22000055;;113355::553388––554488 ·· wwwwww..ssmmww..cchh 553399
Ecology
Ragweed (Ambrosia artemisiifolia)is an annual, within these fields. An information sheet is avail-
monoecious (male and female flowers on the same able on www.ville-ge.ch/cjb/neo.html. The rag-
plant) weed from the Asteraceae family [4], usually weed pollen is sized from 18 to 22 mm ad has small
sized 20 to 120 cm (figure 1a, 1b, 1c). It spreads by non-sharp spikes at its surface on electron mi-
its fruits some 10 weeks after the flowering season croscopy (figure 2). Its pollination period extends
[5]. This invasive neophyte species likes bare or in west Switzerland from beginning of August to
freshly moved grounds. It is greatly favoured by mid October with a peak from mid August to the
human activities and is growing along roads and end of September. Ragweed pollen production be-
cultivated fields, in fallow lands, in meadows, in gins at sunrise and continues during the morning
gardens and on building sites. It appreciates hot, reaching its highest count around midday [6].
dry and rich soils with neutral or slightly acid pH. Temperature and relative humidity have minimal
Sunflower fields frequently reveal the presence of effect on the day-by-day ragweed pollen count. In
ragweed. Both belong to the same botanical fam- contrast rainfall and unstable atmospheric condi-
ily: it is therefore difficult to control chemically the tions have a considerable impact on ragweed
infestation and they become strongly competitive pollen counts.
Figure 1
a. Plantlet;
b. Flowers just before
pollinisation;
c. Ambrosia plant
flowering.
a b
c
World epidemiology
In Europe, only Ambrosia maritimaL. is native. and Spain) and Ambrosia coronopifolia (perennial
Four species of ragweed, Ambrosia artemisiifolia ragweed) were introduced accidentally to Europe,
L. (short or common ragweed), Ambrosia trifidaL. the first already at the end of the 19thcentury [7].
(giant ragweed), Ambrosia tenuifolia(only in France Ambrosia artemisiifoliais mentioned in France and
Ragweed (Ambrosia) progression and its health risks 540
Figure 2
weed [8]. North America remains the main foyer
Ragweed pollen.
of ragweed where up to 50% of all cases of polli-
nosis are related to Ambrosia pollen [9, 10]. Some
areas of Japan [11], China [12] and subtropical Aus-
tralia [13] are also infested by this weed. In Europe
ragweed sensitisation is increasing [14, 15] and this
weed is even appearing in Sweden since 1996 [16]
and in the Baltic states [17]. Short ragweed is now
growing on the footsteps of the mountains in a
band ranging from the Rhone valley of France
[18–20] to Hungary were 90% of the ground sur-
face is colonised by ragweed [21]. It is also spread-
ing in central Italy [22, 23] and through the Po val-
ley [24–26], in Austria [27, 28], in Bulgaria [29] and
in some states of former Yugoslavia where it ben-
efits from the fallow lands created by the recent war
[18]. In the colonised areas, ragweed becomes rap-
idly the main allergen as it is in North America and
more recently in the French Rhône-Alpes region
Germany since 1863. Common ragweed plant re- [18]. Natives who are living with ragweed pollen
mained discreet over several decades and became since a long time seem to develop a natural toler-
more frequent for instance in France in the Lyon ance to it when compared to newly arrived immi-
area only around 1950. In the US, up to 10% of grants who demonstrate a 3 fold increase in typi-
the overall population is sensitised to short rag- cal late summer allergic symptoms [30].
Swiss epidemiology
The presence of ragweed in Switzerland was [36]. Indeed since 2001, new infested fields have
reported for more than 100 years. Since the last been discovered and higher pollen count measured
decade signs of an increased presence of ragweed [37–39]. This global increase did not yet result in
have been reported mainly in the cantons of Basel a general increase in allergy during August and
[31–33], Ticino [31, 34], Geneva [31] and recently September, although a few possible native ragweed
Zurich [35]. It has been demonstrated that there is pollinosis have been described in Zurich [35] and
a good correlation between the high pollen counts Geneva [40]. In 2003, several ragweed populations
of the Lyon area and the much lower counts of the were also discovered in southern Ticino [41]. Field
Geneva area, suggesting the importance of long research conducted by the Swiss Commission
distance pollen transport by the wind [36]. Never- for Wild Flower Protection CPS/SKEW during
theless during some days there are major discrep- 2002–2003 allowed drawing an actual distribu-
ancies between the 2 towns suggesting that there tion map of ragweed in Switzerland (figure 3 and
is also a local production of ragweed in Geneva www.cps-skew.ch).
