Biomedical subjects

M Coosemans

Publications and source records attributed to M Coosemans.

At least 19 recordsLinked to original sources

PubMed2000

Molecular identification of Anopheles minimus s.l. beyond distinguishing the members of the species complex.

Correct species identification is the starting point for studying the epidemiological role of vectors. Identification is mostly achieved using morphological criteria, but this fails when sibling species and species with overlapping morphological characters are involved. The problem with the identification of Anopheles minimus s. l., one of the most widespread malaria vectors in South-East Asia, is twofold: it is a complex of at least two isomorphic species, and based on morphology, members of the complex are difficult to distinguish from closely related species. An identification method was developed for An. minimus species A and C, and four related species, An. aconitus, An. pampanai, An. varuna and An. jeyporiensis. PCR-amplified internal transcribed spacer 2 (ITS2) ribonuclear DNA (rDNA) fragments were digested with restriction endonuclease BsiZI. Clear diagnostic banding patterns for the six species were obtained on agarose gels. Testing field-collected specimens from different regions in South-East Asia indicated that the technique will be applicable over a wide geographical area. From this it is clear that molecular identification has to focus not only on the species of complexes, but also on related species if they hamper the morphological identification of the 'sensu lato species'.

Animals↗

PubMed2000

Glucose-6-phosphate dehydrogenase deficiency in northern Vietnam.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency was evaluated in 1676 schoolboys in northern Vietnam. The trait was nearly absent in boys of the Kinh (0.5%) and the Mong (0.7%) ethnic groups that traditionally have lived outside malaria transmission areas. Prevalences among ethnic groups living in the foothills, the breeding area of the main malaria vector Anopheles minimus, ranged from 9.7% to 31%. These findings support the hypothesis of a selective advantage of the trait in Plasmodium falciparum-endemic areas.

Adolescent↗

PubMed1999

Trypanosoma brucei spp. development in the tsetse fly: characterization of the post-mesocyclic stages in the foregut and proboscis.

Post-mesocyclic development of Trypanosoma brucei in the tsetse fly in its migration from midgut to salivary glands, was revisited by sequential microdissection, morphometry and DNA-cytofluorometry. This development started by day 6 after the infective feed, with passage of mesocyclic midgut trypomastigotes through proventriculus and upward migration along foregut and proboscis to the salivary gland ducts. Kinetics of salivary gland infection showed that colonization of the salivary glands by epimastigotes occurred only during the time-limited presence of this developmental phase in the foregut and proboscis. Post-mesocyclic trypanosomes in the foregut and proboscis were pleomorphic, with 4 morphological stages in various constant proportions and present all through from proventriculus up to the salivary gland ducts: 67% long trypomastigotes, 27% long epimastigotes, 4% long epimastigotes undergoing asymmetric cell division and 2% short epimastigotes. Measurements of DNA content demonstrated a predominant tetraploidy for 67% of these trypanosomes, the remainder consisting of the homogeneous diploid short epimastigotes and some long epimastigotes. According to the experimental data, the following sequence of trypanosome differentiation in the foregut and proboscis is proposed as the most obvious hypothesis. Incoming mesocyclic trypomastigotes (2N) from the ectoperitrophic anterior midgut start to replicate DNA to a 4N level, are arrested at this point, and differentiate into the long epimastigote (4N) which give rise, by an asymmetric cell division, to 2 unequal, diploid daughter cells: a long, probably dead-end long epimastigote and a short epimastigote. The latter is responsible for the epimastigote colonization of the salivary glands if launched at the vicinity of the gland epithelium by the asymmetric dividing epimastigote.

Animals↗

PubMed1999

Control of malaria vectors: cost analysis in a province of northern Vietnam.

The cost of permethrin-treated bednets (50% EC; 0.2 g/m2, 2 rounds per year) was compared to the cost of residual spraying with lambdacyhalothrin 10% WP (0.03 g/m2, once yearly) in Hoa Binh, a mountainous province in northern Vietnam. Calculations of the amounts of insecticides needed were based on national guidelines, on data from a cross-sectional survey and on district activity reports. The actual cost of insecticide required per person per year was lower for impregnation (US$ 0.26) than for spraying (US$ 0.36), but the difference was smaller than expected. The total cost for impregnated bednets per person per year amounted to US$ 0.90 compared to USS 0.47 for spraying. The determining factor was the cost of the net, amounting to US$ 0.58 per person per year, assuming a 5-year life of the net. Other material (excluding nets), labour and transport combined, accounted for only 17% of the impregnation cost and 23% of spraying expenses. However, for the National Malaria Control Programme of Vietnam, the cost per person per year for impregnated bednets amounted to US$ 0.32 only, because the vast majority of nets are bought by the population. For spraying, the programme had to bear the entire cost.

