Search

Mosquitoes (Diptera, Culicidae) form a family of insects of considerable public health importance. Mention of their presence/absence was tackled in the literature and by specialized websites for eight African countries: Cape Verde, Mauritania, Senegal, Gambia, Mali, Burkina Faso, Niger and Chad. In total, 216 species have been recorded belonging to 13 genera

CTD S2P mediates nutrient-dependent development., Serine 2 phosphorylation (S2P) within the CTD of RNA polymerase II is considered a Cdk9/Cdk12-dependent mark required for 3′-end processing. However, the relevance of CTD S2P in metazoan development is unknown. We show that cdk-12 lesions or a full-length CTD S2A substitution results in an identical phenotype in Caenorhabditis elegans. Embryogenesis occurs in the complete absence of S2P, but the hatched larvae arrest development, mimicking the diapause induced when hatching occurs in the absence of food. Genome-wide analyses indicate that when CTD S2P is inhibited, only a subset of growth-related genes is not properly expressed. These genes correspond to SL2 trans-spliced mRNAs located in position 2 and over within operons. We show that CDK-12 is required for maximal occupancy of cleavage stimulatory factor necessary for SL2 trans-splicing. We propose that CTD S2P functions as a gene-specific signaling mark ensuring the nutritional control of the C. elegans developmental program.

In thirty years, bed nets treated with pyrethroids have been established as a means of prevention against malaria for personal protection and in public health. One of the actors of these discoveries gives an overview of insecticidetreated bed nets (ITNs) and brings his testimony, more particularly on the circumstances and frames of mind which prevailed in the 1980's, a crucial decade for these breakthroughs which served humanity. In 1983, the first experiment testing the effect of bed nets treated with pyrethroid insecticide was performed and revealed the impact of this method on the reduction of Plasmodium transmission. This discovery was made in an experimental field station in Burkina Faso showing that each of the many entomological parameters measured led to a clear decrease in mosquito-human contact. A few years later, still in Burkina Faso, it was shown that ITNs, massively used in a village, reduced the longevity and vector capacity of mosquito populations, to such an extent that ITNs acted as a means of vector control. These researches were all led within the Centre Muraz of the Organization of Coordination and Cooperation for the Control of Great Endemies (OCCGE) by researchers belonging to the Office of Overseas Scientific and Technical Research (ORSTOM, which later became French National Research Institute for Sustainable Development), and benefited from the scientific and financial support of the Division of Vector Biology and Control from the World Health Organization (WHO).En une trentaine d’années, les moustiquaires imprégnées de pyrétrinoïdes se sont imposées en protection personnelle et en santé publique comme un moyen de prévention du paludisme. Un des acteurs de ces découvertes présente un panorama des moustiquaires imprégnées d’insecticide et apporte ici son témoignage, se fondant particulièrement sur les circonstances et les états d’esprit qui ont prévalu dans les années 1980, décennie cruciale pour ces avancées qui ont servi l’humanité. C’est en 1983 qu’a été réalisée la première expérimentation testant l’effet des moustiquaires imprégnées de pyréthrinoïdes et qui a mis en évidence l’impact de cette méthode sur la réduction de la transmission du Plasmodium. Cette découverte a été faite dans une station expérimentale de terrain au Burkina Faso montrant que chacun des nombreux paramètres entomologiques mesurés allait dans le sens d’une nette réduction du contact moustique–humain. Quelques années plus tard, toujours au Burkina Faso, il a été montré que les moustiquaires imprégnées, utilisées massivement dans un village, réduisaient la longévité et la capacité vectrice de la population de moustiques, à tel point que ces moustiquaires agissaient comme un moyen de lutte antivectorielle. Ces recherches ont toutes été effectuées par des chercheurs de l’Office de la recherche scientifique et technique outre-mer, devenu Institut de recherche pour le développement, dans le cadre du centre Muraz de l’Organisation de coordination et de coopération pour la lutte contre les grandes endémies, en bénéficiant de l’appui scientifique et financier de la Division de la biologie et de la lutte contre les vecteurs de l’Organisation mondiale de la santé.

