Mosquito borne diseases are a group of infections that affect humans. Emerging or reemerging diseases are those that (re)occur in regions, groups or hosts that were previously free from these diseases: dengue virus; chikungunya virus; Zika virus; West Nile fever and malaria. In Europe, these infections are mostly imported; however, due to the presence of competent mosquitoes and the number of trips both to and from endemic areas, these pathogens are potentially emergent or re-emergent. Present and future climatic conditions, as well as meteorological, environmental and demographic aspects are risk factors for the distribution of different vectors and/or diseases. This review aimed to identify and analyze the existing literature on the transmission of mosquito borne diseases and those factors potentially affecting their transmission risk of them in six southern European countries with similar environmental conditions: Croatia, France, Greece, Italy, Portugal and Spain. In addition, we would identify those factors potentially affecting the (re)introduction or spread of mosquito vectors. This task has been undertaken with a focus on the environmental and climatic factors, including the effects of climate change. We undertook a systematic review of the vectors, diseases and their associations with climactic and environmental factors in European countries of the Mediterranean region. We followed the PRISMA guidelines and used explicit and systematic methods to identify, select and critically evaluate the studies which were relevant to the topic. We identified 1302 articles in the first search of the databases. Of those, 160 were selected for full-text review. The final data set included 61 articles published between 2000 and 2017.39.3% of the papers were related with dengue, chikungunya and Zika virus or their vectors. Temperature, precipitation and population density were key factors among others. 32.8% studied West Nile virus and its vectors, being temperature, precipitation and NDVI the most frequently used variables. Malaria have been studied in 23% of the articles, with temperature, precipitation and presence of water indexes as the most used variables. The number of publications focused on mosquito borne diseases is increasing in recent years, reflecting the increased interest in that diseases in southern European countries. Climatic and environmental variables are key factors on mosquitoes’ distribution and to show the risk of emergence and/or spread of emergent diseases and to study the spatial changes in that distributions., Peer reviewed

Los resultados expuestos en este artículo son fruto de diferentes
programas de financiación pública y privada, incluyendo el proyecto
PGC2018-095704-B-100 del Ministerio de Economía y Competitividad
y fondos FEDER, el programa Leonardo de la Fundación
BBVA a JMP y un contrato Juan de la Cierva Formación (FJCI-
2017-34394) a MF., Peer reviewed

La dinámica de transmisión de los parásitos de la malaria aviar depende de las interacciones entre parásitos y vectores, que están influenciadas por
las condiciones ambientales en las que se desarrollan. Ello hace esencial estudiar los factores que determinan las interacciones entre los mosquitos
con las aves y los parásitos que les infectan en ecosistemas naturales para comprender la ecología y la evolución de la transmisión de estas enfermedades.
Dos procesos determinantes en el éxito de transmisión de estos parásitos son, i) las tasas de contacto entre mosquitos y aves infectadas
o susceptibles de infección y ii) la capacidad de desarrollo del parásito en el interior del mosquito pudiendo ser transmitido. Aunque el papel del
comportamiento de alimentación de los mosquitos en la dinámica de transmisión de Plasmodium aviar y la capacidad de desarrollo de los parásitos
de Plasmodium aviar en diferentes especies de mosquitos han sido previamente estudiado, pocos trabajos han estudiado conjuntamente estos dos
procesos en condiciones naturales. Aquí se expone como diferencias en las tasas de alimentación de los mosquitos y la capacidad de desarrollo de
Plasmodium aviar van a determinar la dinámica de transmisión de la malaria aviar en ecosistemas naturales, así como se proporcionan futuras
líneas de investigación que permitirían estudiar la dinámica de transmisión de Plasmodium aviar. La inclusión de los vectores en el estudio de la
ecología del parasitismo, permitirá un mejor conocimiento de las complejas interacciones entre hospedador vertebrado, mosquito y parásito en condiciones
naturales., [EN] The transmission dynamics of malaria parasites depends on the parasites and vectors interactions, which are influenced by the environmental conditions where are developed. Therefore, in order to understand the ecology and evolution of the transmission of these diseases, it is essential to study the factors that determine the interactions between mosquitoes, birds and parasites that infect them in natural ecosystems. There are two processes determining parasite transmission success, i) the contact rates between mosquitoes and infected or susceptible birds, and ii) the capacity of development of the parasite inside the mosquito (vector competence). Different studies have evidenced the role of the mosquitoes feeding behaviour on the transmission dynamics of avian Plasmodium. Likewise, the development capabilities of avian Plasmodium parasites within species of mosquitoes have been studied. However, both processes together in natural conditions have been scarcely studied. Here, it is exposed how differences in feeding rates of mosquitoes and in the development capacity of avian Plasmodium determine the transmission dynamics of avian malaria in natural ecosystems. In addition, future research lines are also exposed, in order to improve the knowledge on the transmission dynamics of avian Plasmodium. The consideration of vectors in the studies on the ecology of parasitism will allow a better understanding of the complex interactions between vertebrate host, mosquito and parasite in natural conditions., és de la Fundaciónpara la Ciencia y la Tecnología (FCT), bajo el Proyecto de Investi-gación “DEEP Research Project PTDC/BIA-EVL/ 29390/2017”.Este estudio estuvo parcialmente financiado por el proyectoPGC2018-095704-B-100 del Ministerio de Ciencia e Innovación co-financiado por fondos FEDER. JMP recibió financiación del pro-yecto Leonardo (convocatoria 2017) para investigadores ycreadores culturales de la Fundación BBVA. La fundación noacepta responsabilidad de las opiniones, declar, Peer reviewed

