Vigilancia del vector del dengue en el límite de su distribución. Una experiencia colaborativa entre los ámbitos científico, municipal y ciudadano / Surveillance of the dengue vector at its distribution limit. A collaborative ex perience between the scientific, municipal and citizen ambits

Resumen Introducción: En Argentina, durante la última década se ha observado una expansión hacia el sur del mosquito Aedes aegypti, acompañada por la expansión en la transmisión del dengue. El objetivo de este estudio fue evaluar el establecimiento de Ae. aegypti en una localidad cercana al límite de su distribución mediante un trabajo colaborativo entre los ámbitos científico, municipal, y ciudadano. Métodos: Se implementó un sistema de vigilancia del vector mediante ovitrampas, el cual se complementó con fotografías y ejemplares aportados por los ciudadanos, y con búsqueda activa de criaderos del mosquito en distintos espacios urbanos de la ciudad de Tandil, Argentina. Resultados: Se demostró el establecimiento de una población de Ae. aegypti en el municipio, tanto por medio de las ovitrampas como por los aportes del conocimiento y participación de la comunidad: la ciencia ciudadana. La información obtenida permitió comenzar a visibilizar la problemática entre los funcionarios municipales y la ciudadanía. Discusión: El dengue es una enfermedad aún invisible en localidades donde se ha estado expandiendo el mosquito vector durante la última década. La participación pública y la información producida con la vigilancia entomológica es la base necesaria para abordar la comunicación social a fin de producir cambios de conducta en las autoridades responsables y en las familias.

Abstract Introduction: In Argentina, during the last decade a southward expansion of the mosquito Aedes aegypti has been observed, accompanied by an expansion in the dengue transmission. The objective of this study was to assess the establishment of the dengue mosquito vector in a locality next to its distribution limits by a collabora tive work among scientific, municipal and citizen ambits. Methods: A vector surveillance system through ovit raps was implemented, and it was complemented by pictures and mosquitoes captured by citizens, and by the active search of breeding sites in different urban spaces of Tandil City, Argentina. Results: The establishment of Aedes aegypti population in the city was demonstrated, both by ovitraps and citizen science contributions. This information made it possible to begin to make the problem visible among municipal authorities and citizens. Discussion: Dengue is an invisible disease in localities in which the mosquito vector has been spreading during the last decade. The information produced by the entomological surveillance is the necessary basis to address social communication to produce behavioral changes in the responsible authorities as well as in the families.

Aedes aegypti spreading in South America: new coldest and southernmost records

The geographic distribution of Aedes (Stegomyia) aegypti (L.) in South America has been expanding during the last decades. Herein we present two new distribution records that extend its southern limits towards localities with extremer environmental conditions than reported to date. San Antonio Oeste constitutes the southernmost finding for the continent (40º44'S), whereas Tandil is the infested locality with the coldest mean annual temperature in Argentina (14.17ºC). The projection of a previous distribution model for Ae. aegypti predicts these two cities as positive and suggests several other localities with suitable conditions for vector proliferation beyond its assumed distribution limits.

Assessment of Culex pipiens bioforms in the world's southernmost distribution limit

The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.

Potential occurrence of Zika from subtropical to temperate Argentina considering the basic reproduction number (R0) / Posible ocurrencia de zika en las zonas subtropical a templada de Argentina considerando el número de reproducción básico (R0) / Potencial de ocorrência de zika em Argentina subtropical e temperada considerando o número de reprodução básico (R0 )

ABSTRACT Objective To assess the potential occurrence of Zika transmission throughout Argentina by the mosquito Aedes aegypti considering the basic reproduction number (R0). Methods A model originally developed for dengue was adapted for Zika. R0 was estimated as a function of seven parameters, three of them were considered temperature-dependent. Seasonal Zika occurrence was evaluated in 9 locations representing different climatic suitability for the vector. Data of diary temperatures were extracted and included in the model. A threshold of R0 = 1 was fixed for Zika occurrence. Sensitivity analyses were performed to evaluate the uncertainty around the results. Results Zika transmission has the potential to occur in all studied locations at least in some moment of the year. In the northern region, transmission might be possible throughout the whole year or with an interruption in winter. The maximum R0 was estimated in 6.9, which means an average of 7 secondary cases from a primary case. The probabilistic sensitivity analysis showed that during winter the transmission can only be excluded in the southern fringe of geographic distribution of the vector and in part of central Argentina. Conclusion Zika virus has the potential to be transmitted in Argentina throughout the current geographic range of the mosquito vector. Although the transmission would be mainly seasonal, the possibility of winter transmission cannot be excluded in northern and central Argentina, meaning that there is a potential endemic maintenance of the disease.

