Domestic host availability modifies human-triatomine contact and host shifts of the Chagas disease vector Triatoma infestans in the humid Argentine Chaco.

Domestic animals may affect human-vector contact and parasite transmission rates. We investigated the relationships between host-feeding choices, site-specific host availability, bug nutritional status, stage and abundance of Triatoma infestans Klug (Heteroptera: Reduviidae) in rural houses of Pampa del Indio during spring. We identified the bloodmeal sources of 865 triatomines collected in 70 sites from four main ecotopes. The main sources in domiciles were human (65.9%), chicken (23.4%) and dog (22.4%); dog (64.4%, 35.3%) and chicken (33.1%, 75.4%) in kitchens and storerooms, respectively; and chicken (94.7%) in chicken coops. Using random-intercept logistic regression clustered by domicile, the fraction of human-fed triatomines strongly decreased with increasing proportions of chicken- and dog-fed bugs, dropping from 96.4% when no chicken or dog slept indoors at night to 59.4% when both did. The fraction of dog-fed bugs significantly decreased with increasing human and chicken blood indices, and marginally increased with an indoor-resting dog. Mixed blood meals occurred 3.62 times more often when a chicken or a dog slept indoors. Host blood source did not affect mean body weight adjusted for body length and bug stage. Indoor-resting chickens and dogs greatly modified human-bug contact rates, and may be targeted with long-lasting systemic insecticides to suppress infestation.

Wild rats as urban detectives for latent sources of asbestos contamination.

Based on a large body of evidence asbestos minerals have been classified as carcinogens. Despite the Italian ban on asbestos in 1992 and the subsequent remediation activities, latent sources of contamination may still represent a hazard where asbestos were particularly used. Using wild rats as sentinel animals, this study aimed at uncovering sites with the greatest potential for non-occupational exposure to asbestos in the city of Casale Monferrato (Piedmont Region, Italy), where the largest Italian manufacturing plant of asbestos-cement had been active. During the study period (2013-2015) a total of 40 wild rats were captured from 16 sampling capture points. The lungs of wild rats have been investigated by using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The SEM-EDS detected the presence of asbestos fibers (tremolite/actinolite, amosite, and chrysotile) in rats' lungs from 11 sampling points. The hypothetical rats' home-range and the observed site-specific concentration of asbestos fibers per gram of dry lung tissue were used to identify areas to be targeted by additional search of latent sources of asbestos. In conclusion, our results showed that the use of wild rats as sentinel animals may effectively integrate the strategies currently in use to reduce the exposure to asbestos.

Importance of Common Wall Lizards in the Transmission Dynamics of Tick-Borne Pathogens in the Northern Apennine Mountains, Italy.

During the investigations on ticks and tick-borne pathogens (TBP) range expansion in the Northern Apennines, we captured 107 Podarcis muralis lizards. Sixty-eight animals were infested by immature Ixodes ricinus, Haemaphysalis sulcata and H. punctata. Borrelia burgdorferi s.l. was detected in 3.7% of I. ricinus larvae and 8.0% of nymphs. Together with the species-specific B. lusitaniae, we identified B. garinii, B. afzelii and B. valaisiana. Rickettsia spp. (18.1% larvae, 12.0% nymphs), namely R. monacensis, R. helvetica and R. hoogstraalii, were also found in I. ricinus. R. hoogstraalii was detected in H. sulcata nymphs as well, while the two H. punctata did not harbour any bacteria. One out of 16 lizard tail tissues was positive to R. helvetica. Our results support the hypothesis that lizards are involved in the epidemiological cycles of TBP. The heterogeneity of B. burgdorferi genospecies mirrors previous findings in questing ticks in the area, and their finding in attached I. ricinus larvae suggests that lizards may contribute to the maintenance of different genospecies. The rickettsiae are new findings in the study area, and R. helvetica infection in a tail tissue indicates a systemic infection. R. hoogstraalii is reported for the first time in I. ricinus ticks. Lizards seem to favour the bacterial exchange among different tick species, with possible public health consequences.