Figure 3
Ambrosiaartemisii-
foliadistribution in
Switzerland updated
in December 2003.
Elaborated by the
CPS (Commission
suisse pour la pro-
tection des plantes
sauvages) and the
CRSF (Centre du
réseau suisse de
floristique) on a man-
date of the SAEFL
(Swiss Agency for
Environment, Forest
and Landscape).
SWISS MED WKLY 2005;135:538–548 · www.smw.ch 541
Clinical spectrum
It is usually easy to diagnose ragweed related between mugwort and ragweed pollens is of at least
allergies because the symptoms occur typically in 80% [47]. Reacting epitopes are profilins, but also
August and September after the pollination of the major mugwort allergens (Art v 1 and Art v 2)
other common grasses. The diagnosis should be and the major ragweed allergens (Amb v 1 and
confirmed by a positive skin prick tests and/or a Amb v 2), which are 2 highly homologous 60 kd
positive serum specific IgE for ragweed. Clinical and 28–46 kd components. This close botanical re-
manifestations are rhino-conjunctivitis (87%), lationship has clinical relevance because it has been
asthma (42%) and more rarely contact dermatitis shown that mugwort and ragweed pollen extracts
or urticaria [42]. Symptomatic ragweed allergic induce comparable nasal obstruction in patients
rhinitis affects vigilance and cognitive functioning allergic to mugwort [47]. Therefore it can be ex-
[8] and leads to a lower worker productivity [43]. pected that mugwort allergic patients would also
Symptoms can begin with as little as 5–10 pollens/ react to ragweed pollen. Because mainly mugwort
cubic metres [44]. Pollen grains reach the upper pollen is accountable for late summer pollinosis
respiratory tract but are too large to penetrate and asthma in Switzerland [48], it can be assumed
in the lower airways to lead to asthma. Allergen that the rise of ragweed may increase the preva-
carrying paucimicronic particles, sized less than lence and the severity of mugwort allergic related
5 mm, which are smaller than pollens, can be symptoms when the threshold value of ragweed
released during light rain or thunderstorm and are pollen in the air will be reached. Allergenic rela-
responsible for asthma attacks [10]. The preva- tionship can also be found between taxonomically
lence of asthma in ragweed infected areas such as diverse pollens [49]. For instance, Amb v 1, the
the Rhône-Alpes area affects up to 12% of the pop- ragweed’s major allergen, can also cross-react with
ulation during the pollen period and can classically Phl p 4, the timothy grass’s major allergen [50]. An
be severe [19]. oral allergy syndrome has been described with
Ragweed can cross-react with numerous other Cucurbitaceae such as melon, watermelon or cu-
grasses from the Asteroidae subfamily such as cumber and the Musaceae such as banana [51, 52],
mugwort and sunflower [45, 46]. Cross-reactivity as well as contact urticaria [53].
Treatment of ragweed allergy
The management of ragweed rhino-conjunc- in the more severe spectrum of allergic asthma,
tivitis and asthma includes allergen avoidance, regardless of the allergen [57–59]. Early controlled
medication and immunotherapy. Outdoor aller- trials showed no or little efficacy of ragweed injec-
gens are difficult to avoid but it can be recom- tion specific immunotherapy (SIT) [60, 61]. Later
mended to practice sport in the evening when the studies have recognised SIT as an efficacious pro-
pollen count is the lowest, except those evenings cedure to reduce nasal symptoms during ragweed
when long-range transport of pollen occurs. It is antigen exposure [62, 63]. SIT is also beneficial in
also advisable to avoid exercising on days that rains asthma but this effect is not sustained during the
and dry periods alternate or just before or after a second year of immunisation therapy [64]. The
thunderstorm. The air concentration of submi- indication of SIT in ragweed-induced asthma is
cronic particules is higher and well dispersed in therefore still debated [64]. A few studies have pos-
these cases, increasing therefore the risk for a se- tulated that SIT with a single allergen may exert a
vere asthma attack. But if the rain is sufficiently preventive effect against sensitisation to other air-
abundant the risk of an allergic reaction is reduced. borne allergens. Unfortunately, a recent study has
Medical treatment of rhino-conjunctivitis consists shown that SIT in monosensitised adults to com-
mainly in intranasal topical glucocorticosteroids mon airborne allergens, does not prevent ulterior
and oral H -antihistamines [54]. There is an addi- sensitisation to ragweed north of Milano [65].
