The Parasite Load of Trypanosoma cruzi Modulates Feeding and Defecation Patterns of the Chagas Disease Vector Triatoma infestans.

Trypanosoma cruzi is the causal agent of Chagas disease, a parasitic zoonosis transmitted mainly through the feces of triatomine insects. Triatoma infestans is the main triatomine vector of this disease in South America. Previous research has shown that T. cruzi infection modifies the behavior of triatomines. We evaluated, for the first time, the effect of parasite load on feeding and defecation behavior, which we quantified by using real-time PCR. The detection time of the host was shorter in infected individuals, and the number of bites increased, while the dejection time was reduced when compared with the non-infected group. A significant correlation between the parasite load and the behavioral changes registered in the infected triatomines was found. These results would indicate that the intensity of T. cruzi infection modulates the feeding and defecation behavior of T. infestans, increasing the vector competence of this triatomine vector.

Trypanosoma cruzi infection in the wild Chagas disease vector, Mepraia spinolai: Parasitic load, discrete typing units, and blood meal sources.

BACKGROUND: Mepraia spinolai, a wild vector of Trypanosoma cruzi in Chile, is an abundant triatomine species that is frequently infected by the parasite that causes Chagas disease. The aim of this study was to determine if the parasitic load of T. cruzi in M. spinolai is related to its blood meal source and the infecting DTUs of T. cruzi. METHODS: The vector was captured in rural areas. In the laboratory, DNA was extracted from its abdomen and T. cruzi was quantified using qPCR. Real time PCR assays for four T. cruzi DTUs were performed. Blood meal sources were identified by real-time PCR amplification of vertebrate cytochrome b gene sequences coupled with high resolution melting (HRM). RESULTS: Trypanosoma cruzi was detected in 735 M. spinolai; in 484 we identified one blood meal source, corresponding to human, sylvatic, and domestic species. From these, in 224 we were able to discriminate the infecting DTU. When comparing the parasitic loads between the unique blood meal sources, no significant differences were found, but infections with more than one DTU showed higher parasitic loads than single infections. DTU TcI was detected in a high proportion of the samples. CONCLUSIONS: Higher parasitic loads are related to a greater number of T. cruzi DTUs infecting M. spinolai, and this triatomine seems to have a wide span of vertebrate species in its diet.

Trypanosoma cruzi Parasite Load Modulates the Circadian Activity Pattern of Triatoma infestans.

American trypanosomiasis is a disease caused by the flagellate protozoan Trypanosoma cruzi, which is transmitted mainly in endemic areas by blood-sucking triatomine vectors. Triatoma infestans is the most important vector in the southern cone of South America, exhibiting a nocturnal host-seeking behavior. It has been previously documented that the parasite produces changes in some triatomine species, but this is the first time that the behavior of a vector has been evaluated in relation to its parasite load. After comparing the movement events and distance traveled of infected and non-infected T. infestans, we evaluated the change produced by different T. cruzi parasite loads on its circadian locomotor activity. We observed differences between infected and non-infected triatomines, and a significant relation between the parasite load and the increase in locomotor activity of T. infestans, which was accentuated during the photophase. This could have direct implications on the transmission of T. cruzi, as the increased movement and distance traveled could enhance the contact of the vector with the host, while increasing the predation risk for the vector, which could both constitute a risk for vectorial and oral transmission to mammals.

Estimation of the Effect of the Predator Scytodes globula (Araneae: Scytodidae) on Loxosceles laeta (Araneae: Sicariidae) Populations.

It has been reported that Scytodes spiders are predators of spiders of the genus Loxosceles, but the question of the effect of Scytodes globula Nicolet on Loxosceles laeta (Nicolet) populations is still unanswered. The goal of this study is to analyze the population effect of S. globula on the population dynamics of L. laeta by means of simulation with projection matrices, considering the seasonal fluctuation of fecundity, random meetings between the predator and the prey, and limited growth of the L. laeta population. We found that the most important parameters to predict the characteristics of the population at equilibrium are the fertility and the survival function of the spider of advanced developmental stage. Also, the predator S. globula significantly decreases population size, population fluctuations, and the proportion of reproductive individuals of L. laeta The most probable effect of S. globula on L. laeta populations is a decrease of 20% of the population size. This is insufficient to consider this species as an agent of biological control of L. laeta However, the action of S. globula is not negligible because decreasing the L. laeta population by about 20% could mean a decrease of about 15% in the incidence of loxoscelism. This action is probably less effective than other epidemiological measures such as house cleaning and insecticides or arachnicides and probably similar to the direct action of humans eliminating one or two spiders per year in their houses, but it helps.

Adaptation of the spiders to the environment: the case of some Chilean species.

