Zika: probabilidad de establecimiento de su vector, Aedes aegypti, en Chile / Zika: probability of establishment of its vector, Aedes aegypti, in Chile

Resumen El virus Zika ha despertado una alarma mundial en los últimos años, representando un problema importante para la salud pública. En este estudio evaluamos el riesgo potencial de exposición a virus Zika en Chile, asociado a la probabilidad de establecimiento del vector Aedes aegypti en el país. Se utilizaron técnicas de modelación de nicho para proyectar los requerimientos bioclimáticos del vector (nicho global), identificando las zonas de alta idoneidad para la especie en el país. Luego, se superpuso la distribución potencial del vector en Chile con la densidad de población humana, estimando en forma espacialmente explícita el riesgo asociado a la co-ocurrencia potencial de ambos. Identificamos que existe idoneidad bioclimática para A. aegypti en Chile continental, desde el área tropical del norte hasta regiones templadas, principalmente en zonas costeras. La población potencialmente expuesta podría alcanzar 1,8 millones de personas, con 1,3 millones en nivel medio y 21.000 en niveles altos de riesgo potencial de exposición. Los resultados expuestos aquí muestran que existe una significativa probabilidad de éxito de colonización del vector principal de virus Zika en Chile continental en caso de una introducción. Por lo tanto, la prevención, monitoreo y control se vuelven un tema importante para evitar la llegada de este vector a Chile continental.

The Zika virus has raised world alarm in recent years, representing a major public health problem. In this study we evaluated the potential risk of exposure to Zika virus in Chile, associated with the probability of establishment of the vector Aedes aegypti in the country. Niche modelling techniques were used to project the bioclimatic requirements of the vector (global niches), identifying zones of high suitability for the species within the country. Then, the potential distribution of the vector in Chile was overlapped with the human population density, estimating the risk associated to the potential co-occurrence of both in a spatially explicit manner. We identified bioclimatic suitability for A. aegypti in continental Chile, from the northern tropical area to temperate regions, mainly in coastal zones. The exposed population could reach 1.8 million people, with 1.3 million in a medium level of potential risk and 21,000 in a high level. These results support that there is a significant probability of success for the Zika virus main vector to colonize continental Chile in case of an introduction. Therefore, prevention, monitoring, and control play an important role in avoiding the arrival of this vector to our country.

¿Qué dicen los números de la evolución temporal de la enfermedad de Chagas? / What do the numbers tell us about the temporal evolution of Chagas’ disease?

Chagas disease remains highly prevalent in Chile, especially between the regions of Arica and Parinacota, and Coquimbo. Since 1999 it is considered that in Chile the vector transmission was interrupted. Under this premise, the epidemiological dynamics should be changing. We analyzed the evolution of the prevalence of Chagas’ disease analyzing 64,995 xenodiagnosis performed in the laboratory of Parasitology of the Faculty of Medicine of the University of Chile between 1949 and 2014. The evolution of the mortalities and incidences from the databases of the Ministry of Health in the periods in which it was analyzed. The rates of domiciliary infestation and the number of vector insects sent to the Public Health Institute and its trypano-triatomine indices were also analyzed. The prevalence of Chagas’ disease in inhabitants of risk areas remained stable in this period as well as mortality. The incidence rate shows a progressive increase with a tendency towards stabilization. A significant decrease in sampling effort was found, declining by two orders of magnitude, especially since 2000. The progressive increase in morbidity had no clear relation to the interruption of the vector chain nor to the greater diagnostic effort occurred in 2009, since it was evident from before. While home infestation declines, reports of intrusion of solitary individuals and wild foci of T. infestans have increased. Trypano-triatomine indices were maintained with high values in all vector species. This study shows a worrying situation, for while on the one hand the interruption of the vector transmission and improvement in the research systems is emphasized, the concern for this disease seems to be decreasing with less diagnostic efforts and lower education at the higher level, and by the other hand the numbers show that the problem if it is not increasing, at least maintains its careless historical magnitude.

