Machine learning approach as an early warning system to prevent foodborne Salmonella outbreaks in northwestern Italy.

Salmonellosis, one of the most common foodborne infections in Europe, is monitored by food safety surveillance programmes, resulting in the generation of extensive databases. By leveraging tree-based machine learning (ML) algorithms, we exploited data from food safety audits to predict spatiotemporal patterns of salmonellosis in northwestern Italy. Data on human cases confirmed in 2015-2018 (n = 1969) and food surveillance data collected in 2014-2018 were used to develop ML algorithms. We integrated the monthly municipal human incidence with 27 potential predictors, including the observed prevalence of Salmonella in food. We applied the tree regression, random forest and gradient boosting algorithms considering different scenarios and evaluated their predictivity in terms of the mean absolute percentage error (MAPE) and R2. Using a similar dataset from the year 2019, spatiotemporal predictions and their relative sensitivities and specificities were obtained. Random forest and gradient boosting (R2 = 0.55, MAPE = 7.5%) outperformed the tree regression algorithm (R2 = 0.42, MAPE = 8.8%). Salmonella prevalence in food; spatial features; and monitoring efforts in ready-to-eat milk, fruits and vegetables, and pig meat products contributed the most to the models' predictivity, reducing the variance by 90.5%. Conversely, the number of positive samples obtained for specific food matrices minimally influenced the predictions (2.9%). Spatiotemporal predictions for 2019 showed sensitivity and specificity levels of 46.5% (due to the lack of some infection hotspots) and 78.5%, respectively. This study demonstrates the added value of integrating data from human and veterinary health services to develop predictive models of human salmonellosis occurrence, providing early warnings useful for mitigating foodborne disease impacts on public health.

Hazard perception and possibility of simplifying food safety management systems in small businesses in Piedmont region, Italy.

Small food businesses, because of their limited resources, are hard pressed to comply with the requirements of a conventional food safety management system (FSMS). To overcome it, the European legislation provides some flexibility in the application of FSMS. With this study, we evaluated the change in the perception and awareness of hazards in food production and in the attitudes of food business operators (FBOs) after a regional regulation was introduced to allow flexibility and a campaign of training activities on the FSMS simplification opportunities. Training activities targeting various stakeholders have been carried out in Piedmont region since 2014. A total of 283 FBOs from the dairy and the meat supply chains were recruited for a two-round survey. Overall, the majority of the FBOs believed that application of an FSMS helps to overcome official controls, to produce healthy foods, to better manage the production process, and for staff training; its usefulness for enhancing customer trust was judged of limited value. FBO knowledge on the possibility of simplifying the FSMS activities increased significantly between surveys, suggesting the success of the information campaigns. Over time, simplification increased in the meat but not in the dairy supply chain, where it involved nearly 70% of FBOs. The cost of FSMS (mainly due to microbiological analysis) and the time it takes were the main reasons for FBO resistance to its application. Simplification of FSMS procedures were welcomed by the vast majority (>90%) of FBOs. The perception of hazards was low and generic, suggesting the need for targeted training activities.

Analysis of the environmental and host-related factors affecting the distribution of the tick Dermacentor marginatus.

Understanding and responding to the ecological, social and economic conditions that facilitate disease emergence and transmission represents a substantial challenge for epidemiologists and health professionals. In this article we integrate knowledge about the human and the vector population, to provide a context from which to examine the underlying causal factors of D. marginatus-borne diseases emergence in the study area. Within this framework we analyse the biotic and abiotic factors that drive D. marginatus population dynamics and the role of its typical host for dispersal. These investigations suggest that D. marginatus is a tick species prone to spatially overlap its presence with human population presence. Then we consider the public health implications for the residents, when simply carrying out trivial outdoor activities may increase the risk to contact an infected tick.

Presence of host-seeking Ixodes ricinus and their infection with Borrelia burgdorferi sensu lato in the Northern Apennines, Italy.