RESUMEN Objetivo Evaluar la posibilidad de transmisión de zika en la Argentina por el mosquito Aedes aegypti considerando el número de reproducción básica (R0). Métodos Se adaptó para el zika un modelo desarrollado originalmente para el dengue. Se estimó R0 en función de siete parámetros, tres de los cuales se consideraron dependientes de la temperatura. Se evaluó la ocurrencia estacional de zika en nueve localidades que representan diferente aptitud climática para el vector. Se obtuvieron los datos de las temperaturas diarias y se incluyeron en el modelo. Se fijó un umbral de R0 = 1 para la ocurrencia de zika. Se realizaron análisis de sensibilidad para evaluar la incertidumbre de los resultados. Resultados En todos los lugares estudiados es posible la transmisión de zika al menos en algún momento del año. En la región norte, la transmisión podría ser posible durante todo el año o con una interrupción en invierno. Se estimó el R0 máximo en 6,9, lo que significa un promedio de siete casos secundarios a partir de un caso primario. El análisis de sensibilidad probabilística demostró que durante el invierno la transmisión sólo puede ser excluida en la franja sur de distribución geográfica del vector y en parte de la región central de Argentina. Conclusión El virus del Zika puede ser transmitido en Argentina en todo el rango geográfico actual del mosquito vector. Aunque la transmisión sería principalmente estacional, no es posible descartar la posibilidad de transmisión invernal en el norte y centro de la Argentina, lo que significa que la enfermedad puede mantenerse de manera endémica.

RESUMO Objetivo Avaliar a ocorrência potencial de transmissão de zika em Argentina pelo mosquito Aedes aegypti considerando o número de reprodução básico (R0). Métodos Foi adaptado para zika um modelo originalmente desenvolvido para dengue. R0 foi estimado como uma função de sete parâmetros, três deles considerados dependentes da temperatura. A ocorrência de zika sazonal foi avaliada em nove locais que representam diferentes adequações climáticas para o vetor. Os dados das temperaturas diárias foram extraídos e incluídos no modelo. Um limite de R0 = 1 foi fixado para a ocorrência de zika, e foram realizadas análises de sensibilidade para avaliar a incerteza em torno dos resultados. Resultados A transmissão de zika pode ocorrer em todos os locais estudados pelo menos em algum momento do ano. Na região norte, a transmissão pode ser possível durante todo o ano ou com uma interrupção no inverno. O R0 máximo foi estimado em 6.9, o que significa uma média de 7 casos secundários a partir de um caso primário. A análise de sensibilidade probabilística mostrou que durante o inverno a transmissão só pode ser excluída na franja sul da distribuição geográfica do vetor e em parte da Argentina central. Conclusão O vírus Zika tem o potencial de ser transmitido na Argentina ao longo da atual faixa geográfica do vetor. Embora a transmissão seja principalmente sazonal, a possibilidade de transmissão no inverno não pode ser excluída no norte e centro da Argentina, o que significa que existe uma potencial manutenção endêmica da doença.

Distribution of the members of the Pipiens Assemblage in the sympatric area from Argentina: which is where and when?

Given their medical and veterinary relevance, the members of the Pipiens Assemblage are a worldwide target of ecological research. The distribution of Culex pipiens s.s. and Cx. quinquefasciatus converge in Buenos Aires, Argentina, where hybrids have been detected. Each member of the assemblage exhibits a distinct eco-physiological behaviour that can affect its efficiency in pathogen transmission. Our aim was to identify the environmental drivers for the spatio-temporal distribution of each member, focusing on latitudinal and urbanisation gradients. Immatures of mosquitoes were surveyed in artificial containers found within 11 public cemeteries, raised up to the adult stage and identified by their male genitalia. The distribution of each member was associated with the environment in a Generalized Linear Model. The variable accounting for most of the heterogeneity was latitude; Cx. quinquefasciatus was collected more frequently at northern cemeteries, whereas Cx. pipiens and hybrids were more likely at the southern extreme. The urbanisation gradient was also associated with the occurrence of Cx. quinquefasciatus and hybrids at the high and low end, respectively. Other relevant variables were cemetery total area, the proportion with graves and the presence of plastic flowers in the containers. The spatial distribution of the members of the Pipiens Assemblage within the sympatric region in South America is driven by environmental features. The information presented herein provides essential baseline data for surveillance programs and control activities.