Animals↗

PubMed1999

Identification of two species within the Anopheles minimus complex in northern Vietnam and their behavioural divergences.

Elucidating the complex taxonomic status of the major malaria vector taxa and characterising the individual species within each complex is important for understanding the complexity of the vector system in the south-east Asian region and will allow to estimate the impact of vector control measures. This applies to countries such as Laos, Cambodia and Vietnam that spend about 60% of their malaria control budget on implementing vector control activities. We used isozyme electrophoresis to clarify the Anopheles minimus s.l. species composition in northern Vietnam and identify behavioural divergences of individual species. Using different collection methods, adult mosquitoes were caught at monthly intervals from June to November 1995 in four villages. An. minimus s.l. could be distinguished from closely related species, An. aconitus and An. jeyporiensis, at the Octanol dehydrogenase (Odh) enzyme locus. Significant positive Fis values gave clear evidence of nonrandom mating within the An. minimus s.l. population. The highest heterozygote deficiency was observed at locus Odh, which was diagnostic for 2 sympatric An. minimus species in Vietnam similar to the An. minimus A and C species known from Thailand. We found no evidence for restricted gene flow between monthly samples, villages, or collection methods in either of the two An. minimus species. They occurred in sympatry, but in different proportions depending on the collection site, and had dissimilar resting and biting behaviours. Thus a vector control strategy will have a nonuniform effect on the various components of this diverse vector system.

Alcohol Oxidoreductases↗

PubMed1999

Diversity of malaria in rice growing areas of the Afrotropical region.

It is well known that 'in many instances the rice agrosystem perfectly fits the ecological requirements of pathogens or vectors' and in fact 'malaria, schistosomiasis and Japanese encephalitis are important vector-borne diseases associated with rice production in developing countries' (IRRI, 1987). In spite of these fears, rice cultivation has been on the increase in the African region in response to demographic and economic pressures. However, although rice fields provide suitable breeding places for Anopheles mosquitoes and rice cultivation leads to an increase in the biting rates, the species which are adapted to these sites are not the same in all parts of Africa. Several examples illustrate this phenomenon: An. funestus in the rice fields of Madagascar, An. pharoensis in saline water rice fields in the delta of the Senegal river, An. arabiensis in northern Cameroon and Burundi, An. gambiae Mopti form in the Kou Valley (Burkina Faso) and An. gambiae Savanna form in the rice fields of Kafine near Bouaké (Côte d'Ivoire). The vectorial capacities of these species are not the same and malaria inoculation rates are not necessarily increased in the riceland agroecosystem. The consequences for malaria of introducing rice cultivation depend on the situation before its introduction: it could be worsened in unstable malaria areas but not in stable malaria areas. Therefore, sound epidemiological and entomological knowledge are needed before causing any environmental modifications for agricultural purposes and there should be regular monitoring to avoid any outbreak.

Burkina Faso↗

PubMed1998

A simple field test for detecting pyrethroids on impregnated nets.

We tested a modified Beilstein method for detecting pyrethroids on bednets under laboratory conditions using an emulsifiable concentrate of permethrin (50 EC) for viability as a simple standardized field test and to judge its reliability for detecting different insecticide doses. At the recommended doses of permethrin (0.5 g/m2), sensitivity was near 100%, even when small pieces of fabric were tested and time of extraction was limited. In unwashed nets sensitivity stayed high (80-95%) down to 0.1 g active ingredient/m2. In untreated nets false positives were rare (0-2%). The test could become a valuable tool in vector control programmes: it is cheap, easy to learn and to perform. The Lot Quality Assurance Sampling method, using an upper and lower performance threshold, could be applied for monitoring the impregnation campaigns.

Insecticides↗

PubMed1998

Intraspecific isozyme polymorphism of Anopheles gambiae in relation to environment, behavior, and malaria transmission in southwestern Burkina Faso.