1
tive role for ocular topical H antihistamines and Since 1900 oral administration of ragweed was
1
oral or topical cromones in rare situations. Med- used for hyposensitisation of hay fever. A pilot
ical treatment of asthma includes intrabronchial study on encapsulated oral immunotherapy with
glucocorticoids, long and short acting b agonists ragweed Amb a 1, proved to be safe and attenuated
2
and oral anti-leucotrienes [55]. Second line drugs the symptomatic response to ragweed exposure
are oral cromones, inhaled ipratropium, oral glu- [66]. A recent randomised controlled study on
cocorticoids and sustained release theophilline. sublingual immunotherapy (SLIT) with ragweed
Patients with moderate to severe ragweed related extract, confirmed the efficacy and safety of this
rhinitis benefit from omalizumab, a recombinant treatment and strongly suggested a dose response
monoclonal antibody, in a dose dependent fashion relationship [67]. A Cochrane systematic review on
[56]. Although there are no available publications SLIT was unable to draw conclusions about rag-
in ragweed pollen induced asthma, several recent weed SLIT because there was only one study that
multicentre trials have demonstrated its efficacy fulfilled the inclusion criteria [68].
Ragweed (Ambrosia) progression and its health risks 542
Ragweed is particular health hazard
Ragweed is a true plague in the colonised areas very quickly and every single plant can produce an
where it becomes the main allergen for various rea- average of 3000 to 6000 seeds per plant and large
sons. Its pollen is very allergenic and very low con- specimens up to 60000 seeds, which can germinate
centration such as 5–10 pollen per cubic meter of after lying up to 40 years in the ground [69]. These
air are sufficient to trigger allergic reactions in sen- seeds are mainly disseminated by human activities
sitive patients. Moreover, every ragweed plant pro- such as vehicle movements, infested soil trans-
duces enormous quantities of pollen if compared ports, plots of grains for birds and possibly by plots
to other grasses. Ambrosia artemisiifolia spreads of agricultural seeds.
The situation in Geneva
In Geneva, the plant is mentioned by botanists Geneva, especially between Rolle and Aubonne, to
since 1940 [70]. Ambrosia airborne pollen has been Chavornay and around Lausanne [73].
recorded in the air for the first time in 1967 [71],
and then every year since the beginning of the con- Pollen
tinuous measurements in 1979. The Geneva Am- Daily average pollen counts are measured in
brosia Group, founded in 2000, was alarmed by Geneva with a Hirst type volumetric spore trap
the increase of annual pollen index, which could situated on top of the Geneva University Hospital
potentially result from local pollen sources: some since 1979. Suspended particulate matter is col-
heavy infested fields were found in 2001. Ground lected on coated plastic tape and was analysed by
control for ragweed infestation in the canton of light microscopy by R. M. Leuschner (Basel) from
Geneva has started methodologically the same 1979 to 1984 and 1989–1992. Since 1993 Meteo-
year [72]. There are now also reports from infested Suisse in Payerne analyses the pollen, in accor-
places in the canton of Vaud, along the lake of dance with international standard methods [74].
Figure 4
Ragweed pollen
annual index in
Geneva 1989–2004.
Figure 5
(Modified from Mau-
rer 2003 [57]) Two-
hours concentration
of ragweed pollen
recorded by the
pollen traps located
in the centre of the
city (HUG) and in the
surrounding of an
infested field near
Geneva (Bernex):
episode showing
long-range trans-
ported pollen regis-
tered in the evening
on 3rdSeptember and
local pollen peak on
4thSeptember in the
morning.
