Dottorato in MALATTIE INFETTIVE, MICROBIOLOGIA E SANITA' PUBBLICA

Titolo della tesi: Occurrence, distribution and ecology of Anopheles maculipennis complex mosquitoes and risk of malaria re-emergence in Italy

Despite the eradication of malaria across most European countries in the 1960's and 70's, the anopheline vectors are still present. The possibility of acquiring malaria by locally infected mosquitoes is poorly investigated, although autochthonous malaria cases have been occasionally reported in several European countries. The risk of re-emergence of malaria is related to the occurrence in a territory of a competent vector mosquito where an imported case is introduced. The aim of this study is to collect data that will be used to assess the current risk of re-introduction and emergence of indigenous cases of malaria. The specific objective of this thesis is focused on determining the current presence, density and distribution of Anopheles vector mosquitoes and their role in malaria circulation in an area of Italy historically endemic for malaria. Vectorial capacity of the main potential malaria vector found, and malariogenic potential was estimated. Specific studies have been also conducted to clarify some biological and ecological aspects of the Italian Anopheline species belonging to Anopheles maculipennis complex: i. Evaluation of the feeding pattern and the anthropophilic degree, both estimated by blood meals analysis of fed mosquitoes and human landing catches. ii. Comparison and evaluation of the performance of different trap types for collecting adult mosquitoes. The study area is North-East Italy, a particularly sensitive region due to the abundant presence of mosquitoes and ecological areas suitable for their development. Entomological data were collected by longitudinal and targeted surveys carried out in two selected sites during 2018-2020. Mosquitoes were collected in resting sites and by different traps; human-bait night collections were also performed. Mosquitoes were identified morphologically and molecularly and molecular analyses were also applied to fed females for host identification. A total of 886 Anopheles belonging to Maculipennis complex and collected in Veneto region were identified at species level as An. messeae/daciae (709, 80.0%), An. maculipennis s.s. (167, 18.8%) and An. atroparvus (10, 1.2%). Anopheles messeae/daciae was abundant in few scattered areas (Verona e Rovigo province) and its occurrence was linked to rice field cultivation and wetlands. Results indicate that this species fed preferably on large mammals, displaying an opportunistic feeding pattern. Feeding on humans is also possible but very uncommon, suggesting a generally low receptivity. Vectorial capacity was estimated in the site with the highest An. messeae/daciae abundance. However, the values were zero in July and very low in August, constituting a negligible risk for malaria transmission (<0.05 for both Plasmodium falciparum and P. vivax). Infectivity, that represents the susceptibility of mosquitoes to different Plasmodium species, was retrieved by literature: it is considered low for both plasmodia with a higher rate for P. vivax. Vulnerability, that is determined by the number of gametocyte carriers circulating locally is possible only in Verona province, where a certain number of malaria human cases are reported every year. In conclusion, the main potential malaria vector in selected area of North-East Italy is An. messeae/daciae. Considering its abundance only locally relevant, the feeding preference for animals and a low degree of anthropophily, it can be considered a vector unable to maintain a local circulation of malaria. In the study area, the overall malariogenic potential appears extremely low. Therefore, a return to a situation of endemic malaria should be considered not possible.