Erfolgreiches internationales Rotary-Jugendseminar über Malaria
Spannende Diskussionen und Ergebnisse in Pristina (cba)
Mit der Bekämpfung von Malaria und weiteren durch Mücken
übertragbaren Krankheiten befassten sich bei einem Rotary Seminar in
Pristina 40 junge Menschen aus Deutschland, der Türkei, Griechenland
und Kosovo. Die Beteiligten, Studentinnen und Studenten aus vielfältigen
Fachrichtungen, beispielsweise Medizin, Geologie, Recht, Biologie und
Wirtschaft, waren im Alter zwischen 18 und 25 Jahren. Organisiert wurde
das Seminar durch die Rotary Clubs Radolfzell-Hegau, Sisli-Istanbul und
Pristina International mit der Unterstützung des Länderausschusses
Deutschland-Türkei sowie der jeweiligen Rotary Distrikte.
„Neben den spannenden, kreativen Diskussionen und Ergebnissen im
Hinblick auf das Thema, war es etwas besonderes, die Atmosphäre zu
erleben. Während dieses englischsprachigen Seminars gab es eine
enge, bestens funktionierende Zusammenarbeit, unabhängig von
Nationalität, Sprache, Religion, Alter oder Geschlecht“, erklärten die
beiden Projektleiter Wolfgang Uebel, Vorsitzender des
Länderausschusses und Mitglied des RC Radolfzell-Hegau, und Manfred
Raupp, Länderausschuss-Sekretär und Mitglied des RC Lörrach. Rotary
habe damit erneut ein Zeichen zur Völkerverständigung, Freundschaft
und Friedenssicherung setzen können.
Das dreitägige Seminar wurde von Matthias Feil aus Konstanz geleitet.
Er ist ebenfalls Mitglied des RC Radolfzell-Hegau, arbeitet bei SAP und
ist vertraut mit der Durchführung von Workshops mit Hilfe modernster
Managementmethoden, beispielsweise Design Thinking. „Dabei arbeiten
Menschen unterschiedlicher Disziplinen in einem kreativitätsfördernden
Umfeld zusammen. Ziel ist es, gemeinsam tragbare Lösungen zu finden
und Konzepte zu entwickeln“, beschreibt Matthias Feil die
Vorgehensweise.
Zur Einführung waren zwei Experten auf dem Gebiet der von Mücken
übertragenen Krankheiten angereist: Florence Fouque, Leiterin des
TDR-Referats für Vektoren, Umwelt und Gesellschaft der Welt-
Gesundheitsorganisation (WHO), und der Präsident der World Mosquito
Control Association Norbert Becker zeigten den Teilnehmern die aktuelle
Situation, die Gefahren und die Herausforderungen auf. So zählt die
WHO jährlich weltweit 216 Millionen Malaria-Infektionen mit mehr als
500000 Todesfällen.
In unterschiedlicher Zusammensetzung machten sich die Teilnehmer
dann an die Arbeit und entwickelten Ideen, die selbst die Fachleute
staunen ließen. Angedacht wurde unter anderem ein „Automatisches
Epidemie-Prognose- und Reaktionssystem“ zum Sammeln und
Bereitstellen von Daten mittels Smartphone. Eine Gruppe schlug eine
App zur Aufklärung und Prävention vor. Ein Team beschäftigte sich mit
der Kartierung unzugänglicher Regionen, um die Versorgung mit
Medikamenten sicher zu stellen. Eine weitere Gruppe entwickelte unter
dem Namen „The Zapper“ eine elektrische, durch Sonnenenergie
autarke Insektenfalle, mit der die gesammelten Stechmücken zudem als
Dünger oder Tierfutter weiterverwendet werden könnten.
Beeindruckt von den Ergebnissen, an denen nun teilweise weiter
gearbeitet werden soll, zeigten sich zum Ende des Workshops die
beiden Fachleute sowie der Rektor der Universität Prishtina Marjan
Dema, der an seiner Hochschule die Räumlichkeiten und die
Infrastruktur zur Verfügung stellte. „Die Reife und Kreativität der Ideen,
die uns die Teilnehmerinnen und Teilnehmer am Ende des Seminars
präsentierten, waren ganz erstaunlich“, erklärte Ilir Krasniqi, Präsident
des gastgebenden RC Pristina International abschließend und freute
sich, dass über die außergewöhnliche Rotary Veranstaltung sogar in den
Abendnachrichten des Senders RTK berichtet wurde.
