日本には約110種の蚊が産する。その中で医学的に重要なのは, 幼虫(ボウフラ)が人里近くの水域に発生し, 雌成虫がヒトから好んで吸血する種である。西日本ではアカイエカ(南西諸島ではネッタイイエカにおきかわる), チカイエカ, コガタアカイエカ, ヒトスジシマカなどが最も重要である。これらの種は生態がことなるので, その被害に対する効果的対策もことなる。雌成虫が吸血源となる動物を発見して完了するまでの過程は複雑で, わかつていない点もある。

Biology of mosquitoes.

The ecology of mosquito vectors and malaria parasites affect the incidence, seasonal transmission and geographical range of malaria. Most malaria models to date assume constant or linear responses of mosquito and parasite life-history traits to temperature, predicting optimal transmission at 31 °C. These models are at odds with field observations of transmission dating back nearly a century. We build a model with more realistic ecological assumptions about the thermal physiology of insects. Our model, which includes empirically derived nonlinear thermal responses, predicts optimal malaria transmission at 25 ° C( 6°C lower than previous models). Moreover, the model predicts that transmission decreases dramatically at temperatures > 28 °C, altering predictions about how climate change will affect malaria. A large data set on malaria transmission risk in Africa validates both the 25 °C optimum and the decline above 28 °C. Using these more accurate nonlinear thermal-response models will aid in understanding the effects of current and future temperature regimes on disease transmission.

/pdf/optimal-temperature-for-malaria-transmission-is-dramatically-47ra14blcf.pdf

Optimal temperature for malaria transmission is dramatically lower than previously predicted.

Recent field studies have suggested that the dynamics of West Nile virus (WNV) transmission are influenced strongly by a few key super spreader bird species that function both as primary blood hosts of the vector mosquitoes (in particular Culex pipiens) and as reservoir-competent virus hosts. It has been hypothesized that human cases result from a shift in mosquito feeding from these key bird species to humans after abundance of the key birds species decreases. To test this paradigm, we performed a mosquito blood meal analysis integrating host-feeding patterns of Cx. pipiens, the principal vector of WNV in the eastern United States north of the latitude 36 degrees N and other mosquito species with robust measures of host availability, to determine host selection in a WNV-endemic area of suburban Chicago, Illinois, during 2005-2007. Results showed that Cx. pipiens fed predominantly (83%) on birds with a high diversity of species used as hosts (25 species). American robins (Turdus migratorius) were marginally overused and several species were underused on the basis of relative abundance measures, including the common grackle (Quiscalus quiscula), house sparrow (Passer domesticus), and European starling (Sturnus vulgaris). Culex pipiens also fed substantially on mammals (19%; 7 species with humans representing 16%). West Nile virus transmission intensified in July of both years at times when American robins were heavily fed upon, and then decreased when robin abundance decreased, after which other birds species were selected as hosts. There was no shift in feeding from birds to mammals coincident with emergence of human cases. Rather, bird feeding predominated when the onset of the human cases occurred. Measures of host abundance and competence and Cx. pipiens feeding preference were combined to estimate the amplification fractions of the different bird species. Predictions were that approximately 66% of WNV-infectious Cx. pipiens became infected from feeding on just a few species of birds, including American robins (35%), blue jays (17%, Cyanocitta cristata), and house finches (15%, Carpodacus mexicanus).

https://www.vetmed.wisc.edu/WNV/publications/Hamer%20et%20al.%202009%20AJTMH.pdf

Host Selection by Culex pipiens Mosquitoes and West Nile Virus Amplification

Background: An increasing knowledge of the global risk of malaria shows that the nations of the Americas have the lowest levels of Plasmodium falciparum and P. vivax endemicity worldwide, sustained, in part, by substantive integrated vector control. To help maintain and better target these efforts, knowledge of the contemporary distribution of each of the dominant vector species (DVS) of human malaria is needed, alongside a comprehensive understanding of the ecology and behaviour of each species. Results: A database of contemporary occurrence data for 41 of the DVS of human malaria was compiled from intensive searches of the formal and informal literature. The results for the nine DVS of the Americas are described in detail here. Nearly 6000 occurrence records were gathered from 25 countries in the region and were complemented by a synthesis of published expert opinion range maps, refined further by a technical advisory group of medical entomologists. A suite of environmental and climate variables of suspected relevance to anopheline ecology were also compiled from open access sources. These three sets of data were then combined to produce predictive species range maps using the Boosted Regression Tree method. The predicted geographic extent for each of the following species (or species complex*) are provided: Anopheles (Nyssorhynchus) albimanus Wiedemann, 1820, An .( Nys.) albitarsis*, An .( Nys.) aquasalis Curry, 1932, An .( Nys.) darlingi Root, 1926, An .( Anopheles) freeborni Aitken, 1939, An .( Nys.) marajoara Galvao & Damasceno, 1942, An .( Nys.) nuneztovari*, An .( Ano.) pseudopunctipennis* and An .( Ano.) quadrimaculatus Say, 1824. A bionomics review summarising ecology and behaviour relevant to the control of each of these species was also compiled. Conclusions: The distribution maps and bionomics review should both be considered as a starting point in an ongoing process of (i) describing the distributions of these DVS (since the opportunistic sample of occurrence data assembled can be substantially improved) and (ii) documenting their contemporary bionomics (since intervention and control pressures can act to modify behavioural traits). This is the first in a series of three articles describing the distribution of the 41 global DVS worldwide. The remaining two publications will describe those vectors found in (i) Africa, Europe and the Middle East and (ii) in Asia. All geographic distribution maps are being made available in the public domain according to the open access principles of the Malaria Atlas Project.

