[The malariology centenary (1898-1998). 1898]

This editorial note presents the journal initiative to celebrate the Malariology Centenary. It includes the reprint of the first annual report of the Society for Malaria Studies (founded in 1898), presented by Angelo Celli on December 3rd, 1898, to the first meeting of the Society and published in the Journal of the Royal Italian Society of Hygiene (volume 20, issue 12, 31st December 1898). The text is followed by explanatory footnotes and relevant references. An exhaustive historical essai, including the english version of the Celli's report, is scheduled to appear as supplement to volume 41, and the same volume will host the contributions issued from the international conference. "The malaria challenge after one hundred years of malariology", held in Roma at the Accademia Nazionale dei Lincei on November 16-19, 1998.

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.

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.

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.

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.

Odor-mediated host preferences of West African mosquitoes, with particular reference to malaria vectors

The role of odors in mosquito host preferences was studied in a village near Ouagadougou, Burkina Faso. Two odor-baited entry-traps were put beside one another and a choice of host odor-laden air was blown out of them. Odors of a human and a calf (of similar mass) were drawn from two tents in which each was separately concealed. Allowances were made for trap position, differences in human-subject attractiveness, CO2 levels, and trap contamination with alternative host odors. Choices for the human-baited trap greater than the 0.5 random expectation were made by Anopheles gambiae s.l. (0.96) and An. pharoensis (0.68). The choices for the human-baited trap of Culex antennatus were significantly lower than 0.5 (0.25), whereas for the Cx. decens species group (0.56), the difference was not significant. Interpretation of the latter result was complicated by the significant effect of CO2 levels on the index. Species caught in low numbers but whose trap distribution showed a bias towards the human-baited trap were An. funestus (total numbers in the human-baited trap to the calf-baited trap = 9:0), Mansonia africana (17: 1), Aedes dalzieli (22:4), and Ae. hirsutus (13:1); species showing bias towards the calf-baited trap were An. rufipes (0:11), Cx. duttoni (0:17), and Cx. nebulosus (2:35). Mansonia uniformis was the only species distributed randomly between the two traps. Molecular identification of the An. gambiae s.l. samples revealed a marked difference in trap distribution: for the human-baited trap the ratio was 52% An. arabiensis to 48% An. gambiae s.s.; for the calf-baited trap, it was 92% An. arabiensis to 8% An. gambiae s.s.

Advances in the identification of Dirofilaria repens and Dirofilaria immitis by a PCR-based approach

The differential epidemiology of D. repens and D. immitis is still poorly understood due to the lack of a diagnostic method which would make possible the routine identification of these parasites as developing larvae either in the vector or in unsuitable hosts, including man. The PCR-based method here described allows: i) the unambiguous identification of mature and immature adult worms in bioptic material, of microfilariae in blood samples and of developing larvae in mosquito vectors; ii) the analysis of samples stored either dry or in various preservation media, with the exception of formalin. The high specificity and sensitivity of the diagnosis improve the perspectives for comparative epidemiological investigations on D. repens and D. immitis in areas where the two nematodes are sympatric.

Molecular identification of sympatric chromosomal forms of Anopheles gambiae and further evidence of their reproductive isolation

Three chromosomal forms of Anopheles gambiae s.s., designated as Bamako, Mopti and Savanna, were studied for diagnostic PCR assays based on the analysis of the X-linked ribosomal DNA (rDNA). The study was performed on a 1.3 kb fragment containing part of the 28S coding region and part of the intergenic spacer region. The amplified material was cut with fourteen restriction enzymes to detect Restriction Fragment Length Polymorphisms (RFLPs). The enzymes Tru9I and HhaI produced patterns of DNA bands which differentiated Mopti from Savanna and Bamako; moreover, a distinct 'hybrid' pattern was recognized in the F1 female progeny from the cross of Mopti with either one of the other two chromosomal forms. The diagnostic significance of the PCR-RFLP assay was verified on 203 karyotyped females from field samples collected in two villages in Mali and one village in Burkina Faso. Agreement was observed between the chromosomal and the molecular identifications. No 'hybrid' molecular patterns were detected even among carriers of rare heterokaryotypes hypothetically produced by crosses between Mopti and Savanna. The results confirm previous observations indicating barriers to gene flow within An. gambiae s.s. and supporting the specific status of the taxonomic units proposed on cytogenetic ground.

