Epidemiology of the Region

Following the introduction of the NMCEP in 1991, malaria transmission in all regions of Việt Nam saw a strong decline in both reported incidence and deaths (Goldlust et al., 2018). However, since implementing the guidelines there have been two notable features for the Mekong Delta, a sudden drop of cases in 2000–2001 and an overall promising trend for all indicators (Erhart et al., 2007). Along with the Northeast, the Mekong Delta is the fastest region to direct all its provinces and cities to fulfil the requirements of Zone 1 classification, indicating no malaria transmission (MoH, 2020).

Identifying and analyzing the vectors and parasites of the region may help to resolve the recorded epidemiological data. The main vector for malaria transmission along the Mekong River and its tributaries is Anopheles epiroticus, a species of the Sundaicus complex (Hii & Rueda, 2013). Due to ecological changes, An. epiroticus has an extremely low infectious rate (Erhart et al., 2004a; Trung et al., 2004) as well as a reduced vectorial capacity (Dusfour et al., 2004a; Dusfour et al., 2004b; Trung et al., 2004), which explains the substantial regional drop in malaria frequency from 2000 to 2001 (Goldlust et al., 2018). The dominance of this species also determines the local pattern of malaria transmission, the peak of which occurs during the dry seasons (April–May and October–November) when salinity is highest (Erhart et al., 2004b). From a historical perspective, An. subpictus was established as a secondary vector during the early 2000s, but dramatic socioeconomic changes including the expansion of brackish waters due to shrimp farming has since contributed to the complete disappearance of this species.

Although drug-resistant malaria parasites were first documented for Việt Nam in the GMS, the Mekong Delta itself has remained free of these variants up until now. In 2022, the number of drug-resistant P. vivax, P. falciparum and mixed malaria cases of every province in the region was zero. As the species, strain and sensitivity to treatment of a parasite is an accurate predictor of the severity of illness and mortality rate that it might cause, the ongoing situation in the Mekong Delta’s is not considered as complex. However, with its proximity to locations with high levels of resistance to first-line antimalarial drugs, such as the Việt Nam Central Highlands and neighboring Cambodia, there is a very real risk of introducing new cases and vectors to this region (Delacollette et al., 2009). Hence, existing public health surveillance must remain vigilant.