Introduction: The rise of reemerging pathogens such as DENV and CHIKV presents a major public health threat. With half the global population at risk, Paraguay experiences particularly high infection rates. Despite this, data on the seroprevalence of these viruses in this country is lacking. This study aims to assess the seroprevalence of anti-DENV IgG and anti-CHIKV IgG among blood donors in Paraguay. Material and Methods: Serum samples from 546 blood donors across seven regional departments and Asunción were collected from March to May 2023. Participants filled out a questionnaire and underwent eligibility screening. Serum samples were tested for anti-DENV IgG and anti-CHIKV IgG antibodies using immunoassays. Data were analyzed using IBM SPSS version 23.0. Results: The median (IQR) age of donors was 34 (26-44), and 47.1% were female. Anti-DENV IgG prevalence was 87.7%, ranging from 73.7% to 100% by location, with an age-related association. Donors aged 18 to 25 had a 79.2% seroprevalence, while those over 46 had the highest at 91.5% (p=0.010). Anti-CHIKV IgG prevalence was 37.2%, with men showing a seroprevalence nearly 10% higher than women, but no significant age-related differences were observed. Regional variation in CHIKV seroprevalence was not significant. Conclusions: This study reveals a high seroprevalence of both DENV and CHIKV in Paraguayan blood donors. The high DENV seroprevalence reflects the impact of past outbreaks, while the notable CHIKV prevalence underscores the effects of recent outbreaks. Continuous surveillance, improved diagnostics, and effective vector control measures are essential to mitigate these arboviruses’ impact in Paraguay.

Introduction: Hepatitis A (HAV) and E (HEV) remain to pose a substantial global health burden. This study aims to estimate the seroprevalence of anti-HAV IgG and anti-HEV IgG antibodies among blood donors in Paraguay, a region with limited available data on these infections. Material and Methods: A total of 452 serum samples were collected from blood donors across five Paraguayan regions from March to May 2023. Participants completed a questionnaire and underwent eligibility screening. Serum was analyzed for anti-HAV IgG and anti-HEV IgG antibodies using immunoassays, and data were processed in IBM SPSS 23.0, setting statistical significance at p<0.05. Results: Overall, 68.1% of donors tested positive for anti-HAV IgG, with higher prevalence in older age groups (p<0.001) and significant regional differences (p<0.001). Notably, a low seroprevalence was found in the 18-25 age group (36.4%), highlighting a potential gap in immunity. In contrast, anti-HEV IgG was detected in 6.0% of samples, with no significant differences observed across age groups or regions, where prevalence ranged from 0% to 11.1% across different departments. Men exhibited a non-significant trend toward higher anti-HEV IgG seroprevalence compared to women (p=0.082). Conclusions: High anti-HAV IgG seroprevalence in older donors and low coverage among younger adults, suggesting the need to expand HAV vaccination efforts. The relatively low HEV seroprevalence in Paraguay aligns with regional data and may reflect recent introduction or limited transmission of the virus. These results provide a valuable epidemiological baseline for guiding future public health interventions and vaccination strategies in Paraguay.