Begeistert waren aber auch vor allem die Teilnehmer, die natürlich
neben der Arbeit zusätzlich ein kleines Programm zum Kennenlernen
von Land und Leuten erleben durften. Dabei hörte Heiner Grönewald,
ebenfalls Mitglied des Länderausschusses und Begleiter der Gruppe,
folgenden Ausspruch, den ein Kosovar zu einem Griechen sagte und
den wohl keiner der Organisatoren besser hätte formulieren können:
„Dies ist die beste Erfahrung meines Lebens“.
Bilder:
Das Rotary-Seminar in Pristina zum Thema „Bekämpfung von Malaria
und weiteren durch Mücken übertragbaren Krankheiten“ brachte gute
Ergebnisse. Darüber freuten sich die 40 Teilnehmerinnen und
Teilnehmer, die Organisatoren und Unterstützer. Bild: Leon Goelz
Nach der Einführung durch die Experten Florence Fouque und Norbert
Becker wurde im Workshop gemeinsam an möglichen Lösungen für die
verschiedenen Problemfelder gearbeitet. . Bild: Leon Goelz
Die Ergebnisse können sich sehen lassen und sollen jetzt teilweise
weiter entwickelt werden. Seminarleiter Matthias Feil (re.) war ebenso
begeistert wie die beiden Projektverantwortlichen Wolfgang Uebel (2.v.li.) und Manfred Raupp (Bildmitte). Bild: Leon Goelz
mosquito-born diseases
Prof. Dr. Norbert Becker
Rotary Seminar at the University of Prishtina (Kosovo)
2019
Mosquitoes – their burden, systematics, vector biology and control
by PD Dr habil. Norbert Becker, Scientific Director of the German Mosquito Control Association (KABS); Executive Director of the European Mosquito Control Associtaion (EMCA); Associate Professor at the University of Heidelberg, Germany.
In his presentation Dr Becker highlighted that mosquitoes are the most dangerous organisms for human beings. Each minute a human is dying because of a mosquito bite, mainly children in the age group of 1 to5 years and mostly in Africa, south of the Sahara. Amongst the more than 3500 mosquito species known today, about 1000 species can transmit diseases and 60 species mainly anophelines (Malaria mosquitoes) are serious vectors. Still more than 3 billion people are at risk to be infected by mosquito-borne diseases. Each year the WHO counts about 216 million malaria infections and more than 500.000 deaths. Arboviruses like dengue, dengue haemorrhagic fever, Chikungunya, Zika and Japanese Encephalitis become more and more important when we consider that each year more than 390 million people are infected by arboviruses (arthropod-borne viruses). However, the case fatality rate is much lower than with malaria. It is estimated that less than 50.000 people die each year due to a good case management. Lymphatic filariasis is not deadly but at least 120 million people are infected by nematode worms. Mosquitoes also changed the world-politics when we consider that Alexander the Great died (323 BC) on a mosquito bite in Bagdad in the age of 32 years when he almost ruled the known western world at that time.
Mosquitoes look back to a long evolutionary development. They are known since the Mesozoic period (>100 million years ago) and have already bitten dinosaurs. Human beings (Homo sapiens) are only 200.000 years on the globe, our ancestors about 5 million years. So mosquitoes are 500 times longer on the globe as human beings. As a result of this long evolutionary process mosquitoes adapt to a great variety of aquatic habitats and can be found in almost all kinds of standing water e.g. heavily organic polluted (cess pools) or unpolluted freshwater, small water collections (buckets, vases), temporarily flooded plains, swampy woodlands, rice fields, rainwater barrels, water catch basins, tree holes or rock pools, only to mention a few. We know at present 3.528 mosquito species, in Europe more than 100 species and in Germany 52 species. Since 1995 six new species were introduced to Germany by the globalisation favourite by climate change.
