Histological study of Trichosomoides nasalis (Nematoda: Trichinelloidea) in the nasal cavities of the murid Arvicanthis niloticus, with associated pathology.

Histological study of the nasal cavities and upper maxillae of Arvicanthis niloticus naturally infected with Trichosomoides nasalis shows that the female worms reside in the epithelial monolayer of the nasal mucosa of the posterior and median cavities. Eggs laid by T. nasalis were infiltrated between the female body wall and the epithelial lining. Small groups of eggs, mixed with mucus and polymorphonuclear cells, were found in the nasal lumen, freed by rupture of the stretched epithelium. Two females and a few eggs were also found in the connective tissues. One male was found in a female uterus and two were apparently in the lumen of the nasal cavity but the surrounding tissues were disrupted. No male was identified in the lamina propria of the mucosa. However, significant inflammatory lesions occurred in the lamina propria, similar to those induced by the males of Anatrichosoma spp. which live in this part of the mucosa. In rodents, the lesions resulted in rhinosinusitis characterised by a lymphocytic infiltration leading to nasal obstruction.

[A comparison of 2 capture methods for sampling the population of Anopheles funestus Giles in a Sudanese savannah village (Dielmo, Senegal)]. / Comparaison de deux méthodes de capture pour l'échantillonnage des populations d'Anopheles funestus Giles dans un village de savane soudanienne (Dielmo, Sénégal).

We conducted a comparative study of two collection methods for sampling An. funestus populations--human bait catch and indoor pyrethrum spray--in the Sudanese savannah area of Senegal from April 1996 to March 1997. An. funestus females were captured every month during the study period. The resting density per dwelling was 1.9 times higher than those obtained with human landing catch. The population dynamics were similar with two peaks situated respectively at the beginning of the rainy season between May-July and during the dry season January-March. A significant correlation of population densities between collection methods was detected.

[Differential changes in IgG1 and IgG3 against a major antigen of blood stage Plasmodium falciparum (MSP1(19)) as a function of the parasite transmission period: study among immune Senegalese adults]. / Evolution différentielle des IgG1 et des IgG3 dirigées contre un antigène majeur des formes sanguines de Plasmodium falciparum (msp1(19)) en fonction de la période de transmission paustre: une étude chez des sujets adultes prémunis au Sénégal.

This study examined the evolution of P. falciparum specific IgG1 and IgG3 antibodies "before" and "after" the highest transmission period in clinically immune Senegalese adults settle in Dielmo, a holoendemic area for P. falciparum transmission. Plasma was tested for antibodies to an antigen (Q-KNG- MSP1(19)) known to react with IgG1 and/or IgG3 in the majority of these individuals. There was a decrease in titers in individuals with low, but not high titer IgG1 whereas specific IgG3 remained unchanged following the highest transmission period. These results raise the question of the differential role of anti-MSP1(19)g-IgG1 antibody fractions in the maintenance of immunity to P. falciparum.

[Feeding behaviour of Anopheles funestus resting females in Senegal]. / Préférences trophiques des femelles endophiles d'Anopheles funestus au Sénégal.

The feeding behaviour of An. funestus resting females was studied in eleven sites in Senegal along a west-east transect in two biogeographical zones (the Sudanese and Sudanese-Guinean zones) by an ELISA technique. Mosquitoes were collected by pyrethrum spray catches. For the 1563 blood meals tested, the main hosts were humans, cows, sheep and horses representing respective proportions of 85%, 9.9%, 1.3% and 3.8%. No blood meal was taken on chicken. The percentage of non-reacting blood meals was 2.6%. A heterogenity of feeding behaviour was observed in the sample locations. The anthropophilic rates were higher in the northern Sudanese zone as versus the southern Sudanese and Sudano-Guinean zones.

Spatial and temporal variations of the chromosomal inversion polymorphism of Anopheles funestus in Senegal.

