This study aimed to describe the spatial and temporal epidemiology of imported malaria and its risk factors in Roraima, Brazil and Bolivar, Venezuela using secondary data from the two states from 2016 to 2018. In Roraima, females, cases aged 20-49 compared to those <10 years, miners and ‘other’ occupations were more likely to report being an imported malaria case compared to those working in agriculture and domestic sectors. This was similar to Bolivar, except that, in addition to the occupations mentioned above in Roraima, those engaging in tourism and construction were also more likely to be an imported case. Indigenous people and P. falciparum cases were more likely to report imported malaria in both states. Spatially, hotspots of imported malaria were reported from the north-east municipalities of Roraima throughout the study period.
Similar to the study by Arisco et al, after adjusting using logistic regression, women were at higher risk of imported malaria in Roraima state 17. This finding is different from other studies that reported being male as a risk factor for imported malaria 29,30. This finding could be suggestive of an epidemiological shift from men to women, who may be increasingly engaging in mining and other occupations with high risk of malaria transmission. Other plausible reasons could be demographic shifts in migration patterns, from migration of predominantly men to family units with both genders. However, further studies are required to understand this finding. However, analysis for interaction between sex and occupation showed that occupuation was an effect modifier of the effect of sex on being an imported cases, with the effects differing by occupational category.
Additionally, being a miner was the main risk factor of imported malaria in both Roraima and Bolivar states. Miners are at an increased risk of malaria infection due to prolonged exposure when working at mining sites (mining deforestation associated), which promotes habitats for Anopheles vectors and heightened host-vector contact 31–33. Increased surveillance, extension of control and preventive measures (long lasting insecticidal nets [LLINs], long-lasting insecticidal hammocks [LLIHs]) to this at-risk group are critical to achieving malaria control and elimination.
In both the areas, the 20-49 age group was the most at risk of being an imported malaria case. Similar findings were reported in other studies 17. This could be linked to migration, since most migrant populations that come to Roraima are in these groups (20 and 39 years) 17. These younger adults are more likely to be involved in occupations such as mining and have more freedom to leave their homes to migrate to other states or countries to look for work, thereby increasing risk of imported malaria infection.
P. falciparum cases were more likely to be imported than P. vivax in both states. This could be a reflection of imported malaria associated with working in mining areas, since other studies have shown that P. falciparum was predominant in several gold mining regions, even though P. vivax consists of 75% of malaria cases in the Americas 4,34. Imported malaria was predominantly reported in non-indigenous population in both the states. Similar findings have been reported in other studies 17, primarily because non-indigenous people are involved in gold mining more than the indigenous. In Roraima, only 4.7% of cases in indigenous people were reported their occupation as mining compared to 28.6% on non-indigenous people. Similarly, 27.7% versus 52.4% worked in mining in Bolivar.
Spatial analysis revealed hotspots of imported malaria reported in the north-eastern part of Roraima bordering Bolivar and Guyana throughout the study period. This could be due to the location of illegal mining areas in these hotspot municipalities or because these municipalities are the central route of migration between the countries 29. Lover et al. reported that many Brazilian miners travelled to Guyana to work in mining and returned to Boa Vista for medical care 21. This is a plausible occurrence in this study, with Boa Vista municipality in Roraima reporting 55% (6,192) of imported cases during the study period (Figure 2). Increasing health services including malaria clinics in this area will reduce self-medication with under-the-counter antimalarials which are frequently reported in gold miners, though not legal in Brazil 35. Distribution of preventive measures such as LLINs, LLIHs, and health education in these hotspot municipalities can help reduce malaria transmission in these groups. An earlier study reported Brazilian miners did not know how malaria was transmitted and associated malaria infection with contaminated water and food 36.