A result of the long-term evolution are frequent zoonosis. Usually mosquito-borne diseases are zoonosis, pathogens are transmitted from mosquitoes to animals, but in the course of co-evolution some of the disease pathogens spread to the human population. We know today more than 500 viruses (100 infect humans and 40 life stock) transmitted by mosquitoes. Five human protozonooses (Malaria parasites) are transmitted by mosquitoes and last but not least nematodes (worms) like Wucheria, Brugia or Dirofilaria. All diseases are very old: Malaria is known since more than 2500 years, dengue more than 1000 years and lymphatic filariasis more than 3100 years. The co-evolution of vectors, pathogens/parasites and humans resulted in a complex life cycles which are difficult to interrupt e.g. by the development of vaccines.
Frequently mosquitoes are diminishing the life quality as well, especially in river valleys with wide-spread inundation areas and floods in the summer time. Not seldom, more than 1000 females of the so-called floodwater mosquitoes can attack a person in less than 2 minutes e.g. in the Upper Rhine Valley and the consequence is that people cannot spend time outside their houses from late afternoon or restaurants are empty, people sell their properties which loose value due to the natural disaster with mosquitoes. In many areas the demand for mosquito control is great. The economic loss in the Upper Rhine valley alone amounts to 12 million Euro. Therefore, more than 20 organisations in almost all European countries conduct mosquito control dealing with more than 2 million hectares of breeding sites. These organisations are usually members of the “European Mosquito Control Association” (EMCA).
Before mosquito control operations are initiated studies on the biology of the mosquitoes has to be conducted. All mosquitoes need a water body for their development. About 4 days after the blood meal the mosquito females lay either single eggs (Floodwater mosquitoes, e.g. Aedes vexans, tiger mosquitoes, Aedes albopictus) above the water line or egg batches (e.g. house mosquitoes, Culex pipiens) on the surface for instance in water containers. Water and temperature are important factors for the development of the mosquitoes. The higher the temperature the faster is the development in the water. All mosquito species have 4 larval and one pupal instar in the water body before the adults are emerging from the pupae.
Both sexes of the adults need nectar or other sugar containing fluids for their life activities. However, mosquito females need a blood meal to develop eggs. They need proteins from the blood source for the egg yolk development, therefore only mosquito females are biting. Before the blood meal the mosquitoes have to mate. Usually the males build swarms and attract the females by the sound of their body fibrations (ca. 600 Hertz). The females are flying into the male swarm and are caught by a male mosquito to transfer the sperm into spermateca. Now the female needs a blood meal to develop the eggs.
The females are attracted by the breath of the host for the blood meal especially the carbon dioxid as well as by lactic and butter acid and other substances as components of sweat. The female pierce the skin by 6 stylets into the blood vessel and suck about 3 times of its body weight to lay between 100 and 400 eggs. They can suck several times and lay several egg batches without a new copulation. Before they suck blood, they release saliva with proteins and histamine into the wound to avoid blood agglumination and to support the blood sucking process. Humans react with allergic reactions with a small inflammation against the saliva.
According to their biology we can differ between several mosquito groups:
a) The floodwater mosquitoes: Here the females lay their single eggs in depressions in the floodplains which are frequently flooded. When the eggs are flooded during increasing water levels the larvae are hatching and develop through 4 larval and one pupal instar to the adults. The number of floods influence the abundance of the floodwater mosquitoes. The adults of some species like Aedes vexans and Ae. sticticus can migrate long distances (up to more than 15 km) when they search for a victim for the blood meal (humans or animals). The floodwater mosquitoes are usually the species which cause tremendous nuisances. Not seldom > 100 million larvae per hectare flooded area can be counted. The adult floodwater mosquitoes can live several weeks per generation. In autumn the adults are dying and the larvae overwinter in the egg shell. They can survive several years in the egg shell if no flood occurs. The tiger mosquitoes have a similar biology but they don’t lay their eggs in ponds but usually in artificial breeding sites also above the water line such as rain water barrels or buckets with water. They hatch when the water level in the container raises e.g. due to rainfall or when people refill the barrels.
