Công trình nghiên cứu khoa học: Báo cáo tại hội nghị khoa học toàn quốc chuyên ngành sốt rét-ký sinh trùng-côn trùng giai đoạn 2001-2005. Tập 1. Bệnh sốt rét

Up one level

Analysis of pyrethroid insecticides uptake of impregnated mosquito nets and their residual effects in vector control

Uptake of insecticides of impregnated mosquito nets and their residual effects were analyzed in the laboratories of the Chemistry Department of Ha Noi National University and the National Institute of Malariology, Parasitology and Entomology between November 2000 and November 2002. Residual effects were determined by bioassays using WHO method WHO/VBC/81.806, WH/VBC/89.981. Uptake of insecticide was analyzed by liquid-liquid extraction with solvent mixture of n-hexane : aceton (1:2, v/v), using solvent mixture of n-hexane : dichloromethane (3:1, v/v) for purifying of extract on the silicagel column and n-hexane : dichloromethane {1:1, v/v} for ion of the pyrethroid compounds from the column, then their quantitative detennination carried out by GC/ECD. Method of Solid Phase Microextraction (SPME) combined with Gas Chromagraphy/Electron Capture Detection(GC/ECD} was studied for establishment of analytical scheme in order to determine residues of some pyrethroid compounds extracted by optic silica fiber coated poliacrylate from solution of vials containing standards, extracted compounds at 25°C keeping 35-45 minutes (equilibrium partitioning time). An analysis experiment was carried out in order to determine recovery and accuracy of the method, using liquid-liquid extraction method for comparison of the results. The nets treated with Fendona 10SC, ICON 2.5 CS, K-othrin 1SC and Imperator 50EC were found effective with Anopheline control. The residual effect to An.dirus reached to 5-6 months. The analytical method of pyrethroid impregnanted nets has been developed and half life time of these chemicals was: 125-188 days (on synthetic net) and 129-167 days (on cotton net), respectively.

Application of remote sensing and GIS technology in monitoring and forcasting of malaria risks

Possibilities of application of remote sensing (RS) and geographic information system (GIS) technology in monitoring and forecasting of malaria risk were studied in Ham Thuan Nam district of the central province of Binh Thuan where malaria was endemic in 2003. A strong relationship between natural and environmental factors and eco-socio indicators and malaria transmission in the different places of the district was found. The mapping of district malaria was made with the data of malaria morbidity during the years 1996-2002, the malaria control measures of the local people as well as geographical, meteorological parameters of climatic, temperature, humidity, rainfall, stream system, irrigation and flora information. Epidemiological, entomological and environmental maps have been established based on the retrospective and existing data of SPOT, LADSAT and ASTER satellite imagery. It is suggested that malaria is highly risky in northern communes of the district while it is lower in the Southern ones. These maps can be useful for the health facilities in monitoring and early forecasting of malaria and setting up appropriate and effective malaria control measures.

Assessment of the current coverage and diminished rate of mosquito nets usage in malaria control in Thua Thien Hue (1995-2003)

An evaluation of the current coverage and diminished rate of mosquito nets usage for malaria control plays an important role in malaria control planning. A survey was carried out between 1995 and 2003 in 15 hamlets of five communes of 3 malaria endemic districts in Thua Thien-Hue province. A high rate of bed-net usage was found in the surveyed hamlets. In average, the coverage reached the rate of 2.0+-0.3 nets per person. However a considerable rate of damaged nets (4.7+-1.2%) was also recorded in the surveys. Further surveys and studies should conducted to determine the ways the bed-nets go down and get diminished for planning of more appropriate malaria control measures.

Biological and ecological characteristics of Anopheles dirus peyton and harrison, 1979 in Vietnam in the laboratory and modelling procedure of mosquito rearing for biological researching

Blood fed An.dirus collected from Khanh Phu commune, Khanh Vinh district, Khanh Hoa province were reared in the insectariums of National Institute of Malariology, Parasitology and Entomology. The optimal conditions for development of mosquitoes are following: Temperature from 23oC to 26oC; humidity of 70% to 80%; light times of 10 hours per 24 hours with 90 Lux to 150 Lux; level water in the rearing tool is from 10mm to 20mm. Larvae were fed by a mixture of one part of pig liver power + two parts of hread power + one part of small fish food powder + one part of young corn power + 3 tables vitamin B, per 200 mg mixture. Mass death of larvae was ohserved while protozoa intensively developed in the rearing aquarium. Mosquitoes fed by human blood were found to lay more eggs (from 45 eggs to 258 eggs) compared to that of those fed on white mice (from 15 eggs to 148 eggs). Colonization model of this mosquito species has been established for biological researches.