The presentation of some odorous materials such as xylene or toluene under the snout of rats has been shown to elicit 15–30 Hz fast-wave bursts in both the olfactory bulb and dentate gyrus. Electrical stimulation of the olfactory bulb elicits an evoked potential (latency of first peak is 16–18 ms) in the dentate gyrus. The present study demonstrates that scopolamine or atropine blocks toluene-induced fast-wave bursts in the dentate region and to a lesser degree in the olfactory bulb while leaving dentate gyrus electrically evoked potentials intact. Further, rhythmical burst stimulation of the olfactory bulb at fast-wave frequencies will elicit fast-wave-like oscillations in the dentate gyrus. These fast-wave-like events, unlike evoked potentials to single-pulse stimulation, are abolished after muscarinic receptor antagonism with atropine. Mechanisms at the olfactory bulb and dentate gyrus that produce fast oscillations may involve muscarinic cholinergic synapses while the simple transmission of single, non-oscillatory olfactory signals to the dentate gyrus does not.

Kisspeptins, encoded by the Kiss1 gene, play a key role in the regulation of reproductive function, although very little is known about the ontogenesis of this system. The present study aimed to determine the period of arcuate nucleus (ARC) kisspeptin cell birth and the embryonic stage and neuroanatomical sites of onset of kisspeptin immunoreactivity. Bromodeoxyuridine (BrdU) was administered to female rats at various gestational stages and double immunohistochemistry against kisspeptin and BrdU was performed on brain sections from their offspring. The period of neurogenesis of ARC kisspeptin neurones begun between embryonic day (E) 12.5 and E13.5, reached its peak at E15.5 and was not completely over at E17.5. Kiss1 mRNA was detected in mediobasal hypothalamic punches of embryos aged E14.5, E16.5, E18.5 and E22.5 by real-time reverse transcriptase-polymerase chain reaction. Accordingly, kisspeptin-immunoreactive (-IR) cells were consistently detected in the embryonic ARC from E14.5 and their number increased until E18.5 to reach approximately half the level observed in adults. Between E18.5 and E22.5, the number of kisspeptin-IR cells and hypothalamic Kiss1 expression significantly decreased, regardless of sex, and this decrease persisted until birth. Taken together, these results demonstrate that rat ARC kisspeptin neurones are born locally during an extended embryonic period and are able to synthesise kisspeptins rapidly after their birth, consistent with the hypothesis of a role during embryonic activation of the hypothalamic-hypophyseal-gonadal axis. A sex-independent decrease of kisspeptin-IR cell numbers was observed during the perinatal period, suggestive of important regulations of kisspeptin neurones around birth.

Eighty-two wild monkeys belonging to the two species Chlorocebus aethiops and Erythrocebus patas were collected in the northern part of Senegal, West Africa. Thick blood smears were performed and Giemsa stained. Slides were microscopically examined with a sensitivity of the method estimated at 2 parasites per mm3 of blood. No blood parasites were observed. This negative result is in line with previous studies which never showed evidences of malaria parasites in monkeys from African savannahs. This intriguing absence is underlined.

An entomological study was performed to document the transmission of Plasmodium, agents of human malaria in Antananarivo, capital of Madagascar. Human landing mosquitoes were collected at night during two years, between May 2003 and September 2005, in the two sites of Ambohimiandra-Manakambahiny and Ambolokandrina. The genuses of collected mosquitoes were, in order of abundance, Culex, Mansonia and Anopheles. The only potential vector was Anopheles arabiensis. Its maximal abundance was observed in January (22 and 15 bites per man per night, outdoors, respectively in the two sites), during the rainier month of the austral summer This anopheles was biting indoors, in bedrooms, but its agressivity was always higher outdoors than indoors. Its maximal agressivity was observed indoors between 00 and 01 am. The absence of An. gambiae and An. funestus in the catches on the one hand, and the absence of An. arabiensis infected by Plasmodium falciparum on the other hand, are discussed.