Host-seeking ticks were collected in the Northern Apennines, Italy, by dragging at 35 sites, at altitudes ranging from 680 and 1670 m above sea level (asl), from April to November, in 2010 and 2011. Ixodes ricinus (4431 larvae, 597 nymphs and 12 adults) and Haemaphysalis punctata (11,209 larvae, 313 nymphs, and 25 adults) were the most abundant species, followed by Haemaphysalis sulcata (20 larvae, five nymphs, and 13 adults), Dermacentor marginatus (42 larvae and two adults) and Ixodes hexagonus (one nymph). Greatest numbers of ticks were collected at locations characterised by southern exposure and limestone substratum, at altitudes <1400 m asl; I. ricinus was most abundant in Turkey oak (Quercus cerris) wood, whereas H. punctata was mostly collected in hop hornbeam (Ostrya carpinifolia) wood and on exposed rocks. Ixodes ricinus was also found up to 1670 m asl, in high stand beech (Fagus sylvatica) wood. The overall prevalence of Borrelia burgdorferi sensu lato (sl) in 294 host-seeking I. ricinus nymphs was 8.5 %. Borrelia garinii was the most frequently identified genospecies (64.0 % of positive nymphs), followed by B. valaisiana, B. burgdorferi sensu stricto, B. afzelii, and B. lusitaniae. Based upon the comparison with the results of previous studies at the same location, these research findings suggest the recent invasion of the study area by the tick vector and the agents of Lyme borreliosis.

Key source habitats and potential dispersal of triatoma infestans populations in Northwestern Argentina: implications for vector control.

BACKGROUND: Triatoma infestans -the principal vector of the infection that causes Chagas disease- defies elimination efforts in the Gran Chaco region. This study identifies the types of human-made or -used structures that are key sources of these bugs in the initial stages of house reinfestation after an insecticide spraying campaign. METHODOLOGY AND PRINCIPAL FINDINGS: We measured demographic and blood-feeding parameters at two geographic scales in 11 rural communities in Figueroa, northwest Argentina. Of 1,297 sites searched in spring, 279 (21.5%) were infested. Bug abundance per site and female fecundity differed significantly among habitat types (ecotopes) and were highly aggregated. Domiciles (human sleeping quarters) had maximum infestation prevalence (38.7%), human-feeding bugs and total egg production, with submaximal values for other demographic and blood-feeding attributes. Taken collectively peridomestic sites were three times more often infested than domiciles. Chicken coops had greater bug abundance, blood-feeding rates, engorgement status, and female fecundity than pig and goat corrals. The host-feeding patterns were spatially structured yet there was strong evidence of active dispersal of late-stage bugs between ecotopes. Two flight indices predicted that female fliers were more likely to originate from kitchens and domiciles, rejecting our initial hypothesis that goat and pig corrals would dominate. CONCLUSIONS AND SIGNIFICANCE: Chicken coops and domiciles were key source habitats fueling rapid house reinfestation. Focusing control efforts on ecotopes with human-fed bugs (domiciles, storerooms, goat corrals) would neither eliminate the substantial contributions to bug population growth from kitchens, chicken coops, and pig corrals nor stop dispersal of adult female bugs from kitchens. Rather, comprehensive control of the linked network of ecotopes is required to prevent feeding on humans, bug population growth, and bug dispersal simultaneously. Our study illustrates a demographic approach that may be applied to other regions and triatomine species for the design of innovative, improved vector control strategies.

Range expansion of Ixodes ricinus to higher altitude, and co-infestation of small rodents with Dermacentor marginatus in the Northern Apennines, Italy.

