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V Petrarca

Publications and source records attributed to V Petrarca.

At least 37 records · Page 2Linked to original sources
PubMed1998

Cloning of inversion breakpoints in the Anopheles gambiae complex traces a transposable element at the inversion junction.

Anopheles arabiensis, one of the two most potent malaria vectors of the gambiae complex, is characterized by the presence of chromosomal paracentric inversions. Elucidation of the nature and the dynamics of these inversions is of paramount importance for the understanding of the population genetics and evolutionary biology of this mosquito and of the impact on malaria epidemiology. We report here the cloning of the breakpoints of the naturally occurring polymorphic inversion 2Rd' of A. arabiensis. A cDNA clone that cytologically mapped on the proximal breakpoint was the starting material for the isolation of a cosmid clone that spanned the breakpoint. Analysis of the surrounding sequences demonstrated that adjacent to the distal breakpoint lies a repetitive element that exhibits distinct distribution in different A. arabiensis strains. Sequencing analysis of that area revealed elements characteristic of transposable element terminal repeats. We called this presumed transposable element Odysseus. The presence of Odysseus at the junction of the naturally occuring inversion 2Rd' suggests that the inversion may be the result of the transposable element's activity. Characteristics of Odysseus' terminal region as well as its cytological distribution in different strains may indicate a relatively recent activity of Odysseus.

Animals↗
PubMed1998

Mark-release-recapture experiments with Anopheles gambiae s.l. in Banambani Village, Mali, to determine population size and structure.

Mark-release-recapture experiments with Anopheles gambiae s.l. were performed during the wet seasons of 1993 and 1994 in Banambani, Mali. All recaptured mosquitoes were identified to species by PCR analysis and, when possible, by chromosomal analysis to chromosomal form. Two species of the An. gambiae complex were present: An. gambiae s.s. and An. arabiensis; their ratio differed greatly from one year to the next. Three chromosomal forms of An. gambiae s.s. were found--Bamako, Savanna and Mopti. The drier 1993 was characterized by a high frequency of An. arabiensis and of the Mopti chromosomal forms of An. gambiae s.s. These trends were consistent with large-scale geographical patterns of abundance along a precipitation gradient. We observed no difference in dispersal between the two species, nor among the chromosomal forms of An. gambiae s.s. Therefore, in this situation at least, it is reasonable to group such data on the An. gambiae complex as a whole for analysis. Population size of An. gambiae s.l. females in the village was estimated to be 9000-11,000 in 1993 and 28,000 in 1994. The corresponding numbers were somewhat higher when independently-derived values of daily survival were used. These were consistent with estimates of effective population size obtained from patterns of gene frequency change.

Animals↗
PubMed1998

Morphometric multivariate analysis of field samples of adult Anopheles arabiensis and An. gambiae s.s. (Diptera: Culicidae).

The Afrotropical complex of sibling species Anopheles gambiae Giles includes the most efficient vectors of human malaria south of the Sahara. Anopheles arabiensis Patton and An. gambiae s.s. Giles are the members of the complex more adapted to the human environment. They are sympatric and synchronic over most of their distribution range; however, they show a different involvement in malaria transmission, with An. gambiae being more anthropophilic and endophilic than An. arabiensis. Discriminating between them is essential for a correct assessment of epidemiological parameters. The identification is currently achieved through recognition of species-specific chromosomal inversions or by molecular biology techniques. Both methods require considerable technical resources, not always available in the field. We carried out a morphometric analysis of field and laboratory samples of An. arabiensis and An. gambiae s.s. from sites in Madagascar, Burkina Faso, Mali, and Liberia to evaluate the degree of morphological differentiation. We examined 17 morphometric characters in samples representing each of the geographic sites. All of the measures were significantly larger for An. arabiensis (regardless of the collection site), demonstrating an intrinsic greater body size of this species. To assess the reliability associated with the multivariate statistic, we applied the discriminant function analysis, which provided a method for predicting to which group a new case will most likely be assigned. In a blind experiment, the morphometric method correctly identified approximately 85% of field-collected An. arabiensis and An. gambiae s.s., which provided a relatively simple method to approximate the relative frequencies of the 2 species in areas in which their concurrent presence was already known. The influence of laboratory conditions on the morphometrics of the 2 species was also analyzed.

Animals↗
PubMed1998

Humoral response to Plasmodium falciparum Pf155/ring-infected erythrocyte surface antigen and Pf332 in three sympatric ethnic groups of Burkina Faso.