The sylvatic transmission cycle of Trypanosoma cruzi in a rural area in the humid Chaco of Argentina.

Little is known about the sylvatic transmission cycle of Trypanosoma cruzi in the Gran Chaco ecoregion. We conducted surveys to identify the main sylvatic hosts of T. cruzi, parasite discrete typing units and vector species involved in Pampa del Indio, a rural area in the humid Argentinean Chaco. A total of 44 mammals from 14 species were captured and examined for infection by xenodiagnosis and polymerase chain reaction amplification of the hyper-variable region of kinetoplast DNA minicircles of T. cruzi (kDNA-PCR). Ten (22.7%) mammals were positive by xenodiagnosis or kDNA-PCR. Four of 11 (36%) Didelphis albiventris (white-eared opossums) and six of nine (67%) Dasypus novemcinctus (nine-banded armadillos) were positive by xenodiagnosis and or kDNA-PCR. Rodents, other armadillo species, felids, crab-eating raccoons, hares and rabbits were not infected. Positive animals were highly infectious to the bugs that fed upon them as determined by xenodiagnosis. All positive opossums were infected with T. cruzi I and all positive nine-banded armadillos with T. cruzi III. Extensive searches in sylvatic habitats using 718 Noireau trap-nights only yielded Triatoma sordida whereas no bug was collected in 26 light-trap nights. Four armadillos or opossums fitted with a spool-and-line device were successfully tracked to their refuges; only one Panstrongylus geniculatus was found in an armadillo burrow. No sylvatic triatomine was infected with T. cruzi by microscopical examination or kDNA-PCR. Our results indicate that two independent sylvatic transmission cycles of T. cruzi occur in the humid Chaco. The putative vectors of both cycles need to be identified conclusively.

Genetic variability, phylogenetic relationships and gene flow in Triatoma infestans dark morphs from the Argentinean Chaco.

The recent discovery of sylvatic populations of Triatoma infestans outside the Andean Valleys of Bolivia prompted an evolutionary question about the putative ancestral area of origin and dispersal of the species, and an epidemiological question regarding the possible role of these sylvatic populations in the recolonization process of insecticide-treated houses. The finding of a population of sylvatic melanic T. infestans (dark morphs) in the Argentinean dry Chaco at 7 km from a peridomestic bug population of typical coloration gave us the opportunity to test both questions simultaneously by employing phylogenetic and population genetic approaches. For this purpose we analyzed sylvatic and peridomestic bugs using sequence-based mitochondrial and nuclear markers (mtCOI and ITS-1) and microsatellites. Sylvatic bugs were confirmed to be T. infestans and not hybrids, and showed high levels of genetic variability and departures from neutral expectations for mtCOI variation. New ITS-1 and mtCOI haplotypes were recorded, as well as haplotypes shared with peridomestic and/or domestic bugs from previous records. The peridomestic population was invariant for ITS-1 and mtCOI, but showed variability for microsatellites and signatures of a population bottleneck, probably due to a limited number of founders. Phylogenetic analyses were consistent with the presence of ancestral haplotypes in sylvatic bugs. According to F-statistics and assignment methods there was a significant differentiation between sylvatic and peridomestic bugs and gene flow was low and asymmetric, with more bugs moving from the peridomicile to the sylvatic environment. These results support the hypothesis of the Chaco region as the area of origin of T. infestans, and a limited role of sylvatic melanic T. infestans in peridomestic infestation in the Argentinean Chaco.

Detection of "Candidatus Rickettsia sp. strain Argentina"and Rickettsia bellii in Amblyomma ticks (Acari: Ixodidae) from Northern Argentina.