Immature ticks (Ixodes ricinus and Dermacentor marginatus) were collected from small rodents (Apodemus spp. and Myodes glareolus), in the Northern Apennines, Italy, at an altitude up to 1650 m above sea level (a.s.l.), from 2009 through 2012. While D. marginatus had been found at the same location in studies carried out in 1994, I. ricinus was very rare or absent. Prevalence (95% confidence interval) of infestation by I. ricinus larvae on Apodemus spp. was 54.4% (47.5, 61.2), and it was greater than prevalence of D. marginatus larvae on the same hosts (23.3%, 17.8, 29.5). The mean (standard deviation) numbers of I. ricinus and D. marginatus larvae per individual Apodemus spp. were similar: 2.3 (4.1) and 2.1 (9.8), respectively. The monthly infestation pattern of the two tick species on Apodemus spp. were different. I. ricinus larvae were more frequent in June and September, than in July-August. I. ricinus nymphs were generally rare, and were most frequently found in July. The prevalence of D. marginatus larvae peaked in July-August, whereas nymphs were mostly active in August-September. Increasing population densities of roe deer (Capreolus capreolus), and increasing temperatures, in the last decades, in the Apennine area might have contributed to the observed range expansion of I. ricinus.

Domestic animal hosts strongly influence human-feeding rates of the Chagas disease vector Triatoma infestans in Argentina.

BACKGROUND: The host species composition in a household and their relative availability affect the host-feeding choices of blood-sucking insects and parasite transmission risks. We investigated four hypotheses regarding factors that affect blood-feeding rates, proportion of human-fed bugs (human blood index), and daily human-feeding rates of Triatoma infestans, the main vector of Chagas disease. METHODS: A cross-sectional survey collected triatomines in human sleeping quarters (domiciles) of 49 of 270 rural houses in northwestern Argentina. We developed an improved way of estimating the human-feeding rate of domestic T. infestans populations. We fitted generalized linear mixed-effects models to a global model with six explanatory variables (chicken blood index, dog blood index, bug stage, numbers of human residents, bug abundance, and maximum temperature during the night preceding bug catch) and three response variables (daily blood-feeding rate, human blood index, and daily human-feeding rate). Coefficients were estimated via multimodel inference with model averaging. FINDINGS: Median blood-feeding intervals per late-stage bug were 4.1 days, with large variations among households. The main bloodmeal sources were humans (68%), chickens (22%), and dogs (9%). Blood-feeding rates decreased with increases in the chicken blood index. Both the human blood index and daily human-feeding rate decreased substantially with increasing proportions of chicken- or dog-fed bugs, or the presence of chickens indoors. Improved calculations estimated the mean daily human-feeding rate per late-stage bug at 0.231 (95% confidence interval, 0.157-0.305). CONCLUSIONS AND SIGNIFICANCE: Based on the changing availability of chickens in domiciles during spring-summer and the much larger infectivity of dogs compared with humans, we infer that the net effects of chickens in the presence of transmission-competent hosts may be more adequately described by zoopotentiation than by zooprophylaxis. Domestic animals in domiciles profoundly affect the host-feeding choices, human-vector contact rates and parasite transmission predicted by a model based on these estimates.

Habitat and occurrence of ixodid ticks in the Liguria region, northwest Italy.

Questing ticks were collected during monthly dragging sessions (March-August 2011) in three provinces of the Liguria region, north-western Italy, to evaluate the species occurrence, spatial distribution and relative abundance. A total of 1,464 specimens were collected in 94 dragging sites. Ixodes ricinus was the most abundant species (81.3 % of collected ticks), followed by Haemaphysalis punctata (10.9 %), Dermacentor marginatus (5.5 %), Ixodes frontalis (1.3 %), and Rhipicephalus spp. (0.9 %). Ixodes frontalis is reported for the first time in Liguria. An aggregation of I. ricinus positive sites was observed in inland areas characterized by dense forests dominated by deciduous trees (Castanetum and Fagetum phytoclimatic zones), especially in the west of the region where the differences in the Normalized Difference Vegetation Index (NDVI) were higher between inland and coastal sites. Random-effect logistic regression was used to model the associations of NDVI and season with the probability of finding host-seeking I. ricinus nymphs [corrected]. The NDVI was a good predictor of I. ricinus nymphs abundance, and confirmed its utility in discriminating habitat suitability for this vector in north-western coastal Italy, where dry habitat conditions may limit the distribution of this species.

Heterogeneities in the ecoepidemiology of Trypanosoma cruzi infection in rural communities of the Argentinean Chaco.