Spiders are small arthropods that have colonized terrestrial environments. These impose three main problems: (i) terrestrial habitats have large fluctuations in temperature and humidity; (ii) the internal concentration of water is higher than the external environment in spiders, which exposes them continually to water loss; and (iii) their small body size determines a large surface/volume ratio, affecting energy exchange and influencing the life strategy. In this review we focus on body design, energetic, thermal selection, and water balance characteristics of some spider species present in Chile and correlate our results with ecological and behavioral information. Preferred temperatures and critical temperatures of Chilean spiders vary among species and individuals and may be adjusted by phenotypic plasticity. For example in the mygalomorph high-altitude spider Paraphysa parvula the preferred temperature is similar to that of the lowland spider Grammostola rosea; but while P. parvula shows phenotypic plasticity, G. rosea does not. The araneomorph spiders Loxosceles laeta and Scytodes globula have greater daily variations in preferred temperatures at twilight and during the night, which are set to the nocturnal activity rhythms of these species. They also present acclimation of the minimum critical temperatures. Dysdera crocata has a low preferred temperature adjusted to its favorite prey, the woodlouse. Spider metabolic rate is low compared to other arthropods, which may be associated with its sit and wait predatory strategy particularly in primitive hunter and weavers. In mygalomorph spiders the respiratory system is highly optimized with high oxygen conductance, for example G. rosea needs only a difference of 0.12-0.16 kPa in the oxygen partial pressure across the air-hemolymph barrier to satisfy its resting oxygen consumption demands. Water loss is a significant stress for spiders. Paraphysa parvula shows an evaporative water loss 10 times more than usual when the temperature approaches 40°C and the participation of book lungs in this loss is about 60%. This species and others show seasonal changes in water loss accounted for by changes in cuticle permeability. The case of Chilean spiders shows how the ecophysiology in spiders is associated to their design and body size and how is affected by fluctuating Mediterranean environments, suggesting that the adaptive process can be seen as a route of optimizing the use of energy to cope with environmental restrictions imposed by the interaction with the terrestrial environment and lifestyle.

Interactions Between the Chilean Recluse Spider (Araneae: Sicariidae) and an Araneophagic Spitting Spider (Araneae: Scytodidae).

In Chile, all necrotic arachnidism is attributed to the Chilean recluse spider, Loxosceles laeta Nicolet, a species that shares the microenvironmental habitats with the spitting spider Scytodes globula Nicolet. The latter species has been proposed as a potential predator of L. laeta. For this research, we studied the interaction between both species during individual encounters to assess the possibility of population regulation of L. laeta cohorts exposed to this potential predator. We found that in most encounters S. globula prevailed. Also, S. globula preys on spiderlings of L. laeta, with a population effect on cohorts of this species. These findings suggest that S. globula may be influencing L. laeta populations in central Chile. The population regulation of L. laeta by predation would be important because this species, in the absence of predators, has a high reproductive rate, and it can maintain populations of large size. However according to our results, although S. globula may aid in the reduction of both spiderling and adult L. laeta populations, and perhaps other Loxosceles species, it is insufficient for biological control of Loxosceles species. Its presence together with other control measures such as hygiene of the rooms can help to decrease loxoscelism incidence.

[Development and population parameters of cohorts of the Chilean recluse spider Loxosceles laeta]. / Desarrollo de cohortes y parámetros poblacionales de la araña del rincón Loxosceles laeta.

BACKGROUND: Despite the abundant eco-epidemiological knowledge of the Chilean reclusive spider, Loxosceles laeta, which causes all forms of loxoscelism in Chile, the main characteristics of this species its stages of development remains poorly known especially in the medical area. OBJECTIVE: In this study we address these issues with the goal of providing clear images of the development of this species and for the first time on population projections as well as the relationship between mature and immature instars, useful data for the control and prevention of accidental bites. RESULTS: We found that L. laeta is an r-selected species, with R0=2.1, a generation time of G=2.1 years, with a concentration of the reproductive value of females between the first and second year of life. We determined the average sizes and development times of all instars. The first vary between 2.3 mm at birth and about 13 mm at adulthood. The total development time was about 1 year. DISCUSSION: The population projection by Leslie matrix suggested great capacity for growth and dispersal with clear seasonal population fluctuations associated with reproduction. It also showed that the proportion of immature varied seasonally between 80 and 90 %, which means that a house with three or four visible adult spiders actually has a population between 20 and 40 spiders in total.

Desarrollo de cohortes y parámetros poblacionales de la araña del rincón Loxosceles laeta / Development and population parameters of cohorts of the Chilean recluse spider Loxosceles laeta

Background: Despite the abundant eco-epidemiological knowledge of the Chilean reclusive spider, Loxosceles laeta, which causes all forms of loxoscelism in Chile, the main characteristics of this species its stages of development remains poorly known especially in the medical area. Objective: In this study we address these issues with the goal of providing clear images of the development of this species and for the first time on population projections as well as the relationship between mature and immature instars, useful data for the control and prevention of accidental bites. Results: We found that L. laeta is an r-selected species, with R0 = 2.1, a generation time of G = 2.1 years, with a concentration of the reproductive value of females between the first and second year of life. We determined the average sizes and development times of all instars. The first vary between 2.3 mm at birth and about 13 mm at adulthood. The total development time was about 1 year. Discussion: The population projection by Leslie matrix suggested great capacity for growth and dispersal with clear seasonal population fluctuations associated with reproduction. It also showed that the proportion of immature varied seasonally between 80 and 90 %, which means that a house with three or four visible adult spiders actually has a population between 20 and 40 spiders in total.