Tire-breeding mosquitoes of public health importance along an urbanisation gradient in Buenos Aires, Argentina

Used vehicle tires are a source of mosquito vectors and a means of their introduction and expansion. With the aim of assessing the effects of urbanisation on the main mosquito vectors in temperate Argentina, the infestation levels of Aedes aegypti (L.) and Culex pipiens L. were studied in used tires from highly urbanised cities to low-urbanised small towns in Buenos Aires. Immatures of both species accounted for 96 percent of the 9,722 individuals collected; the total individuals collected represented seven species. The percentage of water-filled tires containing mosquitoes [container index (CI)] was 33 percent and the percentage of infested sites [site index (SI)] was 65.2 percent. These indexes decreased significantly from low to high urbanisation levels for both mosquito species. The relative abundance (RA) of Ae. aegypti immatures was slightly higher toward large cities, but showed no difference for Cx. pipiens. The CI of shaded tires was significantly higher than the CI of exposed tires for both mosquito species. There was no difference in RA values between shaded and sunlit tires. The CI and the SI were highest during the summer across the urbanisation levels, except for Cx. pipiens, which continued to increase during the autumn in small towns. Results related to urbanisation gradient, sunlit exposure and seasonality are discussed.

Aedes aegypti, Aedes albopictus, and dengue in Argentina: current knowledge and future directions

Since the reinfestation of South American countries by Ae. aegypti, dengue fever (DF) and dengue hemorrhagic fever (DHF) have become a major public health concern. The aim of this paper was to review the information related with Aedes vectors and dengue in Argentina since the reintroduction of Ae. aegypti in 1986. The geographic distribution of Ae. albopictus is restricted to the Northeast, and that of Ae. aegypti has expanded towards the South and the West in comparison with the records during the eradication campaign in the 1960s. Since 1998, 4,718 DF cases have been reported concentrated in the provinces of Salta, Formosa, Misiones, Jujuy and Corrientes. Despite the circulation of three dengue virus serotypes (DENV-1, -2 and -3) in the North of the country, DHF has not occurred until the present. The information published over the last two decades regarding mosquito abundance, temporal variations, habitat characteristics, competition, and chemical and biological control, was reviewed. Considering the available information, issues pending in Argentina are discussed. The presence of three DENV, the potential spread of Ae. albopictus, and the predicted climate change suggest that dengue situation will get worse in the region. Research efforts should be increased in the Northern provinces, where DHF is currently an actual risk.

Control of Aedes aegypti with temephos in a Buenos Aires cemetery, Argentina

Avaliou-se a eficácia de um larvicida, temefós, para controlar Ae. aegypti em um cemitério de Buenos Aires, Argentina. Os criadouros reduziram de 18,4 por cento no primeiro período de estudo (nov de 1998 a maio de 1999, sem temefós) para 2,2 por cento no segundo (nov de 1999 a maio de 2000, duas aplicações), e para 0,05 por cento no terceiro (nov de 2000 a maio de 2001, cinco aplicações). As. ovitrampas com ovos diminuíram de 17 por cento no primeiro período para 5,8 por cento no segundo e para 2,9 por cento no terceiro. Os resultados sugerem que, em Buenos Aires, as populações de Ae. aegypti são altamente susceptíveis ao temefós. É recomendável seu uso para prevenir eventuais epidemias e não para o controle rotineiro.

Seasonal pattern of abundance of Aedes aegypti (Diptera: Culicidae) in Buenos Aires city, Argentina

In Buenos Aires, the most crowded city of Argentina, there is a potential risk of dengue virus transmission by the mosquito Aedes aegypti during late summer. The temporal patterns of oviposition activity and abundance of breeding sites of this vector were studied in two cemeteries of the city. Between September 1998 and August 1999, we examined 142 ovitraps weekly and a total of 18,010 water-filled containers. Both study areas showed remarkable differences in the percentages of positive ovitraps (19 percent vs 8 percent) and breeding sites (18 percent vs 1 percent), but similar temporal abundance patterns. The percentage of breeding sites was higher in summer and autumn than in spring and winter, and the percentage of positive ovitraps was higher in summer than in the other three seasons. Immatures were recorded from the first week of October to the second week of July, and oviposition activity from the third week of October until the end of April. In both cemeteries and with both methodologies the highest infestation levels were registered in March (ovitraps: 41.8 percent and 20.6 percent, breeding sites: 39.2 percent and 3.4 percent). These highest abundances took place after several months with mean temperatures above 20§C and accumulated rainfalls above 150 mm. A sharp decline in oviposition activity was observed when monthly mean temperature decreased to 16.5§C, and no eggs were found below 14.8§C. Seasonal fluctuation of Ae. aegypti abundances in mid-latitudes like Buenos Aires would allow reduction of the egg mosquito population through the elimination of containers during the coldest months, which are free of adults.