/pdf/the-dominant-anopheles-vectors-of-human-malaria-in-the-2eb67sefgb.pdf

The dominant Anopheles vectors of human malaria in the Americas: Occurrence data, distribution maps and bionomic précis

The parasites that cause malaria depend on Anopheles mosquitoes for transmission; because of this, mosquito population dynamics are a key determinant of malaria risk. Development and survival rates of both the Anopheles mosquitoes and the Plasmodium parasites that cause malaria depend on temperature, making this a potential driver of mosquito population dynamics and malaria transmission. We developed a temperature-dependent, stage-structured delayed differential equation model to better understand how climate determines risk. Including the full mosquito life cycle in the model reveals that the mosquito population abundance is more sensitive to temperature than previously thought because it is strongly influenced by the dynamics of the juvenile mosquito stages whose vital rates are also temperature-dependent. Additionally, the model predicts a peak in abundance of mosquitoes old enough to vector malaria at more accurate temperatures than previous models. Our results point to the importance of incorporating detailed vector biology into models for predicting the risk for vector borne diseases.

/pdf/the-effect-of-temperature-on-anopheles-mosquito-population-447llajka8.pdf

The Effect of Temperature on Anopheles Mosquito Population Dynamics and the Potential for Malaria Transmission

Objective: To define the insecticide resistance status of Triatoma infestans to deltamethrin (pyrethroid), malathion (organophosphate) and bendiocarb (carbamate) in Bolivia. 

Methods: Fifty populations of T. infestans were sampled in Bolivian human dwellings. Quantal response data were obtained by topical applications of 0.2 mu l of insecticide-acetone solutions on nymphs N1 of the F1 generations. For most populations, dose-mortality relationships and resistance ratios (RR) were analysed. Discriminating concentrations were established for each insecticide with a susceptible reference strain and used on the other field populations. A tarsal-contact diagnostic test using insecticide impregnated papers was designed to rapidly identify deltamethrin-resistant populations in the field. 

Results Discriminating concentrations for topical applications were 5, 70 and 120 ng active ingredient per insect for deltamethrin, bendiocarb and malathion, respectively. The diagnostic concentration for deltamethrin was 0.30% for the 1-h exposure by tarsal contact. All populations sampled in human dwellings exhibited significant levels of resistance to deltamethrin, from 6 to 491 and varied among regions. Resistant populations did not recover complete susceptibility to deltamethrin when the synergist piperonyl butoxide (PBO) was used. None of the sampled populations exhibited significant resistance to bendiocarb (all RR50 < 1.8) or malathion (all RR50 < 2.2). 

Conclusion In Bolivia, most 'domestic'T. infestans populations are resistant to deltamethrin. Because insecticide vector control is the only selection pressure, resistance likely originates from it. Switching from pyrethroids to organophosphates or carbamates could be a short-term solution to control this vector, but other alternative integrated control strategies should also be considered in the long term.

https://hal.archives-ouvertes.fr/hal-01254858/document

Insecticide resistance of Triatoma infestans (Hemiptera, Reduviidae) vector of Chagas disease in Bolivia.