The polymorphism of paracentric inversions of An. funestus polytene chromosomes was studied along a transect in Senegal in order to assess their variations at the spatial and temporal level. There was an increase in the degree of chromosomal polymorphism from the West to South-East. At the geographical level the variations in inversion frequencies were highly significant whatever the chromosomal arm considered. However, the variations in the chromosomal inversion frequencies did not change significantly over either seasons or years, except for inversion 3b in the village of Dielmo. Such geographical variability within a relatively limited area, associated to temporal stability, suggest a restricted gene flow between the populations studied, probably due to discontinuities in the An. funestus distribution and to its bioecology.

[Trichosomoides nasalis Biocca & Aurizi, 1961 and T. spratti n. sp. (Nematoda: Trichinelloidea), from the nasal cavity of murids]. / Trichosomoides nasalis Biocca & Aurizi, 1961 et T. spratti n. sp. (Nematoda: Trichinelloidea), parasites des fosses nasales de muridés.

The nematode parasite of the nasal mucosa of rodents, Trichosomoides nasalis, is common in the murid Arvicanthis niloticus, in Senegal. The morphological study of this material allowed us to augment the original description, made with specimens recovered in Italy from Rattus norvegicus. This analysis shows that specimens from Rattus fuscipes in Australia, which had been identified to this species, represent a distinct species (smaller, with an average of five intrauterine males per female instead of one), which we name T. spratti n. sp.

First isolation of the Rift Valley fever virus from Culex poicilipes (Diptera: Culicidae) in nature.

Following the reemergence of Rift Valley fever (RVF) virus in southeastern Mauritania in 1998, an entomological survey was undertaken in the boundary area in Senegal to assess the extent of the virus circulation. During this study, RVF virus (36 strains) was isolated for the first time from Culex poicilipes in nature. The possible role of Cx. poicilipes as an RVF vector is discussed regarding its biology and ecology.

[Anopheline population genetics]. / Génétique des populations anophéliennes.

Population genetic studies of vectors are essential for (i) the determination of their taxonomic status and consequently the definition of their vectorial role in the transmission of pathogenic agents; (ii) the evaluation of the species genetic variability and the estimation of their capacities of adaptation to selection pressure; (iii) an estimation of gene flow among populations in order to evaluate their degree of isolation and gene circulation, especially resistance genes. Among the malaria vectors taken as examples on three continents, Africa, South-East Asia and Latin America, the large majority of the species showed an important polymorphism. The Gambiae Complex, which is by far the most studied one, includes at present 7 species with the recent description of An. quadriannulatus A and B from Ethiopia. An. gambiae s.s. includes itself 5 chromosomal forms. One of them, the Mopti form, should be considered as a species unto itself. For An. arabiensis, a strong differentiation has been observed among the populations from Senegal and the Indian Ocean Islands. The kdr mutation, which confers resistance to pyrethroid knockdown effect, has never been found either in the Mopti form, or An. arabiensis, indicating a restricted gene flow between these latter two and An. gambiae s.s. The speciation process of the Gambiae Complex seems to be a recent phenomenon due to environmental selection pressure. Species of the Funestus Group are distinguishable by morphological characters. The genetic study of An. funestus s.s. did not show the presence of a complex, in spite of high polymorphism and population structure. Anophelines from eastern areas present an important biodiversity. The Minimus Complex includes two species, A and C, which are widely distributed in South-East Asia. Species A is strongly endophilic, on the contrary species C is at once more exophilic and zoophilic. The latter species might have been selected by DDT indoor house spraying. After numerous taxonomic investigations, the Dirus Complex includes now 7 species. In Latin America, An. pseudopunctipennis clustered into three geographic populations which are under a speciation process. One covers North America and Guatemala, the other South America and Belize, whilst the last one is restricted to Grenada Island. On the contrary, An. darlingi showed little morphologic and genetic variability throughout the species geographic range suggesting the existence of a single species. The main objective of these studies is to implement a more selective approach of vector control programs in relation to the incriminated species, their bioecology and their role in malaria transmission. The improvement of efficiency and selectivity of vector control is becoming a major goal in order to make the best out of the available tools and control the impact of interventions on the environment.

