In the Americas, the number of confirmed malaria cases decreased by 65.4% between 2000 and 2023, and malaria elimination is now in sight for many countries. Argentina is currently free of autochthonous malaria transmission. Until 2011, cases of malaria were concentrated in Northwestern Argentina, near the border with Bolivia, a country that continues to have malaria transmission. The Orán department (Salta province, Northwestern Argentina) had particularly high transmission near a main road that is a pathway for migration from Bolivia. The purpose of this study was to identify which factors best explain the extent and timing of changes in the proportion of malaria cases in this area that were locally transmitted versus acquired in another country. Combining information from routinely collected case investigations, epidemiological surveillance data, and satellite imagery, we used a logistic model and a multi-level model of change to identify how demographic and place-level variables influence the proportion of malaria cases that were imported over time. The findings showed that the proportion of cases that were imported varied significantly over time, with a clear trend from predominantly autochthonous cases at the beginning of the study in 1977 (94.52%) to a majority of imported cases in 1992 (53.33%), a pattern that continued and intensified, reaching 76% imported cases by the end of the series in 2009. Nationality and place of work were key demographic factors influencing this shift. In particular, there was a change in transmission patterns after a cross-border intervention was launched in 1996. As Argentina has obtained certification of malaria elimination, these results may inform focal strategies for preventing re-introduction.

Early warning systems rely on statistical prediction models, with environmental risks and remote sensing data serving as essential sources of information for their development. The present work is focused on the use of remote sensing for the estimation of transmission risk and the prediction of malaria cases in northwest Argentina. This study was conducted in the city of San Ramón de la Nueva Orán, where cases of the disease have been reported from 1986 to 2005. The relationship between reported malaria cases and climatic/environmental variables—including the normalized difference vegetation index (NDVI), normalized difference water index (NDWI), and land surface temperature (LST)—obtained from Landsat 5 and 7 satellite images was analyzed using multilevel Poisson regression analyses. An increased abundance of reported malaria cases was observed in summer. An ARIMA (autoregressive integrated moving average) temporal series model incorporating environmental variables was developed to forecast malaria cases in the year 2000. The analysis of the relationship between malaria cases and environmental and climatic factors showed that malaria cases were associated with increases in LST and mean temperature and a decrease in the NDVI. Early warning systems that provide information about spatial and temporal predictions of epidemics could help to control and prevent malaria outbreaks. Based on these findings, this study is expected to support the development of future prevention and control measures by health officials.

Argentina was certified malaria-free by the WHO in 2019 after eight years with no instances of local transmission. Epidemiological surveillance was focused

Phytotelmata are natural water-holding microhabitats that support diverse aquatic communities, including immature mosquitoes. We analyzed the diversity, composition, and interaction network structure of Culicidae associated with two bromeliad species, Aechmea distichantha and Vriesea friburgensis, in two localities of the Yungas ecoregion in northwestern Argentina: La Florida Provincial Reserve (LFPR) (Tucumán) and Isla de Cañas (Salta). Immature mosquitoes were sampled during 2017–2018, and community structure was evaluated using Hill numbers, nonparametric richness estimators, bipartite network analysis, and canonical correspondence analysis (CCA). A total of 12 mosquito species were identified, with richness ranging from 5 to 9 species depending on bromeliad species and locality, with the highest richness recorded in V. friburgensis in LFPR. Sampling completeness ranged from 96.8% to 100%. Bipartite network analysis showed moderate connectance (0.50), low modularity (Q = 0.188), intermediate nestedness (NODF = 46.94), and low global specialization (H2′ = 0.273), suggesting a relatively generalized interaction structure. Culex coronator and Cx. imitator dominated the assemblage, while other species exhibited more restricted associations. The CCA indicated that species composition was mainly associated with bromeliad height above ground, internal water temperature, sediment, and pH. These results highlight the importance of microhabitat heterogeneity in structuring mosquito assemblages in Neotropical phytotelmata.

Phytotelmata are natural water-holding microhabitats that support diverse aquatic communities, including immature mosquitoes. We analyzed the diversity, composition, and interaction network structure of Culicidae associated with two bromeliad species, Aechmea distichantha and Vriesea friburgensis, in two localities of the Yungas ecoregion in northwestern Argentina: La Florida Provincial Reserve (LFPR) (Tucumán) and Isla de Cañas (Salta). Immature mosquitoes were sampled during 2017-2018, and community structure was evaluated using Hill numbers, nonparametric richness estimators, bipartite network analysis, and canonical correspondence analysis (CCA). A total of 12 mosquito species were identified, with richness ranging from 5 to 9 species depending on bromeliad species and locality, with the highest richness recorded in V. friburgensis in LFPR. Sampling completeness ranged from 96.8% to 100%. Bipartite network analysis showed moderate connectance (0.50), low modularity (Q = 0.188), intermediate nestedness (NODF = 46.94), and low global specialization (H2’=0.273), suggesting a relatively generalized interaction structure. Culex coronator and Cx. imitator dominated the assemblage, while other species exhibited more restricted associations. The CCA indicated that species composition was mainly associated with bromeliad height above ground, internal water temperature, sediment, and pH. These results highlight the importance of microhabitat heterogeneity in structuring mosquito assemblages in Neotropical phytotelmata.

For eight years prior to Argentina's malaria-free certification in 2019, there were no instances of local transmission. Epidemiological surveillance focused on detecting Plasmodium vivax in areas where the last cases had been reported. During the national malaria surveillance program (2016-2018) in Salvador Mazza (Salta Province, northwestern Argentina), several neighborhoods were randomly selected for the collection of human blood samples to detect any silent circulation of P. vivax. Diagnosis of malaria parasites relied on traditional microscopy and molecular detection using blood collected on filter paper, by amplifying and sequencing a portion of the Plasmodium cytochrome b gene. An autochthonous case of P. vivax was identified in an asymptomatic 64-year-old individual in La Bendición neighborhood, Salvador Mazza. The individual had never traveled to any P. vivax-endemic region. This case is the first detected among 92 samples collected from various localities along Argentina's borders with Bolivia (northwest) and Brazil (northeast). This finding highlights the possibility of silent circulation of P. vivax in areas previously assumed to be malaria-free and raises concerns regarding the timing of the certification, prompting a reevaluation of the current situation. The extent of P. vivax circulation among asymptomatic individuals remains largely unknown. This is the first molecularly confirmed asymptomatic case of P. vivax reported following malaria-free certification in Argentina and the Southern Cone region. Currently, there is no active epidemiological or entomological surveillance in the area where the case was recorded. The permeable nature of the border facilitates disease transmission, and the lack of information about the movement of asymptomatic individuals is particularly concerning. It is imperative that the surveillance system responds effectively to maintain the status as a malaria-free country, prioritizing this within the national health system agenda due to the potential implications of silent malaria circulation and the risk of re-emergence and re-establishment.