In this study, 11,192 serum samples were obtained from individuals living in Bushehr (n = 322, 2.9%), East-Azarbaijan (n = 494, 4.4%), West-Azarbaijan (n = 126. 1.1%), Khuzestan (n = 2071, 18.5%), Sistan and Baluchestan (n = 2658, 23.7%), Kerman (n = 441, 3.9%), Guilan (n = 125, 1.1%) and Hormozgan Provinces (n = 4955, 44.3%). The mean (± SD) age of the subjects was 35.4 (± 14.6) years (range, 1 to 95), and 53.4% (n = 5974) were female. 10,860 (97%) of participants were Iranian and the remaining 332 (3%) were originally from Afghanistan (n = 325), India (n = 3), Pakistan (n = 3) and Bangladesh (n = 1). Regarding profession, the majority of participants were housewives (n = 4460, 39.8%) and freelancers (n = 3491, 31.2%).

408 cases (3.6%) had a history of abroad travel, of which the main destinations were the UAE (n = 157, 38.5%), Iraq (n = 112, 27.4%), Pakistan (n = 106, 25.9%) and Turkey (n = 17, 4.9%).

The results of DENV IgG ELISA revealed that 256 serum samples (2.3%) were positive for DENV IgG, while CHIKV IgG was tested positive by Anti Chikungunya Virus IgG ELISA test in only 11 serum samples (0.1%). All CHIKV seropositive cases were from Sistan and Baluchistan Province (Table 1a, Fig. 2) (P-value < 0.001). However, apart from Guilan and West-Azarbaijan Provinces, DENV IgG seropositivity was observed in all provinces with the highest seroprevalence in Sistan and Baluchestan (181/2658, 6.8%), followed by Khuzestan (32/2071, 1.5%), Bushehr (3/322, 0.9%), Hormozgan (37/4956, 0.7%), Kerman (2/441, 0.5%) and East-Azarbaijan Provinces (1/493, 0.2%) (Table 1a, Fig. 2) (P-value < 0.001).

Geographical distribution of DENV IgG and CHIKV IgG seropositive cases by province and city. West-Azarbaijan province: Bazargan = 1. East-Azerbaijan province: Jolfa = 2. Guilan province: Astara = 3. Khuzestan province: DashtAzadegan = 4, Khoramshahr = 5, Ahvaz = 6, Bandar-e Mahshahr = 7, Abadan = 8, Hendijan = 9. Bushehr province: Genaveh = 10, Bushehr = 11, Kangan = 12, Asaluyeh = 13. Hormozgan province: Parsian = 14, Bandar Lengeh = 15, Bandar Khamir = 16, Qeshm = 17, Bandar Abas = 18, Hajiabad = 19, Rudan = 20, Minab = 21 Sirik = 22, Jask = 23. Kerman province: Manujan = 24, Qalehganj = 25, Kahnooj = 26, Rudbar-e Jonubi = 27, Faryab = 28, Jiroft = 29, Anbarabad = 30. Sistan and Baluchestan province: Zarabad = 31, Konarak = 32, Chabahar = 33, Rask = 34, Sarbaz:35, Saravan = 36, Mirjaveh = 37.  = Location of all detected CHIKV IgG seropositive cases

As is demonstrated in Table 1b and Fig. 2, in Sistan and Baluchestan Province, 6 out of 7 studied cities showed seropositive cases with the highest DENV IgG seropositivity recorded in Rask (13.5%) and Chabahar (11.2%) followed by Sarbaz (7.5), Konarak (4.4%), Saravan (1.4%) and Mirjaveh (0.5%). In Khuzestan Province, 5 out of 6 studied cities had DENV IgG seropositive cases including Dasht Azadegan (3%) and Khorramshahr (2.5%), Ahvaz (1.4%), Bandar-e Mahshahr (1.3%) and Hendijan (0.06%). In Bushehr Province, only Bushehr city showed DENV IgG seropositive cases (2.2%). In Hormozgan Province, DENV IgG seropositivity was observed in 8 out of 10 cities including Bandar Khamir (1.6%), Jask (1.3%), Rudan (1.1%), Minab (1.0%), Sirik (0.8%), Hajiabad (0.7%), Bandar Lengeh (0.4%) and Bandar Abbas (0.3%). In Kerman Province, Menujan was the only city where seropositive cases (1.8%) were detected.

No statistically significant correlation was observed between DENV IgG seropositivity and gender, as female and male participants showed seroprevalence rates of 2.2% and 2.4%, respectively (P-value = 0.644). However, the CHIKV IgG seropositivity was significantly higher in male cases (0.2%) compared to female participants (0.02%) (P-value = 0.13) (Table 2). Neither in the case of DENV nor in the case of CHIKV was there a significant correlation between the seropositivity and nationality (Table 2). Statistical analysis revealed that there was a significant association between age and DENV IgG seropositivity as the mean age was higher in seropositive cases (41.2 ± 15.3) than in seronegative individuals (35.3 ± 14.5) (P-value < 0.001). Although a similar trend was observed about CHIKV IgG seropositivity and age, the difference was not statistically significant (P-value = 0.245). Similar results were observed in comparing the seropositivity rates among different age groups including < 10, 10–20, 21–30, 31–40, 41–50 and > 50 years. Regarding DENV IgG seroprevalence, most seropositive cases belonged to the 41–50 and > 50 age groups (P-value < 0.001). While all CHIKV-positive cases were > 30 years of age, there was no statistically significant association between CHIKV IgG seroprevalence and age group (P-value = 0.890) (Table 2).

DENV IgG was identified in people with different professions and the highest seropositivity rate was observed in farmers (5.7%), healthcare workers (4.1%) and housewives (2.7%) (P-value = 0.001). CHIKV IgG, however, was identified only in housewives (0.2%) and self-employed cases (0.03%) (P-value = 0.277) (Table 2).

The DENV IgG seropositive cases were detected only in 2021 (83/7559, 1.1%) and 2022 (173/3057, 5.5%) (P-value < 0.001). All 11 CHIKV IgG-positive cases were identified in 2022 (11/3057, 0.4%) (P-value < 0.001) (Table 2).

Interestingly, all CHIKV IgG positive participants reported no history of travel abroad. No statistically significant association was found between traveling abroad and seropositivity for CHIKV. However, 67 out of 256 (26.17%) DENV IgG positive individuals had a history of traveling, among which 61, 5 and 1 had travelled to Pakistan, Iraq, and the UAE, respectively. DENV seropositivity was notably higher in participants who reported a history of traveling abroad (67/408, 16.4%) than those who had not a history of traveling abroad (249/10784, 2.3%) and the difference was statistically significant (P-value < 0.001) (Table 2).

7 participants showed simultaneous positive results for both DENV IgG and CHIKV IgG. All these cases were from Rask city of Sistan and Baluchestan province.