Resumen Introducción: La enfermedad de Chagas sigue siendo altamente prevalente en Chile, especialmente entre las regiones de Arica y Parinacota y de Coquimbo. Desde 1999 se considera que en Chile se encuentra interrumpida la transmisión vectorial. Bajo esta premisa, la dinámica epidemiológica se debiera estar modificando. Objetivo: Analizar la evolución temporal de la enfermedad de Chagas en Chile Material y Métodos: Analizamos la evolución de la prevalencia de la enfermedad de Chagas a través del análisis de resultados de 64.995 xenodiagnós-ticos realizados en el laboratorio de Parasitología de la Facultad de Medicina de la Universidad de Chile, entre 1949 y 2014. Se estudió la evolución de las mortalidades e incidencias disponibles en las bases de datos del Ministerio de Salud en los períodos en que fue posible. Se analizaron las tasas de infestación domiciliaria y el número de insectos vectores enviados al Instituto de Salud Pública y sus índices tripano-tratominos. Resultados: La prevalencia de la enfermedad de Chagas en habitantes de zonas de riesgo se mantuvo estable en este período, al igual que la mortalidad. La tasa de incidencia muestra un incremento progresivo con tendencia a la estabilización. Se encontró un significativo decrecimiento del esfuerzo de muestreo, decayendo dos órdenes de magnitud, especialmente desde 2000. El aumento progresivo de la morbilidad no tiene clara relación con el corte de la cadena vectorial ni con el mayor esfuerzo diagnóstico ocurrido en 2009, ya que era evidente desde antes. Mientras que la infestación domiciliaria disminuye, han aumentado los reportes de intromisión de individuos solitarios y los focos silvestres de T. infestans. Los índices tripano triatominos se mantienen con valores altos en todas las especies vectores. Discusión: Este estudio muestra una situación preocupante, ya que mientras por una parte se destaca el corte de la transmisión vectorial y mejora en los sistemas de pesquisa, la preocupación por esta enfermedad parece ir decreciendo con menores esfuerzos diagnósticos y menor enseñanza a nivel superior, y por otra parte los números muestran que el problema si es que no está aumentando, al menos mantiene su descuidada magnitud histórica.

Sylvatic foci of the Chagas disease vector Triatoma infestans in Chile: description of a new focus and challenges for control programs

Triatoma infestans is one of the main domestic vectors of Chagas disease. Reports of wild habitat occurrences have recently increased. In Chile, after a successful elimination campaign of T. infestans domestic infestation, a sylvatic focus was reported in bromeliads in the metropolitan region. Here, we report a new focus of sylvatic T. infestans inhabiting rock piles in the Valparaíso region in central Chile. All T. infestans captured were nymphal instars living among the stones, which were inhabited by several mammal species, along with the sylvatic triatomine vector Mepraia spinolai. We found a prevalence of infection with Trypanosoma cruzi of 36.54 percent in T. infestans, similar to the previous report for sylvatic specimens from bromeliads. Sylvatic populations of T. infestans should be studied at different geographic scales to elucidate their role in the maintenance of the sylvatic transmission cycle of T. cruzi and their possible role in threatening the domestic elimination of this vector. This information should be used to re-design the control programs in Chile to avoid the re-establishment of the domestic cycle.

Helmintofauna del roedor Abrothrix olivaceus (Sigmodontinae) en áreas sub-urbanas de Santiago de Chile / The helminthfauna of the rodent Abrothrix olivaceus (Sigmodontinae) in su-urban localities of Santiago, Chile

The wild rodent, Abrothrix olivaceus, is a widespread species in Chile using different habitats troughout the territory. Its helminthfauna has been partially studied in wild enviroments in Chile. In this work five nematodes and one species ofcestode were found. Three of them are first record in this host: Syphacia obvelata, Physaloptera calnuensis and Heterakis spumosa, and this last one, is first record in Chile. It is suggested that one structuring factor is the locality: one of the three localities studied had more mean abundance and prevalence in two parasites species and as a component community. It is also suggested that other structuring factor of this helminth community is the introduction of parasites from foreign species. This is the first study of its helminthes in sub-urban localities and in the Region Metropolitana.