We conducted a cross-sectional survey of Trypanosoma cruzi infection of Triatoma infestans as well as dogs and cats in 327 households from a well-defined rural area in northeastern Argentina to test whether the household distribution of infection differed between local ethnic groups (Tobas and Creoles) and identify risk factors for host infection. Overall prevalence of infection of bugs (27.2%; 95% confidence interval = 25.3-29.3%), dogs (26.0%; 95% confidence interval = 23.3-30.1%), and cats examined (28.7%; 95% confidence interval = 20.2-39.0%) was similar. A multimodel inference approach showed that infection in dogs was associated strongly with the intensity and duration of local exposure to infected bugs and moderately with household ethnic background. Overall, Toba households were at a substantially greater risk of infection than Creole households. The strong heterogeneities in the distribution of bug, dog, and cat infections at household, village, and ethnic group levels may be used for targeted vector and disease control.

Trans-sialidase inhibition assay detects Trypanosoma cruzi infection in different wild mammal species.

The detection of Trypanosoma cruzi infection in mammals is crucial for understanding the eco-epidemiological role of the different species involved in parasite transmission cycles. Xenodiagnosis (XD) and hemoculture (HC) are routinely used to detect T. cruzi in wild mammals. Serological methods are much more limited because they require the use of specific antibodies to immunoglobulins of each mammalian species susceptible to T. cruzi. In this study we detected T. cruzi infection by trans-sialidase (TS) inhibition assay (TIA). TIA is based on the antibody neutralization of a recombinant TS that avoids the use of anti-immunoglobulins. TS activity is not detected in the co-endemic protozoan parasites Leishmania spp and T. rangeli. In the current study, serum samples from 158 individuals of nine wild mammalian species, previously tested by XD, were evaluated by TIA. They were collected from two endemic areas in northern Argentina. The overall TIA versus XD co-reactivity was 98.7% (156/158). All 18 samples from XD-positive mammals were TIA-positive (co-positivity, 100%) and co-negativity was 98.5% (138/140). Two XD-negative samples from a marsupial (Didelphis albiventris) and an edentate (Dasypus novemcinctus) were detected by TIA. TIA could be used as a novel tool for serological detection of Trypanosoma cruzi in a wide variety of sylvatic reservoir hosts.

Improved chemical control of Chagas disease vectors in the dry Chaco region.

The effectiveness of two doses of suspension concentrate (SC) pyrethroid insecticides in suppressing peridomestic populations of Triatoma infestans (Klug) was evaluated in 28 rural communities located in Santiago del Estero province, northwestern Argentina, including 388 houses and 1,516 identified sites. Four treatments were randomly assigned to peridomiciles within each community: 5% SC beta-cypermethrin at standard (S, 50 mg active ingredient [AI]/m2) and double dose (2S), and 2.5% SC deltamethrin at standard (D, 25 mg [AI]/m2) and double dose (2D). Simultaneously, we assessed the effects of both pyrethroids applied at standard doses against domestic infestations. Bug infestation at the site level was assessed by timed manual collections with a dislodging agent at baseline, 13 and 21 mo postspraying (MPS). In domiciles, D and S nearly suppressed all T. infestans infestations up to 21 MPS. In peridomestic sites infested before interventions, multiple logistic regression analysis showed that site-level reinfestation at 13 MPS was significantly lower for treatment 2D (1%) than for other treatments, whereas 2S (6%), D (5%), and S (14%) did not differ significantly between them. The risk of reinfestation after spraying was significantly greater in goat or pig corrals than in other peridomestic ecotopes (in which treatments did not differ significantly), and in sites infested before interventions than in uninfested sites. The application of SC deltamethrin at double dose in goat or pig corrals may suppress T. infestans foci and achieve more sustained effects in the dry Chaco.

Hidden sylvatic foci of the main vector of Chagas disease Triatoma infestans: threats to the vector elimination campaign?