Colonization of An.minimus under laboratory conditions

Anopheles minimus collected from Hoa Son commune, Luong Son district, province of Hoa Binh, have been maintained by artificial copulation in the insectariums since October, 1997. On July, 2001, the reared An.minimus population had natural mating in 30x30x30 cm cages and developed stably. The rearing conditions are: the density of rearing larvae were 0.4 individual per square centimeter of rearing water surface; the density of adult mosquitoes were 0.025 individual per cubic centimeter of cages. The larvae food was mixture of 6 gram bred powder + 2 grams green been powder + 2 grams shrimp powder + 10 mg vitamin B1. Lavae were fed 2 times per day, with the 0.018 gram of mixed powder in total, for each 20x25x3 cm size tray. Adult mosquitoes were fed on white mouse, every second day. The insectary conditions: the light intensity was 130-220 Lux, the lighting duration was 8/24 hours, the temperature was 22-28oc, the relative humidity was 70-85%.

Distribution of Anopheles and malaria vectors in forests landscapes of North Vietnam

Distribution of Anopheles and malaria vectors were investigated in four most common and sentative forest landscapes of the North Vietnam from September 2002 to October 2005. Thirty Anopheles species have been collected from four representative forest landscapes of Northern Vietnam, of which 20 species were collected in primitive jungle, 21 species in secondary jungle, 16 species in sparsely bushy forest, and 6 species in flooded brackish water forest. Both in vectors as An.minimus. An.dirus and secondary vectors as An.aconitus. An.jeyporiensis, An.maculatus, An.subpictus, An.sinensis and An.vagus were found in the study sites. Most of Anopheles species were widely found while a few species as An.cucphuongensis. An.bengalensis, An.baileyi were collected only in primitive jungle, and An.subpictus. An.indefinitus were found only in brackish flooded water forest. Anopheles donaldi (Reid, 1962) was first found in Vietnam. Main vector An.minimus was found in almost all the surveyed landscapes of primitive jungle, secondary forest and sparsely bushy forest in North Vietnam. In secondary forests, a higher density of primary vector of An.minimus s.1. and percentage of An.minimus A (human biting preferable) compared to An.minimus C (cattle biting preferable) in other landscapes. An.dirus, (previously playing an important epidemic role in some places of the Northern slope of Truong Son mountains range) was found at a very low density. It is suggested that their distribution is clustering due to the narrowing of forest landscapes.

Effectiveness of health communication on malaria control for Mong people in Bao Yen district

A longitudinal study was conducted in Bao Yen district from July 2001 to June 2002 to evaluate the perception and behaviours related to malaria infection and the effectiveness of malaria education for Mong ethnic minority groups. The interviewed people were found to have poor perception and knowledge on malaria. Fifty four percent of the Mong people did not malaria control. The risk of malaria infection among the people living near the edge of streams and staying overnight in the forest was found higher by 2.76 and 2.82 folders, respectively compared to another ones. It is recommended to carry out appropriate and effective health education on malaria control for the Mong people by direct contacting and giving messages on the causes of malaria transmission, the benefit of sleeping in mosquito nets and so on through village health workers. The bed-nets distribution and implementation of health education on malaria control through village health workers for Mong people was found effective in reducing malaria infection and increasing the number of bed-net users.

