Cross-sectional seroepidemiological survey of malaria in endemic areas with different activities of malaria control

A single cross-sectional seroepidemiological survey of malaria antibody was conducted in 1982 in Klang District, Rayong Province in three villages under different phases of malaria control activity to determine whether a single survey could be used to delineate malaria endemicity in Thailand and to compare the usefulness of ELISA and the indirect haemagglutination test (IHA) in the assessment of malaria endemicity. Village 11 was a control area with high infection rate with an annual slide positive rate of 16.3% in 1981. Village 6 was also a control area but was in the late attack phase in which residual insecticide spraying has been ceased since 1976. Village 7 was a consolidation area. Finger-tipped blood was collected from 189, 191 and 132 individuals from villages 11, 6 and 7 respectively, and the plasma tested for anti-P. falciparum antibody with ELISA and IHA. With ELISA, it was shown that the seropositive rate in population of village 11 (84.6%) was significantly higher than those of other two villages (48.9% in village 6 and 28.8% in village 7). After age stratification, it was shown that the differences were observed in every age group except in the greater than or equal to 45 year age group of village 6. With IHA, a significantly higher seropositive rates in population of village 11 was evident when they were compared with the corresponding age groups of 6-14, 15-29 and 30-44 years in village 7, and the age group of less than or equal to 5 year in village 6.(ABSTRACT TRUNCATED AT 250 WORDS)     

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 3 years. 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 480 man 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: 360 man 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 190 bites/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 11,002 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/100 persons/year) in this study site. A calculated sporozoite rate of maximum 1/300,000 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.     

Can source reduction of mosquito larval habitat reduce malaria transmission in Tigray,Ethiopia?

The development of irrigation schemes by dam construction has led to an increased risk of malaria in Tigray, Ethiopia. We carried out a pilot study near a microdam to assess whether environmental management could reduce malaria transmission by Anopheles arabiensis, the main vector in Ethiopia. The study took place in Deba village, close to a dam; Maisheru village, situated 3-4 km away from the dam, acted as a control. Baseline entomological and clinical data were collected in both villages during the first 12 months. Source reduction, involving filling, draining and shading of potential mosquito-breeding habitats was carried out by the community of Deba in the second year and routine surveillance continued in both villages during the second year. Anopheles arabiensis was highly anthropophilic (Human Blood Index=0.73), biting early in the night before people went to bed. The major breeding habitats associated with the dam were areas of seepage at the dam base (28%), leaking irrigation canals (16%), pools that formed along the bed of streams from the dam (13%), and man-made pools (12%). In the pre-intervention year, 5.9-7.2 times more adult vectors were found in the dam village compared with the control village. There was a 3.1% higher prevalence of an enlarged spleen in children under 10 years in the dam village than in the control village during the pre-intervention period, but no statistically significant difference was found in the incidence of falciparum malaria between the two villages during the same period. Source reduction was associated with a 49% (95% CI=46.6-50.0) relative reduction in An. arabiensis adults in the dam village compared with the pre-intervention period. There were very few cases of malaria during the intervention period in both villages making it impossible to judge whether malaria incidence had been reduced. These preliminary findings suggest that in areas of low intensity transmission community-led larval control may be a cheap and effective method of controlling malaria. Further, large-scale studies are needed to confirm these findings.     

Sociocultural factors and malaria in the desert part of Rajasthan, India

BACKGROUND & OBJECTIVES: Malaria is a new emerging problem of Indian Thar Desert. The study was attempted to find out some sociocultural factors associated with malaria transmission in this region and to supplement social solutions to ongoing malaria control efforts in the desert part of Rajasthan. METHODS: Interview technique was used for data collection on pre-tested schedules. In all 30 households (15 from low socioeconomic group and the same number of households from the high socioeconomic group) in a village were selected following systematic random sampling technique. A total of 450 respondents were selected randomly in 15 villages of Jaisalmer district, Rajasthan. RESULTS: One-third of the respondents had neither taken treatment for malaria nor took part in the vector control operations because they did not consider mosquito bites to be harmful and took malaria as a mild disease. Outdoor sleeping habits, sharing bed with children, uneasy and suffocation feeling in using mosquito bednets or any other protective device also contributed to the spread of malaria in the study villages. INTERPRETATION & CONCLUSION: Community should be educated as a whole particularly the low socioeconomic group of people to bring changes in their beliefs, sociocultural and health practices to protect themselves from mosquito bites by using bednets, repellents and other devices, such as wire mesh screening of house doors and windows.     