Ixodid ticks were collected from vegetation and from humans, wild and domestic mammals in a rural area in the semi-arid Argentine Chaco in late spring 2006 to evaluate their potential role as vectors of Spotted Fever Group (SFG) rickettsiae. A total of 233 adult ticks, identified as Amblyomma parvum, Amblyomma tigrinum and Amblyomma pseudoconcolor, was examined for Rickettsia spp. We identified an SFG rickettsia of unknown pathogenicity, "Candidatus Rickettsia sp. strain Argentina", in A. parvum and A. pseudoconcolor by PCR assays targeting gltA, ompA, ompB and 17-kDa outer membrane antigen rickettsial genes. Rickettsia bellii was detected in a host-seeking male of A. tigrinum. Amblyomma parvum is widespread in the study area and is a potential threat to human health.

First finding of melanic sylvatic Triatoma infestans (Hemiptera: Reduviidae) colonies in the Argentine Chaco.

Triatoma infestans (Klug), the most important vector of Chagas disease in southern South America, is a highly domiciliated species with well-known sylvatic foci only in the Bolivian Andean valleys and in the Bolivian Chaco, where melanic insects designated as "dark morphs" were found. After the tentative identification of two melanic bugs collected from parrot nests in a forest reserve in the Argentine Chaco as T. infestans, we conducted an intensive search there using mouse-baited sticky traps in summer 2006 and 2007. Four live T. infestans bugs were collected in trees without parrot nests in 288 trap-nights, whereas no bug was collected from inside trees with active parrot nests in 51 trap-nights. To increase bug captures, hollow tree trunks that recently had had Amazona aestiva (Berlepsch) and Aratinga acuticaudata (Vieillot) parrot nests were treated with insecticide fumigant canisters exhibiting strong knockdown power. Four (22%) of 18 trees were positive for T. infestans with a dark phenotype. A fragment of the mitochondrial gene COI of 8 of the 14 triatomine bugs collected was successfully sequenced and confirmed as T. infestans. Most of the bugs were captured from Aspidosperma quebracho-blanco (Schlechter) hollow tree trunks harboring parrot nests. All of the T. infestans collected from the nearest house located at 10 km from the sylvatic foci displayed normal chromatic characters. The repeated finding of T. infestans in sylvatic habitats, albeit at very low density, shows that this species is capable of maintaining viable sylvatic foci in the absence of human hosts and immigration from domestic populations. These are the first confirmed findings of sylvatic T. infestans colonies in Argentina and of dark morphs in the Argentine Chaco.

Seasonal variations in active dispersal of natural populations of Triatoma infestans in rural north-western Argentina.

The flight dispersal of Triatoma infestans Klug (Hemiptera: Reduviidae) is one of the main mechanisms determining community re-infestation after control interventions. An empirical model of flight initiation coupled with data from a longitudinal study predicted that the flight dispersal of T. infestans would peak in summer. To test this prediction, longitudinal light trap collections were conducted during 3-8 nights in March (late summer), July (winter) and November (spring) 2003, and in March 2004 in a rural community in north-west Argentina. Following each light-trapping collection date, all peridomestic sites around light traps were inspected to assess the relative abundance and nutritional status of T. infestans at each site. A total of 21 adult and five nymph T. infestans, six Triatoma guasayana Wygodzinsky & Abalos, and nine Triatoma garciabesi Carcavallo et al. were collected in 96 light-trapping nights, whereas 696 T. infestans were collected from the peridomestic sites that surrounded the light traps. The arrival of T. infestans in the light traps occurred in 64% of catch stations and peaked in the summer surveys (10-14 bugs) compared with spring and winter surveys. When winds were < 5 km/h, the arrival of adult T. infestans at the light traps was significantly associated with maximum temperature and relative humidity. This is the first field report of seasonal variations in the flight dispersal activity of T. infestans.

Long-term reduction of Trypanosoma cruzi infection in sylvatic mammals following deforestation and sustained vector surveillance in northwestern Argentina.