El ratón oliváceo (Abrothrix olivaceus) se distribuye ampliamente a lo largo de Chile abarcando diversos ambientes. Su helmintofauna ha sido parcialmente estudiada en diversas áreas silvestres del país. En este trabajo se encontraron cinco especies de nemátodes y un cestode. Tres de estas especies parásitas se registran por primera vez en este hospedador: Syphacia obvelata, Physaloptera calnuensis y Heterakis spumosa, y esta última se registra por primera vez en Chile. Se sugiere que uno de los factores estructurantes es la localidad de muestreo: una de las tres localidades estudiadas presentó significativamente mayor abundancia media y prevalencia en dos especies de parásitos y como comunidad componente. Se sugiere que otro factor estructurante es la introducción de parásitos desde especies exóticas. Éste es el primer estudio de la helmintofauna de este roedor en localidades suburbanas y en la Región Metropolitana.

Conducta de picada y defecación de Mepraia spinolai en dos hospederos frecuentes en su habitat / Feedind behaviour of Mepraia spinolai in two frequent hosts from its habitat

The aim of this study was to compare the feeding and defecation behavior of wild and laboratory-reared specimens of Mepraia spinolai confronted to the rabbit, Oryctolagus cuniculus, and the wild rodent, Octodon degus as hosts. Time variations in bite, blood ingestion and defecation were analized, including weight gain after a blood meal. Considering bite duration significant differences were found according to the origin of insect. Laboratory reared specimens spent less biting time when fed on rabbit. No differences were found in blood ingestion time nor in defecation time. Blood meal was significantly different according to origin of the insect. Wild specimens of M. spinolaifed more blood than the laboratory ones. From these results it was apparent that there are not significant differences in the bug behavior when they are confronted to these hosts, being both mammals of a similar epidemiological importance.

Se estudió la conducta de alimentación y defecación de ejemplares de Mepraia spinolai provenientes de laboratorio y terreno alimentados sobre conejo, Oryctolagus cuniculus, y sobre roedores degu, Octodon degus. Se analizaron las diferencias en el tiempo de picada (latencia de picada), tiempo de ingesta de sangre, tiempo de defecación y cantidad de sangre ingerida en condiciones de laboratorio. El análisis del tiempo de picada, mostró que hubo diferencias significativas según origen de las vinchucas; esto es que los ejemplares de laboratorio demoraron el menor tiempo en picar a los conejos de terreno con el mismo hospedero, quienes tomaron el mayor tiempo. No hubo diferencias significativas para el tiempo de ingesta de sangre ni para el tiempo de defecación. Se encontraron diferencias entre grupos al comparar la cantidad de sangre ingerida; los insectos provenientes del terreno consumieron la mayor proporción de sangre comparados con los criados en laboratorio. De acuerdo con los resultados, estos insectos son generalistas en cuanto a hospederos y por tanto ninguno de ellos demostró tener una mayor importancia en el rol epidemiológico de mantención del parásito en el ciclo silvestre de la enfermedad.

Primer hallazgo de vectores de la enfermedad de Chagas asociados a matorrales silvestres en la Región Metropolitana, Chile / First finding of Chagas disease vectors associated with wild bushes in the Metropolitan Region of Chile

Background: Insects of the subfamily triatominae are the biological vectors of Trypanosoma cruzi, the causal agent of Chagas disease. Aim: To search for wild colonies of triatomines in the Metropolitan Region of Chile. Material and Methods: Ad hoc traps were placed in two endemic zones of the Metropolitan Region of Chile, during 30 nights. The dejections of 16 T infestans and 43 M spinolai specimens were examined under the microscope, searching for live metacyclic trypomastigotes. A polymerase chain reaction (PCR) was performed in macerates of all insects looking for T cruzi DNA. Results: A total of 269 bugs were captured. Forty four were Triatoma infestans and 225 were Mepraia spinolai. They were not syntopic, since T infestans was restricted to a Southern zone (Calera de Tango) while M spinolai was only found in the Northern zone (Til-Til). Both species were found associated to terrestrial bromeliads (Puya sp) but M spinolai was also detected in stony grounds. Microscopic examination of dejections yielded a trypano-triatomine index of 56.3 and 32.6 for T infestans and M spinolai, respectively. PCR detected T cruzi DNA in 41 and 43 percent of T infestans and M spinolai specimens, respectively. Conclusions: The finding of T infestans in a wild habitat is noticeable. This is the first report of such phenomenon in Chile. The high infection rates with T cruzi, explains the maintenance of Chagas disease wild cycle in Chile.