BACKGROUND: Establishing the sources of reinfestation after residual insecticide spraying is crucial for vector elimination programs. Triatoma infestans, traditionally considered to be limited to domestic or peridomestic (abbreviated as D/PD) habitats throughout most of its range, is the target of an elimination program that has achieved limited success in the Gran Chaco region in South America. METHODOLOGY/PRINCIPAL FINDINGS: During a two-year period we conducted semi-annual searches for triatomine bugs in every D/PD site and surrounding sylvatic habitats after full-coverage spraying of pyrethroid insecticides of all houses in a well-defined rural area in northwestern Argentina. We found six low-density sylvatic foci with 24 T. infestans in fallen or standing trees located 110-2,300 m from the nearest house or infested D/PD site detected after insecticide spraying, when house infestations were rare. Analysis of two mitochondrial gene fragments of 20 sylvatic specimens confirmed their species identity as T. infestans and showed that their composite haplotypes were the same as or closely related to D/PD haplotypes. Population studies with 10 polymorphic microsatellite loci and wing geometric morphometry consistently indicated the occurrence of unrestricted gene flow between local D/PD and sylvatic populations. Mitochondrial DNA and microsatellite sibship analyses in the most abundant sylvatic colony revealed descendents from five different females. Spatial analysis showed a significant association between two sylvatic foci and the nearest D/PD bug population found before insecticide spraying. CONCLUSIONS: Our study shows that, despite of its high degree of domesticity, T. infestans has sylvatic colonies with normal chromatic characters (not melanic morphs) highly connected to D/PD conspecifics in the Argentinean Chaco. Sylvatic habitats may provide a transient or permanent refuge after control interventions, and function as sources for D/PD reinfestation. The occurrence of sylvatic foci of T. infestans in the Gran Chaco may pose additional threats to ongoing vector elimination efforts.

Factors affecting infestation by Triatoma infestans in a rural area of the humid Chaco in Argentina: a multi-model inference approach.

BACKGROUND: Transmission of Trypanosoma cruzi by Triatoma infestans remains a major public health problem in the Gran Chaco ecoregion, where understanding of the determinants of house infestation is limited. We conducted a cross-sectional study to model factors affecting bug presence and abundance at sites within house compounds in a well-defined rural area in the humid Argentine Chaco. METHODOLOGY/PRINCIPAL FINDINGS: Triatoma infestans bugs were found in 45.9% of 327 inhabited house compounds but only in 7.4% of the 2,584 sites inspected systematically on these compounds, even though the last insecticide spraying campaign was conducted 12 years before. Infested sites were significantly aggregated at distances of 0.8-2.5 km. The most frequently infested ecotopes were domiciles, kitchens, storerooms, chicken coops and nests; corrals were rarely infested. Domiciles with mud walls and roofs of thatch or corrugated tarred cardboard were more often infested (32.2%) than domiciles with brick-and-cement walls and corrugated metal-sheet roofs (15.1%). A multi-model inference approach using Akaike's information criterion was applied to assess the relative importance of each variable by running all possible (17,406) models resulting from all combinations of variables. Availability of refuges for bugs, construction with tarred cardboard, and host abundance (humans, dogs, cats, and poultry) per site were positively associated with infestation and abundance, whereas reported insecticide use showed a negative association. Ethnic background (Creole or Toba) adjusted for other factors showed little or no association. CONCLUSIONS/SIGNIFICANCE: Promotion and effective implementation of housing improvement (including key peridomestic structures) combined with appropriate insecticide use and host management practices are needed to eliminate infestations. Fewer refuges are likely to result in fewer residual foci after insecticide spraying, and will facilitate community-based vector surveillance. A more integrated perspective that considers simultaneously social, economic and biological processes at local and regional scales is needed to attain effective, sustainable vector and disease control.

Strong host-feeding preferences of the vector Triatoma infestans modified by vector density: implications for the epidemiology of Chagas disease.