Three new species of Phlebotomine sandflies belonging to the genus Sergentomyia FrançaParrot are described from Madagascar: Sergentomyia sclerosiphon n. sp. S. namo n. sp. and S. anka n. sp. The taxa are created on the basis of the morphology of females. The males of S. sclerosiphon n. sp. and of S. anka n. sp. have been associated to the females according to the homologies of a fragment of the mtDNA cytochrome b sequences. The original morphology of the spermathecae and the sclerification of a part of the individual spermathecal ducts allow the creation of a new subgenus, Vattieromyia subg. nov., which includes these three new species.

Sergentomyia majungaensis, a new species of Phlebotomine sandfly, is described from Madagascar. The female is characterised by an unusual antennal formula (1/IV-V to VII; 2/VI to VIII-XV) and smooth and narrow spermathecae, with a common duct, whose shape is intermediate between Sergentomyia and Parrotomyia subgenera. The male has the same antennal formula than Grassomyia (1/IV-XV) but no hairs on the mesanepistern and a longer third antennal segment.

SUMMARYOocysts fromAnopheles stephensimosquitoes fed on murine blood infected withPlasmodium berghei berghei, were fixed for electron microscopy 6–12 days post-feeding. Ultrastructural analysis focused on Golgi-related trafficking pathways for rhoptry and microneme formation during sporogony. A small Golgi complex of 1–3 cisternae is formed close to the spindle pole body from coated vesicles budded from the nuclear envelope which is confluent with the endoplasmic reticulum. Rhoptries begin as small spheroidal bodies apparently formed by fusion of Golgi-derived vesicles, lengthening to 3–4 μm, and increasing in number to 4 per sporozoite. Ultrastructural data indicate the presence of a novel mechanism for vesicle transport between the Golgi complex and rhoptries along a longitudinal 30 nm – thick fibre (rootlet fibre or tigelle). Filamentous links between vesicles and rootlet indicate that this is a previously undescribed vesicle transport organelle. Genesis of micronemes occurs late in bud maturation and starts as spheroidal dense-cored vesicles (pro-micronemes), transforming to their mature bottle-like shape as they move apically. Filamentous links also occur between micronemes and subpellicular microtubules, indicating that as in merozoites, micronemes are trafficked actively along these structures.

The male of Phlebotomus (Anaphlebotomus) fontenillei n. sp. is described from Namoroka area (Madagascar). Its belongs to the subgenus Anaphlebotomus: style with four spines, coxite without basal process and paramere with two branches. It shares with P. berentiensis an original and exclusive antennal formula: 2/III-XII which distinguishes them from P. fertei. P. fontenillei n. sp. differs mainly from P. berentiensis by about 40 setae in tuft on the ventral face of the coxite, the length of the genital ducts and the position of the spines on the style. Sequence of the second internal transcribed spacer (ITS2) of the ribosomal DNA (rDNA) is very informative: the male of P. fontenillei n. sp. cannot be linked to the female of P. huberti (male unknown) regarding the size of amplified DNA fragment (459 bp versus 600 respectively) and the high degree of variability. There are few differences (10 mutations) between the sequences of P. fontenillei n. sp. and P. berentiensis which are closely related species.

The female of Phlebotomus (Anaphlebotomus) fertei Depaquit, LégerRobert, 2002 is described from Madagascar. The spermathecae have separated ducts, a body with an enlarged-sclerified dilatation and a deriviated large bladder with thin walls and long head. P. fertei female has the following characters: long antennal segments, pharyngeal armature with small teeth and cibarium with 15 to 30 denticles, and very long legs. Its remarkable spermatheca is closely related to that of P. berentiensis. The status of P. (Anaphlebotomus) berentiensis (LégerRodhain, 1978) is revised into this paper. The female is redescribed and the male is described for the first time. The latter has an unusual antennal formula (2/III-XII), a cibarium with four teeth and about 30 denticles, no tuft of setae on the coxite, four spines on the style, including a very long proximal one. Males and females were linked to each other based on morphological and molecular characteristics (second internal transcribed spacer of the ribosomal DNA and ND4 gene of the mitochondrial DNA). The inclusion of these taxa into the subgenus Anaphlebotomus Theodor, 1948 is exclusively based on male characters as listed by Theodor (style with four spines, no basal lobe on the coxite, paramere with two or three branches). The very heterogeneous characters of the females do not allow their use for the definition of this subgenus, which is probably not homogeneous.