Introducción: A pesar del abundante conocimiento eco-epidemiológico de la araña del rincón, Loxosceles laeta, causante de todos los cuadros de loxoscelismo en Chile, sigue siendo una especie poco conocida en el ambiente médico, especialmente las características y tiempos de sus estados de desarrollo. Objetivo: En este estudio abordamos estos aspectos con el objetivo de aportar imágenes claras del desarrollo de esta especie y por primera vez de sus características y proyecciones poblacionales y de la relación entre estados maduros e inmaduros, datos útiles para el control y prevención de los accidentes por mordedura. Resultados: Loxosceles laeta es una especie r-estratega, con un R0 = 2,1, un tiempo generacional G = 2,1 años y con concentración del valor reproductivo de las hembras entre el primer y segundo año de vida. Determinamos los tamaños promedio y los tiempos de desarrollo de todos los estados. Los primeros varían entre los 2,3 mm al nacer y alrededor de 13 mm al estado adulto. Los tiempos totales de desarrollo son de aproximadamente un año. Discusión: La proyección de la población con matriz de Leslie sugiere una gran capacidad de crecimiento y dispersión, pero con claras fluctuaciones poblacionales estacionales asociadas a la reproducción. Además se muestra que la proporción de estados inmaduros fluctúa estacionalmente entre 80 y 90%, lo que implica que una casa con tres o cuatro arañas adultas visibles, en realidad tiene una población entre 20 y 40 arañas en total.

Correspondence between evoked vocal responses and auditory thresholds in Pleurodema thaul (Amphibia; Leptodactylidae).

Thresholds for evoked vocal responses and thresholds of multiunit midbrain auditory responses to pure tones and synthetic calls were investigated in males of Pleurodema thaul, as behavioral thresholds well above auditory sensitivity have been reported for other anurans. Thresholds for evoked vocal responses to synthetic advertisement calls played back at increasing intensity averaged 43 dB RMS SPL (range 31-52 dB RMS SPL), measured at the subjects' position. Number of pulses increased with stimulus intensities, reaching a plateau at about 18-39 dB above threshold and decreased at higher intensities. Latency to call followed inverse trends relative to number of pulses. Neural audiograms yielded an average best threshold in the high frequency range of 46.6 dB RMS SPL (range 41-51 dB RMS SPL) and a center frequency of 1.9 kHz (range 1.7-2.6 kHz). Auditory thresholds for a synthetic call having a carrier frequency of 2.1 kHz averaged 44 dB RMS SPL (range 39-47 dB RMS SPL). The similarity between thresholds for advertisement calling and auditory thresholds for the advertisement call indicates that male P. thaul use the full extent of their auditory sensitivity in acoustic interactions, likely an evolutionary adaptation allowing chorusing activity in low-density aggregations.

[Geometry of living systems and its importance in Medicine]. / Geometría de los sistemas vivos y su importancia en Medicina.

We analyze the most relevant concepts about complexity of sciences, showing examples and consequences in medical sciences. In the first section we introduce some basic concepts about fractals and its relationship with the geometry of nature and chaos dynamics. We also introduce notions of critic systems, the role of energy in them and we propose a conceptual model for living systems. In this model we identify the non-linear dynamics as the dynamics of the living forms and fractals as the form resulting from that dynamics. In the second section we review medical and biological examples: infectious diseases, cardiovascular and behavior dynamics, from which useful concepts and medical hypotheses emerge. One of the most important concepts, is the proposition that homeostasis would have an irregular dynamic. Then, we could expect that healthy individuals should be characterized by irregular dynamics, but old or sick individuals would change, probably decreasing the complexity of its dynamics. Therefore, we ask ourselves if the use of therapies to obtain a constant internal medium can be a mistake.

Geometría de los sistemas vivos y su importancia en Medicina / Geometry of living systems and its importance in Medicine

We analyze the most relevant concepts about complexity of sciences, showing examples and consequences in medical sciences. In the first section we introduce some basic concepts about fractals and its relationship with the geometry of nature and chaos dynamics. We also introduce notions of critic systems, the role of energy in them and we propose a conceptual model for living systems. In this model we identify the non-linear dynamics as the dynamics of the living forms and fractals as the form resulting from that dynamics. In the second section we review medical and biological examples: infectious diseases, cardiovascular and behavior dynamics, from which useful concepts and medical hypotheses emerge. One of the most important concepts, is the proposition that homeostasis would have an irregular dynamic. Then, we could expect that healthy individuals should be characterized by irregular dynamics, but old or sick individuals would change, probably decreasing the complexity of its dynamics. Therefore, we ask ourselves if the use of therapies to obtain a constant internal medium can be a mistake.

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