The length of the gonotrophic cycle varies the vectorial capacity of a mosquito vector and therefore its exact estimation is important in epidemiological modelling. Because the gonotrophic cycle length depends on temperature, its estimation can be satisfactorily computed by means of physiological time analysis. A model of physiological time was developed and calibrated for Anopheles pseudopunctipennis, one of the main malaria vectors in South America, using data from laboratory temperature controlled experiments. The model was validated under varying temperatures and could predict the time elapsed from blood engorgement to oviposition according to the temperature. In laboratory experiments, a batch of An. pseudopunctipennis fed at the same time may lay eggs during several consecutive nights (2–3 at high temperature and > 10 at low temperature). The model took into account such pattern and was used to predict the range of the gonotrophic cycle duration of An. pseudopunctipennis in four characteristic sites of Bolivia. It showed that the predicted cycle duration for An. pseudopunctipennis exhibited a seasonal pattern, with higher variances where climatic conditions were less stable. Predicted mean values of the (minimum) duration ranged from 3.3 days up to > 10 days, depending on the season and the geographical location. The analysis of ovaries development stages of field collected biting mosquitoes indicated that the phase 1 of Beklemishev might be of significant duration for An. pseudopunctipennis. The gonotrophic cycle length of An. pseudopunctipennis correlates with malaria transmission patterns observed in Bolivia which depend on locations and seasons. A new presentation of cycle length results taking into account the number of ovipositing nights and the proportion of mosquitoes laying eggs is suggested. The present approach using physiological time analysis might serve as an outline to other similar studies and allows the inclusion of temperature effects on the gonotrophic cycle in transmission models. However, to better explore the effects of temperature on malaria transmission, the others parameters of the vectorial capacity should be included in the analysis and modelled accordingly.

/pdf/a-physiological-time-analysis-of-the-duration-of-the-7rgi4en2az.pdf

A physiological time analysis of the duration of the gonotrophic cycle of Anopheles pseudopunctipennis and its implications for malaria transmission in Bolivia.

Background
The Human Blood Index (HBI, proportion of bloodmeals of a mosquito population obtained from man) is relevant to epidemiological assessment and to the modification of measures to interrupt malaria transmission since the vectorial capacity of the vector varies as the square of the HBI Anopheles pseudopunctipennis is a main malaria vector in South America Unfortunately, few data exist concerning HBI values in its range of distribution and none from Bolivia where this species is considered as an important malaria vector in the central Andes

/pdf/host-choice-and-human-blood-index-of-anopheles-1k2wzlfehp.pdf

Host choice and human blood index of Anopheles pseudopunctipennis in a village of the Andean valleys of Bolivia

Bolivia is a high-endemic country for Chagas disease, for which the principal vector is Triatoma infestans (Triatominae). This is a mainly domestic species that is also found in the wild environment. Recently, an increasing number of studies have shown the importance of Triatominae resistance to insecticides, especially in Bolivia. Data regarding the susceptibility/resistance of wild and domestic populations of T. infestans to deltamethrin are presented. For the first time, domestic populations of the department of Santa Cruz were tested, showing low resistance. Although most of the wild populations were found to be susceptible to deltamethrin, three populations from three departments showed a mortality rate of less than 100%. This result is emphasised here.

/pdf/susceptibility-and-resistance-to-deltamethrin-of-wild-and-3diwa8gg1r.pdf

Susceptibility and resistance to deltamethrin of wild and domestic populations of Triatoma infestans (Reduviidae: Triatominae) in Bolivia: new discoveries

Background: Triatoma infestans is the main vector of Chagas disease in the southern cone countries. Present control
strategies based on indoor and outdoor residual insecticide spraying are not sufficient to control disease
transmission, particularly in Bolivia. Techniques based on the management of the human environment may
be good alternatives or supplements.
Methods: Social and entomological surveys were carried out in four villages of Bolivia situated in the dry inter-
Andean Valleys and the Chaco region. Risk factors for house infestation by T. infestanswere identified, and an ecohealth
intervention based on education and community participation was carried out to reduce the risks of house
infestation. It consisted of implementing simple and low cost vector control techniques such as coating of mud
walls, cleaning activities and removal of poultry that enter rooms to lay eggs.
Results: The eco-health intervention significantly reduced the number of infested bedrooms, the mean abundance
of T. infestans in bedrooms and beds, especially in the Chaco region. Mud wall coating was well accepted
and could be proposed as a supplementary tool to the National Program of Chagas Disease Control to enhance
the effects of insecticide sprayings.
Conclusions: Even if cleaning activities were still neglected, community participation proved to be effective in
reducing house infestation.

https://hal.archives-ouvertes.fr/hal-01251517/document

Tamara Chavez

Papers

Insecticide resistance of Triatoma infestans (Hemiptera, Reduviidae) vector of Chagas disease in Bolivia.

A physiological time analysis of the duration of the gonotrophic cycle of Anopheles pseudopunctipennis and its implications for malaria transmission in Bolivia.

Host choice and human blood index of Anopheles pseudopunctipennis in a village of the Andean valleys of Bolivia

Susceptibility and resistance to deltamethrin of wild and domestic populations of Triatoma infestans (Reduviidae: Triatominae) in Bolivia: new discoveries

Experimental control of Triatoma infestans in poor rural villages of Bolivia through community participation.