The humoral immune response against synthetic peptides of two Plasmodium falciparum blood-stage antigens, Pf155/ring-infected erythrocyte surface antigen (RESA) (EENV)6 and Pf332 (SVTEEIAEEDK)2, in individuals belonging to three sympatric ethnic groups (Mossi, Rimaibe, and Fulani) living in the same conditions of hyperendemic transmission in a Sudan savanna area northeast of Ouagadougou, Burkina Faso were examined. The Mossi and Rimaibe are Sudanese Negroid populations with a long tradition of sedentary farming, while the Fulani are nomadic pastoralists partly settled and characterized by non-Negroid features of possible Caucasoid origin. A total of 764 subjects (311 Mossi, 273 Rimaibe, and 180 Fulani) were tested. A lower P. falciparum prevalence was observed in the Fulani of all age groups. The serologic results clearly indicate the existence of interethnic differences in the capacity to respond to these two P. falciparum antigens. The Mossi and Rimaibe showed similar responses, whereas the Fulani displayed consistently higher prevalences and levels of antibodies against both epitopes tested. The anti-(EENV)6 and anti-(SVTEEIAEEDK)2 seroprevalences were 29.9% and 38.9% in Mossi, 29.7% and 39.2% in Rimaibe, 86.1% and 76.1% in Fulani (all P values of Fulani-Mossi and Fulani-Rimaibe comparisons << 0.001). Anti-RESA and anti-Pf332 antibody levels were approximately 65% (P << 0.001) and 45% (P << 0.001), respectively, higher in seropositive Fulani than in seropositive Mossi and Rimaibe, who showed very similar values. The observed differences cannot be explained in terms of interethnic heterogeneity of malaria exposure since these communities have lived in the same area for more than 30 years and the P. falciparum inoculation rate, measured during two consecutive years, was substantially uniform for the three ethnic groups. The possibility of remarkable heterogeneities in the capacity to mount immune responses against P. falciparum antigens among populations with different genetic backgrounds must be taken into account in the development of anti-malaria vaccines.

Adolescent↗
PubMed1998

Baseline immunity of the population and impact of insecticide-treated curtains on malaria infection.

It has been shown that insecticide-treated bed nets or curtains may reduce morbidity and mortality from malaria in hyper-holoendemic areas of sub-Saharan Africa. This protection could partially depend on the transitory imbalance between the anti-malaria immunity acquired by the population before the intervention and the lowered sporozoite load resulting from the anti-vector measure. To verify if the efficacy of the intervention is influenced by the baseline immune status of the population, we compared the protective effect of permethrin-impregnated curtains (PIC) against malaria infection among groups with different baseline levels of anti-malaria immunity. We analyzed the impact of PIC on the Plasmodium falciparum infection rate in two rural villages of Burkina Faso inhabited by three ethnic groups: the Fulani, Mossi, and Rimaibé. These have been previously shown to differ for several malariologic indices, with the Fulani being characterized by lower infection and disease rates and by higher immune response to P. falciparum with respect to the other ethnic groups. The PIC were distributed in June 1996 and their impact on malaria infection was evaluated in groups whose baseline levels of immunity to malaria differed because of their age and ethnic group. Age- and ethnic-dependent efficacy of the PIC was observed. Among the Mossi and Rimaibé, the impact (parasite rate reduction after PIC installation with respect to the pre-intervention surveys) was 18.8% and 18.5%, respectively. A more than two-fold general impact (42.8%) was recorded in the Fulani. The impact of the intervention on infection rates appears positively correlated with the levels of anti-malaria immunity. Since decreased transmission entails a reduction of immunity, the efficacy of the intervention in the long term cannot be taken for granted. The expected complementary role of a hypothetical vaccine is stressed by these results, which also emphasize the importance of the genetic background of the population in the evaluation and application of malaria control strategies.

Animals↗
PubMed1998

The distribution and inversion polymorphism of chromosomally recognized taxa of the Anopheles gambiae complex in Mali, West Africa.