Effectiveness of stand-by treatment for forest workers

Effectiveness of malaria stand-by treatment with CV8 and artesunate was comparatively investigated in interventional studies in Khanh Trung commune (Khanh Vinh district of Khanh Hoa province) between January 2001 and January 2002. The local people in Suoi Ca hamlet who frequently go to work and overnight in forest were given antimalarial drugs CV8 and those in Suoi Lach hamlet who have the same style of life were given with artesunate for self-treatment in case they contract with malaria. Blood films were taken and examined before and after they went to and came back from the forest. Doses used during their stay in the forest were also recorded. The sampled people were divided into two groups: the group with people who frequently go to work in the forest (F.G.F) and the group with people who frequently go and stay overnight in temporary huts in the forest (G-O.F). A prior-intervention survey showed the malaria infection rate of two groups of 13.1 % and 18.3%, respectively. The difference was markedly significant between the FGF and G-O.F (P<0.05). The high risks of malaria infection for the forest going and forest overnight were determined with OR of 1.6 and 1.8, respectively. A remarkable reduction of malaria infection rate was found two-year implementation, especially in the group of CV8 stand-by treatment from 10.4% to 0.5% in the F.G.F and from 14.6% to 0.6% in the G-OF. The reduction in the groups with iutesunate stand-by treatment was from 19.3% to 2.6% in the FGF and from 28.4% to 4.1 % in the G-O.F. The indices of effectiveness before and after the intervention in the F.G.F and the G-O.F were 97% and 95%, respectively.

Effects of piperaquine phosphate on plasmodium and its sub-chronic toxicity

Locally produced piperaquine phosphate was studied at the laboratory of National Institute of Malariology, Parasitology and Entomology. The IC 50's values of piperaquine phosphate (PQP) in cultured P falciparum were 58 and 76 nmol/L for T96 clone and isolated K1 strain, respectively. PQP was found to inhibit chloroquine-resistant Plasmodium berghei in mice. The total treatment doses of 401 and 501 mg (three-day treatment course) on experimental mice was followed up for 28 days. None of dosed mice died, the cure rate was 20% and the recrudescence was 80% with a low parasite density. The piperaquine phosphate's sub-chronic toxicity in rabbits was also investigated in this study. Piperaquine phosphate (PQP), at the doses of 50 and 100 mg/kg of body weight per day for 28 consecutive days, was administered orally. The influences of PQP on rabbits' laboratory indices and weights were observed during and after the PQP administration. Rabbits orally treated with PQP acted and ate normally. At the dose of 50mg/kg per day for 28 consecutive days, the body weights of rabbits increased significantly through the study days (P< 0.05), but did not change significantly biochemical\9 SGOT, SGPT, bilirubin and protein and some hematological indices (leukocytes, leukocyte formula and hemoglobin), but significantly increased erythrocytes and creatinine on Day 14 and Day 28. At the treated dose 100 mg/kg per day x 28 days. biochemical indices (SGOT, protein) and some hematological indices (erythrocytes. leukocytes and leukocyte formula) were not changed significantly (P>0.05) through study days but creatinine, bilirubin and SGPT were significantly changed (P<0.05).

Evaluation of antimalarial drug administration in central and plateau provinces and recommendation of control measures

The administration and utilization of antimalarial drugs were investigated in the surveys conducted in three provinces of Gia Lai, Quang Nam and Ninh Thuan (a total of 27 communes in 9 districts were surveyed). A poor management of antimalrial drugs was found in numerous surveyed units. Approximately 40% of the surveyed units were found unable to plan the antimalarial drug requirement and 60% of surveyed units were not staffed with workers specializing in antimalarial drug management. The receiving and distribution of antimalarial drugs were loosely, expiry dates and manufacturing information were not given on the delivery sheets. District stocks were in poor maintenance conditions in term of thermo-proof equipment, ventilation and fire distinguishers. In term of drug use, an improved quality of diagnosis and treatment of malaria was found in most of the surveyed units as compared to that of the previous time (accurate rates of diagnosis and treatment were 90% and 85%, respectively). Malaria staff at different level were not regularly updated with new information in the official guidelines of malaria diagnosis and treatment. They, therefore, were not skillful in selecting adequate therapeutic regimens. The awareness of the local people on malaria and antimalarial drugs was also limited.

