Malaria Knowledge and Infection Among Migrant Population in the China-vietnam Border: A Questionnaire-based Survey

Background remain as one of the greatest challenges facing elimination in China. Malaria control interventions among migrant population across border relies on personal protection from mosquito bites. the knowledge of the link between mosquitoes and malaria will inform malaria control and elimination programmes on those risk population. Methods


Introduction
Malaria prevalence in border areas is often higher than in other areas due to lower access to health services, treatment-seeking behaviour of marginalized populations, di culties in deploying prevention programmes to hard-to-reach communities, often in di cult terrain, and constant movement of people across porous national boundaries [1]. Though China has eliminated malaria and no indigenous case was reported since 2017, border areas still pose a great challenge to the achievement of malaria elimination [2][3][4]. Malaria elimination was challenged by diversity and complexity of the determinants in the border areas [5]. The border areas in Guangxi province, covered 8 counties, neighbouring with Vietnam, was once high endemic area [6]. The malaria incidence in those 8 counties was ranged from 125.58 to 605.77 per 10,000 [7]. After continuous effort by the government and technical staff, the incidence has sharply declined to 0.22 per 100,000 in 2010 and no local Plasmodium falciparum was reported since 1996. Ningming County was one of the 8 border counties, once belong to a malaria hyperendemic area, with 31,200 malaria cases and 1.9 per 10,000 incidence reported in 1953 [8]. Plasmodium vivax was the predominant species since P. falciparum was no longer reported after 1988. However, the imported malaria cases in Ningming County, similar as the nationwide, has increased due to the frequently economic exchange. The blood examination conducted from 2000 to 2010 has reported 7 positive slides among totally 3,439 migrant population with the positive rate was 0.20%. Hence, the imported malaria caused by frequent migration was the greatest challenge for the border areas since Anopheles mosquito still exist in this county. Since less published documents have investigated and evaluated the malaria risk in this border county, herein we carry out malaria knowledge survey and parasitological study among the migrant population.

Methods
Study sites and samples.

Demographic study
A total of 108 migrant population returning to Guangxi Province from Vietnam between March 2018 and September 2019 were enrolled in this study. All participants were Vietnamese with 52.8% male (n = 57) and 47.2% female (n = 51). The average age of participants was 32 years ranging from 16 to 54 years. Most were aged at the years of 20-30 (36.1%) and 30-40 (40.7%). The occupations of all participants were mainly migrant workers (50.9%) and farmers (37.0%). The overwhelming majority of participants experienced 1time journey from Vietnam to China (78.7%), ranging from 0 to 6. There were 26 people (24.1%) who stayed in China for less than a week, 50 people (46.3%) in 1 month, 14 people (13.0%) in one month to 6 months, and 5 people (4.6%) in more than 6 months. Most of them went to Guangxi (80.6%), a small number of them worked in Guangdong (5.6%).

Malaria knowledge and control prevention behaviors
A survey of malaria knowledge among all participants found that knowledge of malaria transmission was only 19.4%, and knowledge of malaria symptoms was 23.2%. Awareness of the risk of death from malaria was 7.4%, and awareness of prevention methods was 14.8%. No signi cant difference was found among occupations except for migrant workers, whose knowledge rate were higher than other occupations including farmers and plant workers. In terms of prevention and control conditions, 80.6% of the participants had mosquito nets in their homes and 58.3% had screen doors and windows installed. At night, 73.2% of them had 2 persons who were under the bed net at night, whereas 7.4% was 1 person. The usage rate of bed nets accounted for over 49.1%. In addition, a small proportion (7.4%) of participants had the habit of sleeping rough in summer.

Malaria parasitological study
Of the 108 participants, 5.6% (n = 6) of those infected tested positive for malaria. The positive rate was 7.0% for males (P > 0.05) and 3.9% for females. There were no statistically signi cant differences in the positive rate among different age, sex, family size, nationality and occupation (Table 1). Further, no statistically signi cant differences occurred in the number of outbound visits, overseas stay time, entry and exit locations, and the positive detection rate of malaria knowledge (P > 0.05). The positive rate of home without using mosquito net was 4.8% (1/21), the positive rate of home without mosquito net installation was 6.8% (3/44), the positive rate of home without using mosquito coil incense was 3.6% (2/55), the positive rate of having the habit of sleeping rough was 0.0% (0/8), but the differences in positive rate between different behaviors were not statistically signi cant (P > 0.05) (Table2).