Data from polytene chromosome studies on the Anopheles gambiae complex in Mali were reviewed. The banding pattern was successfully scored in 17,705 specimens from 76 sampling sites representing the main ecological strata of the country. Two members of the complex, namely An. arabiensis and An. gambiae, were found widespread and frequently sympatric, with the latter prevalent in most localities. Population genetic analysis of the inversion polymorphisms indicated the existence of panmictic conditions for An. arabiensis only, whereas the parallel study of An. gambiae supported its splitting into at least three reproductive units, characterized by different 2R chromosome arrangements, designated Bamako, Mopti and Savanna. The chromosomal evidence was consistent with the hypothesis of complete reproductive isolation between Bamako and Mopti. Partial isolation between these two taxa and Savanna was suggested by the scoring of hypothetical hybrid 2R heterokaryotypes in various samples, but the actual hybrid origin of these specimens was not confirmed. Different patterns of geographical and seasonal distribution were shown as follows. An. arabiensis prevails in arid savannas (Sahel and Northern Sudan savanna) out of the flooded or irrigated zones; it is able to withstand the most arid conditions of Saharan localities and its breeding might extend throughout the dry season. An. gambiae Savanna and Bamako prevail in relatively humid savannas (Southern Sudan savanna) and their breeding generally occurs only during the rainy season. The Savanna taxon was almost absent in flooded or irrigated zones and in riverine localities; the Bamako taxon is distributed along the upper river Niger and its tributaries. An. gambiae Mopti extends its range in all ecological zones present in Mali including the Sahel and predesertic areas, showing high relative frequencies up to absolute dominance in flooded or irrigated areas; its breeding is highly successful also during the dry season. Rainfall at the sampling sites was found to correlate positively with the frequency of Savanna and negatively with the frequency of Mopti. The remarkable ecological flexibility of the latter was found associated with wide seasonal and geographical variations in its 2R inversion polymorphism bc/u. Higher frequencies of the bc arrangement were recorded both in the Southern localities during the dry season and in the Northern more arid localities during the rainy season. The absence or scarcity of An. arabiensis and An. gambiae Savanna in most flooded or irrigated zones suggests their competitive exclusion by An. gambiae Mopti.

Animals↗
PubMed1996

Different response to Plasmodium falciparum malaria in west African sympatric ethnic groups.

The comparison of malaria indicators among populations that have different genetic backgrounds and are uniformly exposed to the same parasite strains is one approach to the study of human heterogeneties in the response to the infection. We report the results of comparative surveys on three sympatric West African ethnic groups, Fulani, Mossi, and Rimaibé, living in the same conditions of hyperendemic transmission in a Sudan savanna area northeast of Ouagadougou, Burkina Faso. The Mossi and Rimaibé are Sudanese negroid populations with a long tradition of sedentary farming, while the Fulani are nomadic pastoralists, partly settled and characterized by non-negroid features of possible caucasoid origin. Parasitological, clinical, and immunological investigations showed consistent interethnic differences in Plasmodium falciparum infection rates, malaria morbidity, and prevalence and levels of antibodies to various P. falciparum antigens. The data point to a remarkably similar response to malaria in the Mossi and Rimaibé, while the Fulani are clearly less parasitized, less affected by the disease, and more responsive to all antigens tested. No difference in the use of malaria protective measures was demonstrated that could account for these findings, and sociocultural or environmental factors do not seem to be involved. Known genetic factors of resistance to malaria did not show higher frequencies in the Fulani. The differences in the immune response were not explained by the entomological observations, which indicated substantially uniform exposure to infective bites. The available data support the existence of unknown genetic factors, possibly related to humoral immune responses, determining interethnic differences in the susceptibility to malaria.

Adolescent↗
PubMed1996

Anopheles gambiae complex (Diptera:Culicidae) near Bissau City, Guinea Bissau, West Africa.

Cytogenetic studies on mosquitoes collected inside bednets near Bissau City confirmed the presence of Anopheles melas Theobald and An. gambiae Giles sensu stricto, the latter species prevailing in rainy season samples (approximately 80% in average) and the former in dry season samples (> 90%). Seasonal and ecogeographical variations in the frequency of species and chromosomal inversions were analyzed. The analysis of An. gambiae sensu stricto confirmed the existence of the Bissau chromosomal form. The deficiency of heterokaryotypes in most samples indicated the possible coexistence of another chromosomal form not completely panmictic (i.e., randomly mating) with the Bissau form.

Animals↗
PubMed1995

Characterization of the Culex pipiens complex (Diptera: Culicidae) in Madagascar.

Morphological analysis of phallosome and multilocus electrophoresis were used to characterize populations of the Culex pipiens L. complex from Madagascar. Samples phenotypically and genetically corresponding to Cx. p. quinquefasciatus Say were found on the east and west coasts, whereas, on the high plateau, 1 sample was composed mostly of phenotypical Cx. p. pipiens L., genetically introgressed with quinquefasciatus at some loci (Hbdh, Aat-2, and Hk-1). A hybrid zone between the 2 taxa was detected on the plateau on a genetic basis, whereas at the morphological level a predominance of Cx. p. quinquefasciatus specimens and deficit of intermediates was observed. Accordingly, morphological analysis failed to describe satisfactorily the hybridization phenomena. Despite the high level of gene exchange, a complete mixing of the 2 gene pools apparently does not occur, possibly because of differential selective pressures in the climatically heterogeneous environment of the Madagascar plateau.

