Inferring distributional shifts of epidemiologically important North and Central American sandflies from Pleistocene to future scenarios.

Nine sandfly species (Diptera: Psychodidae) are suspected or proven vectors of Leishmania spp. in the North and Central America region. The ecological niches for these nine species were modelled in three time periods and the overlaps for all time periods of the geographic predictions (G space), and of ecological dimensions using pairwise comparisons of equivalent niches (E space), were calculated. Two Nearctic, six Neotropical and one species in both bioregions occupied a reduced number of distribution areas. The ecological niche projections for most sandfly species other than Lutzomyia shannoni and Lutzomyia ovallesi have not expanded significantly since the Pleistocene. Only three species increase significantly to 2050, whereas all others remain stable. Lutzomyia longipalpis shared a similar ecological niche with more species than any other, although both L. longipalpis and Lutzomyia olmeca olmeca had conserved distributions over time. Climate change, at both regional and local levels, will play a significant role in the temporal and spatial distributions of sandfly species.

Impact of climate change on vector transmission of Trypanosoma cruzi (Chagas, 1909) in North America.

Climate change can influence the geographical range of the ecological niche of pathogens by altering biotic interactions with vectors and reservoirs. The distributions of 20 epidemiologically important triatomine species in North America were modelled, comparing the genetic algorithm for rule-set prediction (GARP) and maximum entropy (MaxEnt), with or without topographical variables. Potential shifts in transmission niche for Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) (Chagas, 1909) were analysed for 2050 and 2070 in Representative Concentration Pathway (RCP) 4.5 and RCP 8.5. There were no significant quantitative range differences between the GARP and MaxEnt models, but GARP models best represented known distributions for most species [partial-receiver operating characteristic (ROC) > 1]; elevation was an important variable contributing to the ecological niche model (ENM). There was little difference between niche breadth projections for RCP 4.5 and RCP 8.5; the majority of species shifted significantly in both periods. Those species with the greatest current distribution range are expected to have the greatest shifts. Positional changes in the centroid, although reduced for most species, were associated with latitude. A significant increase or decrease in mean niche elevation is expected principally for Neotropical 1 species. The impact of climate change will be specific to each species, its biogeographical region and its latitude. North American triatomines with the greatest current distribution ranges (Nearctic 2 and Nearctic/Neotropical) will have the greatest future distribution shifts. Significant shifts (increases or decreases) in mean elevation over time are projected principally for the Neotropical species with the broadest current distributions. Changes in the vector exposure threat to the human population were significant for both future periods, with a 1.48% increase for urban populations and a 1.76% increase for rural populations in 2050.

Behavioural and electrophysiological responses of Triatoma dimidiata nymphs to conspecific faecal volatiles.

The behavioural and electrophysiological (electroantennography) responses of the first two instars of Triatoma dimidiata (Hemiptera: Reduviidae) Latreille to fresh and dry faecal headspace volatile extracts from fifth instar conspecific nymphs and synthetic compounds were analysed in this study. Recently emerged nymphs (3-5 days) aggregated around filter paper impregnated with dry faeces and around filter paper impregnated with extracts from both fresh and dry faeces. Older first instars (10-15 days) and second instars aggregated around filter paper impregnated with fresh and dry faeces, and their respective headspace extracts. Dry faecal volatile extracts elicited the strongest antennal responses, followed by fresh faecal extracts. Gas chromatography-mass spectrometry analysis of dried faecal headspace volatiles demonstrated the presence of 12 compounds: 2-ethyl-1-hexanol, 1,2,4-trimethylbenzene, n-octadecane, n-nonadecane, n-eicosane, n-heneicosane, n-tricosane, n-pentaeicosane, n-hexaeicosane, n-octaeicosane, nonanal, and 4-methyl quinazoline. In fresh faecal headspace extracts, only nonanal was clearly detected, although there were other trace compounds, including several unidentified sesquiterpenes. Four of the 11 compounds tested individually elicited aggregation behaviour at concentrations of 100 ng/µL and 1 µg/µL. A blend containing these four components also mediated the aggregation of nymphs. These volatiles may be valuable for developing monitoring methods and designing sensitive strategies to detect and measure T. dimidiata infestation.

Towards a paradigm shift in the treatment of chronic Chagas disease.