2) The house mosquitoes such as Culex pipiens or Culiseta annulata: These mosquitoes overwinter as females in stables or cellars where the frost is absent. In spring time usually in April in Central Europe they leave the hibernation places, suck blood usually inside the houses during night (sleeping rooms) and lay their eggs on the surface of water bodies, . usually rain water containers in garden areas but also in a large variety of different natural and artificial breeding sites. After two days of embryonic development the larvae hatch straight into the water body and develop via four larval and one pupal instar to the adults which usually search for a blood meal close to their breeding sites and frequently during nights in sleeping rooms when humans search for sleeping.
3) The Fever mosquitos (Anopheles species). In Germany we have 7 Anopheles species. Some of them such as Anopheles messae or Anopheles daciae, An. atroparvus , An claviger or An. plumbeus were transmitting malaria e.g. in the Upper Rhine Valley or along the coasts in northern Germany where they developed in marshes. The most common anophelines prefer semi-permanent or permanent water bodies with vegetation. They bite humans but some prefer frequently cattle as host for the blood meal. They overwinter also as adult mosquitoes and occur usually not in great numbers. An. plumbeus can be a great pest in rural areas where abundant farming occurs with non-used cess pits as mass breeding sites of An. plumbeus. This species bites also during daytimes. Globally the most dangerous mosquito is a Anopheles species, namely Anopheles gambiae in Africa which kills each minute a person.
4) Beside the above described groups we have also more rare species such as Coquillettidia, Uranotaenia etc.
Major Mosquito-Borne Diseases
Malaria: The human malaria parasites are: Plasmodium falciparum (causing Malaria tropica); Plasmodium vivax (Malaria tertiana); Plasmodium ovale (Malaria tertiana); Plasmodium malariae (Malaria quartana) and Plasmodium knowlesi. The parasites possess a very complex life cycle in humans (in the liver and red blood cells) and in mosquitoes. We have more than 60 important malaria vectors, but the most serious one is Anopheles gambiae s.l., the main vector of the frequently deadly Malaria tropica which occurs in Africa south of the Sahara. Each year we have 216 mill. new clinical cases of which 80% occur in Africa. 500.000 people mainly children are dying each year according to the WHO and the costs for malaria control alone in Africa amounts to approximately 2 bill. US$.
Arbovirosis: The main arbovirosis are caused by the so-called Flaviviruses (belonging to the Yellow fever group). The main diseases are dengue, dengue haemorrhagic fever, Zika and West-Nile fever. The main vectors of dengue and Zika are the tiger mosquitoes, Aedes aegypti and Aedes albopictus which breed predominately in human settlings (e.g. in water barrels etc).
Most problematic is dengue haemorrhagic fever which is caused by a secondary infection with a different serotype than the first dengue infection which cause usually mild symptoms. However, the antibodies produced by the human immune system during the first infection are not able to neutralize the viruses of a serotype different of the one of the first infection. The viruses can proliferate during the second infection in epithelial cells of the blood vessels which become permeable and the victim is dying on bleeding to death.
West-Nile viruses are transmitted mainly by Culex mosquitoes like our house mosquito Culex pipiens, which occurs wide-spread in Europe and world-wide. Usually it is a zoonosis between birds and mosquitoes, however, humans and horses can also be infected and this can be deadly. In 2018 almost 1500 people were infected in Europe and almost 200 people died (e.g. in Greece: 45; Italy and Romania: each 42; Serbia 35).
Chikungunya viruses are alpha-viruses and also transmitted by tiger mosquitoes (Aedes albopictus). The first outbreak in Europe occurred in 2007 in Italy when about 300 people were infected and one person died. The vector was the Asian tiger mosquito Aedes albopictus which was imported as neozoen by used tires to Italy in 1990 and spread since that along the mediterranean coast and even to Germany as blind passengers in vehicles coming from Italy.
Lymphaitic filariasis is caused by a nematode, mostly Wuchereria bancrofti which is transmitted mainly by Culex mosquitoes. The adult worms develop in the lymph system and can block the lymph fluid which leads to swelling of legs etc (Elephantiasis).