Evaluation of environment changes of replanted forest to distribution of malaria vectors and vector control measures in Lao Cai and Son La provinces

An EC supported project was carried out from March 1999 to March 2002 in the provinces of Lao Cai and Son La to evaluate the influences of environment changes on malaria vector and vector control measures in re-planted forests. A close relationship of the forest changes and the distribution of Anopheline mosquito and malaria vector has been found. An.minimus s.l. was found in all kinds of forest in two provinces. An.takasagoensis and An.minimus C were collected in the forests of Chieng Yen commune, Moc Chau district of Son La province. An.minimus A was collected in the secondary forest of Ban Cam commune, Bao Thang district of Lao Cai province. An.maculatus collected in Chieng Yen commune, Moc Chau district of Son La province was determined a sibling species complex. It is not necessary to use insecticide for vector control in areas with no malaria parasite even if a high density of An. minimus was found.

Field evaluation of effectiveness of Alé 10SC (Alphacypermethrin) impregnated bednets in malaria vector control in Northern Vietnam

The study was conducted from November 2003 to November 2004 in Quyet Chien commune, Hoa Binh province's Tan Lac district to evaluate the effectiveness of bed-net impregnation with Alo 10SC at a dose 25mg a.i/m2 based on bioassays, entomological indices and side effects and influences of washing of bed-nets on insecticide residual effects. Polyester bed-nets impregnated with Ale 10SC at dose of 25mg ai/m2 were found to have 6-month residual effects and to remain effective in malaria vector control after one wash (60 days after treatment). Alé 10SC bed-net impregnation was found to reduce the density of day time indoor resting and human biting of An.minimus mosquitoes. Inconsiderable side effects among spraymen, dippers and villagers in the treatment areas caused by bed-net impregnation at the dose of 25mg ai/m2 were observed.

Field evaluation of effectiveness of Solfac WP10 and Solfac EW050 in malaria control in North Vietnam

Residual effects, side effects of house spraying with Solfax WP10 and bednets impregnated with Solfac EW050-the insecticides of perythroid group were studied in the field trials between October 2001 and October 2002 in Phu Cuong commune, Tan lac district of Hoa Binh province. Washing influence on residual effects of impregnated bed-nets was also assessed. House spraying with Solfac 10WP at a dose of 50mg a.i/m2 was found to produce 6-month residual effect on wood walls (the mosquito mortality six months after treatment was 70.60%), and 2 months on brick wall (the mosquito mortality two months after treatment was 61.33%). Solfac EW050 impregnated polyester bed-nets at the dose 50mg a.i/m2 were found to produce 6-month residual effect on unwashed net (the mosquito mortality six months after treatment was 70.40%). Solfac EW050 impregnated bed-nets at a dose 50mg a.i/m2 were found to maintain 2-month residual effect on twice washed net (the mosquito mortality six months after treatment was 73.64%). House spraying with Solfac WP10 and bed-nets impregnated with Solfac EW050 were found to cause inconsiderable side effects for exposed people that disappeared without medical treatment.

Field evaluation of effectiveness of house spraying with Alé 10SC (Alphacypermethrin) in malaria vector control in North Vietnam

Residual effects of house spraying with Alé 10SC (Alphacypermethrin)-an insecticide of perythroid group was studied in a field trial between November 2003 and November 2004 in Quyet Chien commune, Tan Lac district of Hoa Binh province. Alé 10SC at a dose 30mg a.i/m2 was treated on the different kinds of house wall and investigated to evaluate the residual effects using bioassay techniques and entomological indices. Side effects on exposing people were also assessed. Alé 10SC house spraying was found to produce 6-month residual effect on wood and brick walls (the mosquito mortality six months after the treatment was 51.3%-52.6%, respectively). Alé 10sc was also determined to reduce the indoor day time resting and human biting of An.minimus. No side effects for the Alé 10SC sprayers and people living in the treated areas were found.

Geographical study of species complex of Anopheles minimus in the Central provinces and Plaetau

An.minimus is one of the primary malaria vectors in the central provinces and Plateau of Vietnam. A correct identification of the species of this complex is necessary to studying their distribution, epidemiological role and effective vector control measures. Polymerase chain reaction (PCR) analysis of the collected mosquito samples showed the presence of two populali,ms of An.minimus A and C in the different geographical places in the Northern Center. Central Center and Plateau, while An.minimus A was found only in Southern Center (Binh Thuan province). An.mimnimus A was found predominant in most of the study sites except in Van Canh (Binh Dinh province) and mainly collected by human landing and CDC light trap. An.minimus C was found in less density and more preferable to cattle biting. The study is ongoing for further fidings.