Single-strand conformation polymorphism analysis for identification of four members of the Anopheles funestus (Diptera: Culicidae) group.

Members of the Anopheles funestus Giles group are difficult to identify because of the morphological overlap that exists within the group. This inability to distinguish species, as well as the fact that the species vary in their behavior and biting preferences, complicate the successful planning and maintaining of malaria control programs. In this article we discuss the use of a single-strand conformation polymorphism (SSCP) assay to distinguish 4 members of the An. funestus group collected at 10 different localities in Africa. rDNA genes differ at numerous sites among closely related species. Using conserved primers, the D3 domain in the 28S gene was amplified, electrophoresed on SSCP gels, and species-specific patterns were observed. Intraspecific variation was detected in An. funestus specimens from East and West Africa. Analyzing 108 An. funestus, 78 An. vaneedeni Gillies & Coetzee, 21 An. rivulorum Leeson, and 2 An. lessoni Evans, we concluded that SSCPs can be used successfully as a molecular tool for the identification of these species.

Mitochondrial and ribosomal internal transcribed spacer (ITS2) diversity of the African malaria vector Anopheles funestus.

The pattern of sequence variation in the mitochondrial DNA cytochrome b gene (cyt-b) and ribosomal DNA internal transcribed spacer 2 (ITS2) was examined in Anopheles funestus from Senegal and Burkina Faso in West Africa and Kenya in East Africa. From both West African countries, samples included individuals hypothesized to represent reproductively isolated taxa based upon different karyotypes and behaviours. Analysis of the cyt-b data revealed high haplotypic diversity (86%) and an average pairwise difference per site of 0.42%. Sequence variation was not partitioned by geographical origin or karyotype class. The most common haplotype was sampled across Africa (approximately 6000 km). Analysis of the ITS2 data revealed one of the longest spacers yet found in anophelines (approximately 704 bp). In common with other anopheline ITS2 sequences, this one had microsatellites and frequent runs of individual nucleotides. Also in common with data from other anopheline ITS2 studies, the An. funestus sequences were almost monomorphic, with only two rare polymorphisms detected. The results from both markers are congruent and do not support the hypothesis of reproductively isolated chromosomal taxa within An. funestus. Whether the lack of support by mitochondrial DNA (mtDNA) and ribosomal DNA (rDNA) sequences is a result of the recent origin of the presumptive taxa, or of the absence of barriers to gene flow, remains to be elucidated, using more rapidly evolving markers such as microsatellites.

The complexity of the malaria vectorial system in Africa.

The malaria vectorial system in Africa is very complex. Five very efficient vector species transmit malaria: Anopheles gambiae, An. arabiensis, An. funestus, and the sometimes overlooked An. nili and An. moucheti. This paper focuses on morphological, behavioural and genetic differences observed among populations within each vector species. It emphasises that future strategies for controlling vectors should take into account this heterogeneity.

Similar feeding preferences of Anopheles gambiae and A. arabiensis in Senegal.

This study in Senegal compared the feeding preferences of Anopheles gambiae and A. arabiensis while controlling for equal accessibility to hosts located outdoors under bed net traps. All fed A. gambiae complex females were identified with the aid of the polymerase chain reaction and their blood meal sources were identified by enzyme-linked immunosorbent assay. A total of 605 anophelines, including 281 A. gambiae and 301 A. arabiensis, were captured, 32.2% in the human-baited traps and 67.8% in bovine-baited traps. 30.3% of A. gambiae fed in the former and 69.7% fed in the latter; the corresponding figures for A. arabiensis were 29.6% and 70.4%. Thus, when the hosts were located outdoors and made equally available, the feeding preferences of A. gambiae and A. arabiensis were similar (P = 0.81). These results suggest that biases existed in previous studies, most of which suggested that A. arabiensis was more zoophilic than A. gambiae. Alternatively, the feeding behaviour of these 2 species may differ in various parts of Africa.