The fight against Mosquitoes
The basis for the fight against this diseases was the understanding of the role of mosquitoes in the transmission of the pathogen/parasite. Walter Reed (1851-1902) proved conclusively that mosquitoes carry yellow fever from person to person. Sir Ronald Ross demonstrated in 1897 as military physician in India that anophelines transmit malaria. The discovery of Quinine extracted from the bark of the Cinchona tree was a breakthrough in the fight against malaria. Today we have some synthetic drugs or combination of them e.g. malarone which kill stages of the Malaria parasite (Plasmodium spp.) in the human body. Natural derivates such as artemisinin deriving from Artemesia are still very important weapons in the fight against malaria.
Control of the mosquito vectors
The fight against mosquitoes is a steady fight between “cerebral (human) and evolutionary (mosquito) intelligence. The development of resistance of mosquitoes is a good example how mosquito neutralize “human weapons”. What we could learn from the past is that we have to use all weapons which we have to our disposal and that we have to use them in an integrated manner. Col. William Gorgas, 1904, head of the sanitary department in Panama demonstrated this when the Panama Canal was build. Only by the appropriate control of Malaria and Yellow fever and their vectors, the Panama canal could be build. Gorgas approach comprised: drainage of the water, larviciding, brush and grass cutting, prophylactic quinine administration, screening of the patience and adult mosquito killing.
With the discovery of DDT (Dichlorodiphenyltrichloroethane) at the beginning of the 20 th century the modern mosquito control started. A drawback was the quick onset of resistance against DDT and the environmental residues and accumulation in the food chain (fat body). Therefore, DDT is banned in many countries in the second half of the 20 th century in Europe and the search for alternative insecticides to the organochlorines started. The second generation were the organophosphates (developed 1932) which do not persist in the environment, but they are more toxic than e.g. DDT. The third and fourth generation were the carbamates (developed in the 1950s) and pyrethroids (in the 1960s). In the 1970s the search for biorational insecticides like “Insect Growths Regulators (IGRs)” and microbial control agents (Bacillus thuringiensis israelensis (B.t.i.) and Lysinibacillus sphaericus (L.s.) started.
In many programmes integrated approaches are undertaken favorited by the World Health Organisation (WHO) as in the “Roll Back Malaria Programme (RBM)” - an alliance of international, national governmental organisations and NGOs (e.g. WHO, Wold Bank, UNICEF, Bill and Melinda Gates foundation, PMI). The RBM programme is mainly based on the use of a) long-lasting insecticidal nets (LLINs) treated with pyrethroids, b) indoor residual spraying (walls are sprayed with insecticides as DDT, bendiocarb or pyrethroids) to kill resting anopheline femals inside the houses) and c) effective diagnosis and medical treatment of malaria cases. This strategy lead to a significant reduction of malaria cases especially in Africa.
However, there are also drawbacks of this strategy:
1) onset of resistance against pyrethroids;
2) human behaviour (people stay outside their houses during the transmission time for Plasmodium in the evening and have no protection by the nets);
3) The strategy targets endophagic and endophilic Anopheles species like An. gambiae which bite inside the houses and stay after the bite inside the houses. However, exophagic and exophilic species which bite outside the houses are not killed and still transmit malaria. Exophilic species have a positive selection pressure and become more abundant. Today the number of malaria cases is increasing in some areas again.
As a conclusion, the practised strategy had to be altered and should be more integrated and include also “Larval Source Management (LSM)” what is supported by WHO. LSM comprises source reduction (e.g. removal of breeding sites for anophelines and larviciding mainly with microbial control agents such as B.t.i..
Control programmes in Europe e.g. the programme of the German Mosquito Control Associtaion (KABS) can be an example for the successful implementation of integrated biological control strategies.