SWISS MED WKLY 2005;135:538–548 · www.smw.ch 543
Annual pollen index reached the value of 150 for tended. Bernex is a densely inhabited area and re-
the first time in 1993 (figure 4). The pollen counts peated exposition to such pollen concentrations
then rose sharply from 1993 before dropping in can lead to sensitisation [72].
2001, 2002 and 2003, mainly because adverse
weather conditions that limited the amount of Plants
long-range transport of ragweed pollen from the A floristic investigation of Geneva based on a
French Rhône-Alpes area like the local dispersal. kilometre square scale, conducted from 1990 to
Results from 2004 show evidence that the problem 2000, showed the presence of A. artemisiifolia in
has not diminished. A more detailed study includ- 33 km2, representing a frequency of 11%. The map-
ing several pollen traps has confirmed that long- ping of ragweed plants has also been conducted
distance transport of pollen from French Rhône- yearly from 2001 to 2003. At the end of 2003, 33
Alpes region under south-west wind episodes is an locations with common ragweed were reported
important source for the ragweed pollen registered along or among fields, fallow lands, gardens, waste
in Western Switzerland and in particular in places, building yards, roads and railways with
Geneva [36, 72]. Figure 5 shows that pollen from abundance ranging from just a few to 100000
long-distance transport is recorded in the evening plants and covering areas of 3 m2to 5000 m2(fig-
in different pollen traps from the area, while pollen ure 6). Eight locations were heavily infested [72].
from local sources is recorded in the morning, at In 2004 this mapping effort could not be updated
the time it is released from plants, a result that because of lack of financial resources, but another
confirms those from Laaidi et al. 2003 [18]. It is 5 small additional localities were found by local
remarkable that local pollen peaks are very high, botanists. A total of 215000 m2 are known to be
even if the infested field is still not yet very ex- already infested with ragweed, with annual plant
counts estimated to vary from some 10000 to more
than a million specimens.
Figure 6
Common ragweed Ragweed epidemiology survey among
distribution in
Geneva allergists in 2004
Geneva at the end
of 2003. The response rate among Geneva allergists in
private practice was satisfactory: 18 out of 25
(72%) practitioners returned the questionnaire.
Only 8 out of 18 were consulted for ragweed re-
lated allergy. The majority of the 8 practitioners
have encountered 1 or 2 ragweed allergic patients
during the 2004 ragweed pollinisation period. Two
third of these ragweed allergic patients have been
sensitised outside Switzerland, in ragweed en-
demic regions such as the USA, France, Italy, Aus-
tria and Hungary. The amount of ragweed allergy
with evidence of sensitisation in Geneva remains
still low with possibly 4 to 5 cases in 2004.
A serious threat
Ambrosia is a major health threat. The entire found no ragweed invasion in the 100 observed
sanitary network has to recognise that ragweed in- fallow lands, suggesting again that we are still at
festation is a serious concern in the state of Geneva an early stage of ragweed colonisation. This early
and the rest of Switzerland. Ragweed pollen counts stage of infestation is corroborated by the rarity of
measured in Geneva increased over the last decade ragweed allergy cases due to Geneva indigenous
although low pollen indexes due to adverse sensitisation. Nevertheless, a few new cases related
weather conditions can be recorded some years. to local sensitisation have been diagnosed in
The number of colonised fields, gardens, building Geneva in 2004. This trend will need to be con-
sites and along roads and railways is indeed in- firmed over the coming years with repeated epi-
creasing in Geneva, as shown by the precise car- demiological surveys in Geneva and in other places
tography of the whole canton. Swiss fallow land in Switzerland.