Parasites can manipulate their hosts to increase their transmission success. Avian malaria parasites(Plasmodium) are thought to alter the cues such as host odour, used by host-seeking mosquitoes. Birdodour is affected by secretions from the uropygial gland and may play a role in modulating vector-host interactions. We tested the hypothesis that mosquitoes are more attracted to the uropygial secre-tions and/or whole-body odour (headspace) ofPlasmodium-infected house sparrows (Passer domesticus)than to those of uninfected birds. We tested the attraction of nulliparous (e.g. uninfected mosquitoeswithout previous access to blood) Culex pipiensfemales towards these stimuli in a dual-choice olfactome-ter. We used Gas Chromatography-Mass Spectrometry (GC–MS) analyses to assess whetherPlasmodiuminfection is associated with differences in the chemical composition of uropygial secretions. Mosquitoeswere more attracted to the odours of infected than uninfected birds, regardless of sex. However, the significant interaction between infection status and the stimuli (uropygial secretion or headspace) showedthat mosquitoes were more attracted to the headspace of infected birds; no differences were found in thecase of uropygial secretions. The compounds in the volatile lipophilic fraction of the uropygial secretiondid not differ between infected and uninfected birds. These results support the host manipulationhypothesis since avianPlasmodiumparasites may be capable of altering their host’s body odour, therebymaking infected individuals more attractive to mosquitoes., This study was funded by projects CGL2015-65055-P and PGC2018-095704-B-100 from the Spanish Ministry of Science and Innovationand European Regional Development Fund (FEDER, Spain), and P11-RNM-7038 from the Junta de Andalucía (Spain). ADF was supported by a Severo-Ochoa grant from the Spanish Ministry of Economy and Competitiveness (SVP-2014-068571). LG was supportedby a Marie Sklodowska-Curie Fellowship from the European Commission (grant number 747729, ‘‘EcoEvoClim”).

