M. Coosemans

Malaria transmission and major malaria vectors in different geographical areas of Southeast Asia

During the last decade, major progress in malaria control has been achieved in Vietnam, Laos and Cambodia. However, malaria is still a potentially fatal disease in some hilly‐forested areas and continues to be endemic in a few coastal foci. To estimate the risk that stems from the major vectors after a decade of intensive malaria control, an entomological study based on human landing collections was conducted between April 1998 and November 2000 in six study villages (four in Vietnam, one in Cambodia and one in Laos) located in different physio‐geographical areas. Five villages were selected in places where new cases of malaria still occurred. In the sixth village, in the northern hilly area of Vietnam, no case of malaria was detected during the past 3u2003years. In three study villages of the hilly forested areas of Cambodia and central Vietnam, Anopheles dirus A still played an important role in malaria transmission and maintain perennial transmission inside the villages despite its low density. Anopheles minimus A was found in all study villages except in the southern coastal village of Vietnam. Its role in malaria transmission, however, varied between localities and surveys. In one study village of central Vietnam it was almost absent (one specimen collected over 480u2003man nights), and in another village sporozoite positive specimens (2.8%) were only observed during the first two surveys whereas this species disappeared from the collections from November 1998 onwards (six surveys: 360u2003man nights). In the northern study site An. minimus A and C were found in all collections, but no local malaria transmission occurred. However, the constant presence of these two species associated with a high longevity (parous rate up around 80% and 65%, respectively), suggests that transmission can occur at almost any time if parasite reservoirs are reintroduced in the area. The proper management of malaria cases and population movement is, therefore, important to prevent outbreaks and the reintroduction of malaria in northern Vietnam. In the study site of the Mekong delta, An. sundaicus occurred at high densities (up to 190u2003bites/man/night). The recent changes in land use from rice cultivation to shrimp farming probably explains the increase of this brackish water breeding species during the study period. However, none of the 11u2003002 specimens was positive for Plasmodium circumsporozoite protein (CSP). The relative low survival rate as estimated by the parous rate (around 47 %) may reflect its low vectorial status that could explain the very low malaria incidence (1.9 case/100u2003persons/year) in this study site. A calculated sporozoite rate of maximum 1/300u2003000 is enough to explain this low malaria incidence. Despite the successes in malaria control, the vector An. dirus A continues to play an important role in malaria transmission, whereas An. minimus A showed temporal and spatial variation in its role as vector. The role of An. sundaicus as vector could not be confirmed because of the low incidence in the coastal study village. Other Anopheles species may be locally involved, but in the five study villages where malaria is still present they probably do not contribute significantly to malaria transmission. The study also points towards the fact that in Southeast Asia it will become increasingly difficult to incriminate Anopheles species in malaria transmission while the risk for malaria transmission still persist.

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’.

Review of the Minimus Complex of Anopheles, main malaria vector in Southeast Asia : from taxonomic issues to vector control strategies

Backgroundu2002 The Minimus Complex of Anopheles subgenus Cellia is composed of two sibling species, A and C, on the Southeast Asian mainland, and a third allopatric species E that occurs in the Ryukyu Archipelago (Japan), a malaria‐free region. Anopheles minimus s.l. is considered to be one of the main malaria vector in the hilly forested regions of Southeast Asia. Despite a large number of studies over its range of distribution, it is difficult to have a global view of the ecological and bionomical characteristics of the individual species as different identification methods were used, generally without specific identification of the sibling species.

Personal protection by long-lasting insecticidal hammocks against the bites of forest malaria vectors

Objectiveu2002 In Southeast Asia, malaria vectors bite outside the houses before bedtime, and forest dwellers rarely use insecticide‐treated nets (ITNs). Thus, we tested the protection of long‐lasting insecticidal hammocks (LLIH) using Olyset™ technology against exophagic vectors in two forest villages of Cambodia.

Motivation à l'acquisition et à l'utilisation des moustiquaires imprégnées dans une zone à paludisme stable au Burundi

Resumé Au Burundi, lacquisition, lacceptation et 1utilisation des moustiquaires imprégnées vendues à un prix promotionnel (2

True versus Apparent Malaria Infection Prevalence: The Contribution of a Bayesian Approach