observation net covering several cantons, has
Ragweed (Ambrosia) progression and its health risks 544
Causes of ragweed progression in Europe
The wide spread progression of ragweed weed production by 61% [78]. Despite many un-
through south and continental Europe has several certainties, CO concentrations have already in-
2
potential explanations that all seem to have a di- creased by 29% since pre-industrial times and are
rect or indirect link with human activities. Since still expected to rise [79]. The climate change sce-
the accidental introduction of Ambrosia artemisiifo- nario could therefore be one of the factors favour-
liaL. andtrifidaL., from North America to France ing the spread of ragweed through Europe and
and Hungary in the second half of the 19thcentury, Switzerland [10, 80]. Climatic changes will also
these weeds have encountered ideal conditions to favour ragweed colonisation towards the more
develop in Europe. The growing economical de- northern and higher areas, which were initially too
velopment and extensive deforestation favoured cold for its spread. An example is the Czech Re-
the increase of industrial and urban fallow land. public where a climatic change model showed a po-
Both are probably important factors since ragweed tential for extensive ragweed proliferation in the
grows in freshly moved grounds and along culti- country [81]. Traffic related air pollution is a major
vated fields. In many areas the increase in ragweed contributor to global warming, but may also play
colonisation is related to the development of sun- a role in the propagation of allergic sensitisation to
flower culture. European common agriculture pollen and therefore possibly to ragweed [82].
policies (ECAP) may have contributed to some ex- However, no consistent results regarding heavy
tent to the colonisation of ragweed, as it has a tro- traffic exposure and symptoms of allergic asthma
pism for fallow land. Similarly, the war that led to or rhinitis have been found [83]. Ragweed infesta-
the fragmentation of Yugoslavia, created a situa- tion at an early stage has been found preferentially
tion where numerous fields were left to lie fallow along the communication net such as railways and
and where destruction of houses led to extensive highways. The two most rapid progressing rag-
waste lands that favoured ragweed colonisation. weed colonised areas in Switzerland are Geneva
Transport of soils contaminated with seeds for and the Ticino, which both act as main traffic entry
buildings or embankments, for example along the gates into the country. Pendulum daily traffic be-
TGV railway Lyon–Marseille, is also an important tween a ragweed infected area such as the Rhône-
cause of ragweed progression in France. The po- Alpes region and the Geneva area could generate
tential effect of global climate change on allergenic seeds deposition on the side of the main commu-
pollen production is still a field of investigation. nication ways. Agricultural machinery such as
There is good evidence that the climatic reheating combine-harvester are now frequently rented and
is correlated to a mean advance of 3 weeks in the transported over long distances. There are several
pollination periods of most winter and spring examples of farming machinery rented in the Lyon
plants in Switzerland over the last 21 years of ob- ragweed infested regions that are transported to
servation [75–77]. This has however not been the Geneva or Lausanne area. In fact, a farmer dis-
shown for ragweed, but one can assume that sim- covered in Geneva, in the late 90th, that one of his
ilar trends might be measured in the coming fields was infested by ragweed. This field had been
decade. A recent study has demonstrated that a harvested the previous year with an infested com-
doubling of the CO concentration in environ- bine-harvester rent from an infested area.
2
mentally controlled greenhouses stimulated rag-
Can we still do something
Despite the fact that several countries have im- The chance of success of fighting ragweed has
plemented various eradication measures, ragweed to be assessed before starting an expensive cam-
continues to invade new regions. We still do not paign in Geneva and Switzerland. Switzerland is
know if they really work and which one works best. still at an early stage of ragweed invasion, which
There is of course the historical successful ragweed possible favours action. The “Conservatoire et
eradication campaign that started in Gaspesia in Jardins botaniques de la Ville de Genève” esti-
1937. This province is still free of ragweed nowa- mated costs for the inventory, the surveillance and
days [84]. Nevertheless any later campaign in the coordinated action against existing ragweed lo-
North America in hotter areas did not obtain a re- cations in Geneva on approximately SFR 30000.
duction in pollen loads. The main identified rea- In view of previous international campaigns
sons are the lack of continuation of eradication and despite the fact that success cannot be guaran-
measures and/or the lack of coordination between teed, every attempt should be made to eradicate
the various concerned administration and/or land- ragweed in Geneva and Switzerland, especially at
owners. these reasonable costs. Unfortunately, financial re-
sources have not reached this amount in 2004.