Glucose-6-phosphate dehydrogenase deficiency among some different ethnic groups in Vietnam

To determine the prevalence of G6DP deficiency in some areas of Vietnam, the surveys were carried out on 7.767 subjects (4.869 males, 2.898 females) from 16 different ethnic groups in 10 provinces of Vietnam from 1996 to 2005. G6PD deficiency surveys were done by two methods: A qualitative visual fluorescent test (test kits from Sigma Diagnostics) and rapid test (Akira Hirono- 1998). The prevalence of G6DP deficiency was found varied from area to area: The lowest rate was in Lak, Dak Lak province (0.8%) and higher in Hoa Binh province (23.5%). The high rates of G6PD difficiency were found in the groups of Muong (28.6%), Tho (22.6%), Thai (19.8%) and Tay (14.6%). The low ones were found in the groups of Hmong (0.3%), Kinh (0.7%), M'nong (1.3%) and Ba na (1.7 %). In the other ethnic groups, G6PD deficiency rates were 9.7 %; 8.9%; 7.8%; 3.7%, 3.5%; 3.4%; 2.3 % respectively in Dao, Van Kieu, Pa Co, Nung, Xtieng, Raglai, Gia Rai groups.

In vitro monitoring of therapeutic efficacy of artesunate for uncomplicated falciparum malaria and the sensitivity of P.falciparum to artemisinin in vitro in Phu Rieng rubber plantation, Binh Phuoc province

In vivo monitoring therapeutic efficacy of artesunat for uncomplicated P.falciparum malaria and the sensitivity of P.falciparum to artemisinin in vitro in Phu Rieng rubber plantation, Binh Phuoc province, from 2002-2004. Thirty eight patients (in 2002) and 43 patients (in 2003) were treated with artesunate, total dose 16mg/kg for 7 days. Their progress followed for 28 days under WHO standard protocol. Twenty of pre-treatment P.falciparum isolates (in 2002) and 38 isolates (2003) were tested in vitro to artemisinin. The in vivo results showed that mean fever clearance time was 1.4 days and 1.6 days (p>0.05); mean pars site clearance time was 1.8 and 2.7 days (p=0.03); cure rate was 87.0 and 90.7% (p>0.05) in 2002 and 2003, respectively. Early treatment failure was not found. Sensitivity test in vitro of P.falciparum isolates showed geometric mean EC50 values of 39.5 (in 2002) and 34.4 nmol/l (in 2003) for artemisinin. In this study, cure rate of a 7 day course was higher cure rate of a 5 day course from other studies at the same site (87.0 and 90.7 vs 55 and 64%). These results may have implication for antimalarial treatment guideline of Ministry of Health.

Kariotype and polytene chromosomes of Anopheles (Cellia) sundaicus (Rodenwaldt, 1925)in An Thoi Dong, Can Gio, Ho Chi Minh city

Anopheles sundaicus (Rodenwaldt, 1925) is a principle malaria vector on islands and along the coastal areas of Southeast Asia with a wide geographical distribution. A study on taxon An.sundaicus was conducted in An Thoi Dong commune (Can Gio district of Ho Chi Minh city) for understanding of its genetic structure and species status in comparison with the populations from Thailand and Indonesia using metaphase karyotype and polytene chromosome evidence. The results showed that: the karyotype of An. sundaicus in An Thoi Dong can be distinguished with A, B, C from Thailand and Indonesia in size, shape and the number of heterochromatin regions of sex chromosome and autosome. The map polytene chromosome of An.sundaicus in An Thoi Dong was different from A, B, C from Thailand and Indonesia in size, shape and the number of bands on X chromosome and 2R chromosome. It suggests that An.sundaicus in An Thoi Dong can be a new species in taxon Anopheles sundaicus and called D form.