Selective introgression of paracentric inversions between two sibling species of the Anopheles gambiae complex

The Anopheles gambiae complex includes the major vectors of malaria in sub-Saharan Africa where > 80% of all world-wide cases occur. These mosquitoes are characterized by chromosomal inversions associated to the speciation process and to intraspecific ecological and behavioral flexibility. It has been postulated that introgressive hybridization has selectively transferred inversions on the second chromosome between A. gambiae and A. arabiensis, the two most important vectors of malaria. Here we directly test this hypothesis with laboratory experiments in which hybrid populations were established and the fate of chromosomal inversions were followed. Consistent with the hypothesis, "foreign" X chromosomes were eliminated within two generations, while some "foreign" second chromosomes persisted for the duration of the experiments and, judging from the excess of heterozygotes established stable heterotic polymorphisms. Only those second chromosome inversions found naturally in the species could be introgressed.

Polymerase chain reaction-identification of Dirofilaria repens and Dirofilaria immitis

On the basis of known DNA sequences of Dirofilaria repens and D. immitis we designed specific primers for the amplification by Polymerase Chain Reaction (PCR) of the DNA from the two species. The PCR-based identification was found to be unambiguous and allowed specific diagnosis of microfilariae in blood samples, of developing larvae in the mosquito vector and of immature adults in bioptic material, overcoming the serious constraints of the morphological separation of these filarial parasites at the pre-adult stages. The technique was found to be very sensitive and applicable to samples stored either dry or in various preservation media, with the exception of formalin. The reliable identification of D. repens and D. immitis from bioptic material is expected to greatly enhance the chances of detecting human infections and to further clarify the role of the two parasites as pathogens of man. The possibility of routine identification of developing larvae in the vector will substantially improve the perspectives for epidemiological investigations, particularly in Southern European regions, such as Italy, where the two nematode species are largely sympatric.

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.

Comparison between urinary pyridinium cross-links and hydroxylysine glycosides in monitoring the effects of ovariectomy and 17 beta-estradiol replacement in aged rats

This study was undertaken to assess the sensitivity of hydroxylysylpyridinoline (HP), lysylpyridinoline (LP), galactosylhydroxylysine (GHyl) and glucosylgalactosylhydroxylysine (GGHyl) to monitor bone response to estrogen deficiency and replacement by comparing their excretory patterns in ovariectomized aged (11-14 months old) rats. The ovariectomized (OVX) rats were randomized into two groups: (1) OVX plus vehicle; (2) OVX plus 17 beta-estradiol (17-beta E, 10 micrograms/kg, s.c., 4 days/week). Treatment with 17-beta E started immediately after OVX and continued for 60 days. The collagen catabolites were measured in urine for 1 month before OVX and thereafter for 60 days. In temporal coincidence with urine collection, bone area and bone mineral density (BMD) of lumbar vertebrae, femoral diaphysis and distal metaphysis were measured by dual-energy X-ray absorptiometry. In the untreated rats, BMD of the femoral metaphysis and lumbar vertebrae decreased significantly and the urinary excretion of LP, HP, GHyl and GGHyl increased with different patterns. In the treated rats, 17-beta E replacement prevented the increment in LP excretion, partially prevented the increase in HP excretion, but had no effect on the excretion of GHyl and GGHyl. In conclusion pyridinolines and glycosides have different sensitivities to the bone response to OVX. Glycoside excretion after OVX also reflects metabolic processes not strictly related to bone loss and, in contrast with LP, is not sensitive to estrogen replacement.

