Population genetic structure of the malaria vector Anopheles minimus A in Vietnam

Anopheles minimus A, a major malaria vector in Southeast Asia, is the main target of vector control in this area. The impact of these control measures can be influenced by the population structure of the target species. In rural areas, An. minimus breeds along the banks of small clear-water streams, yet in the suburbs of Hanoi, northern Vietnam, there is an An. minimus population whose immature stages develop in water tanks. This study uses allozyme data (1) to assess the population structure of An. minimus A and (2) to evaluate the taxonomic status of the urban An. minimus population from Hanoi. The population from the suburbs of Hanoi was identified as An. minimus A. Although significant genetic differentiation was observed between rural and urban An. minimus A populations, they have not differentiated substantially by genetic drift. Limited macrogeographical differentiation was observed between two rural populations at distances of more than 1000 km. Consequently, geographical distance is not the primary factor in differentiating An. minimus A populations having the typical breeding ecology. The estimated effective population size is consistent with the moderate macrogeographical differentiation. Furthermore, no genetic structuring was observed between adult mosquitoes having different behaviour. The macrogeographical population structure indicates that genes may spread over large areas, whereas the presence of an 'urban' An. minimus A population shows the ability of this species to adapt to anthropogenic environmental changes.     

Population dynamics of Meloidogyne incognita on black pepper plants in two agro-ecological regions in Vietnam

The objective of our study was to examine the effect of local environmental conditions, especially air temperature and rainfall, in two agro-ecological regions in Vietnam on the population dynamics of Meloidogyne incognita on black pepper plants and on percentage root galling. The two study sites were situated in Cam Lo, Quang Tri province (North Central Coast) and Buon Ma Thuot, Dac Lac province (Central Highlands). At the study sites, 13 plant-parasitic nematode taxa belonging to 12 genera were identified. Ten of these taxa were present in both study sites. Helicotylenchus certus, Hemicriconemoides cocophilus and Pratylenchus coffeae were only found in Buon Ma Thuot. Based on nematode population densities, M. incognita was the most abundant taxon present. Rainfall and air temperature differed significantly between the two study sites. The most important climatic difference was rainfall: in Buon Ma Thuot, the rainy season lasted 2 months longer and the monthly rainfall during the rainy season was much higher compared to Cam Lo. Although this difference resulted in some differences in the population dynamics of M. incognita in the soil and roots of the black pepper variety Vinh Linh, the highest root population densities were observed in both study sites during the first half of the dry season. In Cam Lo, the highest percentage root galling was observed during the first half of the dry season. In Buon Ma Thuot, the highest percentage root galling was observed towards the end of the rainy season. Estimating the population densities if M. incognita to decide on the application of a management strategy should be done during the first half of the dry season.     

Water Level Flux in Household Containers in Vietnam - A Key Determinant of Aedes aegypti Population Dynamics

We examined changes in the abundance of immature Aedes aegypti at the household and water storage container level during the dry-season (June-July, 2008) in Tri Nguyen village, central Vietnam. We conducted quantitative immature mosquito surveys of 171 containers in the same 41 households, with replacement of samples, every two days during a 29-day period. We developed multi-level mixed effects regression models to investigate container and household variability in pupal abundance. The percentage of houses that were positive for I/II instars, III/IV instars and pupae during any one survey ranged from 19.5-43.9%, 48.8-75.6% and 17.1-53.7%, respectively. The mean numbers of Ae. aegypti pupae per house ranged between 1.9-12.6 over the study period. Estimates of absolute pupal abundance were highly variable over the 29-day period despite relatively stable weather conditions. Most variability in pupal abundance occurred at the container rather than the household level. A key determinant of Ae. aegypti production was the frequent filling of the containers with water, which caused asynchronous hatching of Ae. aegypti eggs and development of cohorts of immatures. We calculated the probability of the water volume of a large container (>500L) increasing or decreasing by ≥20% to be 0.05 and 0.07 per day, respectively, and for small containers (<500L) to be 0.11 and 0.13 per day, respectively. These human water-management behaviors are important determinants of Ae. aegypti production during the dry season. This has implications for choosing a suitable Wolbachia strain for release as it appears that prolonged egg desiccation does not occur in this village.     

Population density, water supply, and the risk of dengue fever in Vietnam: cohort study and spatial analysis

Background

Aedes aegypti, the major vector of dengue viruses, often breeds in water storage containers used by households without tap water supply, and occurs in high numbers even in dense urban areas. We analysed the interaction between human population density and lack of tap water as a cause of dengue fever outbreaks with the aim of identifying geographic areas at highest risk.

Methods and Findings

We conducted an individual-level cohort study in a population of 75,000 geo-referenced households in Vietnam over the course of two epidemics, on the basis of dengue hospital admissions (n = 3,013). We applied space-time scan statistics and mathematical models to confirm the findings. We identified a surprisingly narrow range of critical human population densities between around 3,000 to 7,000 people/km² prone to dengue outbreaks. In the study area, this population density was typical of villages and some peri-urban areas. Scan statistics showed that areas with a high population density or adequate water supply did not experience severe outbreaks. The risk of dengue was higher in rural than in urban areas, largely explained by lack of piped water supply, and in human population densities more often falling within the critical range. Mathematical modeling suggests that simple assumptions regarding area-level vector/host ratios may explain the occurrence of outbreaks.

