Fighting Mosquito Borne Diseases
Zika, dengue fever, chikungunya and yellow fever are examples of vector-borne diseases (VBD) transmitted by day-time active mosquitoes. In 128 countries, in particular in tropical and sub-tropical regions of Asia and Latin America (notably highly populated countries, such as Thailand, Brazil, India and Pakistan) these diseases are a major health risk and a negative economic factor.
In 2010, infections with the dengue virus were registered in Croatia, France and Italy. In 2012 and 2013, patients having dengue fever were found on the isle of Madeira/Portugal transmitted by Ae. aegypti. Chikungunya infections occurred in Italy (2007) and Spain/France (2015). Eggs, larvae, pupae and adult mosquitoes of Aedes albopictus were repeatedly detected in the south of GerMany in autumn 2014 and in 2015. Researchers assume from these findings that Asian tiger mosquitoes can survive the winter and settle in Germany. Over the past few decades, the incidence of dengue has grown dramatically. Recent studies indicate the existence of approximately 390 million dengue infections per year and that 3,9 billion people, in 128 countries are at risk of being infected with the dengue virus. The WHO has set the goal to constrain and control the spreading of dengue fever by 2020, however there are major obstacles in achieving this goal. Some vaccines are in advanced trial stages, but not effective against all serotypes (phase 3 results of the Sanofi Pasteur vaccine as front runner just concluded), and have negative effects in some age classes. WHO guidelines for vaccine trials are very detailed and specific in their requirements of scientific investigation before licensing (phase 1, 2, 2b and 3, finally phase 4 after licensing).
As previously mentioned, for dengue fever preliminary vaccine trials are running, but the results are not satisfactory. In general, regarding mosquito vector-borne diseases, vaccines are either quite imperfect, like DengVaxia for dengue fever (recently licenced by Sanofi- Pasteur), or do not yet exist as is the case for the Zika virus. In relation to yellow fever, the vaccine is even in some cases lethal. Classical mosquito control measures, such as bed-nets and municipal spraying in the streets, have proven to be of little effectiveness in combating disease cases. In mosquito control, some activities in demonstration of efficacy using bed-nets via the WHO are performed. One reason that the nets are not fully effective is that vectors of dengue, the species Aedes aegypti and Aedes albopictus are active in the morning and evening, but not very active at night. Another important aspect in eliminating mosquitoes by classical pesticides and insecticides, beside the danger to human health, is that the elimination of mosquitoes would also deprive many fish, birds, and reptiles of a food source and even destroy critical pollinator for plants. It is well-known that the emergence of insecticides resistance in Ae. aegypti and Ae. albopictus is described in the literature, which adds to the challenge.
The above issues regarding combating mosquito VBD are major challenges worldwide. The main focus of this Action is to develop a quantitative understanding by using mathematical modelling and techniques for the effect of introducing a new mosquito repellent technique usable for textiles, paints and other applications to combat VBD. The deduced data will help to improve the repellent technology and their specific applications but also trigger a proper understanding of transmission ways. Herein modified nano- and micro-particles applicable to many carrier substances are investigated, which continuously release mosquito repellents or insecticides, as an effective tool to suppress mosquito-transmitted diseases.
The main aim is the disease burden reduction of vector-borne diseases such as dengue fever with its 4 distinct serotypes and secondary infection as main risk factor of severe disease.
Major problems and challenges, especially in dengue fever are:
1. In the present generation of vaccines: a) only limited vaccine efficacy of around 60% b) and further reduced efficacy against some of the dengue serotypes c) and finally even negative efficacy in seronegative persons, putting them at higher risk of severe disease than without vaccination. This especially of importance in young age classes with high numbers of seronegative susceptible and in travellers from non-endemic countries. The scientific community has spent that last 40 to 50 years in the attempt to develop vaccines against dengue fever.
2. Present mosquito control measures, mainly via insecticides, have shown limited to no effect on disease transmission (besides their health risks for humans and the appearance of resistance in mosquitoes). The main problem in this case is not that the total number of mosquitoes is decisive for present huge inter-annual fluctuations of dengue fever cases, but the long-time scales of human susceptibility against the different serotypes.
Repellents could be a way forward and now in combination with new technologies for smart dosages, i.e. micro- and nanoparticles applied to a variety of products including textiles, wall colors, tiles etc. The aim is also to protect relevant groups of people left out by other control measures like vaccines, essentially these are children, pregnant women and travellers. This poses significant new technological, socio-epidemiological and mathematical questions. Technical, because of the interaction between nanoparticles, repellents and fabrics or colours; socio-epidemiological, because of questions about where to protect first, what logistics is needed, which resources should be deployed for which control measure, like for imperfect vaccines, repellents and insecticides.