Animals↗
PubMed1995

Plasmodium falciparum malaria in sympatric ethnic groups of Burkina Faso, west Africa.

Plasmodium falciparum parasite rate, parasite density and anti-CS antibodies were assessed in 196 subjects (age > 10 yrs) belonging to three sympatric West African ethnic groups, namely Mossi, Rimaibé and Fulani, all exposed to very high seasonal malaria transmission in the same rural village near Ouagadougou, Burkina Faso. No interethnic differences were noted in the use of antimalaria measures nor in the exposure to malaria vectors. However, interethnic differences were found in each of the three malariological indices. The Fulani appeared markedly less parasitized and more responsive to the CS-antigen than the Mossi and the Rimaibé who had very similar indices, except in the case of parasite density. These findings suggest a higher resistance to malaria of the Fulani ethnic group, possibly involving human genetic factors and/or the influence of extrinsic variables (e.g., socio-cultural) among which diet differences should be considered.

Adolescent↗
PubMed1994

Ecological genetic studies in the chromosomal form Mopti of Anopheles gambiae s.str. in Mali, west Africa.

Among the sibling species of the Afrotropical Anopheles gambiae complex, the nominal taxon (An. gambiae s.str.) is the major malaria vector. Its bionomics suggest a man-dependent speciation process which involves, in West Africa, various incipient species chromosomally recognized by different combinations of 2R paracentric inversions. One of the most recent evolutionary steps of such a speciation process appears to be the chromosomal form Mopti, which is associated with dry season irrigation in arid zones, and is characterized by a remarkable ecological flexibility related to three 2R alternative arrangements, namely bc, u and +, whose expected karyotypes are found in Hardy-Weinberg equilibrium. The study of this chromosomal polymorphism in samples from a 16-locality transect in Mali shows wide variations and highly significant correlation with both temporal and spatial climatic differences. Mosquitoes homokaryotypic for 2Rbc are the actual dry season and arid areas breeders. The regular rise of 2Rbc frequency, up to fixation, during each dry season, corresponds to the South-North clinal increase of the same arrangement along the transect, from about 30% in the humid savanna to near fixation in the South-Saharan zone. This coherent ecological genetics case provides full support to the hypothesis of the adaptive nature of paracentric inversions. Moreover, the very peculiar system of combinations of contiguous 2R inversions, utilized by Mopti as well as by other chromosomal forms of An. gambiae, suggests a process of polygenic reorganization based on linkage disequilibria and involving the inversions as driving selection units.

Animals↗
PubMed1994

Species composition and inversion polymorphism of the Anopheles gambiae complex in some sites of Ghana, west Africa.

Samples of Anopheles gambiae s.1. were collected from eight localities belonging to four of the five main ecological strata of Ghana. Analysis of ovarian polytene chromosomes revealed the presence of A. gambiae s.s. in all the sites studied, while A. arabiensis was detected only in the extreme northern locality of Navrongo and A. melas in some southern sites. Anopheles arabiensis showed a degree of inversion polymorphism comparable to the one observed in other West African countries. The analysis of the chromosomal polymorphism of A. gambiae s.s. showed the presence of the FOREST form in the rain forest localities and the SAVANNA form in the coastal savanna sites. The MOPTI form occurred sympatrically with the SAVANNA form in the northernmost locality. The possible influence of the presence of various taxa of the A. gambiae complex and of their intra-specific variants on malaria vectorial system is discussed.

Animals↗
PubMed1994

[Biology of the vectors and transmission of Plasmodium falciparum, P. malariae and P. ovale in a village in the savanna of west Africa (Dielmo, Senegal)].

From April 1990 to March 1992 a longitudinal entomological study was carried out in Dielmo village, Senegal, an area of Sudan-type savanna. Mosquitoes were sampled by night-bite collections and pyretnrum spray collections. Seven anopheles species were identified: An. gambiae s.s. An. arabiensis, An. funestus, An. pharoensis, An. rufipes, An. squamosus and An. ziemanni. Present throughout the year, An. gambiae s.l. and An. funestus represented more than 98% of anopheles captured on man. A yearly wave of An. gambiae s.l. was observed in the rainy season and An. funestus was generally more abundant in the dry season. The sporozoite rate was 1.5% and 1.3%, respectively, for these two species. Sporozoite typing by monoclonal antibodies indicated that the proportion of infected salivary glands was 92.7% P. falciparum, 18.2% P malariae and 8.2% P. ovale. The inoculation rate was calculated to be respectively 111, 21 and 8 infective bites per human for P. falciparum, P. malariae and P. ovale during the first year. Transmission was highest in the second year, with respectively 272, 54 and 25 infective bites per human.