Long-term variations in the dynamics and intensity of sylvatic transmission of Trypanosoma cruzi were investigated around eight rural villages in the semiarid Argentine Chaco in 2002-2004 and compared to data collected locally in 1984-1991. Of 501 wild mammals from 13 identified species examined by xenodiagnosis, only 3 (7.9%) of 38 Didelphis albiventris opossums and 1 (1.1%) of 91 Conepatus chinga skunks were infected by T. cruzi. The period prevalence in opossums was four-fold lower in 2002-2004 than in 1984-1991 (32-36%). The infection prevalence of skunks also decreased five-fold from 4.1-5.6% in 1984-1991 to 1.1% in 2002-2004. Infection in opossums increased with age and from summer to spring in both study periods. The force of infection per 100 opossum-months after weaning declined more than six-fold from 8.2 in 1988-1991 to 1.2 in 2002-2004. Opossums were mainly infected by T. cruzi lineage I and secondarily by lineage IId in 1984-1991, and only by T. cruzi I in 2002-2004; skunks were infected by T. cruzi IId in 1984-1991 and by IIc in 2002-2004. The striking decline of T. cruzi infection in opossums and skunks occurred in parallel to community-wide insecticide spraying followed by selective sprays leading to very low densities of infected Triatoma infestans in domestic and peridomestic habitats since 1992; to massive deforestation around one of the villages or selective extraction of older trees, and apparent reductions in opossum abundance jointly with increases in foxes and skunks. These factors may underlie the dramatic decrease of T. cruzi infection in wild reservoir hosts.

Feeding rates, nutritional status and flight dispersal potential of peridomestic populations of Triatomainfestans in rural northwestern Argentina.

Triatoma infestans, the main vector of Chagas disease in Southern Cone countries, frequently infests peridomestic structures housing domestic animals. A total of 814 T. infestans collected from 35 different peridomestic sites in rural northwestern Argentina over 1-4 consecutive seasons was examined for recent blood meals and nutritional status. Bugs from goat or pig corrals had lower qualitative nutritional status and mean weight to length ratios (W/L) than those captured in chicken coops. Males systematically had lower qualitative nutritional status and W/L than females. Using logistic multiple regression, the daily feeding rates of T. infestans were significantly associated with season and stage but not ecotope, whereas the proportion of well-fed bugs varied significantly with all three factors. The seasonal trends in feeding rates and nutritional status were consistent with the local availability and breeding timing of domestic animals. The observed data fed into an empirical model predicted that the probability of flight initiation would peak in summer from pig or goat corrals, not chicken coops, and be insignificant in all ecotopes in spring and fall. Male T. infestans outnumbered females as potential fliers. This is the first study conducted in well-defined habitat units that shows significant heterogeneities in the feeding rates and nutritional status of triatomine populations linked to host demographics and management, and how these affect flight dispersal potential over seasons. Peridomestic bug populations are of great relevance as a source of domestic reinfestation and for the elimination of T. infestans.

Field trials of an improved cost-effective device for detecting peridomestic populations of Triatoma infestans (Hemiptera: Reduviidae) in rural Argentina.

An improved device for detecting peridomestic Triatoma infestans consisting of one-liter recycled Tetra Brik milk boxes with a central structure was tested using a matched-pair study design in two rural areas in Argentina. In Olta (La Rioja), the boxes were installed beneath the thatched roofs and on the vertical wooden posts of each peridomestic structure. After a 5-month exposure, at least one of the recovered boxes detected 88% of the 24 T. infestans-positive sites, and 86% of the 7 negative sites by timed manual collections at baseline. In Amamá (Santiago del Estero), the boxes were paired with the best performing prototype tested before (shelter unit). After 3 months, some evidence of infestation was detected in 89% (boxes) and 79% (shelters) of 18-19 sites positive by timed collections, whereas 19% and 16% of 32 negative sites were positive, respectively. Neither device differed significantly in the qualitative or quantitative collection of every sign of infestation. The installation site did not modify significantly the boxes' sampling efficiency in both study areas. As the total cost of each box was half as expensive as each shelter unit, the boxes are thus the most cost-effective and easy-to-use tool for detecting peridomestic T. infestans currently available.

Seasonal variations of microclimatic conditions in domestic and peridomestic habitats of Triatoma infestans in rural northwest Argentina.