Malaria epi-stratification and intervention methods in the province of Thua Thien-Hue

The former national malaria epi-stratification and its application appeared to be useful in malaria control in the province of Thua Thien-Hue. The targets set up for the malaria control program were over-gained with remarkable reduction of infection and death due to malaria. However, the changed malaria situation required an adaptation. In accordance with the new national epidemiological stratification, Thua Thien-Hue has been restratified into different malaria endemic zones. In the whole province of Thua Thien-Hue, 23 communes with 152 villages and hamlets are stratified into hyper-endemic areas, 17 communes with 115 villages and hamlets are into mezzo-endemic areas, 9 communes and precincts with 90 villages are in lowendemic areas, 6 communes and precincts with 54 villages are in malaria-free area, and 95 commune and precincts with 906 villages are in non-endemic areas. The new epi-stratification based interventions will help develop more appropriate and sustainable malaria control factors.

Malaria epidemiological characters and evaluation on malaria control measures in Son La hydro-electricity plant zone

The study was conducted between 2002 and 2005 in six communes representative for three district of Son La province, which are directly affected by the construction of the Son La hydroelectricity plant. The malaria situation in the construction area was listed in the previous malaria epi-stratification (Prof. Dang Van Ngu) as hypo-endemic zone. The malaria incidence during the years 2002, 2003 and 2004 was 10.89, 11.38, and 10.79, respectively. No deaths due to malaria, severe malaria cases or malaria outbreaks were reported during this period. The malaria incidence was found different in various micro-zones with a twice higher rate in the upper dam communes compared to that in the lower dam ones. Malaria was endemic all year round getting higher in the rain season with a pick in its late months. The measures carried out in the area as case management, re-training of health staff, health education and development of microscopic points appeared significantly effective in malaria control sustaining the malaria prevalence stable in a low rate and reducing the malaria cases by 13.2%, and percentage of malaria cases per/population by 0.9% in 2004 as compared to that in 2002.

Malaria epidemiological stratification and intervention methods in the Vietnam's malaria control program

In 2003, a new malaria epidemiological stratification and intervention method which based on the geography, landscape, elevation, malaria cases, malaria parasites and malaria vectors were implemented in the whole country. This stratification method aimed at identifying zones with different levels of malaria endemicity and number of population at risk of each zone. Based on this stratification, a plan for malaria control, vector control and malaria case management were designed for each zone. According to the new stratification, Vietnam is divided into five different malarious zones as follows: zone without malaria transmission in 4.534 communes with the population of 42.620.426 people (or 54% of the total population); zone at risk of malaria resurgence in 2.923 communes with 18.485.308 people (or 23%); low malaria endemic zone in 1.928 communes with 9.949.205 people (or 12%); moderate malaria endemic zone in 1,003 communes with 5.540.104 people (or 7%); high malaria endemic zone in 771 communes. with 3.074.115 people (or 4%). Based on the above stratification, the number of people, which need to be protected by measures of malaria control, should be 37.154.286 or 46% of the total national population. However, these measures should presently be focused on 3 endemic zones with the population of 18.563.244 people.

Malaria management in Vietnam-Laos border and Ho Chi Minh route in Thua Thien-Hue province

One of the challenges for the current malaria management in the province of Thua Thien-Hue is imported malaria caused by the movement of population across the Vietnam-Laos border and between the malaria endemic zones from Quang Nam to Quang tri provinces along the newly constructed route Ho Chi Minh. Under that circumstance, the active measures have been set up for the control and prevention of malaria infection, especially for risk people. These measure appear to have been initially effective. The incidence, fatality has been controlled. The risk of imported malaria has been over. However, those measures need to be sustained in the border areas and the Ho Chi Minh route to maintain the achievements.

Nested PCR definition of species composition of malaria parasites in Thanh commune, Huong Hoa district Quang Tri province

Nested polymerarase chain reaction (nested PCR) was applied to identify species composition of four human malaria parasite species in Thanh commune, Huong Hoa district of Quang Tri province. Pairs of primers specific to each species of P.falciparum, P.vivax, P.malariae and P.ovale were used. ADN fragments specific to each species was 18ssr-RNA)[5],[10]. The analysis of 152 blood samples showed that only two species of malaria parasites of P.falciparum (71 %) and P. vivax (29%) were present in the study area. Single P .falciparum infection rate was 65.8%, single P.vivax infection rate was 16.4%, and the double infection of P.falciparum and P.vivax was 17.8%.