Treatment for Chagas disease with currently available medications is recommended universally only for acute cases (all ages) and for children up to 14 years old. The World Health Organization, however, also recommends specific antiparasite treatment for all chronic-phase Trypanosoma cruzi-infected individuals, even though in current medical practice this remains controversial, and most physicians only prescribe palliative treatment for adult Chagas patients with dilated cardiomyopathy. The present opinion, prepared by members of the NHEPACHA network (Nuevas Herramientas para el Diagnóstico y la Evaluación del Paciente con Enfermedad de Chagas/New Tools for the Diagnosis and Evaluation of Chagas Disease Patients), reviews the paradigm shift based on clinical and immunological evidence and argues in favor of antiparasitic treatment for all chronic patients. We review the tools needed to monitor therapeutic efficacy and the potential criteria for evaluation of treatment efficacy beyond parasitological cure. Etiological treatment should now be mandatory for all adult chronic Chagas disease patients.

Volatile compounds emitted by Triatoma dimidiata, a vector of Chagas disease: chemical analysis and behavioural evaluation.

In this study, we evaluated the responses of Triatoma dimidiata Latreille (Hemiptera: Reduviidae) to volatiles emitted by conspecific females, males, mating pairs and metasternal gland (MG) extracts with a Y-tube olfactometer. The volatile compounds released by mating pairs and MGs of T. dimidiata were identified using solid-phase microextraction and coupled gas chromatography-mass spectrometry (GC-MS). Females were not attracted to volatiles emitted by males or MG extracts; however, they preferred clean air to their own volatiles or those from mating pairs. Males were attracted to volatiles emitted by males, females, mating pairs, pairs in which the male had the MG orifices occluded or MG extracts of both sexes. However, males were not attracted to volatiles emitted by pairs in which the female had the MG orifices occluded. The chemical analyses showed that 14 and 15 compounds were detected in the headspace of mating pairs and MG, respectively. Most of the compounds identified from MG except for isobutyric acid were also detected in the headspace of mating pairs. Both females and males were attracted to octanal and 6-methyl-5-hepten-2-one, and males were attracted to 3,5-dimethyl-2-hexanol. Males but not females were attracted to a seven-compound blend, formulated from compounds identified in attractive MG extracts.

Fully integrated glass microfluidic device for performing high-efficiency capillary electrophoresis and electrospray ionization mass spectrometry.

A microfabricated device has been developed in which electrospray ionization is performed directly from the corner of a rectangular glass microchip. The device allows highly efficient electrokinetically driven separations to be coupled directly to a mass spectrometer (MS) without the use of external pressure sources or the insertion of capillary spray tips. An electrokinetic-based hydraulic pump is integrated on the chip that directs eluting materials to the monolithically integrated spray tip. A positively charged surface coating, PolyE-323, is used to prevent surface interactions with peptides and proteins and to reverse the electroosmotic flow in the separation channel. The device has been used to perform microchip CE-MS analysis of peptides and proteins with efficiencies over 200,000 theoretical plates (1,000,000 plates/m). The sensitivity and stability of the microfabricated ESI source were found to be comparable to that of commercial pulled fused-silica capillary nanospray sources.

Fine-scale predictions of distributions of Chagas disease vectors in the state of Guanajuato, Mexico.

One of the most daunting challenges for Chagas disease surveillance and control in Mexico is the lack of community level data on vector distributions. Although many states now have assembled representative domestic triatomine collections, only two triatomine specimens had been collected and reported previously from the state of Guanajuato. Field personnel from the state's Secretaría de Salud conducted health promotion activities in 43 of the 46 counties in the state and received donations of a total of 2,522 triatomine specimens between 1998 and 2002. All specimens were identified, and live insects examined for Trypanosoma cruzi. In an effort to develop fine-scale distributional data for Guanajuato, collection localities were georeferenced and ecological niches were modeled for each species by using evolutionary-computing approaches. Five species were collected: Triatoma mexicana (Herrich-Schaeffer), Triatoma longipennis (Usinger), Triatoma pallidipennis (Stål), Triatoma barberi (Usinger), and Triatoma dimidiata (Latreille) from 201 communities located at elevations of 870-2,200 m. Based on collection success, T. mexicana had the broadest dispersion, although niche mapping indicates that T. barberi represents the greatest risk for transmission of Chagas disease in the state. T. dimidiata was represented in collections by a single adult collected from one village outside the predicted area for all species. For humans, an estimated 3,755,380 individuals are at risk for vector transmission in the state, with an incidence of 3,500 new cases per year; overall seroprevalences of 2.6% indicate that 97,640 individuals are infected with T. cruzi at present, including 29,300 chronic cases.