Conclusions

Rural areas may contribute at least as much to the dissemination of dengue fever as cities. Improving water supply and vector control in areas with a human population density critical for dengue transmission could increase the efficiency of control efforts. Please see later in the article for the Editors'' Summary     

Rainfall and plague in Vietnam

In Vietnam, the average number of fleas per rat (flea index) decreases exponentially when the monthly rainfall exceeds 10 cm and the flea index increases exponentially when the rainfall is less than 10 cm per month. Plague in rats and in man is inversely proportional to rainfall. Relative humidity (RH) may limit plague in man when monthly averages for RH and temperature are less than 66 per cent and greater than 26.5°C, respectively.

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Zusammenfassung In Vietnam fällt die durchschnittliche Anzahl Flöhe pro Ratte (Floh-Index) exponiontiell, wenn die monatliche Regenmenge 10 cm überschreitet. Der Floh-Index steigt exponentionell an, wenn die Regenmenge im Monat unter 10 cm beträgt. Das Auftreten von Pest bei Ratten und Menschen ist umgekehrt proportional der Niederschlagsmenge. Die relative Feuchtigkeit kann die Verbreitung der Pest limitieren, wenn die Monatsmittel der RF unter 66% und der Temperatur über 26,5°C betragen.

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Resume Au Vietnam, le nombre moyen de puces par rat (indice de puce) diminue de façon exponentielle lorsque les quantités mensuelles de précipitations dépassent 10 mm. Ce même indice croît au contraire exponentiellement avec des valeurs inférieures à 10 mm. Le nombre de cas de peste tant chez l'homme que chez le rat est inversément proportionnel aux quantités de précipitations. L'humidité relative peut limiter l'extension du mal si elle se maintient au-dessous de 66% (moyenne mensuelle) par des températures moyennes mensuelles de 26,5°C ou davantage.

     

Population dynamics of a Sonneratia caseolaris stand in the Lam River estuary of Vietnam: a restoration perspective

Species composition, age distribution, and their relationship with land height from the datum line (LH) of the Sonneratia caseolaris stand, which grows in the Lam River estuary in Vietnam, were surveyed to obtain fundamental knowledge that aimed at contributing to mangrove restoration. The data gathered on the sandbar consists of three mangrove species and one mangrove associate species, with one non-mangrove species, and were divided into three communities. In terms of the age distribution of the S. caseolaris–Aegiceras corniculatum community, the tree-phase densities for both species are lower than those exhibited by younger phases. In its succession, the seedlings of S. caseolaris and A. corniculatum are primarily recruited at the mean tide level (MWL) in the early stages. Then, A. corniculatum expands to the lower tide zone primarily on mud flat bare land. For both species, full irradiance on the bare land in the low tide zone below MWL is crucial for growth, but S. caseolaris, which propagates by releasing small seeds, can barely survive in the low tide zone because its seeds are easily flushed away. In contrast, A. corniculatum, which propagates using crypto-viviparous seedlings, has a higher survival rate in the low tide zone. As a result, the LH of seedlings of A. corniculatum distribution is significantly lower than that of the distribution of S. caseolaris trees (p?<?0.05). It is important to provide appropriate environmental conditions for forest restoration in order to promote succession. The findings from the current study on population dynamics related to LH and tidal conditions are expected to be applied to platforms for S. caseolaris stands and mangrove restoration.

     

Population diversity of Cistopus indicus inferred from mitochondrial DNA (Cytochrome b) variation from China and Vietnam

ABSTRACT

The octopus Cistopus indicus is an important target of cephalopod fisheries in China. It is widely distributed in the South Pacific and tropical Indian Ocean, from the South China Sea, the Philippines, Malaysia, to Indian and Pakistan seas. We collected specimens from five sites in China and Vietnam (Zhoushan, Wenzhou, Shacheng, Zhanjiang and Mangjie). A fragment of 675bp of cytochrome b (Cytb) was amplified from 95 individuals. A total of 27 haplotypes and 78 variable nucleotide sites was observed. High haplotype diversity and low nucleotide diversity were observed in all populations. The phylogenetic analysis separated these populations into two clades; one was composed of three populations (Zhoushan, Wenzhou and Shacheng), the other of two (Zhanjiang, Mangjie). AMOVA analysis detected that 4.67% of the genetic variation occurred within populations and 95.33% occurred among populations. FST values ranged from 0.014 to 0.993, highlighting the high genetic variation among the populations. Assuming a molecular clock with a rate of 2.15–2.6%/Ma for the Cytb gene, the two clades may have diverged 2.88–3.49 million years ago (Pliocene). Neutral evolution tests and mismatch distribution analysis suggested recent population expansion. The present results revealed valuable information for genetic assessment, management and conservation of this species.     