Mosquito Control in Germany as an example of an successful approach
The control of mosquitoes in Germany has a long history. In the 1920’s and 1930’s breeding sites were treated with petroleum oils. During the 1950’s and 1960’s adulticides were used. In the early 1970’s, the mosquito population was extremely high because of frequent fluctuations of the water level of the Rhine. The people in the villages couldn’t spend any length of time outside their houses. There was an attack rate of more than 1000 female mosquitoes per minute. As a reaction to this natural disaster 44 towns and communities in the Upper Rhine valley on both sides of the river Rhine merged their interest in a united mosquito control programme, the KABS (Kommunale Aktionsgemeinschaft zur Bekämpfung der Stechmückenplage e.V.) which was founded in 1976. Nowadays, 100 municipalities along a 310 kilometre stretch of the Upper Rhine River, with a total population of 2.7 million people, have joined forces to control the mosquitoes, mainly Ae. vexans over a breeding area of some 600 km2 of the Rhine's flood-plain. The budget of the program is approximately 4 million Euros a year which results in overall costs per person per year of approximately 1.5 Euro.
The overall concept is integrated biological control (IBC) and to integrate the protection of humans against mosquitoes and the conservation of biodiversity. When the ecosystem is compared with a web and each group of organisms represents one mesh, the strategy of the KABS aims at the reduction of the mesh representing the floodwater mosquitoes without cutting other meshes in the „food web“ and thus keeping the stability of the ecosystem.
This goal could only be reached in an optimum when biological control methods are used. The conservation and encouraging of predators is an important goal of the programme. Therefore, microbial and biological methods are integrated with environmental management (e.g. improving of the ditch system for regulation of the water level and providing of permanent habitats for aquatic predators such as fish).
The discovery of the gram-positive, endospore-forming soil bacterium, Bacillus thuringiensis subsp. israelensis (B.t.i.) in the Negev desert of Israel in 1976 by Yoel Margalit, has opened the door for the use of microbial control agents as B.t.i. The outstanding advantage of this control agent is its specificity. It kills exclusively mosquito and black fly larvae and few other Nematoceran flies. Thus the environmental impact is negligible. The strategy is also implemented by experienced biologists.
B.t.i. is a soil bacterium and can be found in almost each habitat world-wide as a part of the natural ecosystem. During sporulation the bacillus produces the so-called protein crystal harbouring protein toxins. The Bacillus can be fermented in huge 150.000 litres fermenters for two days at 28°C and oxygen supply. At the end of the fermentation process hundreds of kilograms of the fermentation substances can be harvested containing the toxins. This can be formulated into powders, water dispersible granules (WDGs) as well as to solid granules or fizzy tablets.
When the formulations are applied to the breeding sites the protein crystals are ingested by the mosquito larvae and activated in the mosquito larval gut by proteases. The activated polypeptides (toxins) bind specifically to glyco-receptors in the gut bio-membrane. Pores are built by the toxins in the membrane combined with an influx of water into the gut cell. The cell is swelling and bursting. Finally the mosquito larvae are dying and all other organisms except nematoceran flies (mosquitoes) are not harmed. The specificity of B.t.i. is based on the glycol- receptors which occur only in mosquitoes and some nematoceran flies.
For the successful implementation and use of microbial control agents the following prerequisites are necessary: entomological studies, precise mapping and numbering of all major breeding sites, assessment of the effective dosage in bioassays and in small field tests, adaptation of the application technique to the requirements in the field, design of the control strategy as well as training of the field staff and governmental application formalities.
For almost four decades B. thuringiensis israelensis have been successfully used in Germany as biological control agents against floodwater mosquitoes (e.g. Ae. vexans) and the so-called house mosquito Culex mosquitoes (e.g. Cx. p. pipiens biotype molestus) and since 2015 also against the Asian Tiger mosquito Aedes albopictus. Annually up to 250 km 2 of breeding areas (depending of the number and size of the floods) are treated with B. thuringiensis israelensis, resulting in a reduction of the mosquito population of more than 90% of the emerging population year by year.
The flood plains of the Rhine are usually inundated two and more times each summer. The extent of the flooding depends on the snow-melt in the Alps and on rainfall, and it is constantly necessary to monitor the water flow in the Rhine and in the flood plain. During flooding, Ae. vexans and other floodwater mosquito larvae hatch within minutes or hours at temperatures exceeding 8°C. Before control measures are to be conducted, the larval density and the larval stages are checked by means of sample scoops at representative breeding sites, in order to justify the action being undertaken and to establish the correct dosage and the best formulation used.