Medical drug utilization patterns for febrile patients in rural areas of Mexico.

The objective of this study was to evaluate the medication pattern of febrile patients and determine what proportion of these drugs were included in the Mexican Essential Drugs List. A cross-sectional study was conducted in 32 rural communities located in malarial endemic areas near the Mexico-Guatemala border. Of 817 febrile patients interviewed, 55% self-medicated, while 16% consulted a physician. The most frequently used drugs were antipyretics (68%), antibiotics (25%), and antimalarial drugs (37%), despite the fact that only 2% of all febrile patients were diagnosed with malaria. Antipyrine, acetylsalicylic acid, and acetaminophen represented 84% of antipyretics, and ampicillin, penicillin, and sulfadiazine-trimethoprim represented 51% of total antibiotics. Public health service and self-medicating patients used essential drugs (antipyretics and antibiotics) significantly more than those consulting private physicians. These findings demonstrate the need to foster access to primary health care (PHC) facilities, rational drug prescription by private physicians, and to review guidelines for prescription of antimalarial drugs for febrile patients.

Acquired transmission-blocking immunity to Plasmodium vivax in a population of southern coastal Mexico.

Naturally acquired transmission-blocking immunity to Plasmodium vivax was studied in three groups of patients from the southern coast of Mexico: primary cases (Group A, 61% of the study population), secondary cases with the prior infection seven or more months earlier (Group B, 23%), and secondary cases with the previous malaria experience within six months of the present study (Group C, 16%). Anopheles albimanus mosquitoes were fed with patients' infected blood cells in the presence of autologous or control serum, with or without heat-inactivation. Patients from all three groups had transmission-blocking immunity, although the quality and quantity of this blocking activity was significantly higher in the two secondary patient groups (B and C). Only primary malaria cases produced transmission-enhancing activity (23% of the cases), which was dependent on heat-labile serum components. The levels of patient group transmission-blocking immunity and mosquito infectivity were used to calculate the probabilities of a mosquito becoming infective after taking a blood meal from a P. vivax-infected patient from any one of the three groups. This probability was 0.025, with Group A patients providing the major source of these infections (92% risk from Group A and 4% risk for Groups B and C).

Field trial in Chiapas, Mexico, of a rapid detection method for malaria in anopheline vectors with low infection rates.

A method consisting of filtration of up to 100 macerated mosquitoes in a batch, followed by fixation with glutaraldehyde and concentration of filtrate by centrifugation has been developed to rapidly assess malaria infection in anopheline mosquitoes. Determination of the presence of sporozoites is made by observation of a sample of the final filtrate with a phase microscope. The method is simple and field adaptable, essential factors for the application of any technique to large scale field operations. Application of the technique in El Gancho, Chiapas, Mexico, in February 1984 yielded an infection rate for Anopheles albimanus of 0.9% for intradomicile-collected human bait mosquitoes and 0.1% for peridomicile-collected human bait mosquitoes.

Specific identification of Plasmodium sporozoites using an indirect fluorescent antibody method.

The specific identification of plasmodial sporozoites is not possible on morphological grounds. This study presents a serological method for the identification of sporozoite species, indicating the suitability of this approach for detection and determination of sporozoites in wild vectors collected from malaria endemic areas. Specific antisera and monoclonal antibodies prepared against each of two species of rodent malaria (Plasmodium berghei or P. yoelii) were evaluated for their ability to discriminate among sporozoites of different malaria species (P. vivax, P. gallinaceum, P. berghei, P. yoelii) from varied host types. Antisera produced by intravenous immunization of rabbits or mice and hybridoma-produced monoclonal antibodies reacted only with homologous sporozoites in an immunofluorescent antibody test. Antisera produced by intravenous challenge showed no significant difference in reactivity with fresh sporozoites as compared with sporozoites frozen at -80 degrees C for up to six months, whereas antisera produced by infective mosquito bites showed reduced sensitivity to frozen-stored homologous sporozoites and some cross-reactions with heterologous sporozoites. Antisera prepared against the erythrocytic stages of P. berghei or P. yoelii also cross-reacted with sporozoites of all four plasmodia tested, indicating that it is advantageous to use anti-sporozoite antibodies for the identification of malaria sporozoite species by means of serological tests.

Novel microfabricated device for electrokinetically induced pressure flow and electrospray ionization mass spectrometry.