[Comparative evaluation of the plasmodial infection of Anopheles using ELISA and dissection. Consequences for the estimation of the transmission of malaria in 1995 in Ndiop, Senegal]. / Evaluation comparée par ELISA et par dissection de l'infection plasmodiale des anophèles. Conséquences sur l'estimation de la transmission du paludisme en 1995 à Ndiop, Sénégal.

An entomological study was carried out in Ndiop village, Senegal, an area of sudan-type savana, from January to December 1995, to compare the malaria inoculation rate measured by the dissection of salivary glands of anophelines and the enzyme-linked immunosorbent assay (ELISA). Mosquitoes were sampled by night-bite collections. Species from the Anopheles gambiae complex were identified using the polymerase chain reaction. 1292 females Culicidae were collected. 597 anophelines mosquitoes known to be malaria vectors were captured during 148 man-nights of capture. Of the 572 anophelines investigated, 14 were positive using dissection while 21 were found to be positive with ELISA. The sporozoite rates were 2.5%, 2.2% and 3.8% for An. arabiensis, An. gambiae and An. funestus, respectively. The circumsporozoite rates were 3.5%, 2.2% and 7.7% for these three species, respectively. ELISA detected 1.5 times more positive mosquitoes than dissection. These results are discussed with reference to the duration of the sporogonic cycle, the delay before CSP antigens are apparent, and the daily survival rate of Anopheles mosquitoes.

[Characterization of entomopathogenic Bacillus samples isolated in Senegal and study of their toxicity for malaria vectors]. / Caractérisation de souches de Bacillus entomopathogènes isolées au Sénégal et étude de leur toxicité pour les vecteurs du paludisme.

A screening program developed in Senegal to isolate new strains of entomopathogenic Bacillus has led to the isolation of 194 strains of Bacillus thuringiensis and 9 strains of Bacillus sphaericus from various sites and insect samples. The characterization of these strains regarding their H serotype, their crystal composition and their toxicity against mosquitoes (Culex pipiens, Aedes aegypti and Anopheles stephensi) has led to the isolation of 27 mosquitocidal strains. As malaria is an important public health problem in Senegal, these strains were more completely characterized looking for their toxicity against the two major malaria vectors in Senegal: Anopheles gambiae and Anopheles arabiensis.

Bionomical and cytogenetic heterogeneities of Anopheles funestus in Senegal.

Malaria transmission by Anopheles funestus was investigated from May 1994 to September 1997 in different locations from western to eastern Senegal along the northern border of The Gambia. 10515 A. funestus were captured on human volunteers or by indoor pyrethrum spraying. Circumsporozoite protein rates showed that A. funestus had a high infection rate, 2-7%, in the whole of the study area. Analysis of feeding behaviour showed great variation of anthropophilic rates from western Senegal, where populations were highly anthropophilic, to eastern Senegal, where they were much more zoophilic. In eastern Senegal many females captured in bedrooms had fed outside on horses. Polytene chromosome analysis showed that the general pattern of karyotype distribution is consistent with the hypothesis of 3 chromosomally differentiated populations of A. funestus. In samples from a central part of the study area, analysis showed lack of karyotype intergradation with a deficit of heterokaryotypes, suggesting the presence of 2 genetically differentiated populations in an area of sympatric.

Comparison of behavior and vector efficiency of Anopheles gambiae and An. arabiensis (Diptera:Culicidae) in Barkedji, a Sahelian area of Senegal.