The treatment can be done by ground application when 500 grams of Bti-WDG is suspended in 10 liters of water and applied by pressurized knapsack sprayers. In areas with dense vegetation the helicopter applies Bti-ice-granules. The Bti-water suspension is dropped into fluid nitrogen and the resulting icy pearls containing the Bti toxins can be spread across the breeding sites containing a sufficient number of mosquito larvae by the helicopters. One day after application, spot sample scoops are taken at the reference breeding sites to check mosquito density and thereby establishing the efficacy of the treatment.
For the precise application and real time monitoring helicopters are GPS guided and 3D models are used for the precise assessment of the application areas.
Control of urban mosquito species is mainly carried out by householders or inhabitants. To assist with this, KABS provides information on the biology of container breeding mosquitoes such as the house mosquito Cx. pipiens and the Asian tiger mosquito Aedes albopictus as well as information on appropriate control measures. Bti-Culinexâ tablets have been particularly successful. They kill mosquito larvae in water containers over a period of several weeks monitoring the program
Some 8% of the KABS budget is invested in monitoring mosquito populations, mosquito resistance and environmental impact. All the studies carried out to date have shown that the introduction of B. thuringiensis israelensis has reduced the numbers of nuisance mosquitoes to a tolerable level, but that the diversity of the ecosystem as a whole has not been damaged. So far no resistance occur as well.
Monitoring mosquito abundance: To monitor the abundance of adult mosquitoes, a sufficient number of CO2-baited traps are placed at comparable sites throughout the entire inundation area. These are monitored twice a month from April to September. On each occasion for a whole night, the mosquito density is sampled by means of carbon dioxide light-traps. Catches in areas where no control measures have been undertaken serve as points of reference (100% of the mosquito population) for catches from areas being treated, in order to determine the success of the measures (mortality rate in percent). It has been shown that since the widespread application of B. thuringiensis israelensis in 1981, mass occurrences of mosquitoes have been successfully averted. Naturally, these control measures have had an extremely positive reception among the local people.
Monitoring the environmental impact: It has been essential to document the environmental impact of B. thuringiensis israelensis, in order to provide a scientific basis for rebuting the arguments commonly brought against mosquito control by its opponents. Before large-scale application of microbial control agents was undertaken, the most important members of various aquatic groups (Cnidaria to Amphibia) were screened in the laboratory and in small-scale field trials for their susceptibility to microbial control agents. This study showed that in addition to mosquitoes (Culicidae) and black flies (Simuliidae), only a few species of midges (Chironomidae) were affected by B. thuringiensis israelensis. For the most part, these midges were much less susceptible to B. thuringiensis israelensis than the target organisms or occur mainly in permanent water bodies where no floodwater are developing.
The development of insects in treated and untreated water is regularly monitored using emergence traps. The occurrence and abundance of insects in treated areas is assessed by regular light trap catches. All investigations have shown that while the numbers of Aedes mosquitoes are drastically reduced, all other insects continue to develop in the water and, as winged adults, provide a food resource for birds, amphibians and bats.
Monitoring the resistance: Mosquito populations are checked at regular intervals for the development of resistance. No resistance has been detected after 30 years of treatment with B. thuringiensis israelensis.
Invasion of exotic mosquitoes in Europe and their control
Out of the more than 3500 mosquito species worldwide, only about 30 species have begun to spread far beyond their original geographical borders. The most successful invasive species are Aedes aegypti, Ae. albopictus, Ae. japonicus, Ae. koreicus, Ae. atropalpus and Ae. triseriatus. Initially, these mosquitoes colonize small natural and artificial water bodies, such as water-filled tree holes, rock pools, phytothelms or artificial breeding sites as water barrels, vases, flower pots, buckets or frequently used tires. Usually, these small accumulations of water show a large variation of the size of the water body, in temperature and other abiotic conditions which require special adaptations of these so-called “container breeding mosquitoes”.
Overall, these exotic species possess a high ecological potency and can rapidly adapt to new habitats due to their genetic plasticity and they are easily disseminated by human activities.
Aedes albopictus is an excellent example. This species has spread from tropical areas to areas with temperate climates which do not allow a constant follow-up of generations, e.g. during winter periods. As a consequence, the species goes through a winter diapause during which the larvae in the eggs are not able to hatch and remain in the egg-shell until the living conditions allow a further development.