The level of malaria transmission is usually estimated by some entomological parameters (entomological inoculation rate or reproductive rate and its seasonal variations). However, only one aspect of the malaria transmission is explored by this way, i.e. the transmission of Plasmodium from mosquito to man. The transmission from man to mosquito, the development of parasite in the mosquito midgut, and the role of transmission blocking immunity remain poorly documented. Recent studies on vaccination with gamete antigens showed that transmission blocking immunity, and the natural infectiousness of gametocytes after treatment underlined the need for taking into account a new aspect of malaria epidemiology concerning the transmission of Plasmodium from man to mosquito. In this paper, authors propose and discuss different new indicators and methods to improve our knowledge on malaria epidemiology.

The transmission of Plasmodium is a complex process that requires the encounter of three organisms: the parasite, the host and the mosquito vector. For a better understanding, the transmission of this parasite can be divided in four cyclical steps: 1) the development in man, including gametocytogenesis, 2) the transfer from man to mosquito, 3) the sporogonic development in the mosquito, 4) the transfer from mosquito to man. The present article proposes a review of these different aspects and focuses especially to recent biological knowledge on Plasmodium falciparum in the gametocytogenesis issues, infectivity of gametocytes, sporogonic development and natural factors limiting this development.

First record of Phlebotomine sandflies belonging to the genus Phlebotomus from Madagascar. Description of two new species: Phlebotomus (Anaphlebotomus) fertei n. sp. from three males and Phlebotomus (Anaphlebotomus) huberti n. sp. from two females. Their belonging to the subgenus Anaphlebotomus is supported by several characters. Male have four spines on the style, a coxite without basal tubercle, a paramere with two branches, one to three antero-inferior setae on the mesanepisternum. Female, closely related to the Asiatic species of the same subgenus, has a characteristic pharyngeal armature, about ten cibarial teeth, and annealing spermathecae with long ducts including a short basal common part. These two taxa differ by variation in the second internal transcribed spacer (ITS2) of the ribosomal DNA (rDNA). At the present time, the subgenus Anaphlebotomus includes six species (excluding P. fortunatarum from it), completing the known species from Africa (P. rodhaini and P. rousettus) and from Asia (P. stantoni and P. colabaensis).

The endogenous retrovirus gypsy is expressed at high levels in mutant flamenco female flies. Gypsy viral particles extracted from such flies can infect naive flamenco individuals raised in the presence of these extracts mixed into their food. This results in the integration of new proviruses into the germline genome. These proviruses can then increase their copy number by (1) expression in the flamenco female somatic cells, (2) transfer into the oocyte and (3) integration into the genome of the progeny. Surprisingly, unlike the infection observed in the feeding experiments, this strategy of endogenous proviral multiplication does not seem to involve the expression of the viral env gene.

Some colonic luminal molecules resulting from bacterial metabolism of alimentary or endogenous compounds are believed to exert various effects on the colonic epithelial cell physiology. We isolated surface epithelial cells and intact colonic crypts in order to test bacterial metabolites in the pig model, which is often considered relevant for extrapolation to the physiopathology of the human gastrointestinal tract. Using colonocytes isolated with EDTA, we found that the initial cell viability, estimated by the membrane integrity and oxidative capacity measurement, fell rapidly despite several experimental attempts to preserve it such as the use of a medium designed to increase the adherence of epithelial cells and of a coated extracellular matrix, the presence in the culture medium of the oxidative substrate butyrate, and the use of an inhibitor of the caspases involved in cell apoptosis. In contrast, using dispase and collagenase as proteolytic agents, we were able to obtain pig colonic crypts that maintain an excellent membrane integrity after 4 h. Using this preparation, we were able to test the presumably cytotoxic luminal compounds hydrogen sulfide, ammonia, and deoxycholic acid on colonic crypt viability. Of these, only deoxycholic acid was found to significantly alter the cellular membrane integrity. It is concluded that pig colonic crypts can be useful for the in vitro appraisal of the cytotoxic properties of luminal compounds.