Physical map of the malaria vector Anopheles gambiae

Random cDNA clones, cosmid clones and RAPD polymorphic fragments have been localized by in situ hybridization to the ovarian nurse cell polytene chromosomes of the malaria vector Anopheles gambiae. We thus established 85 molecular markers for 110 sites within the whole A. gambiae polytene chromosome complement. The cDNA clones analyzed were isolated at random, and their exact localizations were determined by in situ hybridization. For 15 of the cDNA clones, a partial nucleotide sequence has been obtained; for nine of them sequence searches in the GenBank database revealed high degrees of similarity with published sequences. The cosmid clones analyzed were obtained as the result of screening with a few of the aforementioned cDNA clones of particular interest, or taken from a small set of randomly isolated cosmid clones. The RAPD clones are polymorphic fragments, potentially diagnostic for the various chromosomal forms of A. gambiae that are currently being analyzed.

Density, survival and dispersal of Anopheles gambiae complex mosquitoes in a west African Sudan savanna village

To obtain information on adult populations of Afrotropical malaria vector mosquitoes, mark-release-recapture experiments were performed with Anopheles females collected from indoor resting-sites in a savanna area near Ouagadougou, Burkina Faso, during September 1991 and 1992. Results were used to estimate the absolute population densities, daily survival rates, and dispersal parameters of malaria vectors in that area. In 1991 a total of 7260 female Anopheles were marked and released, of which 106 were recaptured in the release village and 6 in the neighbouring villages, a total recapture rate of 1.5%. The following year 13,854 female Anopheles were released and 116 recaptured in Goundri and 8 in the neighbouring villages, a total recapture rate of 0.9%. Recaptures were found in three of eight villages near Goundri. Nearly all of the recaptured mosquitoes were An gambiae s.l. Of these, molecular determination revealed that An.gambiae s.s. and An.arabiensis were present in a ratio of approximately 2:3. Two simple random models of dispersal were simulated and the parameters of the models determined by searching for the least-squared fit between simulated and observed distributions. The mean distance moved by individual mosquitoes, estimated in this way, ranged 350-650 m day-1, depending on the model and the year considered. Population densities were estimated using the Lincoln Index, Fisher-Ford and Jolly's methods. The estimates of population size had high standard errors and were not particularly consistent A "consensus' value of 150,000-350,000 mosquitoes is believed to apply for the An.gambiae s.l. female population. Survival was estimated to be 80-88% per day.

Mosquito responses to carbon dioxide in a west African Sudan savanna village

Mosquito responses to carbon dioxide were investigated in Noungou village, 30 km northeast of Ouagadougou in the Sudan savanna belt of Burkina Faso, West Africa. Species of primary interest were the main malaria vectors Anopheles gambiae s.s. and An.arabiensis, sibling species belonging to the An.gambiae complex. Data for An.funestus, An.pharoensis, Culex quinquefasciatus and Mansonia uniformis were also analysed. Carbon dioxide was used at concentrations of 0.04-0.6% (cf. 0.03% ambient concentration) for attracting mosquitoes to odour-baited entry traps (OBETs). The "attractiveness' of whole human odour was also compared with CO2 emitted at a rate equivalent to that released by the human bait. In a direct choice test with two OBETs placed side-by-side, the number of An.gambiae s.l. entering the trap with human odour was double the number trapped with CO2 alone (at the human equivalent rate), but there was no significant difference between OBETs for the other species of mosquitoes. When OBETs were positioned 20 m apart, again CO2 alone attracted half as many An.gambiae s.l. and only 40% An.funestus, 65% Ma.uniformis but twice as many An.pharoensis compared to the number trapped with human odour. The dose-response for all mosquito species was essentially similar: a linear increase in catch with increasing dose on a log-log scale. The slopes of the dose-response curves were not significantly different between species, although there were significant differences in the relative numbers caught. If the dose-response data are considered in relation to a standard human bait collection (HBC), however, the behaviour of each species was quite different. At one extreme, even the highest dose of CO2 did not catch more An.gambiae s.l. than one HBC. At the other extreme, the three highest doses of CO2 caught significantly more Ma.uniformis than did one HBC. An.pharoensis and Cx quinquefasciatus showed a threshold response to CO2, responding only at doses above that normally released by one man. An.funestus did not respond to CO2 alone at any dose in sufficient numbers to assess the dose response. Within the An.gambiae complex, An.arabiensis "chose' the CO2-baited trap with a higher probability than An.gambiae s.s. Also An.arabiensis, the less anthropophilic of the two species, was more abundant in CO2-baited OBETs than in human bait collections.