Knowledge and behavior relating to malaria in malaria endemic villages of Khammouane Province,Lao PDR

In order to provide basic data for evaluation of malaria control measures, a study on the knowledge and behavior of people regarding prevention of malaria was carried out in 8 malaria endemic villages in Khammouane Province of Lao PDR from 1999 to 2000. The total valid questionnaire respondents were 932, with a mean age of 32.3 +/- 14.9. 43.7% of the respondents were illiterate. About 44% of the respondents suffered from malaria in the past. About 55% of the illiterate group slept in mosquito nets, compared to 75.4% for the educated group. About 29% of the illiterate respondents had knowledge of malaria transmission by mosquito bites, compared to 48.8% for the educated groups. Out of 167 non-impregnated mosquito nets examined in two villages, 13 were in bad condition having holes or leaks and 39 female mosquitos including Anopheles spp were collected in these nets by early morning catches. Knowledge of malaria and behavior in relation to the prevention of malaria were significantly related to educational level. Health education as well as general education must be taken into account for communities in malaria endemic areas to become more involved in malaria control strategies.     

Variation in malaria transmission intensity in seven sites throughout Uganda

Knowledge of the baseline malaria transmission in a given environment is important to guide malaria control interventions. However, in Uganda, recent information on malaria transmission intensity is lacking. Therefore, a 1-year entomological study was conducted in seven ecologically different sites throughout the country to assess spatial and temporal patterns in malaria transmission intensity. Anopheles gambiae sensu stricto was the main vector in five of the seven study sites, and An. funestus was the most important vector in the two other sites. In a peri-urban village, An. arabiensis contributed substantially to malaria transmission. Clear differences in annual entomological inoculation rates (AEIR) were observed between the study sites, ranging from 4 infective bites per person per year in the southwestern part of the country to >1,500 infective bites per person per year in a swampy area near the Nile River. Between villages with parasite prevalences of >or= 80% in children between 1 and 9 years old, a 4-fold difference in AEIR was observed. Based on the observed behavior of the vectors, insecticide-treated bed nets will be highly effective in controlling malaria. However, in the high transmission areas, additional measures will be needed to reduce the malaria burden to acceptable levels.     

Seroepidemiology of malaria in northern Thailand: II. Focal and temporal variations in endemicity

Four population groups from regions of Northern Thailand were surveyed for the presence of antibodies to Plasmodium falciparum using the indirect immunofluorescent antibody (IFA) test. Each of the four populations was selected from areas known to represent different patterns of malaria transmission. Group 1 was from an area where there had been no malaria transmission for approximately 30 years. Individuals in this group below age 40 showed an extremely low prevalence of malaria antibodies. Group 2 was chosen from an area where low levels of transmission have continued despite more than 30 years of DDT spraying. In this group the age related pattern of malaria antibodies varied from village to village but in all villages there was a sharp increase in the prevalence of IFA positive tests in individuals over 30. The third group has had continuously high levels of transmission. Although there are differences in the age related prevalence of IFA positives when individual villages are compared, there is a greater prevalence at all ages than in the first two groups. The fourth group was selected from an area where transmission had recently resumed after freedom from indigenous cases for approximately six years. There was little difference in the prevalence of IFA positive individuals below the age of 25 but above that there was a steady increase in prevalence with age. The correlation of IFA antibody positives with known patterns of malaria transmission in these four areas demonstrates the usefulness of this serological technique in assessing malaria endemicity and the effectiveness of control measures as well as in the interpretation of other malaria statistics.     

江苏省全国疟疾监测点疫情分析

目的  了解江苏省疟疾的流行现状及其影响因素，掌握疟疾流行规律和趋势。方法根据疟疾发病情况，选择近年来发病率较高的睢宁县官山镇、铜山县棠张镇、泗洪县天岗湖镇、盱眙县仇集镇和宜兴市张渚镇作为疟疾监测点，调查居民疟疾发病情况、疟疾症状及防蚊措施、按蚊密度及叮人率等相关因素。结果2006年调查15个行政村，7 921户，27 903人，蚊帐拥有率为20. 29%；蚊帐使用率为34. 32%。2005年在清晨50顶蚊帐内捕获中华按蚊750只，平均叮人率为每夜0.17只／人；2006年在清晨50顶蚊帐内捕获中华按蚊1 927只，平均叮人率为每夜0. 38只／人。血检6 089人，平均血检率为2. 72%，检出疟原虫阳性29人，平均阳性率为0.47%。结论发热病人血检数量较少和镜检阳性率较低，中华按蚊密度增高是江苏省淮北地区出现疟疾疫情反复酌主要因素。     