To investigate the quantitative distribution of #Plasmodium falciparum$ gametocytes into the vector bloodmeal, #Anopheles arabiensis$ mosquitoes were fed on 3 volunteers naturally infected with gametocytes. The content of each mosquito midgut was smeared on a microscope slide and Giemsa stained. The distribution of gametocytes ingested by mosquitoes followed a negative binomial distribution, with apparently constant overdispersion (parameter k plus or minus S.E = 3.105 plus or minus 0.392) for the 3 series. This aggregation of gametocytes in some midguts probably facilitates the conjunction of gametes and fertilization. This suggests that #P. falciparum$ gametocytes in the peripheral blood flow of infected man do not follow an independent, homogeneous pattern but show a significant aggregation. (Résumé d'auteur)

The hepatopulmonary syndrome (HPS) consists of a triad of liver dysfunction, increased alveolar-arterial oxygen gradient and intrapulmonary vascular dilations. The mechanisms of impaired arterial oxygenation are still debated but the multiple inert gases elimination technique and more recently contrast echocardiography, greatly facilitated the investigation of such mechanisms. Subsequently the cause of hypoxemia can be attributed to several mechanisms such as ventilation-perfusion mismatch, right-to-left intrapulmonary shunts and alveolar-to-capillary diffusion defect, variously implicated in the severity of the disease. SHP may result from intrapulmonary vascular dilations and angiogenesis but the pathogenesis of such abnormalities is not completely explained. The hypothesis of an imbalance in vasoactive mediators and angiogenic factors has been put forward. Increasing data support the theory that the increase in synthesis and release of nitric oxide (NO) is the key factor modulating vascular tone. If this hypothesis is true, the use of compettive inhibitors of NO synthesis should restore pulmonary vascular tone, reversing the hemodynamic changes and gas exchange impairment of HPS.

Synthesis of aldosterone (Aldo) and corticosterone (B) has been recently reported in rat heart. However, regulation of this synthesis in pathophysiological states remains unknown. Thus, this study aimed to analyze effects of a one-month myocardial infarction (MI) on cardiac steroidogenic system. Levels of terminal enzymes of B (11 beta-hydroxylase: 11 beta H) and aldo (Aldo-synthase: AS) synthesis were assayed by quantitative RT-PCR. Cardiac Aldo and B levels were assessed by celite colum chromatography and radioimmunoassay. MI raised AS mRNA levels by 2.0-fold (p0.05) but downregulated that of 11 beta H by 2.4 fold (p0.05) in the noninfarcted part of the left ventricle (LV). Cardiac steroids production followed a similar pattern of regulation. Aldo level was increased in MI (319 +/- 85 vs 87 +/- 11 pg/mg of protein in control, p0.05) whereas that of B fell (2,412 +/- 318 vs 4,624 +/- 857 pg/mg of protein in control, p0.05). MI also induced an 1.9-fold increase in cardiac Ang II level. Such cardiac regulations were prevented by Ang II-AT1 receptor antagonist losartan (8 mg/kg/day) treatment. The Aldo receptor antagonist spironolactone (20 mg/kg/day) had no effect. Plasma Aldo and B, and adrenal 11 beta H and AS mRNA levels were unchanged whatever the treatment. The MI-induced collagen deposition in noninfarcted area of the LV was reduced by both spironolactone and losartan treatments by 1.6- and 2.5-fold, respectively. These data indicate that MI is associated with tissue-specific activation of myocardial aldosterone synthesis. This activation is mediated by cardiac Ang II via AT1 receptor and the resultant increase of intracardiac aldosterone level may be involved in post-MI ventricular remodeling.