DNA evidence of Trypanosoma cruzi in the Chilean wild vector Mepraia spinolai (Hemiptera: Reduviidae)

Molecular evidence showed 46.2 percent of Trypanosoma cruzi infection in Mepraia spinolai insects from North-Central Chile, which is significantly higher than previous reports of up to 26 percent by microscopic observation. Our results show similar infection levels among nymphal stages, ranging from 38.3 to 54.1 percent, indicating that younger nymphs could be as important as older ones in parasite transmission. A cautionary note must be stressed to indicate the potential role of M. spinolai in transmitting T. cruzi in country areas due to the high infection level detected by molecular analysis.

Abundance of Mepraia spinolai in a Periurban Zone of Chile

Mepraia spinolai is a silvatic species of Triatominae which prefers microhabitats near to or in rock piles. It is also able to maintain similar or higher size populations near houses. The density of bugs in quarries near Santiago, Chile, differed within microhabitats and varied significantly within sites according to season. M. spinolai was not found in sites characterized by human perturbation of quarries. Our results confirm M. spinolai as a silvatic triatomine whose importance as a vector of Chagas disease will depend on contact with humans. This could occur if the habitats where populations of this species are found become exploited for the building of urban areas

Biología comparada de mepraia spinolai en condiciones de laboratorio y terreno: cinco años de estudio / Comparative biology of mepraia spinolai in laboratory and field conditions: 5 years study

En Chile se han descrito dos especies de triatominos: triatoma infestans y mepraia spinolai. De éstas, la primera es la más estudiada por su importancia en el ciclo doméstico de la enfermedad de Chagas en Chile y América. De la segunda en cambio, se conoce poco de su biología e importancia epidemiológica. En este artículo, resumimos los aspectos más relevantes de cinco años de estudio en laboratorio y terreno de los triatominos chilenos, con énfasis en aspectos ecológicos, conductuales y epidemiológicos de M. spinolai. En nuestra experiencia ambas especies demuestran similitudes en sus dinámicas poblacionales, distribución geográfica y preferencias de temperatura en laboratorio. Las principales diferencias son de preferencia alimentaria y de tipo conductual, especialmente en el tiempo de picada que es más corto en M. spinolai y la latencia de evacuación que es muy larga en esta especie, lo cuál explica en parte su bajo impacto epidemiológico

Dinámica comparada de cohortes triatoma infestans en ambiente habitacional / Compared dynamics of triatoma infestans in room environments

Triatoma infestans is a insect with a high colonization capacity, capable of maintaining populations near saturation levels in different environments. However, it has a great lability in its population parameters when exposed to variable environmental conditions. The aim of this work was to explore the response of two cohorts with 4 initial egg densities, in two environmental conditions (shelter at 24 ñ 2.7§ C and 73 ñ 7 percent of relative humidity and room at 16.9 ñ 2.1§ C and 69.8 ñ 5 percent of relative humidity), similar to those commonly found in houses at Santiago, Chile. The proportion of fertile egg was higher in shelter conditions (93.7 vs 74.6 percent). Survival curves were similar in both environments and mortality was not influenced by density or maturity of individuals. Maturation was retarded in both environment, specially in the colder one, compared to constant environments. It is conclused that maturation of T infestants is the most affected parameter in the unprotected environment. Even though, considering the insect's longevity, its reproductive function is probably accomplished. The great lability of T. infestans population parameters, suggests that the finding of favorable microenvironments is essencial for their survival