Rapid transportation systems connect the world’s biota more than any time in earth’s history. Within a couple of hours or days organisms are transported from one continent to another. Beside economic activities, human migration and tourism is increasing the risk for spreading both disease vectors and diseases. Especially the international trade, mainly of used tires and occasionally of lucky bamboo (Dracaena spp.) cuttings, is the vehicle for the spread of most of the invasive mosquitoes.
Between 1995 and 2017 the scientists of the KABS could record in the frame of the routine mosquito monitoring programme five exotic mosquito species for Germany namely Uranotaenia unguiculata (1995), Aedes albopictus (2007), Aedes japonicus (2009), Culiseta longiareolata (2011) as well as Ae. koreicus (2015). All species are considered established in the Upper Rhine valley after having produced at least 3 generations in the new territory and have successfully overwintered.
Whereas the intercontinental spread is mainly facilitated by the global merchandise especially with used tires, the spread within and between neighboring countries is most likely that females of Aedes albopictus are introduced as “blind passengers” in vehicles.
In Europe, Ae. albopictus has probably been present in Albania since at least 1979, but didn’t spread due to the political isolation. However, in the early 1990s Ae. albopictus was passively introduced into Italy, due to the international trade of used tires followed by a rapid spread into other areas in Italy. Having become established in Italy, Ae. albopictus was spreading by vehicles and boats along the Mediterranean coast including France, Spain, Croacia, other Balkan countries, as well as Greece and Turkey. The species is, today, principally present in the whole northern and some parts of the southern mediterranean basin with an increasing tendency of spreading northwards across the Alps into central European countries. Taking into account that Aedes albopictus is a vector of at least 22 arboviruses, including Dengue, Chikungunya, Zika and Yellow Fever viruses and that Italy is a favourite country for German tourists the risk of the introduction of Ae. albopictus into Germany via returning tourists in vehicles from Italy and therefore an increasing public health risk is evident. This risk has to be considered as serious when we take into account that the Asian tiger mosquito is already involved in the autochthonous transmission of dengue and Chikungunya viruses in Europe, namely dengue in Southern France and Croatia and Chikungunya in Italy 2007.
As a consequence, the German Mosquito Control Association (KABS) started in 2005 a monitoring program from Basel to Heidelberg along motorway A5 (E35) coming from Italy as suspected port of entry for Ae. albopictus adults. In the frame of the first monitoring program in the time period 2005 to 2009, Ae. albopictus eggs were found the first time in an ovitrap at a resting station north of the city Weil am Rhein. In order to assess the risk for the introduction of Ae. albopictus a collaboration of scientific, traffic and governmental institutions in close cooperation with the public was initiated. Furthermore, public awareness has been increased by press releases and thorough information via internet, radio and TV to be able to recognize tiger mosquitoes. This was done for the KABS-area in Southwest-Germany and nation-wide by the “Mückenatlas”. The highway monitoring revealed that about 40% of all service and resting stations and some camp grounds along the highway A5 between Basel and Hesse were infested by Ae. albopictus what indicate the permanent introduction of the Asian tiger mosquito into Germany.
The increased public awareness resulted in numerous records of adult Ae. alboipictus females by alert people who have send females to the KABS or the Mückenatlas. Nowadays, we have in Southwest Germany established populatons of the Asian tiger mosquito in cities like Freiburg, Lörrach, Karlsruhe and Heidelberg. All populatons are controlled by the application of Bti and additional with the so-called Sterile Insect Technique (SIT). Males of the Asian tiger mosquito are sterilized by gamma-radiation and are released in infested areas. The sterile males mate with the “wild females” and the offspring is not viable.
The ultimate goal is to assess newly developing Ae. albopictus populations as early as possible and to initiate control activities by the KABS and the Institute for Dipterology a sister organization of KABS.
The successful control programme of KABS can serve as a model also for tropical countries which was proven already in African countries like Kenia, Ghana or Burkina Faso. The transfer of techniques and the close cooperation of organisations between mosquito infested areas can help in the frame of partnerships to control mosquito-borne diseases such as Malaria.