Our objectives were to describe and compare the seasonal variations in microclimatic conditions in domestic and peridomestic ecotopes infested by Triatoma infestans, the main vector of Chagas disease, in rural northwestern Argentina. Using data loggers for 4-7 consecutive days in October 2000, February, May and August 2001, microsite (interior of thatched roofs) and ambient temperatures or relative humidity (RH) were recorded simultaneously and compared with an external reference. The damping effects on microsite temperature and ambient RH increased successively from the goat corral to the chicken coop or pig corral, to the storeroom or human habitation. In the interior of the thatched roofs of the habitation and storeroom, average external minima were increased by +5.0 to +5.6 degrees C in all seasons, and average external maxima were decreased by -4.3 to -5.6 degrees C in October-May and -10.6 degrees C in August. On average, the human habitation damped extreme temperatures by 8 degrees C over a wider range than previously reported. The interior of the thatched roofs of the pig corral and chicken coop exerted intermediate damping effects that varied over seasons, whereas the goat corral's thatch showed little or no damping effects at all. The adobe-and-thatch habitation and storeroom presented nearly optimal and more suitable conditions for T. infestans populations than other open structures housing animals. Global climate changes are expected to affect peridomestic populations of T. infestans much more than domestic bug populations, provided other local conditions are held constant. Heterogeneous habitat conditions are expected to affect T. infestans population parameters, dispersal, control and infection with Trypanosoma cruzi.

Field trials of an improved cost-effective device for detecting peridomestic populations of Triatoma infestans (Hemiptera: Reduviidae) in rural Argentina

An improved device for detecting peridomestic Triatoma infestans consisting of one-liter recycled Tetra Brik milk boxes with a central structure was tested using a matched-pair study design in two rural areas in Argentina. In Olta (La Rioja), the boxes were installed beneath the thatched roofs and on the vertical wooden posts of each peridomestic structure. After a 5-month exposure, at least one of the recovered boxes detected 88 percent of the 24 T. infestans-positive sites, and 86 percent of the 7 negative sites by timed manual collections at baseline. In Amamá (Santiago del Estero), the boxes were paired with the best performing prototype tested before (shelter unit). After 3 months, some evidence of infestation was detected in 89 percent (boxes) and 79 percent (shelters) of 18-19 sites positive by timed collections, whereas 19 percent and 16 percent of 32 negative sites were positive, respectively. Neither device differed significantly in the qualitative or quantitative collection of every sign of infestation. The installation site did not modify significantly the boxes' sampling efficiency in both study areas. As the total cost of each box was half as expensive as each shelter unit, the boxes are thus the most cost-effective and easy-to-use tool for detecting peridomestic T. infestans currently available

Comparison between two artificial shelter units and timed manual collections for detecting peridomestic Triatoma infestans (Hemiptera: Reduviidae) in rural northwestern Argentina.

A new artificial shelter unit was compared with segments of bamboo cane lined with pleated filter paper for detecting peridomestic Triatoma infestans Klug at Amamá and nearby rural villages in northwestern Argentina. The new shelter unit consisted of a black plastic, wide-mouthed jar with a screw cap on the top, and a removable central structure made of pleated corrugated paper. In devices exposed from February to December 1999 at 24 sites positive for T. infestans by timed manual collections with an irritant in April 1999, the cumulative percentage of sites with any sign of infestation detected by the shelter unit increased from 71% after 2 mo to 96% after 10 mo, whereas bamboo cane units concurrently detected only 12-42% of the sites. Sensitivity increased with time of exposure and the abundance of T. infestans per site. In 19 sites negative for T. infestans by inspection, shelters increasingly detected infestation at 16-63% of sites after 10 mo, whereas the bamboo canes only detected one infestation. Shelter units inspected three times over an 11-mo period were significantly more sensitive than a single manual search with an irritant performed in March 2000. Our study provided conclusive field evidence that the shelter unit was more sensitive for detecting peridomestic T. infestans than were timed manual searches, the standard reference method, or bamboo cane units. Rapid timed searches by skilled bug collectors during the early surveillance phase overlooked many peridomestic populations that, in the absence of control, inevitably would increase in abundance and repopulate treated areas.