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138
A. della Torre et al. - Research in molecular malaria entomology
chromosome-2 have been shown to be shared by the
two forms, although often with very different frequencies
of alternative arrangements, leading to the suggestion
of a role of these inversions in ecotypic adaptation
(della Torre et al., 2005). From the biomedical perspective,
the two forms do not appear to show obvious differences
in their efficiency in transmitting malaria;
however, their different temporal and spatial dynamics
and, in particular, the strong association of the M-form
with larval environment created by human activities
such as rice cultivation, is expected to alter the malaria
transmission dynamics, which have shifted from seasonal
and rain-dependent to permanent and dependentfrom-irrigation.
Moreover, the two forms show different
resistance mechanisms to insecticides used to control
vector densities, as shown by the different distribution
in the two OTUs of the knock-down (kdr) alleles
conferring resistance to pyrethroids and DDT. Since
the first description in 2001, the molecular forms have
been the focus of several studies by the international
malaria entomology community, aimed at understanding
the process of genetic and ecological differentiation
between them and to unravel the mechanisms of their
speciation process, which seems to be strictly associated
to and triggered by man-made modifications of the
environment. In the last years the group in Rome has
continued to participate to the international effort by
contributing to studies on the genetic differentiation
between M and S (see also Mancini E et al.,
Santolamazza F et al. and Pombi et al., this abstract
book). One of the most direct contributions of these
studies to the current fight against malaria is the development
of molecular tools for the identification of A.
gambiae species and forms, some of which have
become the methods routinely used by the field entomologists
(Fanello et al., 2002; Santolamazza et al.,
2004; Mancini E et al., this abstract book). The application
of these tools has also allowed to provide a comprehensive
picture of the M and S geographic distribution
(della Torre et al., 2005) and of the differential
spreading of kdr alleles in the two forms (Santolamazza
et al., 2008). Moreover, preliminary information have
been obtained on their feeding habits and sporozoite
infection frequencies in Angola (Calzetta et al., 2007),
Cameroon (Wondji et al., 2005), The Gambia and eastern
Senegal (Caputo et al., in preparation).
The group in the University of Napoli has mainly
focused its research interests on the A. gambiae salivary
glands, an organ that gets into multiple interactions
with both the parasite and the host (Arcà et al.,
1999). In fact, recognition and invasion of salivary
glands by Plasmodium sporozoites is a prerequisite for
a successful transmission, making this organ a very
interesting target of strategies aimed at interrupting
the transmission in the mosquito vector. Moreover, the
salivary secretions carry a large number of factors
whose pharmacological activities affect crucial host
responses such as hemostasis and immunity. The salivary
transcriptome of An. gambiae has been largely
worked out and more than 70 salivary proteins have
been identified to date (Arcà et al., 2005); surprisingly,
so far no functions could be assigned to almost half
of these proteins, pointing out how much we still have
to learn on the salivary secretions of blood sucking
Arthropods. These studies well conjugate basic
research interests on salivary functions and evolution
of blood feeding to potential applications finalized to
the development of novel tools for mosquito and
malaria control. In this respect there are at least two
aspects that came to light recently and may have relevant
implications for malaria control. First, mosquito
salivary proteins may play an important, underestimated
role in the vertebrate immune response to parasite
infection. Indeed, two independent studies in murine
malaria models reported that pre-immunization of
mice by exposure to bites of uninfected mosquitoes
has a protective effect on a following Plasmodium
infection. Actually, this phenomenon is the result of a
shift of the immune response toward a Th1-type, with
induction of IFNg and iNOS, which in turn brings
about lower levels of parasitemia (Donovan et al.,
2007; Fonseca et al., 2007). Moreover, lymph nodes
close to the cutaneous infection site seem to play an
unexpected crucial role in protective antisporozoite
response (Chakravarty et al., 2007). Based on these
experimental evidences it has been suggested that
Anopheles salivary proteins may be useful components
of malaria vaccines. Moreover, these observations have
another important implication. In endemic areas, even
with very high levels of transmission, the number of
bites received by exposed individuals from non-infected
anopheline mosquitoes is much higher than the
bites from infected mosquitoes. Therefore, mosquito
saliva may play an important, so far undervaluated,
role in the acquirement of natural immunity in endemic
areas. Second, human antibody response to A. gambiae
saliva has been suggested as a possible indicator
of the exposure to bites of Anopheline mosquitoes
and, therefore, a potential marker of malaria risk
(Remoue et al., 2006). The detailed molecular knowledge
of the A. gambiae salivary gland protein repertoire
is of crucial importance for the development of
both the aspects mentioned above. For example, comparative
analysis of salivary transcriptomes of different
mosquito species allowed to identify a relatively large
group of salivary proteins that seem to be specific of
Anopheles since they are not found in Aedes or Culex
mosquitoes (Lombardo et al., 2006). Some of these
proteins, if immunogenic, could be very useful as epidemiological
markers of exposure to Anopheles mosquitoes
(see also Ronca R et al, this abstract book).
For example, they could allow the evaluation of the
efficacy of vector control measures or the potential
malaria risk also in those cases in which the use of
classical entomological methods are difficult or even
impossible.
The main research focus of group in the University of
Camerino is represented by the study of the microbiota
associated to different mosquito vectors, in view of
the possible development of paratransgenic protocols