BACKGROUND: Understanding the factors that affect the host-feeding preferences of triatomine bugs is crucial for estimating transmission risks and predicting the effects of control tactics targeting domestic animals. We tested whether Triatoma infestans bugs prefer to feed on dogs vs. chickens and on dogs vs. cats and whether vector density modified host choices and other vital rates under natural conditions. METHODOLOGY: Two host choice experiments were conducted in small caged huts with two rooms between which bugs could move freely. Matched pairs of dog-chicken (six) and dog-cat (three) were assigned randomly to two levels of vector abundance and exposed to starved bugs during three nights. Bloodmeals from 1,160 bugs were tested by a direct enzyme-linked immunosorbent assay. PRINCIPAL FINDINGS: Conditional logistic regression showed that dogs were highly preferred over chickens or cats and that vector density modified host-feeding choices. The relative risk of a bug being blood-engorged increased significantly when it fed only on dog rather than chicken or cat. Bugs achieved higher post-exposure weight at higher vector densities and successive occasions, more so if they fed on a dog rather than on a cat. CONCLUSIONS: Our findings strongly refute the hypothesis that T. infestans prefers to blood-feed on chickens rather than dogs. An increase in dog or cat availability or accessibility will increase the rate of bug feeding on them and exert strong non-linear effects on R(0). When combined with between-dog heterogeneities in exposure, infection, and infectiousness, the strong bug preference for dogs can be exploited to target dogs in general, and even the specific individuals that account for most of the risk, with topical lotions or insecticide-impregnated collars to turn them into baited lethal traps or use them as transmission or infestation sentinels based on their immune response to Trypanosoma cruzi or bug salivary antigens.

Effects of topical application of fipronil spot-on on dogs against the Chagas disease vector Triatoma infestans.

We assessed the insecticidal effects of fipronil spot-on applied to experimental dogs on the blood-feeding success and other vital parameters of the Trypanosoma cruzi vector Triatoma infestans. In the first trial, the cumulative mortality of 30 third or fourth instar nymphs exposed to eight fipronil-treated dogs differed significantly from those exposed to untreated dogs at 1 week post-treatment, but not at baseline or at 2-6 weeks post-treatment. In the second trial, the effects of multiple exposures to fipronil-treated dogs on bug population dynamics were assessed. A population of 80-84 bugs of various life stages were allowed to colonize eight closed experimental huts, and then exposed twice weekly to control or treated dogs over a period of 110 days and censused at monthly intervals. Throughout the trial, multiple exposure to fipronil did not significantly affect bug population size, fecundity, hatching, molting, survival, blood-feeding success and degree of engorgement. Only when engorgement was taken to include only fully fed bugs, did fipronil significantly reduce their degree of engorgement relative to bugs exposed to control dogs. We conclude that at tested dosages fipronil spot-on would have little effect in controlling (peri)domestic Tri. infestans or protecting dogs from contact with the bugs.

Molecular epidemiology of domestic and sylvatic Trypanosoma cruzi infection in rural northwestern Argentina.

Genetic diversity of Trypanosoma cruzi populations and parasite transmission dynamics have been well documented throughout the Americas, but few studies have been conducted in the Gran Chaco ecoregion, one of the most highly endemic areas for Chagas disease, caused by T. cruzi. In this study, we assessed the distribution of T. cruzi lineages (identified by PCR strategies) in Triatoma infestans, domestic dogs, cats, humans and sylvatic mammals from two neighbouring rural areas with different histories of transmission and vector control in northern Argentina. Lineage II predominated amongst the 99 isolates characterised and lineage I amongst the six isolates obtained from sylvatic mammals. T. cruzi lineage IIe predominated in domestic habitats; it was found in 87% of 54 isolates from Tr. infestans, in 82% of 33 isolates from dogs, and in the four cats found infected. Domestic and sylvatic cycles overlapped in the study area in the late 1980s, when intense domestic transmission occurred, and still overlap marginally. The introduction of T. cruzi from sylvatic into domestic habitats is likely to occur very rarely in the current epidemiological context. The household distribution of T. cruzi lineages showed that Tr. infestans, dogs and cats from a given house compound shared the same parasite lineage in most cases. Based on molecular evidence, this result lends further support to the importance of dogs and cats as domestic reservoir hosts of T. cruzi. We believe that in Argentina, this is the first time that lineage IIc has been isolated from naturally infected domestic dogs and Tr. infestans.

Comparative trial of effectiveness of pyrethroid insecticides against peridomestic populations of Triatoma infestans in northwestern Argentina.