The effectiveness of impregnated bed net in malaria control in Laos

Impregnated bed net (IBN) were used in 366 villages in the central and southern three provinces of Lao PDR from 1999 to 2000. It was confirmed that 81.0% of 40000 bed nets, which were donated by Japanese Grant Aid, were delivered within 2 years. The strengthening of information network systems in anti-malaria and strong relationship between community and local authorities ensured the success of operation in a short period. The number of patients and the slide positive rate of malaria decreased markedly in public health facilities in three provinces after the use of IBN. An entomological survey was conducted in Boualapha district, where malaria is endemic, to investigate the IBN efficacy on malaria vector. The density and parous rate of Anopeles dirus, which is the main malaria vector in the area, were markedly decreased in the village where IBN was used. This mosquito's behavior, which was baiting mainly humans during the time when the inhabitants sleep in the IBN, was considered to be advantageous in preventing malaria infection using by IBN. The area of distribution of A. dirus is similar to the high endemic area of malaria in Lao PDR. Thus, it is expected that the expansion of the IBN program in the southern provinces will lead to successful malaria control in subsequent years.     

Malaria incidence in relation to rice cultivation in the irrigated Sahel of Mali

Seven repeated cross-sectional parasitological surveys, collecting a total of 13,912 blood samples, were carried out from September 1995 to February 1998 in three irrigated rice growing villages and three villages without irrigated agriculture in the area surrounding Niono, Mali. Parasite prevalence varied according to season and agricultural zone, but showed similar patterns for villages within the same zone. Overall, malaria prevalence was 47% in the villages without irrigated agriculture and 34% in the irrigated rice growing villages. In a village in the irrigated zone, and a village in the non-irrigated zone, 1067 and 608 children up to the age of 14 years, respectively, were followed in a passive malariological study for the period of 13 months. Fevers were attributed to malaria using a statistical method, taking into account the parasitaemia in afebrile controls from the cross-sectional surveys. The incidence of malaria fevers differed markedly between the two zones and over time. In the village in the irrigated zone, the incidence of malaria fevers was fairly constant over the year at 0.7 per 1000 children per day. In the village without irrigated agriculture, incidence was low during the dry season (at 0.6 per 1000 children per day), whereas it was high during the rainy season (at 3.2 per 1000 children per day). These results correspond well to the malaria transmission observed in a concurrent entomological survey. Rice cultivation in the semi-arid sub-Saharan environment altered the transmission pattern from seasonal to perennial, but reduced annual incidence more than two-fold.     

Effect of rice cultivation on malaria transmission in central Kenya

A 12-month field study was conducted between April 2004 and March 2005 to determine the association between irrigated rice cultivation and malaria transmission in Mwea, Kenya. Adult mosquitoes were collected indoors twice per month in three villages representing non-irrigated, planned, and unplanned rice agro-ecosystems and screened for blood meal sources and Plasmodium falciparum circumsporozoite proteins. Anopheles arabiensis Patton and An. funestus Giles comprised 98.0% and 1.9%, respectively, of the 39,609 female anophelines collected. Other species including An. pharoensis Theobald, An. maculipalpis Giles, An. pretoriensis Theobald, An. coustani Laveran, and An. rufipes Gough comprised the remaining 0.1%. The density of An. arabiensis was highest in the planned rice village and lowest in the non-irrigated village and that of An. funestus was significantly higher in the non-irrigated village than in irrigated ones. The human blood index (HBI) for An. arabiensis was significantly higher in the non-irrigated village compared with irrigated villages. For An. funestus, the HBI for each village differed significantly from the others, being highest in the non-irrigated village and lowest in the planned rice village. The sporozoite rate and annual entomologic inoculation rate (EIR) for An. arabiensis was 1.1% and 3.0 infective bites per person, respectively with no significant difference among villages. Sporozoite positive An. funestus were detected only in planned rice and non-irrigated villages. Overall, 3.0% of An. funestus samples tested positive for Plasmodium falciparum sporozoites. The annual EIR of 2.21 for this species in the non-irrigated village was significantly higher than 0.08 for the planned rice village. We conclude that at least in Mwea Kenya, irrigated rice cultivation may reduce the risk of malaria transmission by An. funestus but has no effect on malaria transmission by An. arabiensis. The zoophilic tendency of malaria vectors in irrigated areas accounts partly for low malaria transmission rates despite the presence of higher vector densities, highlighting the potential of zooprophylaxis in malaria control.     