SWISS MED WKLY 2005;135:538–548 · www.smw.ch 545
Existing phytosanitary interventions
Many actions have been implemented to avoid Herbicides
progression of Ambrosia artemisiifolia. They usu- Based on the French experience since 1985,
ally depend on the type of infested biotope and are various herbicides can be used combined with
often combined. physical elimination strategies. Chemical weed-
killing represents an ecological and health risk and
Elimination strategies should be used with caution and adequately regu-
The plants have to be pulled out systematically lated. Herbicides may be used in agricultural fields
before the maturation of the fruits and ideally be- only. Ongoing experiments on herbicide are cur-
fore flowering latest at the end of July in Geneva rently being implemented in the infested fields and
and the Rhône-Alpes region. This method is effec- meadows in Geneva by the Federal Station of
tive but requires several interventions and a lot of Agronomical Research of Changins. None of the
manpower in heavily infested areas. Sensitive per- tested herbicides have proved a complete efficacy.
sons should avoid this preventive eradication and In sunflower fields, for instance, there is no really
others should protect themselves with gloves and efficient product [73].
masks during the flowering period. Successive cuts
can also avoid flowering and fructification but they Prevention measures
have also significant costs. The period of cutting Several measures can prevent ragweed infesta-
has to be chosen very carefully to avoid seed set- tion in at risk surfaces or in treated surfaces. Tex-
ting of recovering plants [73]. Experiments are tile membranes or re-vegetation have advantages
currently being implemented by the Federal Sta- and disadvantages. To avoid and control ragweed
tion of Agronomical Research of Changins on in- infestation, bare surfaces must be covered and reg-
fested fields in Geneva. Overall these measures are ularly inspected.
necessary and costly. However, they are potentially
insufficient if not done in coordination with and in
addition to other interventions.
What is done and where
Experiences from France in terms of public health and costs are very im-
The enormous potential of dispersion is the portant. For example, in the very heavily infested
strength of this invasive neophyte species. The area of Busto Arsizio, 12% of the population is
analysis of the ragweed invasion in the Rhône- allergic. Here the pollen concentration often ex-
Alpes region since 30 years bears concern, despite ceeds 200 pollen/m3 during the flowering season
several eradication campaigns. The lack of coordi- and reaches for several days 700 pollen/m3. The
nation between the various administrative offices, state hospital of Milano 1 spent approximately
the absence of concerted actions including all the 1’390’000 Euro to treat the ambrosia allergic peo-
infested areas of a region, and the too short du- ple in 2002 [26]. Moreover, the chances of ragweed
ration of these campaigns are responsible for the eradication at this stage of the invasion are com-
lack of success. The neighbouring areas of the promised, in particular for economical reasons.
Rhône-Alpes valley channel like Switzerland and
other French regions (Auvergne, Provence-Côte Experiences from Canada
d’Azur) are now reaching levels of ragweed pollen The historical successful eradication cam-
close to the threshold of alert. In the Rhône-Alpes paign launched in 1938 was based on systematic
area CHF 250’000 are spent yearly only to spread pull-out of the ragweed plant with the help of
information. Practical documentation on the rag- school-children in Gaspesia [84]. There are several
weed fight and pollen counts for various areas geographic reasons that may explain that success
within the Rhône-Alpes region are available and that still prevail today. Gaspesia is located on
downloadable from the internet: www.ambroisie. the shore of the Atlantic ocean, which limits the
info. spreading of the weed, and is situated at the septen-
trional limit of the ragweed distribution. The same
Experiences from Italy type of campaign has nevertheless failed in 1950
The case of northern Italy is exemplary, be- in other parts of Canada and in particular in
cause almost nothing was done despite numerous Montreal. In Quebec the direct cost of ambrosia
warnings to fight ragweed in an early stage of the (health and prevention) reaches an equivalent of
invasion. After 10 to 15 years the passivity of the CHF 49 millions. The campaign against the spread
authoritieshas resulted in the fact that ragweed of ragweed in Quebec has been re-evaluated since
is found almost everywhere. The consequences 1990. It demonstrated that repeated yearly cam-
Ragweed (Ambrosia) progression and its health risks 546
paigns implementing mowing the weed at 2 cm or pollen production can be reduced by 88%, thereby
hand weeding at the second fortnight in July are insuring a relative relief for people allergic to rag-
effective. The seed production reduces and the weed pollen [85, 86].