Observations on migrations and imported malaria in Nghe An province

The control and management of imported malaria in Nghe An have been carried out by Nghe An Center for Malaria Control since 7/1999. As the local malaria transmission has been under the control, management of imported malaria is an important task for the prevention of malaria resurgence. It is estimated that every year, approximately 98.700 times of people (3.3% of total the population) move to malaria endemic areas, most of which go to the Southern province (71.8%) and less number to Laos (3.3%). 78% of positive parasite cases were confirmed imported, of which 70.1% cases infected in the South, 13.8% in Laos. 16% was local transmission. The proportion of P.falciparum and P.vivax was different depending on the areas they came from as 76.5% P.falciparum was found among the people returning from the endemic districts of the province. The rate of P.falciparum was 56.2% among oness coming back from Laos and 45.4% among people coming back from the southern provinces. The malaria parasite infection rate was highest in August and December in accordance with malaria transmission season. A total of 269 malaria patients were treated during two years (2002-2003). The positive slide rate was 42.4% (P.vivax: 63.1%, P.falciparum: 29.8% and mixed: 7%). Infection from South of Vietnam was 50.8% (P.falciparum 20.7%), from Laos was 47.5% (P.falciparum 38.8%), from districts of Nghe An was lowest (1.7%). Transmission from imported cases to local people was not found. Most of the imported malaria cases late admitted to hospital were found to have both forms of parasite: asexual and gametocyte, especially P.vivax (94.4%) of total positive cases suggested a dangerous potential source for the local transmission, where An.minimus is present. Careful prevention of death due to P.falciparum and use of primaquine to contain transmission are recommended. A KAP survey conducted in two communes where there was good management of population migration suggested that local authorities and health facilities have recognized the importance of this task but not yet prectically managed the appropriate and effective activities to control it.

P.falciparum resistance and therapeutic efficacy of antimalarial drugs in some areas of Central Vietnam

In vitro and in vivo assessment of therapeutic efficacy of artesunate single and the combination of artesunate + doxycycline in treatment of P.falciparum malaria was conducted in the three central-plateau provinces of Quang Binh, Quang Tri and Gia Lai from August 2001 to June 2002. Susceptibility in vitro of P.falciparum of 15 strains was studied in the same trial in the provinces of Quang Binh and Gia Lai. Six of 15 strains were found resistant to chloroquine, 1/15 resistant to quinine, 4/15 resistant to mefloquine. One of 15 was found to have a reduced sensitivity to dihydroartemisinin. However, the resistance to quinine and reduced sensitivity to dihydroartemisinin have not been determined. The recrudescence was found higher in the group treated with artesunate single than in one treated with the combination of artesunate and doxycycline (46.7%. compared to 22.6%).

PCR application in identification of malaria species composition and genetic diversity of P.falciparum in Quang Binh province

Multiplex PCR and nested PCR were applied in a study to identify the composition of human malaria parasites and the genetic diversity of P.falciparum from infected blood samples collected in the central province of Quang Binh . A total of 254 malaria blood infected samples were examined with Giemsa staining and PCR techniques showed the presence of three malaria human species: P.falciparum (59%), P.vivax (39.76%), and P.ovale (1.24%) in the sampled patients. A higher prevalence of mixed species infection was found including double infection (29.1%) and two cases of triple infection (0.9%), of which the mixed infections confirmed by PCR was much higher (6.5 folds) as compared to Giemsa staining. Moreover, triple infection was detected only by PCR showing the advantages of this technique. Application of multiplex PCR and nested PCR appeared to be very effective and useful in analyzing of genetic diversity. Three loci for highly polymorphic antigens have been used as genetic markers as: Merozoite Surface Protein 1 (MSPl); Merozoite Surface Protein 2 (MSP2), and Glutamate Rich Protein (GLURP). Analysis of DNA derived from 113 isolates of P.falciparum collected from malaria patients showed 17 allelic variants in Kl and 15 allelic variants in MAD20 which was detected in MSPI locus. Ten allelic variants in FC and 16 allelic variants were detected in MSP2 locus. Thirteen allelic variants were detected in GLURP. The high degree of polymorphism suggests a prospective possibility for characterizing of genetic composition of any parasite population, and applicability of this genotyping in epidemiological studies and vaccine development.