) ont étéévaluées dans une zone à paludisme stable (Imbo Sud, commune de Nyanza Lac) où ce moyen de protection est une nouveauté pour les habitants. La vente des moustiquaires imprégnées sur les collines (subdivision administrative) a été très inégale avec une couverture allant de 10 à 70% des families ayant acheté au moins une moustiquaire. De même sur une de ces collines avec une forte couverture de vente (62%) cette inégalité existe entre des zones administratives différentes (sous‐collines) qui sont pourtant comparables du point de vue socio‐économique mais situées à des altitudes différentes. La couverture réelle a été calculée par sous‐colline (SC), correspondant au pourcentage des families ayant au moins une moustiquaire installée. Cette couverture est de 77% sur la SC‐1 située dans le bas‐fond (780–820 m), et diminue progressivement pour atteindre 14% sur la SC‐3 la plus élevée (890–1480 m). II est interessant de noter que lachat dune moustiquaire nentraîne pas necessairement son utilisation. Environ 30% des moustiquaires achetées à un prix promotionnel ne sont pas retrouvées et la plupart ont été revendues dans le pays voisin. Dautre part entre 7 (SC‐1) et 47% (SC‐3) des moustiquaires retrouvées ne sont pas installées. La motivation à lachat et 1utilisation des moustiquaires dépend essentiellement du degré de nuisance comme en témoigne labondance des rnoustiques sur la SC‐1 située dans le bas‐fond (75 piqûres/homme/nuit) alors que les moustiques sont moins abondants sur la sous‐colline voisine (SC2) mais située à une altitude plus élevée (1 piqûre/homme/nuit). Les auteurs insistent sur la nécessité de divulguer une meilleure information par différents intervenants tels que le personnel des soins de santé, les autorités locales et les instituteurs, en vue daméliorer non seulement le confort des habitants en termes de nuisance, mais également de diminuer le lourd tribu payé par la population à cause du paludisme.

Nationwide inventory of mosquito biodiversity (Diptera: Culicidae) in Belgium, Europe

Aims To present a new approach for estimating the “true prevalence” of malaria and apply it to datasets from Peru, Vietnam, and Cambodia. Methods Bayesian models were developed for estimating both the malaria prevalence using different diagnostic tests (microscopy, PCR & ELISA), without the need of a gold standard, and the tests characteristics. Several sources of information, i.e. data, expert opinions and other sources of knowledge can be integrated into the model. This approach resulting in an optimal and harmonized estimate of malaria infection prevalence, with no conflict between the different sources of information, was tested on data from Peru, Vietnam and Cambodia. Results Malaria sero-prevalence was relatively low in all sites, with ELISA showing the highest estimates. The sensitivity of microscopy and ELISA were statistically lower in Vietnam than in the other sites. Similarly, the specificities of microscopy, ELISA and PCR were significantly lower in Vietnam than in the other sites. In Vietnam and Peru, microscopy was closer to the “true” estimate than the other 2 tests while as expected ELISA, with its lower specificity, usually overestimated the prevalence. Conclusions Bayesian methods are useful for analyzing prevalence results when no gold standard diagnostic test is available. Though some results are expected, e.g. PCR more sensitive than microscopy, a standardized and context-independent quantification of the diagnostic tests characteristics (sensitivity and specificity) and the underlying malaria prevalence may be useful for comparing different sites. Indeed, the use of a single diagnostic technique could strongly bias the prevalence estimation. This limitation can be circumvented by using a Bayesian framework taking into account the imperfect characteristics of the currently available diagnostic tests. As discussed in the paper, this approach may further support global malaria burden estimation initiatives.

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

To advance our restricted knowledge on mosquito biodiversity and distribution in Belgium, a national inventory started in 2007 (MODIRISK) based on a random selection of 936 collection points in three main environmental types: urban, rural and natural areas. Additionally, 64 sites were selected because of the risk of importing a vector or pathogen in these sites. Each site was sampled once between May and October 2007 and once in 2008 using Mosquito Magnet Liberty Plus traps. Diversity in pre-defined habitat types was calculated using three indices. The association between species and environmental types was assessed using a correspondence analysis. Twenty-three mosquito species belonging to traditionally recognized genera were found, including 21 indigenous and two exotic species. Highest species diversity (Simpson 0.765) and species richness (20 species) was observed in natural areas, although urban sites scored also well (Simpson 0.476, 16 species). Four clusters could be distinguished based on the correspondence analysis. The first one is related to human modified landscapes (such as urban, rural and industrial sites). A second is composed of species not associated with a specific habitat type, including the now widely distributed Anopheles plumbeus. A third group includes species commonly found in restored natural or bird migration areas, and a fourth cluster is composed of forest species. Outcomes of this study demonstrate the effectiveness of the designed sampling scheme and support the choice of the trap type. Obtained results of this first country-wide inventory of the Culicidae in Belgium may serve as a basis for risk assessment of emerging mosquito-borne diseases.

Malaria epidemiology in a rural area of the Mekong Delta: a prospective community-based study

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.

Human-induced expanded distribution of Anopheles plumbeus,experimental vector of West Nile virus and a potential vector of human malaria in Belgium

Over the past 10u2003years, the Mekong Delta region in Vietnam has experienced fast socio‐economic development with subsequent changes in malaria vectors ecology. We conducted a 2‐year prospective community‐based study in a coastal rural area in the southern Mekong Delta to re‐assess the malaria epidemiological situation and the dynamics of transmission. The incidence rate of clinical malaria, established on 558 individuals followed for 23u2003months by active case detection and biannual cross‐sectional surveys, was 2.6/100u2003person‐years. Over the 2‐year study period, the parasite rate and malaria seroprevalence (Plasmodium falciparum and P. vivax) decreased significantly from 2.4% to almost 0%. Passive case detection (PCD) of clinical cases and serological follow‐up of newborns carried out in a larger population confirmed the low and decreasing trend of malaria transmission. The majority of fever cases were seen in the private sector and most were unnecessarily treated with antimalarials. Training and involvement of the private sector in detection of malaria cases would greatly improve the quality of health care and health information system.