A cellulose acetate electrophoresis system was used to study the isozyme polymorphism of the Anopheles gambiae complex in a rural village and a city in southwestern Burkina Faso. In both areas A. gambiae Giles was the dominant species (95%) whereas A. arabiensis Patton represented only 5%. Both species were separated readily by octanol dehydrogenase Odh and mannose phosphate isomerase (Mpi) even if they shared some alleles at these two loci. Polymorphism analysis (13 loci) at the intraspecific level of A. gambiae showed a significant difference between the specimens collected in the city from those collected in the village in their allelic and genotypic frequencies of isocitrate dehydrogenase-1 and malate dehydrogenase-1 and in their allelic frequencies for Mpi. No genetic difference was observed between the human biting A. gambiae collected inside or outside the houses in either the village or the city. The Plasmodium falciparum-infected A. gambiae differed from the noninfected ones in their allelic and genotypic frequencies at Mpi and acid phosphatase (Acp). A two-fold difference in infection rate was found for the genotype Mpi130/130 and Acp110/100 compared with other genotypes. However, infected anophelines were found in all genotypes that belonged to these two enzyme systems. Consequently, no refractory mechanism occurs in these natural populations.

Alcohol Oxidoreductases↗

PubMed1998

[The principal arthropod vectors of disease. What are the risks of travellers' to be bitten? To be infected?].

Many blood-sucking arthropods are potential vectors of disease. To become a vector, the arthropod must be susceptible to the infective agent and must survive the incubation period so as to transmit the pathogens to a host. While some arthropod associated diseases affect only man (e.g. malaria) most of these diseases are (anthropo-) zoonoses with man often an accidental host. The risk of contamination depends on the one hand on the biting behaviour of the vector, its biology and distribution, and on the other hand on the sites visited by the traveller, the length of his stay, his activities, the conditions of sleeping accommodation. The risk of contracting malaria is very high in tropical Africa, in the forest area of South America and South East Asia, in Papua New Guinea. Malaria can be prevented if measures (e.g. pyrethroid impregnated bed nets, repellents) are taken to avoid bites of Anopheline mosquitoes between sunset and sunrise, but appropriate chemoprophylaxis must not be neglected. Lethal cases of yellow fever among unvaccinated travellers still occur despite a strict international regulation on vaccination requirements. Dengue is a major health problem in intertropical areas. As no vaccine is available, personal protection measures are recommended against daytime-biting mosquitoes, including the use of protective clothing, repellents. Other arthropod borne diseases among travellers are less common but the risks increase during adventure trips (e.g. zoonotic leishmaniasis, tick-borne relapsing fever) and humanitarian actions (e.g. risk of louse-borne typhus during visits of overcrowded prisons). Tick-borne diseases receive nowadays more attention. These diseases are not only restricted to some occupations (farmers, veterinarians) but also ramblers and campers are at risk. Attached ticks should be removed rapidly and carefully, since several hours of attachment are needed for transmission of spirochetes of LYME disease.

Animals↗

PubMed1996

Trypanosome-binding proteins of the tsetse flies Glossina palpalis gambiensis and G. morsitans morsitans.

In this paper we describe a new, selective approach to identify protein ligand-receptor interactions between an arthropod vector and the parasite it transmits. Biotinylated vector proteins were incubated with living parasites in physiological conditions. After extensive washing, the parasites were subjected to SDS-PAGE electrophoresis and the polypeptides were electroblotted onto nitrocellulose membrane. Staining with avidin-horseradish peroxidase revealed only biotin-labeled proteins from the vector which were bound to the parasite. A multitude of tissue-specific proteins of Glossina palpalis gambiensis and G. morsitans morsitans proteins, able to bind to cultured procyclic trypanosomes of Trypanosoma brucei spp., has been demonstrated. The relevance of these interactions in relation to the developmental journey of the trypanosome in the tsetse fly is briefly discussed.

Animals↗

PubMed1996

[Motivation to acquire and use impregnated mosquito nets in a stable malaria zone in Burundi].

In Burundi, the purchase, acceptance and utilization of impregnated bed nets sold at a promotion price (2 $US) were evaluated in a stable malaria area (South-Imbo, district of Nyanza Lac) where this method of protection was previously unknown to the inhabitants. The sale of the impregnated nets differed between the administrative subdivisions (so-called 'collines') of the area with a coverage varying from 10 to 70% of families. Moreover, in one of these collines with a high overall coverage rate (62%) a difference was also found between the three administrative regions (so-called 'sous-collines') which were socially and economically similar. However, these sous-collines (SC) differed in their geographical location and were found at different altitudes. The real coverage corresponding with the percentage of families showing at least one installed bed net, was calculated for each SC. This coverage was 77% in the SC-1 situated in the low wet area and decreased gradually to 14% in the SC-3 at the highest altitude. The purchase of a bed net does not necessarily mean that people will use them. About 30% of the bed nets bought at the promotion price could not be found and most of them were resold in the neighbouring country (Tanzania). Between 7 (SC-I) and 47% (SC-3) of the bed nets were still packed and not in use. The motivation for buying and using impregnated nets appears to depend essentially on the nuisance level caused by mosquitoes, as shown by the abundance of the mosquitoes in the SC-1 situated in the low wet area (75 bites/man/night) compared to that observed in the SC-2 located at a higher altitude (i bite/man/night). The authors conclude that appropriate health education and information should be developed and promoted by health staff, local authorities and teachers in order not only to improve comfort by decreasing the insect nuisance, but also to decrease the considerable malaria burden in the community.

