Imported malaria: a silent and forgotten threat in malaria free zones?

Countries that declared free of malaria remain vulnerable to the reintroduction and re-establishment of malaria transmission, primarily triggered by the influx of imported malaria. This risk is particularly acute in regions with population movement from endemic zones, limited tracking capacity, or continued presence of competent vectors. Experiences from countries navigating these vulnerabilities can provide valuable lessons for regions currently progressing or sustaining malaria elimination. This study aims to present various strategies and lessons learned in controlling imported malaria and preventing its reintroduction in regions that have reached malaria elimination and maintenance.

A systematic literature search was conducted using the PRISMA ScR framework. Articles were retrieved from three databases (PubMed, Scopus, and ProQuest) and screened based on inclusion and exclusion criteria. The review focused on imported case surveillance, vector surveillance, vector controls, and other measures. Imported case surveillance comprised case detection, as well as case management, and preventive measures.

Among the 149 articles reviewed, 24 were selected for in-depth analysis. Reintroduction events were primarily driven by imported cases from endemic areas, with contributing factors including cross-border population movements, conflicts in countries of origin, and international travel. Additionally, the presence of competent mosquito vectors and the expansion of breeding habitats have facilitated local transmission following importation. All studies implemented imported case surveillance, with case detection activities reported (21 articles) and case management (4 articles) studies. Additionally, some studies included mass drug administration (3 articles) and chemoprophylaxis interventions (3 articles). Several countries incorporated vector surveillance (6 articles), vector control measures (7 articles), and other activities such as cross-border initiatives (3 articles), health promotion (3 articles), and modelling studies (1 article).

The successful prevention of malaria reintroduction has been achieved in countries that implemented comprehensive imported malaria surveillance strategies. Lessons learned indicate that case-based surveillance alone is insufficient; it must be complemented with additional interventions and context-specific activities to ensure sustained elimination and prevent reintroduction.