The results of this study need to be interpreted considering some limitations. First, the major limitation of this study is the use of surveillance data. As such, completeness and representativeness of such data could not be fully ascertained. Second, malaria self-diagnosis or diagnosis and treatment in private health settings could have been unaccounted for. However, in Brazil treatment outside the public sector is prohibited, though there is an informal market for malaria treatment in some municipalities of Roraima, mainly in remote and illegal mining sites. Self-medication is common among miners and could be a problem resulting in an underestimation of actual cases 36,37. Third, important risk factors including education level could not be included in the analysis, since these data were not recorded in Bolivar state. Fourth, unmeasured risk modifiers, such as socio-economic development, living standards, treatment, localized behavioral patterns, population mobility, bed net use and residual indoor insecticide coverage were not included in this study, and could be included in future analysis. Fifth, malaria cases infected in Bolivar state but diagnosed and treated in other states of Venezueala were not accounted in this study.
Globally, a number of pilot studies have been undertaken to test and develop interventions aimed at cross-border populations. For instance, mobile malaria clinics have shown to be effective in increasing access to malaria services for hard-to-reach populations, such as miners 38–40. Mobile teams can complement routine facility-based health services. A study in Myanmar showed that a mobile malaria clinic provided malaria services including diagnosis and testing, provision of control measures, and health education to more people and had wider geographical coverage than a community health center 38. Mobile Malaria Workers (MMWs) have also been able to deliver quality malaria services to migrant populations (seasonal workers) 41. For example, in Cambodia, they were very efficient in interpersonal communication and became the most trusted source of information. MMWs were also well received by the communities they serve and viewed as an economic advantage by the farm owners. MMWs were effective and reliable at providing both prevention, and early diagnosis and treatment to seasonal migrant workers.
In addition, screening posts could serve as important service points for mobile populations 5. These posts can be set up at strategic locations including border crossings and migration portals: taxi stands, and public bus and boat terminals. They can be used to provide intervention packages such as LLINs and LLIHs, pamphlets on signs and symptoms of malaria, and can serve as possible contact points for malaria diagnosis and treatment services in the destination area, and education on malaria prevention 5.
Furthermore, free screening and treatment for asymptomatic malaria can be offered for both returning and travelling migrants at the posts 42. The posts can also serve as surveillance centers to collect information on the destination of travelers and inform relevant public health officials in destination areas. Additionally, treatment of asymptomatic cases can reduce sources of infection from fellow workers or travelers at the destination [12]. However, most current malaria control programs are not integrating approaches such as MMWs or clinics and screening posts through the implementation of outreach clinics in remote areas, or targeting hard-to-access population groups as part of routine services [12]. Another novel approach to improving diagnosis and adherence to treatment among informal miners has been used in French Guiana, where Malakit targets gold miners working illegally with free malaria self-diagnosis and self-treatment kits for P. falciparum 43. Furthermore, it is critical that health planners and policymakers support and fund the expansion of such novel approaches in the drive to eliminate malaria and tailor malaria control and treatment approaches as transmission dynamics change quickly over time due to external and internal factors 44.
In order to better understand the mobility dynamics, profiles of different groups, their demographics, and malaria prevention and treatment-seeking behaviour practices, we recommend conducting respondent-driven sampling (RDS) studies among these populations 27,28,45. The RDS methodology is a modified form of snowball sampling that can be used to recruit groups that do not congregate in stable and identifiable places 46. It is suitable for cross-border populations as it was developed as a method of achieving reliable, statistically robust estimates for populations for whom sampling frames may be impossible to generate 47.
Moroever, regional initiatives that focus on strengthening regional coordination to achieve malaria elimination are critical to addressing challenges to elimination 21. In the Americas, the major regional initiatives are: the Amazon Malaria Initiative (AMI), the Amazon Network for the Surveillance of Antimalarial Drug Resistance (RAVREDA) 48. Other relevant regional initiatives in other parts of the world are the Asia Pacific Malaria Elimination Network (APMEN) 10, the Asia Pacific Leaders Malaria Alliance (APLMA), the African Leaders Malaria Alliance (ALMA), and The Elimination Eight Initiative (E8) 49.