The Dilution Effect Hypothesis (DEH) argues that greater biodiversity lowers the risk of disease
and reduces the rates of pathogen transmission since more diverse communities harbour
fewer competent hosts for any given pathogen, thereby reducing host exposure to the
pathogen. DEH is expected to operate most intensely in vector-borne pathogens and when
species-rich communities are not associated with increased host density. Overall, dilution
will occur if greater species diversity leads to a lower contact rate between infected vectors
and susceptible hosts, and between infected hosts and susceptible vectors. Field-based
tests simultaneously analysing the prevalence of several multi-host pathogens in relation to
host and vector diversity are required to validate DEH. We tested the relationship between
the prevalence in house sparrows (Passer domesticus) of four vector-borne pathogens–
three avian haemosporidians (including the avian malaria parasite Plasmodium and the
malaria-like parasites Haemoproteus and Leucocytozoon) and West Nile virus (WNV)–and
vertebrate diversity. Birds were sampled at 45 localities in SW Spain for which extensive
data on vector (mosquitoes) and vertebrate communities exist. Vertebrate censuses were
conducted to quantify avian and mammal density, species richness and evenness. Contrary
to the predictions of DEH, WNV seroprevalence and haemosporidian prevalence were not
negatively associated with either vertebrate species richness or evenness. Indeed, the
opposite pattern was found, with positive relationships between avian species richness and
WNV seroprevalence, and Leucocytozoon prevalence being detected. When vector (mosquito)
richness and evenness were incorporated into the models, all the previous associations
between WNV prevalence and the vertebrate community variables remained
unchanged. No significant association was found for Plasmodium prevalence and vertebrate
community variables in any of the models tested. Despite the studied system having
several characteristics that should favour the dilution effect (i.e., vector-borne pathogens an area where vector and host densities are unrelated, and where host richness is not associated
with an increase in host density), none of the relationships between host species
diversity and species richness, and pathogen prevalence supported DEH and, in fact, amplification
was found for three of the four pathogens tested. Consequently, the range of pathogens
and communities studied needs to be broadened if we are to understand the
ecological factors that favour dilution and how often these conditions occur in nature., Peer reviewed

Changes in environmental conditions, whether related or not to human activities, are continuously modifying the geographic distribution of vectors, which in turn affects the dynamics and distribution of vector-borne infectious diseases. Determining the main ecological drivers of vector distribution and how predicted changes in these drivers may alter their future distributions is therefore of major importance. However, the drivers of vector populations are largely specific to each vector species and region. Here, we identify the most important human-activity-related and bioclimatic predictors affecting the current distribution and habitat suitability of the mosquito Culex pipiens and potential future changes in its distribution in Spain. We determined the niche of occurrence (NOO) of the species, which considers only those areas lying within the range of suitable environmental conditions using presence data. Although almost ubiquitous, the distribution of Cx. pipiens is mostly explained by elevation and the degree of urbanization but also, to a lesser extent, by mean temperatures during the wettest season and temperature seasonality. The combination of these predictors highlights the existence of a heterogeneous pattern of habitat suitability, with most suitable areas located in the southern and northeastern coastal areas of Spain, and unsuitable areas located at higher altitude and in colder regions. Future climatic predictions indicate a net decrease in distribution of up to 29.55%, probably due to warming and greater temperature oscillations. Despite these predicted changes in vector distribution, their effects on the incidence of infectious diseases are, however, difficult to forecast since different processes such as local adaptation to temperature, vector-pathogen interactions, and human-derived changes in landscape may play important roles in shaping the future dynamics of pathogen transmission.

Changes in environmental conditions, whether related or not to human activities, are continuously modifying the geographic distribution of vectors, which in turn affects the dynamics and distribution of vector-borne infectious diseases. Determining the main ecological drivers of vector distribution and how predicted changes in these drivers may alter their future distributions is therefore of major importance. However, the drivers of vector populations are largely specific to each vector species and region. Here, we identify the most important human-activity-related and bioclimatic predictors affecting the current distribution and habitat suitability of the mosquito Culex pipiens and potential future changes in its distribution in Spain. We determined the niche of occurrence (NOO) of the species, which considers only those areas lying within the range of suitable environmental conditions using presence data. Although almost ubiquitous, the distribution of Cx. pipiens is mostly explained by elevation and the degree of urbanization but also, to a lesser extent, by mean temperatures during the wettest season and temperature seasonality. The combination of these predictors highlights the existence of a heterogeneous pattern of habitat suitability, with most suitable areas located in the southern and northeastern coastal areas of Spain, and unsuitable areas located at higher altitude and in colder regions. Future climatic predictions indicate a net decrease in distribution of up to 29.55%, probably due to warming and greater temperature oscillations. Despite these predicted changes in vector distribution, their effects on the incidence of infectious diseases are, however, difficult to forecast since different processes such as local adaptation to temperature, vector-pathogen interactions, and human-derived changes in landscape may play important roles in shaping the future dynamics of pathogen transmission.