The effects of different pyrethroid insecticides, formulations, and doses on peridomestic populations of Triatoma infestans (Klug) were evaluated in 128 houses with 148 identified infested peridomestic sites in northwestern Argentina between October 2003 and March 2005. Four treatments were randomly assigned within each community: two doses of 5% suspension concentrate beta-cypermethrin in water applied with manual compression sprayers, the standard dose (S) at 50 mg and a double dose (2S) at 100 mg active ingredient (AI)/m2; and two emulsifiable concentrates diluted in diesel fuel and applied with power sprayers, 25% cypermethrin (100 mg [AI] /m2) (CF) and 10% permethrin (170 mg [AI]/m2) (DF). Infestation was assessed by timed manual collections with a dislodging agent at baseline, 5, 12, and 17 mo postspraying, and the sites found to be reinfested at 5 mo postspraying were selectively resprayed. Only 2S eliminated T. infestans from all peridomestic sites up to 12 mo postspraying, and it was significantly more effective than all other treatments. At 5 mo postspraying, more sites treated with CF or DF rather than S had bug colonies that probably represented residual foci, which they also failed in eliminating after a second spray. At 17 mo postspraying, the prevalence of reinfested peridomestic sites was 5% for 2S, 29% for S, 43% for CF, and 54% for DF. The application of suspension concentrate pyrethroids in dose twice as large as that currently in use in the attack phase produces a greater initial impact and may eliminate peridomestic populations of T. infestans.

A prospective study of the effects of sustained vector surveillance following community-wide insecticide application on Trypanosoma cruzi infection of dogs and cats in rural Northwestern Argentina.

Domestic dogs were used as natural sentinels to assess prospectively the long-term impact of selective, community-based spraying with pyrethroid insecticides after community-wide spraying on transmission of Trypanosoma cruzi in rural villages under surveillance between 1992 and 2002. In 2000 and 2002 light infestations by Triatoma infestans were recorded, and 523 dogs and cats were examined serologically or by xenodiagnosis. The prevalence of T. cruzi infection in dogs decreased from 65% at baseline to 8.9% and 4.7% at 7.5 and 10 years after sustained vector surveillance, respectively. The average annual force of infection dropped 260-fold from 72.7 per 100 dog-years at baseline to <0.3% in 2002, as determined prospectively and retrospectively from the age-prevalence curve of native dogs born during surveillance. Multiple logistic regression analysis showed that prevalent cases in dogs in 2000 and 2002 were associated positively and significantly with the peak number of T. infestans caught in domestic areas at the dog's compound during its lifetime. The sustained decline in T. cruzi infections in dogs and cats is the result of selective, community-based insecticide spraying that kept the abundance of infected T. infestans at marginal levels, fast host population turnover, and low immigration rates from areas with active transmission.

Flight initiation of Triatoma infestans (Hemiptera: Reduviidae) under natural climatic conditions.

Flight dispersal of Triatoma infestans Klug is probably the most important mechanism for house reinfestation at a village scale after residual spraying with insecticides. The aim of the current study was to estimate the flight initiation probability of field-collected T. infestans and to assess how this probability was affected by sex, adult age, partial bloodmeal, and the presence of a host inaccessible for feeding. Four experimental series, each consisting of three to six consecutive nights and repeated measurements of flight initiation on each individually marked bug, were carried out in experimental huts inside closed cages under natural climatic conditions. We demonstrate that flight initiation probability of T. infestans is much higher than previously reported, responds to temperature in a sigmoid manner, and is higher in females than males, and that the frequency distribution of the number of flights per individual is highly aggregated in female and male bugs. The age of adults had strong effects on flight initiation, whereas the presence of an inaccessible host and a partial bloodmeal exerted no significant effects in models controlling for the effects of bug weight-to-length ratio. The high flight potential found is consistent with the rapid changes in reinfestation patterns observed in the field. The present estimates of flight probabilities and the identification of factors modifying them provide essential knowledge for modeling reinfestation patterns and for improving control strategies of T.