Altitude↗

PubMed1996

Enzyme polymorphisms in the Anopheles gambiae (Diptera:Culicidae) complex related to feeding and resting behavior in the Imbo Valley, Burundi.

A cellulose acetate electrophoresis system was used to study the Anopheles gambiae complex at 2 villages in Central Imbo Valley and at 1 village in South Imbo Valley (Burundi). In South Imbo, only An. gambiae Giles sensu stricto was present. In the drier Central Imbo, the dominant species was An. arabiensis Patton (97.5%); An. gambiae s.s. represented only 2.5%. Both species were separated readily by Odh and Mpi, because they did not share alleles at those loci. Indoor resting An. gambiae s.s. from South Imbo differed significantly from outdoor resting females at 2 Ioci, Mpi, and Got-2. In Central Imbo, total An. arabiensis did not differ between adjacent villages. Endophagic An. arabiensis significantly differed at loci alpha-Gpd, and Idh-1 between the 2 villages, whereas no difference was observed between exophagic females. Allelic and genotypic frequencies at the locus Mdh-2 were significantly different between indoor and outdoor biting An. arabiensis. Active choice for the best place to bite or to rest seemed to be associated with specific genotypes. The Nei genetic distance values were typical of conspecific populations, ranging from 0.154 to 0.160 between An. gambiae s.s. and An. arabiensis. Even though vector populations were structured at spatial and behavioral levels, they were panmictic, and thus selection of exophilic or exophagic vectors, or both, by insecticide pressure is not likely to occur.

Animals↗

PubMed1996

ParaSight-F test to diagnose malaria in hypo-endemic and epidemic prone regions of Vietnam.

The antigen capture ParaSight-F test was evaluated during a drug sensitivity survey in a hypoendemic region of northern Vietnam. When only asexual blood forms of P. falciparum were considered, sensitivity of ParaSight-F was 100%, specificity 88% (95% CI 95-80%), positive predictive value 68% (95% CI 85-50%) and negative predictive value 100%. ParaSight-F proved very convenient for rapid screening and selection of patients to enrol in a drug sensitivity study. In northern Vietnam, the introduction of the test as a routine diagnostic tool is not justified, considering its high cost, the necessity to carry out the treatment of presumptive Plasmodium vivax cases and the persistence of positive reactions following treatment. However, the test will be a valuable tool in remote areas in emergency situations, where rapid confirmation of a P. falciparum outbreak is required.

Animals↗

PubMed1996

Deltamethrin-impregnated bednets as an operational tool for malaria control in a hyper-endemic region of Burundi: impact on vector population and malaria morbidity.

Within the framework of the National Malaria Control Programme Burundi, impregnated bednets were promoted through health care facilities, schools and local administration in Nyanza Lac district. The decision to buy a bednet was left to the inhabitants and, as a result, coverage rates between 6 and 65% were observed at sub-district level. Three intervention regions were specified based on the intervention start date. From November 1992 until March 1995, bi-monthly parasitological and entomological surveys were carried out in two areas each of Region 1 and Region 2. After introduction of impregnated bednets in Region 1 the proportions of children under 5 with high parasitaemia were reduced by 42 and 53% in the 2 parasitological survey areas, where the average bednet coverages were 55 and 44% respectively. In the survey areas of Region 2 (control) no significant change occurred during the same period. During the second part of the intervention from September 1994, when intervention was also operational in Region 2, significant decreases in the proportion of high parasitaemia (63 and 42%) among children under 5 years were obtained in both parasitological survey areas of Region 2 (average coverages of 51 and 29%). The positive output of the intervention was maintained and even reinforced in the survey areas of Region 1. Bednets as a tool for malaria control entail specific problems such as coverage, daily use, reimpregnation, and renewal of old and torn nets. Further evaluation has to point out the possible shift of the clinical spectrum and the age-specific admission of malaria cases to assess the long-term benefit of this control method.

Animals↗

PubMed1995