The anopheline bioecology and the malaria transmission were studied from January to December 1995 in three villages of the sahelian rural area of Niakhar, Senegal. This area of 29000 inhabitants, has been for several decades, a regional observatory for population and health. The three methods used for collecting mosquitoes were the collection at larval stages, the all night human biting collection, and the pyrethrum spray catch in houses during afternoons. The anophelines collected were, by numerical importance: Anopheles arabiensis, An. rufipes, An. gambiae, An. pharoensis, An. funestus and An. coustani. In the An. gambiae complex, An. arabiensis represented 97% of man biting females and 98% of half gravid resting females (difference not significant); the other reminding species of this complex was always An. gambiae. These two species belonging to the An. gambiae complex were responsible for the totality of the transmission. The anthropophilic index, obtained from half gravid indoor resting An. gambiae s.l., was 83%. The annual biting rate of An. gambiae s.l. varied from 512 to 1558 bites per man per night, depending on the villages. Vectors were observed all year long but their densities were low during the dry season. Vector population presented a notable increase due to the rains, with a maximum of about 10 bites per man per night in September or at the beginning of October; during September the biting rate represented 48% of the annual biting rate. The sporozoitic index of An. gambiae s.l., obtained by ELISA revealing the circumsporozoite protein, was 1.6% for human biting females and 1.8% for half-gravid resting females (difference not significant). Plasmodium falciparum was the only plasmodial species observed among infected anophelines. The annual transmission in the vo villages representative of the Niakhar area were 9 and 12 bites of infected anophelines per man, occurring mainly from August to October. In the third village, not representative of the area regarding permanent breeding places, the transmission was 26 bites of infected anopheline per man per year. These results were discussed in the Senegambian and sahelian contexts.

Patients with Plasmodium falciparum infections were selected with an in vivo chloroquine sensitivity assay in a mesoendemic area of Senegal. Gametocytemia was studied in relation to asexual parasite responses classified as drug-sensitive or showing RI or RII resistance. Gametocyte prevalence and density appeared significantly higher in resistant infections than in sensitive ones. These observations were made on children as well as on adults. The period between first clinical symptom appearance and treatment, varying from 0 to 5 days, was not linked to asexual parasite responses, but was significantly and positively correlated to gametocyte prevalence and density observed seven days after beginning the treatment. The comparison between these results and those previously observed in a hypoendemic area suggests that the dynamic of gametocytemia is independent of the endemic level. These observations illustrate that the dissemination of chimioresistant malaria can be reinforced--via the gametocyte stage--by selective chloroquine pressure.

The urban area of Dakar, Senegal, contains > 5,000 market-garden wells that provide permanent sites for mosquito larvae, in particular Anopheles arabiensis Patton, the major vector of malaria. A study of the bioecology of mosquito larvae was conducted over 1 yr with a monthly visit to 48 of these wells. Overall, 9,589 larvae were collected of which 80.1% were Culicinae and 11.9% Anophelinae. Larvae from stages III and IV (n = 853) were identified to 10 species. An. arabiensis represented 86% of the anophelines collected and An. ziemanni Grunberg 14%. The most common Culicinae species included Aedeomyia africana Neveu-Lemaire, Culex quinquefasciatus Say, and Mimomyia splendens Theobald. Maximum anopheline abundance was observed at the end of the dry season in June, whereas maximum Culicinae abundance was observed at the end of the rainy season in September. Most wells (67%) did not harbor any An. arabiensis larvae and in the remaining 33% the larval abundance was low, averaging 0.54 larvae in stages III-IV per tray sample. To identify factors that determine the abundance of larvae in these wells, a co-inertia (multivariate) analysis was carried out to account for physicochemical variables (depth, turbidity, temperature, pH, conductivity, Na+, Cl-, HCO3-, CO3--, and NO3- concentrations) and biological variables (abundance of mosquito species, predators [e.g., fish, Dytiscidae, Notonectidae, odonates], molluscs [Bulinus and Biomphalaria], and surface plants [water lettuce, Lemna, and filamentous algae]). The co-inertia analysis indicated that the abundance of An. arabiensis was associated with Cx. quinquefasciatus and Cx. decens for the physiochemical data but was not associated with other mosquito species for floro-faunistic data. The conditions associated with abundant An. arabiensis were warm temperature (28-30 degrees C), clear and not too deep water (< 0.5 m), elevated concentrations of HCO3- and CO3--, low concentrations of NO3- and NaCl, low populations of larvivorous fish and invertebrate predators (notably odonates), the presence of water lettuce, and an absence of Lemna. These results indicate that many contributing factors influence the ecology of the immature stages of An. arabiensis.