A novel microchip device for electrospray ionization has been fabricated and interfaced to a time-of-flight mass spectrometer. Fluid is electrokinetically transported through the chip to a fine fused-silica capillary inserted directly into a channel at the edge of the device. Electrospray is established at the tip of the capillary, which assures a stable, efficient spray. The electric potential necessary for electrospray generation and the voltage drop for electroosmotic pumping are supplied through an electrically permeable glass membrane contacting the fluidic channel holding the capillary. The membrane is fabricated on the microchip using standard photolithographic and wet chemical etching techniques. Performance relative to other microchip electrospray sources has been evaluated and the device tested for potential use as a platform for on-line electrophoretic detection. Sensitivity was found to be approximately three orders of magnitude better than spraying from the flat edge of the chip. The effect of the capillary on electroosmotic flow was examined both experimentally and theoretically.

Wide-bandwidth analog correlator and its application to mode-locked laser measurements.

A new instrument for the analog determination of correlation functions of wide-bandwidth signals is described and characterized. The instrument is comprised of microwave electronic components; a double-balanced mixer performs the multiplication operation involved in the correlation process, whereas a constant-impedance line stretcher introduces the variable delay. Measurements indicate that the correlator has a bandwidth of approximately 3 GHz. It is shown that this inexpensive and simple device can be used as a diagnostic tool for mode-locked argon-ion lasers when used in conjunction with a fast photodiode detector.

Effects of transmission-blocking immunity on Plasmodium vivax infections in Anopheles albimanus populations.

Two colonized populations of Anopheles albimanus isolated from the Suchiate region, Chiapas State, Mexico, were compared for their susceptibility to coindigenous Plasmodium vivax. Groups of mosquitoes were fed in vitro with either autologous donor blood or the same blood cells substituted with serum negative for anti-gametocyte antibody. Significant differences in susceptibility between the 2 colonies were encountered if the autologous blood from a patient was fed to mosquitoes: mean infection rates of AnA2-positive groups was double that in AnA1 mosquitoes. Consistent for both colonies, only 23.6% of samples positive from malaria-negative serum-substituted blood were infected with an autologous blood feed. Vector competence in these mosquito populations was partially linked to the human populations's immune response to the parasite.

Plasmodium vivax sporozoite rates from Anopheles albimanus in southern Chiapas, Mexico.

Anopheles albimanus mosquitoes were collected from August 1984 to November 1987 on intra- and peridomicile human bait in Rancheria El Gancho, Chiapas, Mexico. The mosquitoes were desiccated and stored in silicon chambers from 3 mo to 3 yr post-collection prior to being assayed using a direct enzyme-linked immunosorbent assay to detect Plasmodium vivax predominant-type sporozoite protein. Peridomicile-collected mosquitoes had a 10-fold higher sporozoite rate than those collected indoors, but only the latter correlate significantly with the seasonal human parasite index. Mosquito sporozoite burden was also significantly higher in the peridomicile-collected population.

Laboratory oviposition, fecundity and egg hatching ability of colonized Anopheles albimanus from southwestern Mexico.

Fecundity, oviposition patterns and egg hatching characteristics were studied in two colonies of Anopheles albimanus isolated from the Pacific coast of southern Mexico. Fecundity was inversely proportional to the cage space available to the female and was influenced by the bloodmeal source, feeding method and previous feeding history. The length of the gonotrophic cycle decreased with succeeding experience from a mean 6.6 in the first to 2.6 days for the fifth cycle. Oviposition timing was also dependent on availability of oviposition substrate. Hatching success of eggs increased significantly when the oviposition site was witheld until 48 hr post-bloodmeal.

Assessing the impact of density dependence in field populations of Aedes aegypti.

Although many laboratory studies of intra-specific competition have been conducted with Ae. aegypti, there have been few studies in natural environments and none that examined density dependence in natural containers at normal field densities. Additionally, current mathematical models that predict Ae. aegypti population dynamics lack empirically-based functions for density-dependence. We performed field experiments in Tapachula, Mexico, where dengue is a significant public health concern. Twenty-one containers with natural food and water that already contained larvae were collected from local houses. Each container was divided in half and the naturally occurring larvae were apportioned in a manner that resulted in one side of the container (high density) having four times the density of the second side (low density). Larvae were counted and pupae were removed daily. Once adults emerged, wing span was measured to estimate body size. Density had a significant impact on larval survival, adult body size, and the time taken to transition from 4(th) instar to pupation. Increased density decreased larval survival by 20% and decreased wing length by an average of 0.19 mm. These results provide a starting point for a better understanding of density dependence in field populations of Ae. aegypti.