Epidemiological Characteristics of Malaria in the Border Area of ​​2 Provinces Quang Tri - Savannakhet

While in the forest habitats in the North in the period 2002-2005, there was only An. minimus and the main vector density in the study area was higher than in the study of Vu Duc Chinh [5], the study of Nguyen Tho Vien, Ron P. Marchand in Khanh Hoa only caught 16 species [64], in this study the species composition was more.

The general density of Anopheles in the indoor light trap method was quite high: 2.0 individuals/light/night. An.minimus had 3 individuals; density 0.9 individuals/light/night. An.dirus had 17 individuals, density 0.5 individuals/light/night.

Mosquito autopsy results: 24 mosquitoes were dissected, 11/24 mosquitoes laid eggs (physiological age of mosquitoes is over 1 year, high ability to transmit disease).

Through 6 investigation methods at 3 research sites according to the process of SR Institute

- KST - Central CT [69] in villages that carried out chemical intervention against vectors according to the program's instructions [73] still caught quite abundant malaria vectors with 18 Anophelles species .

The number of malaria vectors at the research site before intervention was high, with rich species composition. There were 2 main vectors, An.minimus and An.dirus . Of which, An.minimus was caught at all 3 survey sites; the density of An.dirus entering houses to bite people was high. This is a severe malaria area with chemical intervention for malaria control, but the Anophelles population still developed. The attack index of the main vector: An.dirus was higher indoors than outdoors (light trap density indoors compared to light trap density outdoors), while An.minimus was higher in the livestock barn. The presence and high density of vectors are closely related to the situation of malaria patients at the research sites.

The transmission of malaria in the border area is mainly due to An. dirus (forest malaria). This is the main vector in Laos and also in Huong Hoa, with a high density of biting people in houses. This vector has a low density on the Vietnamese side after spraying residual chemicals.

Comparing the species composition and quantity, the density of Anopheles mosquitoes captured was much higher in Laos, similar to the study by Bounpong Sidayong in 2007, also in Nong-Savannakhet district, the proportion of the three main vectors An.minimus, An.dirus and An.maculatus was very high at 91% of the total number of Anophelles captured [103], which explains the higher malaria incidence in Laos than in Vietnam (5.2% compared to 1.8%) and also shows the effectiveness of the measure of spraying residual chemicals on house walls compared to the measure of lying under insecticide-treated mosquito nets while the rate of having mosquito nets was still low at 2.6 people/net [98]. Comparison with the study by Ron P. Marchand in the South Central region also showed that there were 2 main factors playing a role in malaria, one of which was the high rate of forest malaria [92].

4.1.1.3. Epidemiological characteristics of malaria in the border area of ​​Quang Tri - Savannakhet provinces

Malaria prevalence according to the results of the joint investigation on both sides of the border in November-December 2010: On the Lao side (15 villages), the malaria prevalence was 5.2%; On the Quang Tri side, the malaria prevalence was 1.8%. In the KAP survey on both sides of the border, 92% of people interviewed in Laos and 17% of people interviewed in Vietnam answered that they had crossed the border within the past 12 months, Lao people tend to stay overnight in the border communes of Huong Hoa district.

39.3% of respondents in Laos and 30.5% of respondents in Vietnam said that there had been malaria cases in their families in the past 12 months. Lao people often go to border communes in Vietnam for medical treatment, while Vietnamese people go to Laos for business and trade. The rate of public health use in Laos is still low at 36.5%, nearly 50% go to Vietnam for treatment. The use of village health care is still low at 5.5% in Laos. Lao people often travel to border communes in Quang Tri province, many cases of malaria in Lao people have been detected and treated by medical facilities in Quang Tri province [97]. Similar to the malaria situation in border areas of countries in the Western Pacific region: According to AP Dash et al., imported malaria and border exchanges in countries in the region are an important issue [81]. Similar to the study of Amnat Khamsiriwatchara et al [76], malaria is mainly imported in long-term laborers. Malaria in the border areas of

Quang Tri province is similar to the assessment of Duong Socheat “Border malaria: A major concern for Cambodia” with 78,696 cases (+), 75% P.falciparum, 23% P.vivax , and 65% P.vivax cases at the Thai-Cambodian border [104]. The representative of the Netherlands-Vietnam Health Commission Ron P. Marchand also recognized the role of coordinated malaria management at the border of the two provinces of Quang Tri and Savannakhet [92].

Situation of Vietnamese patients from 4 communes: Xy, Thuan, Thanh, A Xing who returned from Laos with malaria in the 5 years from 2005 to 2009: According to survey data from malaria patients in 4 communes who were treated at the health station, the rate of malaria cases who had been to Laos was 23.5%. There was a statistically significant relationship between malaria cases and border crossings. People in 4 communes who had border crossings had more malaria than those who had not, p<0.05. The results of this study were similar to Dang Han's study in 2 communes Thanh, A Tuc in 2005, the group that had exchanges to Laos had more malaria than the group that had not (7.6% compared to 1.8%) [19].