Knowlesi malaria in Vietnam

The simian malaria parasite Plasmodium knowlesi is transmitted in the forests of Southeast Asia. Symptomatic zoonotic knowlesi malaria in humans is widespread in the region and is associated with a history of spending time in the jungle. However, there are many settings where knowlesi transmission to humans would be expected but is not found. A recent report on the Ra-glai population of southern central Vietnam is taken as an example to help explain why this may be so.     

Forest transition in Vietnam and its environmental impacts

This study assesses the presence of a forest transition – that is, a shift from net deforestation to net reforestation – in Vietnam during the 1990s, and describes its key attributes relevant for global environmental change issues. Using Fuzzy Kappa and other indicators, we compared forest cover estimates and spatial patterns from global and national land cover maps from the early and late 1990s, and compiled other available statistics for years before and after that period. This showed that a forest transition indeed occurred in Vietnam: the forest cover dropped to 25–31% of the country area in 1991–1993, and then increased to 32–37% in 1999–2001. The reforestation occurred at a higher rate than deforestation in the previous decades, and was due in similar proportions, to natural forest regeneration and to planted forests. The carbon stock in forests followed a similar transition, decreasing to 903 (770–1307) Tg C in 1991–1993, and then increasing to 1374 (1058–1744) Tg C in 2005. However, forest density declined during the same period, with an increasing proportion of young and degraded forests. The effects on habitats measured with landscape pattern indices were contrasted: in several regions, the reforestation decreased forest fragmentation, while in others, clearing of old‐growth forests continued and/or forest fragmentation increased. This shows that a transition in forest area is not sufficient to rehabilitate the different ecosystem functions and services of forests. Other forest transitions exist in Tropical Asia and in Latin America. Knowledge about the causes, pattern and environmental impacts of the forest transition in Vietnam is therefore relevant to understand possible emerging regional trends that would have implications for global environmental change.     

The catch and trade of seahorses in Vietnam

Catch monitoring and surveys were used to assess the seahorse trade in Vietnam. Despite low daily catch rates, potentially 6.5 t of dried seahorses (~2.2 million seahorses) were taken annually as bycatch by trawlers operating out of five coastal provinces of Vietnam. Individual seahorse catches were collated by a few local buyers, who supplied wholesalers in three major markets: Ho Chi Minh City, Hai Phong City and Da Nang. Domestic consumption was small and most seahorses were exported, generally through unofficial and unregulated channels across the northern border into Guangxi province of China. Overall, the seahorse trade was of low economic value to Vietnam, but may constitute an important source of income to upper level buyers and exporters. Most fishers and buyers surveyed reported that seahorse catch had declined over time. This paper should help in meeting the new CITES requirements – through implementation of an Appendix II listing in 2004 – that all international trade in seahorses must be monitored and managed for sustainability.     

Renovated: Gender and Cinema in Contemporary Vietnam

This article discusses the changes in Vietnamese cinema from the Socialist to the contemporary period from the viewpoint of gender representation. Under socialist conditions of cultural production, films were made by state-funded studios, with a clear mandate to provide the population with film material appropriate to the state's ideals. Since Doi moi (“Renovation”) in the late 1980s, Vietnam was opened up to market forces and cinematic practices have responded. Issues of gender have come into focus, and films exploring these themes have emerged from both state studios and private investors. Nevertheless conservative social values remain strong, and gender remains an area of dynamic uncertainty.     

Current Status of Taeniasis and Cysticercosis in Vietnam

Several reports on taeniasis and cysticercosis in Vietnam show that they are distributed in over 50 of 63 provinces. In some endemic areas, the prevalence of taeniasis was 0.2-12.0% and that of cysticercosis was 1.0-7.2%. The major symptoms of taeniasis included fidgeted anus, proglottids moving out of the anus, and proglottids in the feces. Clinical manifestations of cysticercosis in humans included subcutaneous nodules, epileptic seizures, severe headach, impaired vision, and memory loss. The species identification of Taenia in Vietnam included Taenia asiatica, Taenia saginata, and Taenia solium based on combined morphology and molecular methods. Only T. solium caused cysticercosis in humans. Praziquantel was chosen for treatment of taeniasis and albendazole for treatment of cysticercosis. The infection rate of cysticercus cellulosae in pigs was 0.04% at Hanoi slaughterhouses, 0.03-0.31% at provincial slaughterhouses in the north, and 0.9% in provincial slaughterhouses in the southern region of Vietnam. The infection rate of cysticercus bovis in cattle was 0.03-2.17% at Hanoi slaughterhouses. Risk factors investigated with regard to transmission of Taenia suggested that consumption of raw meat (eating raw meat 4.5-74.3%), inadequate or absent meat inspection and control, poor sanitation in some endemic areas, and use of untreated human waste as a fertilizer for crops may play important roles in Vietnam, although this remains to be validated.