Since the start of the new season (2025/2026 Season. EW 31 to EW 16/2026), 22,071 suspected cases of dengue have been reported to the National Health Surveillance System; of these, 54 were laboratory-confirmed, with the circulation of DENV-1, DENV-2, and DENV-3 detected. Fifty-six percent of these cases correspond to individuals with no history of travel.
Although dengue circulation is currently low nationwide, and confirmed cases remain scarce and largely isolated, an increase in the reporting of probable cases has been observed in recent weeks—primarily in the jurisdictions of Buenos Aires, Córdoba, the Autonomous City of Buenos Aires, Tucumán, and Santa Fe.
The median age was 40 years. The age group with the highest proportion of cases was 45 to 65 years, followed by the 35 to 44 and 25 to 34 age groups. 58% of the reported cases were female.
During the current season, 9,169 suspected cases of Chikungunya fever were reported, 1,544 of which correspond to confirmed and probable cases. The reported cases with a history of travel were imported from Bolivia, Brazil, Paraguay, and Cuba. In the province of Salta, the first cases without a history of travel were identified—occurring in the context of imported cases with a travel history to Bolivia—thereby confirming the presence of local transmission. During Epidemiological Week 16 (SE16), 435 new cases of Chikungunya fever were reported, compared to SE15.
Regarding spatial distribution, the highest disease burden is concentrated in the NOA region (n=1,459; 95% of the total), with a predominance in Salta, Tucumán, and Jujuy, where the primary transmission foci are established. Concurrently, outbreaks have been recorded in other jurisdictions—such as Catamarca, Santiago del Estero, and Buenos Aires—alongside the detection of the first cases in CABA and Córdoba, thereby demonstrating the recent expansion of the event beyond the initially affected areas.
The median age was 34 years. The age group with the highest proportion of cases consisted of individuals aged 45 to 65, followed by the 25–34 and 35–44 age groups.
Fifty-four percent of the cases were in females. The most frequently reported symptoms were: fever, polyarthralgia, myalgia, headache, diarrhea, and vomiting.
Of the total cases, 932 included information regarding the need for admission, 10% of which (n=92) required hospitalization. Additionally, three severe cases were reported, one of which resulted in death.
St. Louis Encephalitis
During the current season, 397 suspected cases of St. Louis encephalitis were reported. Following a series of diagnostic tests conducted at the INEVH “Dr. Julio I. Maiztegui” National Reference Laboratory, two cases of St. Louis encephalitis were confirmed in the Province of Buenos Aires, in the localities of Florencio Varela and Bragado.
During the current season, 104 suspected cases of West Nile fever were investigated in the country; to date, no confirmed autochthonous cases have been recorded. In Epidemiological Week (EW) 37/2025, a case was confirmed involving a resident of Kansas, United States, who developed compatible symptoms while traveling through Argentina and received medical attention in the province of Buenos Aires. The case was confirmed by the National Reference Laboratory, INEVH “Dr. Julio I. Maiztegui”; the patient presented no epidemiological history consistent with local acquisition, reporting prior exposure in their country of residence—specifically in areas with mosquito populations—during outdoor activities.
Surveillance for Oropouche fever is currently based on laboratory testing of a proportion of cases that test negative for dengue, as well as in individuals with a history of travel to areas where transmission is being recorded during the current season. To date, 904 cases have been investigated, with no positive results recorded.
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In Argentina, autochthonous transmission of the Zika virus was first reported in 2016, with the last outbreak recorded in 2018. Since then, no new cases have been confirmed in the country. During the current season, 1,371 suspected cases were investigated, all yielding negative results. Currently, there is no evidence of active viral circulation; nevertheless, continuous and strengthened epidemiological surveillance is being maintained, aimed at the early detection of suspected cases and the timely identification of any potential reintroduction of the virus.
During the current season, 96 suspected cases of yellow fever have been reported, with no confirmed cases recorded to date. The most recent confirmed cases in the country occurred in 2018, when seven cases associated with a history of travel to Brazil were recorded—all in unvaccinated individuals. Active epidemiological surveillance and the prevention strategy involving vaccination are being maintained in areas with current recommendations.
Thank you for covering the Argentina situation. As a vector biologist at CONICET based in Córdoba — one of the jurisdictions flagged in this report — a few things stand out from this season's data.
The co-circulation of DENV-1, -2, and -3 is particularly concerning. It increases the probability of severe dengue in individuals with prior exposure to a different serotype. This is no longer a single-serotype scenario.
What the case counts also reflect, though rarely discussed, is a spatial diffusion process: dengue doesn't emerge simultaneously across jurisdictions — it spreads outward from major urban centers through human mobility corridors. We documented this pattern across Argentina and Brazil (2018–2025) in a preprint currently under review at Acta Tropica, that I can share on request.
For those interested in the entomological and epidemiological side of these dynamics — in Spanish — I write about this at No Me Molestes Mosquito on Substack.