Laotian patients come to Xy and Thanh communes for treatment frequently. The rate of Laotian patients with positive malaria parasites is high, from 20.0-43.7%, and this is also an important source of infection for the Vietnamese community. Compared to Thua Thien-Hue province [20], the rate of exchange and malaria infection due to cross-border exchange in Quang Tri province is much higher. The malaria situation in communes and villages on both sides of the border with cross-border transmission needs attention and solutions.

4.1.2. Some risk factors for malaria

4.1.2.1. Natural environmental factors

According to Vu Thi Phan, factors of biogeography and climate: temperature, humidity, rainfall, occupation, education, and economy all affect the level of malaria [43]

Direct observation in the field, we found that the research area is mainly settled by two ethnic communities Van Kieu and Pa Ko. The communes under study are located in the border area of ​​Huong Hoa district with mountainous terrain, altitude 500 m > sea level, 70% forest [63], classified according to the malaria epidemiological zoning in 2009 in the area of ​​heavy malaria circulation [33] and not far from the villages in Laos, about less than 2 km while the range of An.dirus can be up to 2.5 km.

Therefore, mosquitoes can easily fly across the border between the villages of Laos and Vietnam and of course can bite people carrying the disease, spreading malaria back and forth between the two sides. That is, if we do not consider the issue of people's exchange, the vector itself can also carry the malaria parasite to spread across the border. Therefore, it can be said that the spread of malaria across the border between Vietnam and Laos along the 12 communes of Huong Hoa district is easy due to the convenient exchange conditions of both people and the distance within the vector's range. Thus, the risk of malaria spreading across the two borders is high and to reduce the rate of malaria, there must be efforts to prevent malaria on both sides [6].

According to researchers on malaria epidemiology, biogeography is an important factor in malaria zonation and in studying malaria seasons. This issue is very important for planning and implementing malaria control plans [43].

The settlement of the Van Kieu and Pa Ko ethnic communities at the research site is dense forest, dense forest edges, many streams, at an altitude of 200 - 500m. Currently, this area is regenerating forest closer and closer to people's houses. The investigation found both main malaria vector species, An. minimus and An. dirus [6], the rate of malaria parasites is higher than in other habitats (p<0.001). According to Vu Thi Phan, dense forest habitat, dense forest edges and many streams are favorable for the development of these two disease-transmitting vector species [43]. According to Nguyen Duc Manh et al., in many persistent malaria sites in the Central region, An. dirus plays an important role in disease transmission [37].

Similar to studies by Vu Duc Chinh [5], Vu Thi Phan [43]; Le Khanh Thuan [55] and Nguyen Xuan Quang [47], Le Thanh Dong [10] acknowledged the relationship between malaria and regional biogeographic environmental conditions such as vegetation, streams, and altitude.

Weather factors and malaria transmission season at the study site.

The results of the study on the monthly development of malaria in the two research groups showed that: the transmission time during the year is continuous, there are malaria cases every month - similar to other studies, but the fluctuations create disease peaks. The previous study on the transmission season in the Central Highlands by Le Khanh Thuan had two disease peaks in the year, the first peak is in the dry season and the second peak is in the rainy season.

The second peak is in the rainy season [56]; Malaria in the SRLH area of ​​Quang Tri province occurs all year round but the monthly increase and decrease are different, the increase and decrease of the disease coincides with the increase and decrease of rainfall and density of the two main vector species ( An.minimus and An.dirus ), and peaks from July to November.

Similar to the research results of Ly Van Ngo in Thanh commune in 2006, malaria parasites were present in all months but increased from August to December and border exchange subjects were also found to have malaria parasites from 1-2% [40].

The most characteristic feature of the weather factors in the study area is that the average temperature and humidity always have very high values, fluctuate a lot (23.08 ± 6.11 o C and 84.0 ± 3.5%), the rainfall fluctuates very much (199.9 ± 198.3 mm), and the seasons are clearly divided. Both temperature and humidity factors are within the favorable limits for the development of both malaria vectors and for the continuous development of the malaria parasite at the stage of completing the sexual reproductive cycle in the mosquito body.

From May to October, it starts to rain, high humidity, and temperatures are suitable for mosquito development. The rate of malaria is highest in the year. From 3.85 - 16.13%. In the dry, cold season from November to April of the following year, the rate of malaria decreases from 8.1% to 2.4%.

Through monitoring malaria reports in the 5 years 2005 - 2009, we found that malaria patients increased seasonally. They increased at the beginning and end of the rainy season, from May to November, highest from August to October, and gradually decreased in November and December.

