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Las últimas décadas han presenciado una acelerada emergencia o el resurgimiento de enfermedades transmitidas por vectores (ETVs) en muchas áreas geográficas, afectando a humanos, animales salvajes y domésticos, lo que representa una gran amenaza para la salud pública y la conservación de la biodiversidad. A pesar del impacto médico y económico de las ETVs, la ecología de estas, especialmente las interacciones entre los hospedadores y los vectores, aún son insuficientemente conocidas. Los estudios epidemiológicos previos han asumido tradicionalmente una interacción aleatoria entre hospedadores y vectores, ignorando los posibles efectos de la heterogeneidad en las características del hospedador, tales como el estado de salud del individuo y la historia evolutiva, en las tasas de transmisión de patógenos. La falta de reconocimiento e incorporación de los posibles efectos de las características del huésped en los modelos epidemiológicos podría dar lugar a estimaciones sesgadas de la dinámica de transmisión de ETVs. Por lo tanto, los cuatro capítulos incluidos en esta tesis se centran en el estudio de los efectos de la heterogeneidad de ciertos rasgos del hospedador en las interacciones hospedador-vector a nivel tanto inter como intraespecífico. Aunque algunos patógenos transmitidos por vectores (PTVs) causan enfermedades en humanos, la mayoría de ellos son zoonóticos, siendo la fauna silvestre el hospedador vertebrado primario. Los mosquitos son vectores primarios de muchos PTVs, como el Plasmodium aviar y el virus de West Nile (WNV). Dado el importante papel de los mosquitos y los hospedadores silvestres en el ciclo de transmisión de los PTVs, en esta tesis se utilizó principalmente un patógeno transmitido por los mosquitos, el Plasmodium aviar, sus vectores naturales Culex pipiens y Culex restuans y el hospedador vertebrado Gorrión Común (Passer domesticus) como sistema de estudio. Las características del huésped pueden tener una profunda influencia en la interacción

Background: Host selection by mosquitoes plays a central role in the transmission of vector-borne infectious diseases. Although interspecific variation in mosquito attraction has often been reported, the mechanisms underlying intraspecific differences in hosts’ attractiveness to mosquitoes are still poorly known. Metabolic rate is related to several physiological parameters used as location cues by mosquitoes, and so potentially affect hostvector contact rates. Therefore, individual hosts with higher metabolic rates should be more attractive to hostseeking mosquitoes. Here, we experimentally investigated the role of bird metabolic rate in the feeding preferences of Culex pipiens (Linnaeus), a widespread mosquito vector of many pathogens affecting human and wildlife health. Results: Passer domesticus (Linnaeus) pairs containing one bird treated with 2,4-dinitrophenol (DNP) and the other injected with phosphate-buffered saline solution (PBS) (i.e. control) were simultaneously exposed overnight to mosquitoes. The treatment did not affect the proportion of mosquitoes biting on each individual. However, mosquito feeding preference was negatively associated with bird resting metabolic rate but positively with bird body mass. These two variables explained up to 62.76% of the variations in mosquito feeding preference. Conclusions: The relationships between mosquito feeding preferences and individual host characteristics could be explained by enhanced anti-mosquito behaviour associated with higher metabolic rates. The potential role of cues emitted by hosts is also discussed. Thus, individuals with high metabolism may actively avoid being bitten by mosquitoes, despite releasing more attractant cues. Since metabolic rates can be related to individual differences in personality and life history traits, differences in mosquitoes’ feeding preferences may be related to intraspecific differences in exposure to vector-borne pathogens

Pathogen-induced host phenotypic changes are widespread phenomena that can dramatically influence host–vector interactions. Enhanced vector attraction to infected hosts has been reported in a variety of host–pathogen systems, and has given rise to the parasite manipulation hypothesis whereby pathogens may adaptively modify host phenotypes to increase transmission from host to host. However, host phenotypic changes do not always favour the transmission of pathogens, as random host choice, reduced host attractiveness and even host avoidance after infection have also been reported. Thus, the effects of hosts’ parasitic infections on vector feeding behaviour and on the likelihood of parasite transmission remain unclear. Here, we experimentally tested how host infection status and infection intensity with avian Plasmodium affect mosquito feeding patterns in house sparrows (Passer domesticus). In separate experiments, mosquitoes were allowed to bite pairs containing (i) one infected and one uninfected bird and (ii) two infected birds, one of which treated with the antimalarial drug, primaquine. We found that mosquitoes fed randomly when exposed to both infected and uninfected birds. However, when mosquitoes were exposed only to infected individuals, they preferred to bite the non-treated birds. These results suggest that the malarial parasite load rather than the infection itself plays a key role in mosquito attraction. Our findings partially support the parasite manipulation hypothesis, which probably operates via a reduction in defensive behaviour, and highlights the importance of considering parasite load in studies on host–vector–pathogen interactions.

[Background] The life-cycle of many vector-borne pathogens includes an asexual replication phase in the vertebrate host and sexual reproduction in the insect vector. However, as only a small array of parasites can successfully develop infective phases inside an insect, few insect species are competent vectors for these pathogens. Molecular approaches have identified the potential insect vectors of blood parasites under natural conditions. However, the effectiveness of this methodology for verifying mosquito competence in the transmission of avian malaria parasites and related haemosporidians is still under debate. This is mainly because positive amplifications of parasite DNA in mosquitoes can be obtained not only from sporozoites, the infective phase of the malaria parasites that migrate to salivary glands, but also from different non-infective parasite forms in the body of the vector. Here, we assessed the vectorial capacity of the common mosquito Culex pipiens in the transmission of two parasite genera., [Methods] A total of 1,560 mosquitoes were allowed to feed on five house sparrows Passer domesticus naturally infected by Haemoproteus or co-infected by Haemoproteus/Plasmodium. A saliva sample of the mosquitoes that survived after 13 days post-exposure was taken to determine the presence of parasite DNA by PCR., [Results] Overall, 31.2% mosquito’s head-thorax and 5.8% saliva samples analysed showed positive amplifications for avian malaria parasites. In contrast to Haemoproteus DNA, which was not found in either the body parts or the saliva, Plasmodium DNA was detected in both the head-thorax and the saliva of mosquitoes. Parasites isolated from mosquitoes feeding on the same bird corresponded to the same Plasmodium lineage., [Conclusions] Our experiment provides good evidence for the competence of Cx. pipiens in the transmission of Plasmodium but not of Haemoproteus. Molecular analyses of saliva are an effective method for testing the vector competence of mosquitoes and other insects in the transmission of vector-borne pathogens.