Adolescent↗
PubMed1993

Effective population size and persistence of Anopheles arabiensis during the dry season in west Africa.

The way that the malaria vectors Anopheles arabiensis and An.gambiae survive the dry season in sub-saharan Sahel or northern Savanna areas of Africa remains enigmatic. We examined this problem by calculating the effective sizes (Ne) of An.arabiensis populations for several locations in West Africa. An indirect/genetic procedure was used, comparing gene frequencies at several time intervals. The amount of drift which occurred provides an estimate of Ne. Most estimates of Ne were approximately 2000 individuals, probably close to the yearly minimum. This supports the hypothesis that populations of An.arabiensis in this region are continuous throughout the year, with many individuals surviving through the dry season, perhaps in a physiologically altered state, rather than extinction or severe bottlenecks during the dry season, followed by recolonization by a few individual survivors or immigrants in the subsequent rainy season.

Africa, Western↗
PubMed1992

Intraspecific chromosomal polymorphism in the Anopheles gambiae complex as a factor affecting malaria transmission in the Kisumu area of Kenya.

The paracentric inversion polymorphisms of Anopheles gambiae and An. arabiensis populations in the Kisumu area of western Kenya were studied in relation to parameters of Plasmodium falciparum transmission. Anopheles gambiae (n = 1,387) was polymorphic for inversions b on chromosomal arm 2R and a on arm 2L, with frequencies of the inverted arrangements of 17% and 43%, respectively. Anopheles arabiensis (n = 484) was polymorphic for inversion b on chromosomal arm 2R and a on 3R, with frequencies of the inverted arrangements of 58% and 5%, respectively. Observed karyotypic frequencies did not deviate from Hardy-Weinberg equilibrium, indicating a condition of panmixia (i.e., random mating) for both species. The overall degree of intraspecific polymorphism was low, confirming findings from other zones of East Africa. No significant differences in inversion frequencies of either An. gambiae or An. arabiensis were observed, either between collecting sites or between similar sampling periods of consecutive years. At the same time, a stable, significant two-fold difference in Plasmodium infection rates was detected among An. gambiae carriers of different inversion karyotypes on chromosome 2. A significant non-uniform distribution of human- and bovid-fed specimens was also detected among the carriers of different 2Rb inversion karyotypes in indoor resting An. arabiensis. Relationships among inversion karyotypes of the two major malaria vectors in the An. gambiae complex and key factors affecting malaria transmission intensity emphasize that intraspecific variation could contribute significantly to the diversity and stability of malaria vectorial systems in Africa.

Animals↗
PubMed1991

Species composition of the Anopheles gambiae complex (diptera: Culicidae) at two sites in western Kenya.

At two sites in the Kisumu area of western Kenya, the species composition of the Anopheles gambiae complex was determined by analysis of ovarian polytene chromosomes. Of 1,915 females, 26.1% were An. arabiensis Patton and 73.9% were An. gambiae Giles; one arabiensis x gambiae hybrid was identified. No major differences in the proportions of An. arabiensis and An. gambiae were observed between sites or between years. The ratio of An. arabiensis/An. gambiae was 6.7:1 (n = 231) in cow-baited traps, 0.2:1 (n = 1,525) in indoor resting samples, and 0.5:1 (n = 145) in all-night human bait catches. The proportion of An. arabiensis decreased progressively from 50.0% to 8.3% (n = 1,129) during 11 wk from September to November 1987; this change was correlated negatively with night temperature and positively with temperature range. In cow-baited traps, 97.4% (n = 194) of An. arabiensis were cow-fed and 95.8% (n = 1,054) of An. gambiae from indoor resting collections were human-fed. In indoor collections, 37.2% (n = 215) of An. arabiensis were cow-fed and 23.1% (n = 26) of An. gambiae from cow traps were human-fed. This demonstrates post-blood-feeding endophily by An. arabiensis and suggests post-blood-feeding exophily by An. gambiae. Malaria infection rates were higher for An. gambiae than for An. arabiensis by a ratio of 3:1 in 1986 (by Plasmodium falciparum ELISA) and 2.3:1 in 1987 (by dissection). Despite the higher proportion of infective An. gambiae, both species in this area serve as efficient vectors through their remarkably stable contact with the human population as demonstrated by their blood feeding and resting behavior.

Animals↗