4.1.2.2. Some economic and social practices and activities affect the development of malaria at the study site.

From the results of interviews with research subjects on awareness, attitudes and practices of PCSR of people in the research area, combined with field observations, we found that in addition to factors of bio-geography and weather, the level of malaria in the community is also influenced by factors of living habits, farming and socio-economic activities related to exposure to malaria mosquitoes of the community. The results of this study are similar to the study of Le Thanh Dong in Binh Dinh province [10].

The customs of the Van Kieu and Pa Ko ethnic groups in Huong Hoa district are often

live in a stilt house with a fireplace in the middle of the house. Some houses still keep livestock under the floor.

conditions to attract mosquitoes into the house. People here often cultivate on the fields and go to the forest, sleep in the fields during the harvest season, so they are more susceptible to malaria. Research results by Nguyen Tho Vien and Ron P. Marchand in Khanh Phu also showed that people who sleep in the forest have people carrying malaria parasites, so malaria spreads in the forest because of the high density of An.dirus [64].

This result is similar to the research results of Dang Tu on the diversity of malaria epidemiology affecting the effectiveness of intervention measures in Huong Hoa district [61].

People in this area often have the habit of traveling to other villages of the same ethnic group, going to Laos to visit, get married, work as hired porters, buy and sell... [61].

Recently, due to the problem of trading precious wood and many types of goods through unofficial channels, many people in the border communes of Huong Hoa often go for many days in the forest to carry smuggled goods and carry wood for hire through unofficial channels. Many people have contracted malaria when they return home. These are also difficulties and challenges in malaria control up to now. This in Huong Hoa district, Quang Tri is similar to the summary assessment of malaria control in the period 2001-2005 and the following periods of the Central Institute of Malaria, Parasitology and Entomology: "Exchange to malaria-infected areas and across large borders increases malaria at the destination and brings malaria back to the homeland" [70].

Lao people near the border are mostly Van Kieu and PaKô people, who have the same language, customs, and practices, so they often cross the border to visit each other and become in-laws. When sick, because they live far from Lao medical facilities but close to medical stations along the border of Huong Hoa district, they often go there for treatment, mostly at medical stations in Xy, Thanh, Thuan, and A Xing communes. This happens regularly, continuously, and is a unique characteristic of the border communes of Huong Hoa district, Quang Tri province, different from the specific malaria characteristics in the border areas of Vietnam according to the study of Le Xuan Hung [28] and other studies in the world such as the study of Sarah J Moore on malaria in the Chinese border, mainly in the agricultural group and during the harvest season [93].

4.2. EPIDEMIOLOGICAL CHARACTERISTICS OF MALARIA AND RELATED FACTORS IN 4 COMMUNES THUAN, XY, THANH, A XING OF HUONG HOA DISTRICT, QUANG TRI PROVINCE IN 2010

4.2.1. Epidemiological characteristics of malaria through cross-sectional survey in 4 communes: Thuan commune, Xy commune, Thanh commune and A Xing commune before intervention (January 2010)

4.2.1.1. Epidemiological characteristics of malaria

Malaria prevalence before intervention (1/2010).

Regarding the malaria prevalence rate of 4 communes. Thuan commune, Xy commune, Thanh commune, A Xing commune before intervention: malaria prevalence rate 2.6%, malaria parasite prevalence rate 2.2%; there were 23.4% (15/64) clinical malaria patients. The rate of splenomegaly was low at 0.3%. Compared with the study in 2001-2002 by Hoang Ha also in 5 communes Xy, Thanh, Thuan, Huong Linh, Huong Phung, malaria prevalence rate 6.1%, malaria parasite prevalence 9.1% [13] and the study by Nguyen Minh Hung also in Thanh commune in 2004, malaria parasite prevalence rate was 9.8% [34], our current research results are lower, due to the effectiveness of many years of malaria control, however, there are still persistent malaria foci at the border.

The rate of patients with SRLS symptoms is lower than the rate of having KSTSR, similar to the study in 2001-2002 also in the 5 communes above [13] , while in the reports in the above localities, these people are often those with clinical fever symptoms but may not be tested or tested without KSTSR, there are also many cases of carrying KSTSR but not showing fever symptoms - not proactively going to medical facilities for examination and treatment, so a number of people carrying KSTSR are still latent in the community, only by proactive investigation can they be detected.

Investigation results in 3 years 2010 - 2012 with 90 cases of malaria, testing showed 69 malaria parasites, 21 people had symptoms of malaria, rate 23.3%, thus up to 76.7% of cases carrying malaria parasites did not have symptoms of malaria at the time of investigation. Similar to the results of Doan Hanh Nhan's investigation in severe malaria areas in 2 districts Huong Hoa and Dakrong in 2007, the rate of malaria parasites carrying people with temperature  37.5 o C, 75.3% of cases had malaria parasites [41]. Compared with Hoang Ha's study in 2