Study of the malaria situation in forested foothill and nearby plain areas of Myanmar.

A longitudinal demographic-parasitological survey on malaria was conducted at 10 weekly intervals starting from September in one foothill village with the population of 1,095 and one epidemiologically comparable plain village with the population of 962 in Kyauktaga township, Bago division, 120 miles north of Yangon. The objective was to describe and analyse the current malaria situation in a forested foothill area and an adjacent plain area. Ten weekly blood film collections for malaria parasite examination, six monthly sera collections on filter paper for serological examination from the whole study population and ten weekly splenic measurements from 2-9 year children were done. The malaria parasite rate in the foothill area was invariably higher than that in the plain area in all age groups throughout the study period. Moreover, the parasite rate decreased with the increase in distance from the forested foothill area indicating that the deep forest malaria may have some influence on the foothill villages. The total age specific parasite rate in foothill villages was found to be highest in the 5-8 year age group and decreased as the age advanced which may be due to the increasing immunity. The study revealed the presence of local transmission in the foothill village. From these data it is evident that new village sites should be chosen at least 5 miles away from the forest fringe and the malaria control measures in the plain area should utilize chemoprophylaxis and effective chemotherapy focusing on the people who travel into the forest.     

Detection of malaria endemicity in community villages in North Sumatra, Indonesia by enzyme linked immunosorbent assay

An enzyme linked immunosorbent assay for malaria was used in North Sumatra, Indonesia as an epidemiological survey tool. The seroepidemiological investigation was concentrated on junior high schools. Serum samples obtained were classified according to the villages of origin of the students. The mean of ELISA values of each village group was compared with the parasite rate in primary schools in their native villages. A good correlation was observed between them (r = 0.96). The present results indicate that a survey of malaria in junior high schools by ELISA could give useful information on malaria prevalence in several peripheral villages. Province-wide information on malaria prevalence could easily be obtained by malaria-ELISA in junior high schools in tropical rural area.     

Building small dams can decrease malaria: a comparative study from Sundargarh District, Orissa, India

The adverse health effect of environmental changes brought about with the construction of large and small dams has often been reported. Here, we present results of a 5-year (2001-2005) study documenting the positive effect of such developmental projects in reducing malaria in an area where malaria transmission is mainly due to the highly efficient anthropophagic vector Anopheles fluviatilis with some contribution from Anopheles culicifacies. The former breeds exclusively in the slow-flowing streams and the latter breeds in a variety of habitats. The study was conducted in San Dulakudar village and comparisons were made with two control villages situated near the stream with similar topography and malaria transmission pattern. Epidemiological data was collected through longitudinal weekly surveillance and cross-sectional surveys in all the study villages. The mean annual malaria incidence rates due to Plasmodium falciparum in children of 1-5 years age group during 2001 before construction of dam was 1304.3 and 785.7 cases/1000 population in dam site village and control villages, respectively. However, after construction of dam, there was gradual reduction in the malaria cases in dam site village and during 2005 the incidence was significantly reduced to 181.8 (P<0.01) whereas it was increased to 1000 in control villages without any significant change in comparison to baseline year (P>0.05). A significant reduction in malaria incidence and parasite rate was also recorded in all the age groups in dam site village without registering any significant change in control villages. The construction of a small dam in the study village altered the water flow above and below the dam thereby making it unfavourable for the breeding of A. fluviatilis which in turn brought about significant impact on malaria transmission.     

Bionomics of malaria vectors and relationship with malaria transmission and epidemiology in three physiographic zones in the Senegal River Basin

