Potenziali vettori di malaria in Maremma: uno studio multidisciplinare
Author(s)
Di Luca, Marco
Date Issued
February 18, 2010
Type
Doctoral Thesis
Abstract
In the last years, in some European Countries the introduction/re-introduction of some Mosquito-
Borne Diseases, including malaria, occurred. In the light of the expected global warming and of the potential spread of exotic pathogens and vectors, a multidisciplinary-study on the possibility that malaria could be reintroduced in Italy was carried out. The Maremma region, a narrow coastal plain hyperendemic for malaria up to early 1950’s, was selected as the study area. Here, hyperendemic levels of the disease were maintained by Anopheles labranchiae, the more competent vector species of the Anopheles maculipennis complex, still present in the region. Moreover, in this area an
autochthonous-introduced Plasmodium vivax case, reasonably transmitted by indigenous An.
labranchiae, occurred in a rural locality of Grosseto in 1997, demonstrating that Maremma is still a suitable area for malaria reintroduction.
This study aimed to characterize the anopheline fauna of Maremma Plain and its Malariogenic
Potential. In particular were assessed the spatial distribution and density of An. labranchiae, showing how the environmental and climatic factors could influence its occurrence in the study area, by using remote sensing techniques. Moreover were characterized some ecological and biological features of this malaria vector, such as its feeding preference and its trophic activity on humans (important elements in the assessment of the Vectorial Capacity), and was described its female reproductive system at ultrastructure level.
Entomological data were collected by longitudinal and sporadic surveys carried out. Mosquitoes
were collected in indoor resting sites and human-bait night collections were also performed.
Environmental parameters that could influence mosquito dynamics were analysed. An.
maculipennis species were identified by egg-exochorion morphology and by Multiplex-PCR.
Historical data on the distribution and bionomics of anopheline species in Maremma, past data on
malaria incidence and current data on imported cases (gametocyte carriers) were also acquired. The theoretical values of Vectorial Capacity of An. labranchiae were assessed by the MacDonald
formula. The reproductive system of three Anopheles species was compared and analyzed by using light microscopy, scanning electron microscopy and transmission electron microscopy. In order to identify the potential breeding sites and to assess the abundance of adults mosquitoes, geostatistical analysis were carried out by using GIS software.
A total of 9629 mosquitoes, belonging to 17 species, were collected. Out of total sample, 9364
(97.2%) were anophelines belonging to the An. maculipennis complex. The results highlighted that
An. labranchiae is the most abundant species in coastal plain of Maremma Plain and its seasonal
trends are different in each site. However, this species was also detected in the internal areas of
Tuscany, Umbria and Lazio Regions. Maps with spatial distribution of An. labranchiae were
produced according to Tran et al.,. Furthermore, a multi-category statistical model based on logistic regression and driven by climatic predictors was computed to describe the yearly absence/presence of An. labranchiae in the main collecting sites.
The results of the surveys and the development of distribution maps show a high Receptivity of the
study area (factor that takes into account presence and density of the vector), related to the occurence of the most relevant breeding sites (rice-fields and marshes) and of the livestock density.
In Maremma a known Infectability of the An. labranchaie with P. vivax, opposite to an apparent
poor competence to transmit afro-tropical P. falciparum strains was already demonstrated. The
study area also confirms a very low Vulnerability due to the scarce presence of gametocyte carriers
potentially circulating during the favourable transmission season.
In the study area, the overall Malariogenic Potential appears to be low, as in other areas of the country where An. labranchiae still persist in relevant densities. So a return to a situation of endemic malaria should be considered not possible (also due to the improved cultural and socioeconomic conditions). Nevertheless the occurrence of isolated cases appears improbable, but not impossible as already occurred in this area in 1997. In fact it is possible that illegal immigrants, coming from endemic malaria countries as seasonal workers, and afraid to attend public health facilities, may introduce gametocytes in rural “at risk” areas. It should be also considered that in the summer, tourists largely occurring in the area could be exposed to mosquito bites more than resident people.
However Maremma Plain represents a suitable study-model for epidemiological and entomological
analysis on the risk assessment of malaria reintroduction. Indeed due to genetic, historical, social and epidemiological reasons, An. labranchiae is the only species that may really represent a potential risk of malaria re-emergence in those countries facing the Western side of the Mediterranean Basin. For this reason epidemiological and entomological surveillance has to go on, especially along the coastal Maremma Plain, where the relevant abundance of An. labranchiae still
represents a concern about the possible reappearance of malaria in Italy.
Additional information
Dottorato di ricerca in Evoluzione biologica e biochimica
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