Parasites can manipulate their hosts to increase their transmission success. Avian malaria parasites (Plasmodium) are thought to alter the cues such as host odour, used by host-seeking mosquitoes. Bird odour is affected by secretions from the uropygial gland and may play a role in modulating vector-host interactions. We tested the hypothesis that mosquitoes are more attracted to the uropygial secretions and/or whole-body odour (headspace) of Plasmodium-infected house sparrows (Passer domesticus) than to those of uninfected birds. We tested the attraction of nulliparous (e.g. uninfected mosquitoes without previous access to blood) Culex pipiens females towards these stimuli in a dual-choice olfactometer. We used Gas Chromatography-Mass Spectrometry (GC–MS) analyses to assess whether Plasmodium infection is associated with differences in the chemical composition of uropygial secretions. Mosquitoes were more attracted to the odours of infected than uninfected birds, regardless of sex. However, the significant interaction between infection status and the stimuli (uropygial secretion or headspace) showed that mosquitoes were more attracted to the headspace of infected birds; no differences were found in the case of uropygial secretions. The compounds in the volatile lipophilic fraction of the uropygial secretion did not differ between infected and uninfected birds. These results support the host manipulation hypothesis since avian Plasmodium parasites may be capable of altering their host’s body odour, thereby making infected individuals more attractive to mosquitoes.

Plasmodium transmission success depends upon the trade-off between the use of host resources to favour parasite reproduction and the negative effects on host health, which can be mediated by infection intensity. Despite its potential influence on parasite dynamics, the effects of infection intensity on both, birds and vectors, and on Plasmodium transmission success are still poorly understood. Here, we experimentally reduced the Plasmodium load in naturally infected wild house sparrows with the antimalarial primaquine to assess the effects of intensity of infection in the vertebrate hosts on Plasmodium transmission to and by mosquitoes. We monitored the survival of Culex pipiens mosquitoes throughout the development of the parasite and the infection status of the mosquitoes by analysing the head-thorax and saliva at 13 days post-exposure to birds. The proportion of mosquitoes infected by Plasmodium and the presence of Plasmodium in saliva were not associated with the medication treatment of birds. However, the experimental treatment affected vector survival with mosquitoes fed on medicated birds showing a higher survival rate than those fed on control individuals. These results provide strong experimental evidence of the impact of parasite load of vertebrate hosts on the survival probability of malaria vectors.

Factors such as the particular combination of parasite–mosquito species, their co-evolutionary history and the host's parasite load greatly affect parasite transmission. However, the importance of these factors in the epidemiology of mosquito-borne parasites, such as avian malaria parasites, is largely unknown. Here, we assessed the competence of two mosquito species [Culex pipiens and Aedes (Ochlerotatus) caspius], for the transmission of four avian Plasmodium lineages (Plasmodium relictum SGS1 and GRW11 and Plasmodium cathemerium-related lineages COLL1 and PADOM01) naturally infecting wild house sparrows. We assessed the effects of parasite identity and parasite load on Plasmodium transmission risk through its effects on the transmission rate and mosquito survival. We found that Cx. pipiens was able to transmit the four Plasmodium lineages, while Ae. caspius was unable to transmit any of them. However, Cx. pipiens mosquitoes fed on birds infected by P. relictum showed a lower survival and transmission rate than those fed on birds infected by parasites related to P. cathemerium. Non-significant associations were found with the host–parasite load. Our results confirm the existence of inter- and intra-specific differences in the ability of Plasmodium lineages to develop in mosquito species and their effects on the survival of mosquitoes that result in important differences in the transmission risk of the different avian malaria parasite lineages studied.