Biomedical subjects
Publications and source records attributed to V Petrarca.
Polytene chromosome analysis was carried out in samples of Anopheles arabiensis from two colonies originating from different sites in the Rift Valley, Ethiopia. Both colonies were found to maintain the main chromosomal inversion variations existing in wild populations. Changes in karyotype frequencies were documented as well as excesses of heterokaryotypes.
The seasonality of malaria transmission was studied in a Gambian village situated in an area where rice was cultivated. Observations were made during two dry seasons, when pump-fed irrigation was used to grow rice, and in the intervening rainy season, when rice was cultivated using a combination of irrigated and rain-fed paddies. Clinical episodes of malaria were mainly confined to the months during and soon after the rainy season. In the wet season the prevalence of parasitaemia was higher in febrile subjects than in afebrile controls but the reverse applied during the dry seasons. However, the biting rates of Anopheles gambiae complex mosquitoes in the two dry seasons (2.5 and 0.8 bites/child/night respectively) were greater than or similar to that in the rainy season (0.6 bites/child/night). The proportion of human bloodmeals (0.53 vs 0.75) and the survival of mosquitoes (parity rates of 0.41 vs 0.58) were both lower in the dry seasons than in the rains. The low prevalence of morbidity due to malaria in the dry season and the observed fall in the sporozoite rate may therefore have been due to a reduction in the vectorial capacity of the An. gambiae population. However, reduced transmission in the dry season may also have been due to the direct effect of high temperatures on the parasite in the vector.
Yolk proteins (vitellogenin and vitellin) proved to be excellent marker molecules for separating Anopheles gambiae Giles and An. arabiensis Patton, two morphologically indistinguishable members of the An. gambiae species complex. A rabbit polyclonal antibody directed against An. gambiae yolk proteins was made species-specific by removing immunoglobulins that crossreacted with An. arabiensis by immunoaffinity chromatography. The resultant antibody was 400 times more sensitive to An. gambiae and was employed as the secondary antibody in a modified double antibody "sandwich" ELISA, which also used monoclonal antibodies to anopheline vitellogenin as the primary or coating antibody. This ELISA easily differentiated soluble yolk protein samples from An. gambiae and An. arabiensis. A field study with 628 females of An. gambiae complex collected in western Kenya demonstrated that the ELISA results were 98.4% in agreement with the standard cytotaxonomic method.
1. Anopheles pharoensis Theobald was found to be the prevalent man-biting anopheline mosquito in the central area of the Senegal River delta. 2. Blood-fed females of An. pharoensis were obtained during September-December 1987 from mosquito bednets in the village of Souhloul, near the Boundoum dam, 70 km NE of St Louis. 3. Dried mosquito specimens were identified morphologically and each thorax processed using monoclonal antibody against the circumsporozoite protein of Plasmodium falciparum. 4. Five An. pharoensis out of 912 examined were sporozoite positive, while ninety-eight An. gambiae Giles sensu lato were all negative. This finding strongly supports the local importance of An. pharoensis as a malaria vector. 5. Successful use of pyrethroid-impregnated bednets against malaria transmission in this situation has helped to achieve more than 90% reduction of malaria prevalence.
Samples of adult females of the Anopheles gambiae complex from thirteen localities of three islands of the Comoro Archipelago (Anjouan, Grande Comore and Moheli) were identified by analysis of ovarian polytene chromosomes as An. gambiae s.s. The samples showed only the inversion polymorphism 2La, the mean frequency of the inverted arrangement being 38%. A significantly higher frequency of the inverted arrangement 2La was observed in the localities with a lower annual rainfall. Similarities between the chromosomal polymorphism of the samples from Comoros and that of coastal eastern African countries suggest a probable continental origin of the An. gambiae s.s. populations in the Comoro Archipelago. A biometric analysis was carried out on the palpal index and the number of coeloconic sensilla, two characters partially diagnostic between fresh- and salt-water members of the gambiae complex. The palpal index of the 2La homozygous inverted females of An. gambiae s.s. was found to be significantly higher than the index of standard homozygotes and heterozygotes, suggesting a relation between the inversion and this biometric character. No An. merus was identified, although larvae of An. gambiae s.l. were observed breeding in brackish water.
Chromosome studies on samples of the Anopheles gambiae complex were carried out in a village of the rice-growing area of the Rusizi Valley (Burundi). A large predominance of An. arabiensis was observed throughout the year. Anopheles gambiae was also present but represented about 4% only of the indoor resting An. gambiae s.l. The finding of human blood-fed specimens in animal shelters suggests partial exophily. Abdominal appearance observations indicated a gonotrophic dissociation during the dry season. Both An. arabiensis and An. gambiae showed a low degree of inversion polymorphism, in agreement with the general picture shown in East Africa. The most frequent karyotypes are typical of wet savannas.
A recently developed DNA probe method was compared with the standard cytogenetic method for identifying the species of individual mosquitoes in the Anopheles gambiae complex. The complex consists of 6 morphologically indistinguishable sibling species that include the major African malaria vectors. Half-gravid, field collected mosquitoes were split into 2 portions: the abdomen was preserved for ovarian nurse cell cytotaxonomy and the head/thorax portion was desiccated for DNA extraction. Cytogenetic examination of the Kenya specimens showed 88 An. gambiae and 108 An. arabiensis. The Zimbabwe specimens consisted of 6 An. gambiae and 55 An. Quadriannulatus. All samples of the 3 species were polymorphic for the major chromosomal inversions previously recorded in field specimens from eastern and southern Africa, indicating that the collections reflected natural levels of intraspecific variation in the field populations sampled. Approximately 97% of the cytologically identified mosquitoes were also identified to species by the DNA probe method, and in every case the DNA probe and cytogenetic methods of species identification produced concordant results.
