Aedes aegypti Linneaus, is the main vector transmitting Dengue virus, in tropical and subtropical regions, and in recent years Dengue fever has rapidly increased its incidence and severity in Latin American and the Caribbean countries¹. This mosquito was eradicated in Ar gentina in 1963 but in 1986 it reappeared in the north-eastern region of the country and by the year 2000 its distribution had rapidly expanded south to Buenos Aires City and its suburbs². In the 2009 outbreak in Argentina, many imported Dengue cases occurred and the first autochtho nous ones were reported in Buenos Aires³. Be sides, during the last dengue national epidemic in 2020, autochthonous cases were recorded as far south as Saladillo city (35°38´00´´S,59°46´00´´O)⁴.

Bahía Blanca city is placed in the southwest of Buenos Aires province (38°43’S, 62°16’W), very near the limit of Patagonian region; with tem perate climate and an annual average rainfall of 600 mm; this city is an important node con necting North and South regions of Argentina by means of railways, roads, sea ports and airport.

The local Municipality started in 2009 an in tegral surveillance program consisting in pro motion and prevention tasks as well as vector surveillance throughout the city, installing ovipositional traps, ovitraps⁵, in Health Units of Pri mary Care.

Neither eggs nor adults or other immature stages of Ae. aegypti were found until March 2016 when the first ovitrap resulted positive; by that same week a first female of Ae. aegypti was captured, and the second one in the following week.

Since then, “Focal Controls” started in those houses in which the adults were found and in those of the surrounding eight blocks, eliminat ing potential breeding sites for Ae. aegypti. All the focal controls were negative during 2016.

In February 2017 larvae and pupae of Ae. ae gypti were found in a 5-litres glass container, not placed at sunlight, with a plant taking roots within dirty water.

Since 2017, the entomological surveillance in Bahía Blanca was reinforced and continued along the four seasons; there are currently dif ferent zones of the city in which Ae. aegypti is present (unpublished data) thus suggesting the area is already affected by this vector.

Knowledge of Ae. aegypti distribution is of great importance for integral programs in which both Estate and Community, have a very impor tant role in vector control leading to determine areas of potential risk of diseases transmission.

The four risk factors for re-establishment of Dengue in Argentina⁶ can be found in Bahía Blanca city, i.e Ae. aegypti present, travellers re turning from neighbouring endemic countries, human population with no immunity to Dengue Fever and finally, in many cases, substandard living conditions.

Although there have already been sporadic reports of Ae. aegypti presence in northern Pata gonia region^7,8, Neuquén and Río Negro, no es tablished populations of this species were found up to date in such places. Instead, the sustained presence of adults and all the immature stages of Ae. aegypti in Bahía Blanca, shows a real pos sibility of the expansion of the species towards all Patagonia region.

We conclude that Government Institutions, such as Municipalities, must continue during the whole year with integral and sustained programmes in which members of the com munity should be included as main actors, well trained to do surveillance, and thus preventing the geographical expansion of this vector, its establishment in the area and the consequent risk of emergence of indigenous Dengue Fever cases in it.