Aedes albopictus in an area of Misiones, Argentina

Until early 1998 the presence of Aedes albopictus had never been detected in Argentina. During April of the same year, few individuals of this species were recorded in 33 breeding sites found in 25 out of 161 inspected houses in the city of Eldorado, Province of Misiones. The homogeneous spatial distribution of the proliferation foci suggests the existence of a generalized infestation in this locality during the study period.

Ecological characteristics of Triatoma patagonica at the Southern limit of its distribution (Chubut, Argentina)

This study aimed at identifying the ecological characteristics of Triatoma patagonica Del Ponte 1929 (Hemiptera: Reduviidae) and evaluating the epidemiological importance of this species at its southernmost distribution limit. We carried out two surveys in the Province of Chubut, in summer and in spring, 1998. In each survey, we interviewed local health care agents for triatomine recognition and reports of the bugs, followed by entomological searches in houses and peridomestic and silvatic biotopes. The presence of T. patagonica was confirmed in two of the five localities indicated by interview. In agreement with previous studies, all these positive localities were east of the 11ºC isotherm, within the Monte phytogeographic province. Triatomine abundance and infestation levels (in peridomiciles and peridomestic biotopes) were higher in summer than in spring, possibly reflecting adverse environmental conditions such as flood and cold winter weather. In the silvatic environment, we found three adult bugs under rocks in summer. In peridomestic sites bugs were only found associated with chickens, which were also the only blood meal source identified. Infection by Trypanosoma cruzi was not detected. We conclude that T. patagonica at its southernmost distribution limit does not represent a risk to public health due to its low abundance, lack of association with humans, and absence of T. cruzi infection.

Suitability of containers from different sources as breeding sites of Aedes aegypti (L) in a cemetery of Buenos Aires City, Argentina

Cemeteries are ideal urban areas to study the importance of different types of containers as breeding sites of Aedes aegypti (L.). In the present study, the suitability of plastic, glass, ceramic and metal containers was evaluated in four patches within a cemetery of Buenos Aires City, Argentina. Between October 1998 and May 2000, we found 215 breeding sites of Ae. aegypti out of 13,022 water-filled containers examined. In two patches containing microenvironments sheltered from the sun, the use of the different types of containers was proportional to the offer (correlation coefficient = 0.99, P < 0.05 in both cases). In the remaining patches, plastic and metal containers were the most and less frequent breeding sites, respectively (P < 0.001 in both cases). The number of immatures per breeding site (median = 4.5) did not show significant differences among the four types of containers examined (H3, 215 = 1.216, P = 0.749). Differences found in patches from a same cemetery suggest that different microenvironmental conditions affect the suitability of each type of container for Ae. aegypti breeding. Plastic containers appeared as key breeding sites that should be removed to reduce the Ae. aegypti population in the study area

Characterization of Triatoma guasayana biotopes in a hardwood forest of Santiago del Estero, Argentina

Triatoma guasayana is a silvatic triatomine species distributed in Argentina, Bolivia and Paraguay. The study was performed in a secondary forest of Santiago del Estero, Argentina. The abundance of T. guasayana was evaluated by census in the following wild biotopes: quimiles (Opuntia quimilo), chaguares (dry bromeliads), logs and underground burrows. Ten biotopes of each type were dismantled in winter (August) and another 40 in summer (January); all fauna was recorded. The biotopes most infested by T. guasayana were quimiles (65 percent), followed by chaguares (55 percent), and logs (25 percent). Quimiles and chaguares were infested in both seasons, whereas logs were positive only in summer and burrows were never infested. Infestation and abundance were higher in summer than in winter. The biotope structure is a key factor for T. guasayana colonization. The larger number of refuges, the constant presence of blood sources and suitable inner microclimatic conditions offered by quimiles may favour the persistence of T. guasayana colonies. The richness of invertebrate fauna per type of biotope was ranked in the same order as that of T. guasayana, suggesting similar microhabitat requirements for all studied arthropods

Environmental characteristics of the cemeteries of Buenos Aires City (Argentina) and infestation levels of Aedes aegypti (Diptera: Culicidae)

Cemeteries with many water-filled containers, flowers, sources of human blood, and shade are favorable urban habitats for the proliferation of Aedes aegypti, a vector of yellow fever and dengue. A total of 22,956 containers was examined in the five cemeteries of the city of Buenos Aires, Argentina. The vector was found in four cemeteries that showed an average infestation level of 5.5 percent (617 positive out of 11,196 water-filled containers). The four cemeteries positive for Ae. aegypti showed significantly different (p<0.01) infestation levels. Vegetation cover and percentage of infestation were significantly correlated (p<0.01), but neither cemetery area nor number of available containers were significantly related to the proportion of positive vases. Our results suggest that the cemeteries of Buenos Aires represent a gradient of habitat favorableness for this vector species, some of which may act as foci for its proliferation and dispersal