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1. Three sibling species of mosquitoes of the Anopheles gambiae complex are found in the Senegal River Basin: An. melas Theobald, An. gambiae Giles and An. arabiensis Patton. 2. An. melas is restricted to the river delta and environs where saltwater breeding places are present. 3. An. gambiae and An. arabiensis are sympatric in the study area; An. arabiensis predominates in coastal zones where it breeds also during the dry season; An. gambiae predominates in inland areas where breeding is mostly restricted to the rainy season (July-September). 4. An. arabiensis is chromosomally polymorphic all over the study area, with much variation of inversion frequencies, particularly for the 2Ra arrangement. 5. An. gambiae is characterized by a very high frequency of the 2Rb-2La inversion arrangement which is typical of the Savanna chromosomal form.
Adult females of Anopheles gambiae s.1. were collected by pyrethrum spray catch in Ouagadougou (Burkina Faso, formerly Upper Volta) and in four neighbouring villages. The collections have been carried out mostly during the 1984 rainy season. Monthly collections in some sampling sites allowed a preliminary longitudinal study. By analysis of nurse cell polytene chromosomes in adult females, An. gambiae s.str. and An. arabiensis were identified in the study area. Both species showed polymorphisms for various paracentric inversions. In all samples of An. arabiensis the frequencies of the alternative karyotypes were in Hardy-Weinberg equilibrium, suggesting panmictic conditions. Conversely, An. gambiae s.str. showed a different situation, since most of its samples had strong deficiency of certain expected heterokaryotypes. This same phenomenon was already observed in Mali, leading to the splitting of gambiae s.str. into different chromosomal forms, partially or totally reproductively isolated from each other. Each chromosomal form is characterized by different chromosomal polymorphisms. Two of these forms, Mopti and Savanna, were detected in the study area. Mopti chromosomal form is apparently associated with the presence of permanent waters (i.e. the "barrages" north of the town), while Savanna is usually found in situations where breeding places are mainly dependent from rain (e.g. in villages far from "barrages" or at the town's center).
Tests to evaluate the susceptibility level in Anopheles gambiae s.1. from Ouagadougou and two nearby villages have been carried out. Anopheles gambiae s.1. larvae from Ouagadougou showed complete susceptibility to organophosphates and carbamates, and adults showed low-level resistance to DDT. Nine percent survival of adult An. gambiae s.1. to one-hour exposure of 4% DDT was observed in samples from Zagtouli village while in those from Koubri village, where dieldrin also was tested, resistance to both organochlorine insecticides was detected.
Tests to evaluate the susceptibility level in Anopheles gambiae s.1. and Culex quinquefasciatus from Ouagadougou and two nearby villages have been carried out. Anopheles gambiae s.1. larvae from Ouagadougou showed complete susceptibility to organophosphates and carbamates, and adults showed low level resistance to DDT. Nine percent survival of adult An. gambiae s.1. to one hour exposure of 4% DDT was observed in samples from Zaghtouli village while in those from Koubri village, where dieldrin also was tested, resistance to both organochlorine insecticides was detected. Culex quinquefasciatus showed susceptibility to fenthion, malathion, fenitrothion, and chlorpyrifos, whereas incipient resistance to temephos was detected. Electrophoretic analysis showed polymorphism of high and low active esterases (Est-2 + Est-3) confirming the association between OP resistance and enhanced esterase activity in this species.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
A longitudinal study in a guinea savanna area in Northern Nigeria showed that indoor resting samples consisted almost entirely of An. gambiae in the wet season, characterized by relatively lower temperature and higher relative humidity, whereas An. arabiensis predominated in the dry season, characterized by relatively higher temperature and lower relative humidity. A significant change was also observed in the frequency of polymorphic chromosomal inversions in the population of An. gambiae. The inverted arrangements 2Rbc, 2Rd and 2La were found more frequent in the dry season samples as compared to the wet season ones.
Four species of the Anopheles gambiae complex were identified in Mozambique (East Africa) by chromosomal analysis. They were An. merus, An. gambiae s.s., An. arabiensis and An. quadriannulatus. An. merus was observed in coastal zones as well as in inner areas where the rivers are tidal and brackish and/or the soil is salty. An. gambiae s.s. is present in the central-northern regions (north of Save river) from the coast to the western mountains. On the coast it is often sympatric with An. merus. It is apparently absent south of Save river. An. arabiensis was observed in samples from the north-western hilly and mountainous areas, sympatrically with An. gambiae s.s., as well as south of Save river where often it is sympatric with An. merus. Only one specimen of An. quadriannulatus was observed. It was from a small sample collected feeding on bovid in a southern locality (Bela Vista-Maputo area). No inversion polymorphism was observed in the 446 An. merus identified. A quite low degree of inversion polymorphism was shown by both An. gambiae s.s. and An. arabiensis, involving 2Rb, 2La and 2Rb inversion systems respectively. By morphological analysis of cytogenetically identified samples of three species of the complex, number of sensilla coeloconica and palpal ratio were confirmed to be useful to distinguish An. merus from An. gambiae s.s./An. arabiensis. The overlapping areas between brackish and freshwater species become smaller when both characters are considered together, 1.5% and 3.5% being the probabilities of confusing An. merus with An. gambiae s.s. and An. arabiensis respectively.