The ecology, population dynamics, and malaria vector efficiency of Anopheles gambiae and An. arabiensis were studied for 2 yr in a Sahelian village of Senegal. Anophelines were captured at human bait and resting indoors by pyrethrum spray. Mosquitoes belonging to the An. gambiae complex were identified by polymerase chain reaction. Of 26,973 females, An. arabiensis represented 79% of the mosquitoes captured and remained in the study area longer than An. gambiae after the rains terminated. There were no differences in nocturnal biting cycles or endophagous rates between An. gambiae and An. arabiensis. Based on an enzyme-linked immunosorbent assay test of bloodmeals, the anthropophilic rate of these 2 vectors were both approximately 60%, when comparisons were made during the same period. Overall, 18% of the resting females had patent mixed bloodmeals, mainly human-bovine. The parity rates of An. gambiae and An. arabiensis varied temporally. Despite similar behavior, the Plasmodium falciparum circumsporozoite protein (CSP) rates were different between An. gambiae (4.1%) and An. arabiensis (1.3%). P. malariae and P. ovale only represented 4% of the total Plasmodium identified in mosquitoes. Transmission was seasonal, occurring mainly during 4 mo. The CSP entomological inoculation rates were 128 bites per human per year for the 1st yr and 100 for the 2nd yr. Because of the combination of a high human biting rate and a low CSP rate, An. arabiensis accounted for 63% of transmission. Possible origin of differences in CSP rate between An. gambiae and An. arabiensis is discussed in relation to the parity rate, blood feeding frequency, and the hypothesis of genetic factors.

High annual and seasonal variations in malaria transmission by anophelines and vector species composition in Dielmo, a holoendemic area in Senegal.

We conducted a three-year entomologic study in Dielmo, a village of 250 inhabitants in a holoendemic area for malaria in Senegal. Anophelines were captured on human bait and by pyrethrum spray collections. The mosquitoes belonging to the Anopheles gambiae complex were identified using the polymerase chain reaction. Malaria vectors captured were An. funestus, An. arabiensis, and An. gambiae. Anopheles funestus was the most abundant mosquito captured the first year, An. arabiensis in the following years. The annual entomologic inoculation rates calculated by enzyme-linked immunosorbent assay were 238, 89, and 150 for the first, second, and third years, respectively. Each year there was a peak of transmission at the end of the rainy season, but transmission occurred year round. The heterogeneity of transmission was found at four different levels: 1) the relative vector proportion according to the place and method of capture, 2) the human biting rate and relative proportion of vectors by month and year, 3) the infection rate of each vector by year, and 4) the number of infected bites for all vectors, and for each species, for the year. Our data show that even in areas of intense and perennial transmission, there exist large longitudinal variations and strong heterogeneity in entomologic parameters of malaria transmission. It is important to take these into account for the study of the variations in clinical and biological parameters of human malaria, and to evaluate this relationship, a very thorough investigation of transmission is necessary.

Four years' entomological study of the transmission of seasonal malaria in Senegal and the bionomics of Anopheles gambiae and A. arabiensis.

From 1993 to 1996, an entomological survey was conducted in the village of Ndiop, Senegal, as part of a research programme on malaria epidemiology and the mechanisms of protective immunity. Mosquitoes were captured on human bait and by indoor spraying. Species from the Anopheles gambiae complex were identified using the polymerase chain reaction, and Plasmodium falciparum infections were detected by enzyme-linked immunosorbent assay for circumsporozoite protein. The vector species identified were A. gambiae (33.9%), A. arabiensis (63.2%), A. melas (0.3%) and A. funestus (2.5%). Similar proportions of A. gambiae (74.2%) and A. arabiensis (73.8%) contained human blood; 27.0% of A. gambiae and 28.3% of A. arabiensis had fed on cattle. The sporozoite rates were similar for A. gambiae (3.2%) and A. arabiensis (3.7%). The annual entomological inoculation rates varied greatly depending on the year. There were 63, 17, 37 and 7 infected bites per person per year in 1993, 1994, 1995 and 1996 respectively. Transmission was highly seasonal, from July to October. A. arabiensis was responsible for 66% of malaria transmission, A. gambiae for 31%, and A. funestus for 3%.