Following the implementation of two dams in the Senegal River, entomological and parasitological studies were conducted in three different ecological zones in the Senegal River Basin (the low valley of Senegal River, the Guiers Lake area and the low valley of Ferlo) every 3 month in June 2004, September 2004, December 2004 and March 2005. The objective of this work was to study the influence of environmental heterogeneities on vector bionomics and malaria epidemiology. Mosquitoes were collected when landing on human volunteers and by pyrethrum spray catches. In the parasitological survey, blood samples were taken from a cohort of schoolchildren under 9 years during each entomology survey. Seven anopheline species were collected: Anopheles arabiensis, Anopheles gambiae M form, Anopheles funestus, Anopheles pharoensis, Anopheles coustani, Anopheles wellcomei and Anopheles rufipes. A. arabiensis, A. funestus and A. pharoensis were predominant in the low valley of the Senegal River, A. funestus in the Guiers Lake area and A. arabiensis in the low valley of Ferlo. Mosquito populations' dynamics varied temporally depending on the rainy season for each zone. The anthropophilic rates varied between 6 and 76% for A. gambiae s.l. and 23 and 80% for A. funestus. Only 4/396 A. pharoensis and 1/3076 A. funestus tested carried Plasmodium falciparum CS antigen. These results suggest the implication of A. pharoensis in malaria transmission. The related entomological inoculation rates were estimated to 10.44 in Mbilor and 3 infected bites in Gankette Balla and were due, respectively, to A. pharoensis and A. funestus. Overall, 1636 thick blood smears were tested from blood samples taken from schoolchildren with, respectively, a parasite and gametocyte average prevalence of 9 and 0.9%. The parasite prevalence was uniformly low in Mbilor and Gankette Balla whereas; it increased in September (16%) and then remained stable in December and March (22%) in Mboula where malaria transmission was not perceptible. However, significant differences were observed over time for parasite prevalence in Mbilor and Mboula villages whereas; it was only in Gankette Balla village where gametocyte prevalence was significantly different over time. Our study demonstrates the influence of ecological changes resulted from dams implementation in the Senegal River on the composition of vectorial system, malaria transmission and epidemiology. Such changes should be thoroughly surveyed in order to prevent any possible malaria outbreak in the Senegal River Basin.     

Temporal and spatial patterns of malaria reinfection in northeastern Venezuela

We stratified the risk of malaria transmission (Plasmodium vivax) in 35 villages along a coastal range in northeastern Venezuela (51 km2) where the main vector is the mosquito Anopheles aquasalis. After 20 years without local malaria transmission, reinfection of the entire area occurred from May to December 1985 by local (continuous) and jump (discontinuous) dispersal. Epidemiologic, environmental, and vector variables were investigated with the aid of a Geographic Information System. Risk factors for malaria transmission were human population density, proximity to pre-adult mosquito habitats (< 500 m), and the number of pre-adult habitats nearby. Most inhabitants, immature mosquito habitats, and malaria cases were located at low elevations and on gentle slopes. High prevalence of malaria during the dry seasons was associated with the presence of permanent bodies of water containing An. aquasalis. Occurrence of a La Ni?a event in 1988 (wet and cool phase of the El Ni?o Southern Oscillation) triggered malaria transmission to unusually high levels, consolidating infection in the area, and rendering traditional control efforts useless. We recommend tracking malaria persistence per village and associated risk factors as methods to reduce the cost of malaria control programs.     

云南西双版纳疟疾暴发区疟疾发病危险因素的病例对照调查

目的研究疟疾暴发区疟疾发病的危险因素. 方法采用病例对照的流行病学调查方法,用预先设计的问卷表收集人口学信息、疟疾知识、蚊帐使用、化学预防和流动史等信息. 结果共调查66例病人和57例对照.采用单因素和多因素回归方法分析了33个因素.单因素分析发现6个因素与疟疾发病有关,多因素分析发现2个独立的因素.男性疟疾发病的几率低于女性(OR=8.53,95% CI 0.97～74.24) ,日落后从劳作地回村者的疟疾发病危险度低(OR=0.06,95% CI 0.01～0.68). 结论在暴发流行区,仅有几个因素影响不同人群的的疟疾发病.日落后从劳作地回村者的疟疾发病危险度低,提示控制措施应重点放在控制和预防村内感染和传播方面.     

Chemotherapeutic malaria control operation by single dose of Fansidar plus primaquine in North Sumatra, Indonesia

Selective age group treatment and village scale chemotherapeutic malaria control operation were carried out in east-coast villages in North Sumatra, Indonesia in 1987/1988. A single dose of Fansidar plus primaquine was adopted as the drug regimen to cut the transmission of malaria at the gametocyte stage. After the treatment on day seven, the gametocyte positive rate was reduced to only 2.7% in 72 Plasmodium falciparum gametocyte carriers. A significant reduction of P. falciparum prevalence in the community was observed after successive selective age group treatment in primary school, however P. vivax prevalence persisted. Village scale active case detection was carried out by one health center staff and two village health volunteers. After eight months P. falciparum prevalence was reduced from 14% to 1%. As the result of the chemotherapeutic control activities covering high-prevalence villages in the coastal area, malaria prevalence in 1988 became very low, as compared with the status in 1985/1986.