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.

Inhibitory effect of amylin on growth hormone responsiveness to growth-hormone-releasing hormone in the rat

The effects of intracerebroventricular (i.c.v.) or intracarotid (i.a.) administration of amylin (AMY) on growth hormone (GH) release induced by GH-releasing hormone (GHRH) were examined in conscious male rats. Amylin (25 ng-5 micrograms/rat, i.c.v. or 10 micrograms/rat, i.a.) was administered 10 min before GHRH (2 micrograms/kg, i.a.). I.c.v. administration of AMY dose-dependently inhibited GH secretion induced by GHRH but when given peripherally, AMY did not modify the GH response to GHRH. Amylin (10(-8)-10(-6) M) had no direct effect on the rat anterior pituitary in vitro either alone or when incubated with GHRH. To characterize the mechanism(s) involved in vivo in the inhibition of GH by AMY, we examined, at first, the effects of AMY on GHRH-induced GH release in rats depleted of somatostatin by pretreatment (4 h before) with cysteamine (300 mg/kg s.c.). The inhibitory activity of AMY on GH secretion elicited by GHRH seems to be independent of hypothalamic somatostatin; in fact, AMY was still active in rats treated with cysteamine. In addition, we examined the effects of i.c.v. AMY administration on clonidine (CLO)-induced GH secretion and on dopamine and noradrenaline content in the brain, since it is known that GHRH is a stimulus sensitive to changes in central catecholaminergic activity. The failure of AMY to affect GH secretion induced by activation of postsynaptic alpha 2-receptors by CLO and the finding that the peptide decreased noradrenaline content in the hypothalamus and striatum, indicates that AMY may inhibit GH release by interfering with the facilitatory influence of the catecholaminergic system on GH secretion.

Forcipomyia (Pterobosca) paludis (Macfie, 1936) (Diptera, Ceratopogonidae) on adult dragonflies (Odonata) in Sardinia, Italy

Ceratopogonid midges, referred to Forcipomyia paludis, were recorded from five dragonfly species in Sardinia, Italy. All ceratopogonids were females and almost all were in the last phase of the gonotrophic cycle (gravid females). Although a parasitic association cannot be excluded, no evidence was obtained of the midge biting activity, neither by direct observation nor indirectly, by detecting the expected lesions on the host cuticle. The attachment to dragonflies of F. paludis (perhaps an autogenous species) might fit well with the hypothesis of a phoretic association which would favour the long range dispersal of the gravid females.

[The places of Mal'aria and the causes of malaria]

According to the Hippocratic medicine remittent and intermittent fevers were caused by bad air (mal'aria) and bad water of marshes, which produced miasmata affecting people living near these environments. This wrong theory was remarkably stable and persistent until the end of the last century, being in fact quite adequate to decribe the epidemiology of malaria in Mediterranean areas, where the transmission of the parasite depended on mosquitoes breeding mainly in marsh ecosystems. The theory was even reinforced with the spreading of severe malaria due to Plasmodium falciparum (more closely associated with warm marshy areas) and when a specific remedy, quinine, came into the picture, improving the distinction of malaria from other fever diseases. After the discovery of the true causes of malaria infection and transmission, scientific medicine developed completely new definitions of malarious environments based on their stratification in terms of transmission risk and several parameters were introduced which provide a measure of the vectorial capacity. This paper focus on the most relevant historical events that have brought to the present knowledge of malarious environments, examining at the same time the effectiveness and limits of the Hippocratic view on the etiology of malaria.

Polymorphisms detected by random PCR distinguish between different chromosomal forms of Anopheles gambiae

We have applied PCR amplification using random primers to distinguish between incipient species of the malaria vector Anopheles gambiae. Individuals belonging to three chromosomally characterized West African forms of this mosquito, which are important epidemiologically as they differ in vectorial capacity, were sampled both from laboratory stocks and from wild populations collected in three localities. The techniques used allowed for the unambiguous classification of the mosquitoes, providing a tool for rapid and efficient diagnosis, which previously relied on cytological examination of polytene chromosomes.