Objective: Fibronectin is a protein of the extracellular matrix with numerous binding sites to the other elements of the matrix and to the cells. The aim of this study was to determine the relative importance of fibronectin isoform expression (FN-EIIIA, FN-EIIIB) during fetal and postnatal development of the rat heart. Methods: In situ hybridisation and immunolabelling approaches were used to describe the cellular synthesis of fibronectin and its distribution throughout the rat heart from 11 d postconception until adulthood. The distribution of fibronectin was compared to that of laminin and of α type III procollagen. Results: The accumulation and pattern of distribution of the major fibronectin mRNA isoforms were identical, that is, there was a progressive decrease in their accumulation as a function of time after 11 d postconception, resulting in a complete absence in the adult. The distribution of fibronectin and procollagen type III mRNAs were, however, quite distinct. At the protein level the time course of synthesis and secretion of the locally synthesised fibronectin (c-FN) did not follow fibronectin mRNA expression, the accumulation of the protein being rather poor, except just before birth, where it was found mainly in the coronary vessels. Conclusions: During the development of the fetal rat heart fibronectin gene transcription is active and progressively decreases with age, whereas the translation of the mRNAs into their corresponding proteins is always relatively poor. If fibronectin is involved in fetal and postnatal morphogenesis of the rat myocardium, it is the plasma form (p-FN) that is most probably involved in the process of growth and differentiation of the rat heart. Cardiovascular Research 1994; 28 :1653-1661

Myocardial fibrosis as a consequence of systemic hypertension is a determinant factor in alteration of cardiac function. It has been postulated that this fibrous reaction is under the influence of an elevation of blood aldosterone. To gain further insight into the mechanisms that result in an accumulation of cardiac collagen, we used a model of aldosterone-salt-induced hypertension in rat. Uninephrectomized male Wistar rats weighting 200 g were perfused with 0.75 microgram/hr aldosterone and received 1% NaCl + 0.3% KCl in the drinking water for 2 months.1) Arterial hypertension was evidenced as soon as 15 days and reached 40% at 2 months. 2) The left ventricle (LV) was hypertrophied by 45% at 2 months and its relative content in mRNA coding for the beta-isoform of the myosin heavy chain was increased by 142%. 3) The microscopic examination of hemalun-eosin stained LV showed a number of important foci of proliferating non-muscular cells, of inflammatory aspect. 4) The LV collagen concentration as measured by hydroxyproline assay was not changed whereas an histological study done on Sirius red-stained slides showed that the interstitial and perivascular collagen network was more important in treated rats. 5). The abundance of mRNAs coding for the alpha 1 chain of type I collagen was increased by 60%. Our results suggest that the fibrous response involves a pretranslational regulation of collagen synthesis.

Three trials with torn bed nets impregnated with permethrin and deltamethrin were made under field conditions at the Soumousso Field Station and the Vallee du Kou rice-field area, both in Burkina Faso, and the Djoumouna fish pond area in the Congo Republic. Even a considerably torn correctly impregnated bed net could be an useful method for limiting human-anopheline contacts. But bed nets in poor condition, i.e. too little impregnated and too much torn, cannot protect the users against anopheline bites. Protection increases with insecticide concentration, but at a high dosage insecticide could have more a repellent than a killing effect. Therefore a balance has to be found for the optimum rate of insecticide treatment of bed nets to obtain a real reduction in malaria transmission and morbidity, in every epidemiological situation.

Recent works carried out in west and central Africa resulted in numerous yellow fever virus isolations from sylvatic mosquitoes in the forest-savanna transitional zone. This virus was also obtained from monkeys, whereas studies on sequence and duration of the observed epizootics permitted a previsional approach of the yellow fever mechanisms in the same belt, the epidemiological importance of which was stressed ("emergence zone"). In the same course of research and publications, the prevalent part of the involved mosquitoes as virus-reservoirs was constantly emphasized ("reservoir-vector"). Recent investigations on transovarial transmission and yellow fever isolations from male mosquitoes caught in the field, provide decisive support to such a conception. It can explain that epizootics may be locally observed several years in succession, despite the fact that yellow fever virus circulation seems to be fundamentally of a dynamic character. Yellow fever virus was recently obtained from ticks and tick-eggs.