Paracheck P.f malaria diagnosis in Ninh Thuan province

Effectiveness of Paracheck P.f test kits were assessed in the peripheral health facilities (provincial hospital, district hospitals and commune health centers) of Binh Thuan province. A different number of positive P.falciparum cases over the province were found with two methods of microscopy and Paracheck P.f test of 13.02% and 16.25%, respectively (p<0.01). However, this difference was found significant only in the provincial hospital (p<0.05) while it was not in the district hospitals and other health services (P> 0.05). Paracheck P.f test was found to be a good method for early malaria diagnosis with high sensitivity and specificity.

Perfection of DNA extraction of malaria parasites in mosquito and determination of vector status of An.minimus and An.dirus by ELISA and PCR

Laboratory analysis and selection of the best procedures of AND extraction of malaria parasite in An.minimus and An.dirus collected in the pilot study site of Khanh Vinh commune (Khanh Vinh district of Khanh Hoa province) using ELISA and PCR techniques were conducted from June 2002 to December 2005. Both methods for extracting DNA of Plasmodium in mosquito of Chelex-100 and phenol appeared useful in extracting of DNA of malaria parasites in ELISA and dried mosquito samples. DNA templates have a good quality for PCR amplification. A high malaria infection rate (7.76%) was found in An.dirus collected during 1993-1998, and 4.25% in ones collected during 1999-2005. In was 7.25% in An.minimus collected before 1998. Both species of An.minimus and An.dirus were determined by ELISA and re-confirmed by PCR as the main malaria vectors in the study areas. The population of An .minimus was found to have remarkably been reduced since 1998, while An.dirus has still been an important malaria vector in the study area.

Pharmacokinetics of antimalaria combination CV8 when given in the manner of therapeutic dosage regimen in healthy male subjects

The study was designed for analysis by non-linear regression of compartmental pharmacokinetic models. The plasma concentration-time data for the first and last dose only would have been sufficient. However, piperaquine exhibited multi-compartmental of the resultant plasmaconcentration-time profiles become more cumbersome (Fig. 1 and 2). At this stage only basic parameters derived from non-compartmental methods are presented. Results from compartmental modeling will be reported in the way of a scientific publication at a later stage. The plasma concentration has been determined in all subjects. The Cmax was found 1015nM/L on Day 1, and was 1015 0 nM/L on Day 3 and T1/2 was 30-57 days and Tmax was 3-5 hours.

Population migration, malaria epidemiology and other malaria related factors in Ea Sup district of Dak Lak province

Population migration and malaria epidemiology characteristics were studied in Ea Sup district, Dak Lak province from 2002-2004. Findings of the study showed that the illegal migration and settlement, most of them were ethnic minority group from the North, had become intensive over the past recent 2-5 years. Most of them would have a permanent settlement (98.8%). The main reason for migration was economic factor (95.5%). The migrants were exposed to the malaria infection during their movement of 1-2 weeks while lacked of means for personal malaria protection such as: lack of bed-net: 83%; lack of anti-malarial drug: 17%. Most of them (97%) lived in temporary houses in the new places isolated from larger community, near to the forest. The malaria prevalence and incidence were higher in the new comers who just arrived 1-2 years but lower in those who had settled for already 3-5 years and the local people. There was no significant difference in malaria infection in gender, ethnic and parasite species. The malaria evolution among migrants was conformed to local transmission seasons. The risk factors to malaria contracting were working and sleeping over night in forest (98%), and poor structure of houses (86%), and living close to forest (not further than 100m). The popular language (Vietnamese) and knowledge of the migrants on malaria and its prevention was higher than that of the local people (77% compared to 52%) but the income was lower (78% and 50%, respectively). The rates of people who lacked and used no bed-net were 67% and 90%, respectively. The health seeking behaviors and approaching to the health information were very low (36-56% and 27-30%, respectively).