Discussion
Movement of infectious diseases such as malaria and COVID-19 across borders poses a major obstacle to achieving and maintaining elimination [1,9,10]. The ndings in our study have revealed that 6 asymptomatic infections detected, accounting for 5.6% of all migrant population from Vietnam. Unlikely the China-Myanmar border, which may pose great challenge for malaria elimination to Yunnan Province due to the high prevalence of P. vivax and P. falciparum in northern Myanmar [11,12], malaria in the China-Vietnam border seems a "forgotten disease" because of the low incidence in northern Vietnam. Hai Phong, located in the northern Vietnam, the average positive predictive values was 0.10% in 2010-2014 [13]. This was not only in Guangxi-Vietnam border, but also similar in Yunnan-Vietnam border. For example, Hekou County in Yunnan Province, the annual malaria parasite rate was lowered to 0.18 per 1,000 in 2008 and was the rst county to achieve malaria elimination in Yunnan-Vietnam border in 2015 [14].
In spite of achieving the goal of malaria elimination in the border counties in Guangxi [7], some challenge could be faced by the frequent mobile population. First, how to detect the asymptomatic infections timely was crucial for the malaria control intervention for both sides in the border. For Vietnam, the high risk of migrant population was proposed as forest goers, who may live in forest borer regions and have poor knowledge of malaria and limited access to preventive and therapeutic services [15,16]. As malaria transmission decline in Vietnam, the high prevalence of asymptomatic and sub-microscopic infections was the main challenge [17][18][19][20]. Asymptomatically infected individuals usually do not seek treatment and generally harbour low parasite density undetectable with microscopy examination. Therefore, parasites could persist in these individuals from one season to the next maintaining local transmission [21]. However, the asymptomatic infections were reported in the Central and South Vietnam, while in our study, it is noted that the Northern Vietnam, also has become a risk concern for the asymptomatic infections. Second, the susceptibility of both P. falciparum to Artemisinin-based Combination Therapy (ACT) and P. vivax to chloroquine was declined in Vietnam [22,23]. The risk of anti-malarial drug-resistance spread to the border, is likely due to importation of multi-drug resistant malaria caused by migrant population [24]. However, the emergence of Kelch 13 mutations associated with increased ring survival rates and parasite clearance delay were found in the China-Myanmar border [25][26][27][28], though there is no evidence showing the emergence of resistance P. falciparum strain against ACT along the China-Vietnam border, more attention should be paid to the pathogen population to monitor and evaluate the potential emergence of ACT resistance. Third, the malaria knowledge rate was low in our study among the migrant population. It is noted that the border residents, especially for the young adults and women have poor malaria knowledge [29,30]. In our study, only 19.4% of the surveyed population understanding malaria transmission through mosquito biting and 23.2% of them understanding malaria symptoms.
The study has some limitations. First, not all the questionnaires in the survey were obtained from the participants, possibly due to the language only used in English version. Second, the study was conducted in Ningming County, one of the 8 border counties in Guangxi, the results obtained from this study may not represent the whole status in the China-Vietnam border.

Conclusions
In summary, the study indicated the low malaria knowledge among the migrant population around the China-Vietnam border, also the asymptomatic infections were detected, which suggesting the risk of reestablishment of malaria facing post-elimination stage in the border. The ndings of this study have shown that the health education focus on those high risk population such as migrant workers and forest goers should be strengthened. In an area like Guangxi where literacy and language could be a barrier, health education based on verbal communication such as web, radio, and mobile phone may be required under the COVID-19 pandemic situation. Further proactive case detection should also be carried out, not only in Ningming County, but also in other border counties in Guangxi, which aimed to timely detect the patients, as well as the asymptomatic infections that could cause the re-establishment of malaria.

Declarations Funding
The work was supported by the key techniques in collaborative prevention and control of major infectious diseases in the Belt and Road (Grant No. 2018ZX10101002-004).

Ethics approval and consent to participate
This study was reviewed and approved by the ethical committee of the National Institute of Parasitic Diseases, Chinese Centre for Disease Control and Prevention (NIPD, China CDC, No. 2019008).

Consent for publication
Not applicable.

Availability of data and materials
The data was collected through paper-based questionnaire and recorded in the private computer with strictly protected ID and password, only can be accessed by the team member of co-authors.

Competing interests
The authors declare that they have no competing interests.
Author's Contributions