Proposed measures in Switzerland
The National pollen network (MeteoSwiss), failures and successes of other countries and cre-
has made possible to announce the presence of rag- ate an adequate monitoring system. To eradicate
weed pollen in Switzerland and in particular in ragweed specific federal legislation is needed re-
Geneva since 1993, at an early stage of invasion. garding the importation of bird grains, since 70%
The ground control of the canton of Geneva has of them are contaminated by ragweed seeds. Farm-
corroborated these findings by detecting an in- ers should be encouraged to announce systemati-
crease in the number of spots, mainly in freshly cally a ragweed infestation to the adequate phy-
moved fields and along streets and railway lines. tosanitary authority. Small surfaces or low inten-
Early measures have been taken since 2001. In sity infestation should be treated by pulling-up
Geneva most ragweed plants have been pulled out plants and when the surface is too large or the den-
one or several times and herbicides have been used sity too high it is best to combine successive cuts
in the agricultural invaded surfaces. Ragweed is and chemical treatments. The use of herbicides
now well known by farmers and may be regularly should be regulated at the federal level depending
controlled mechanically or by herbicides. The on the type of infested field and the stage of growth
Geneva Ambrosia Group has been officially re- of the ragweed plant. Information about the dif-
cognised by the State Council of Geneva (Conseil ferent ragweed eradication methods should be
d’Etat de Genève) on April 21, 2004. Further mea- spread out in all national Swiss languages and on
sures need to be supervised at the federal level the same level as in France. The surveillance of
[87]. A multidisciplinary net will therefore soon be ragweed locations of infestation in Geneva, has
launched by the Swiss federal Office of Public Health confirmed its continuous presence since 2001. The
(SFOPH = OFSP = BAG) in collaboration with seed bank is elevated to very elevated in the ground
Allergy health specialists from Swiss Universities of heavily invaded areas. This will allow germina-
and private practice, the Swiss Agency for Environ- tion for many coming years. The pursuit of anti
ment, Forest and Landscape (SAEFL = OFEFP = ragweed measures and prevention strategies are
BUWAL), the Federal Office for Agriculture (FOA therefore necessary to avoid or limit the formation
= OFAG = BLW), and road and rail maintenance of new seeds and further propagation of the rag-
services. This national group will have to statue on weed infestation.
the best measures to be taken in the light of the
Predictive models
In North America or in the French Rhône- pollen season can be forecasted with statistical
Alpes region, it seems unrealistic to try to eradi- models: one by summing the temperatures and the
cate ragweed at short or medium term. Aerobiol- other by using a multiple regression based on
ogists have therefore implemented forecasting monthly meteorological parameters. These mod-
models based on the probabilistic distribution of els are successfully implemented in the Lyon area
pollen curves [7]. Except for large and rapid fluc- since 2000 by allergists and patients who can an-
tuation of pollen counts, this model allows a good ticipate the risk of ragweed exposure and take pre-
estimate of the exposure risk two days in advance ventive treatment [89].
[88]. Moreover, the start and the duration of the
Conclusion
A low grade but rapidly expending ragweed sanitary authorities will have to coordinate costly
invasion has now started in some locations global measures encompassing regulation, preven-
around Geneva, in the Ticino and in other parts tion, elimination strategies and education. Acting
of Switzerland. Farmers are already well informed now, at reasonable costs may avoid an allergic epi-
of the situation and adequate measures should be demic similar to the one in the neighbouring
taken. There is more concern about industrial, French Rhône-Alpes region, where 12% of the
urban and natural sites of ragweed invasion be- population is allergic to ragweed. This window of
cause the public is insufficiently informed. Federal opportunity should not be missed and every effort
SWISS MED WKLY 2005;135:538–548 · www.smw.ch 547
should be made to stop the ragweed invasion be-
Correspondence:
fore it becomes a public health or agricultural
Prof. C. Hauser
problem. This is also one of the main recommen-
Service of Allergology and Immunology
dations from the World Health Organization con-
University Hospital of Geneva
cerning the future of allergies [90].
24, rue Micheli-du-Crest
CH-1211 Genève 14
E-Mail: [email protected]
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