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Acta Tropica 101 (2007) 249–257

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Peridomestic colonization of Triatoma longipennis (Hemiptera, Reduviidae) and Triatoma barberi (Hemiptera, Reduviidae) in a rural community with active transmission of Trypanosoma cruzi in jalisco state, Mexico

D´epartement Soci´et´es et Sant´e, Institut de Recherche pour le D´eveloppement (IRD), UR 008 and UR 016 Montpellier, France b Departamento de Salud P´ ublica, Centro Universitario de Ciencias de la Salud, Universidad de Guadalajara, Guadalajara, Jalisco, Mexico

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Simone Fr´ed´erique Breni`ere a,∗ , Marie-France Bosseno a , Ezequiel Magall´on-Gastel´um b , Eloy Gualberto Castillo Ruvalcaba b , Margarita Soto Gutierrez b , Eloy Christian Monta˜no Luna b , Jorge Tejeda Basulto b , Franc¸oise Mathieu-Daud´e a , Annie Walter a , Felipe Lozano-Kasten b

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Received 6 July 2006; received in revised form 5 February 2007; accepted 14 February 2007 Available online 21 February 2007

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Abstract

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Infestation of peridomiciles is likely a major risk factor for Chagas disease transmission in Jalisco state, Mexico. An entomological and serological survey of a typical village was conducted between July and September 2003. The peridomestic areas of 100 dwellings were visited and triatomines were searched manually in 369 potential sites. A total of 1821 Triatoma longipennis (93.2%) or Triatoma barberi was captured. Both species frequently occurred in sympatry. The infestation index was 60% for T. longipennis and 16% for T. barberi. T. longipennis occurred throughout the village. Colonization indices were high for T. longipennis (93%) and T. barberi (75%), suggesting that both species have adapted to peridomestic habitats. The bug population size was larger for T. longipennis than for T. barberi. Five very large colonies of T. longipennis were recorded whereas only 1 or 2 bugs were observed in 38% of the positive sites, which suggests intense dispersal activity. Both species exhibited high infection prevalence with Trypanosoma cruzi (46%). Only T. cruzi lineage I was detected. Human seroprevalence was 1.8%. This study serves as an entomological overview of peridomiciliar triatomine colonization in a Mexican village and highlights the current risk of Chagas disease transmission. © 2007 Elsevier B.V. All rights reserved.

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Keywords: Peridomiciliar area; Triatoma longipennis; Triatoma barberi; Seroprevalence; Risk of transmission; Mexico

Corresponding author at: Institut de Recherche pour le D´eveloppement (IRD), D´epartement Soci´et´es et Sant´e, UR 008 Pathog´enie et Epid´emiologie des Trypanosomatid´es, 911 Av. Agropolis, BP 64501, 34394 Montpellier Cedex 5, France. Tel.: +33 4 67 41 6372; fax: +33 4 67 41 63 30. E-mail address: [email protected] (S.F. Breni`ere). 0001-706X/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.actatropica.2007.02.007

1. Introduction Chagas disease is a permanent threat to a quarter of the Latin American population and is endemic to several Mexican states (Cruz-Reyes and Pickering-L´opez, 2006). Human seroprevalence rates up to 20% have been reported in various endemic regions (Dumonteil, 1999) and seropositivity of human blood transfusion has been

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estimated at 1.5% (Guzman-Bracho, 2001). Moreover, clinical autochthonous cases of Chagas disease have been diagnosed (Guzman-Bracho, 2001) and 5000 people suffer from severe chronic Chagas miocardiopathy in Mexico according to the National Institute of Cardiology Ignacio Chavez in Mexico City, (Monteon-Padilla et al., 2002). In the state of Jalisco, serological follow-up in 124 municipalities from 1987 to 1994 indicated a seroprevalence of around 18% (Contreras et al., 2000). In Mexico, 33 species of triatomine vectors exist (Galvao et al., 2003). Three species of the Phyllosoma complex, Triatoma longipennis, T. pallidipennis and T. picturata, are the most important vectors in the states of Jalisco and Nayarit (Magall´on-Gast´elum et al., 1998; Martinez-Ibarra et al., 2001). Recent entomological evaluation of communities in the occidental part of Mexico demonstrates the significance of peridomestic infestation by species of the Phyllosoma complex and suggests that the colonization of peridomestic areas is the main risk factor of Chagas disease transmission. Interestingly, intradomiciliary infestation and colonization were rare or absent (Breni`ere et al., 2004; Magall´on-Gast´elum et al., 2006). Previous reports have also identified Triatoma barberi, a species currently classified within the Protracta complex, and showed a large distribution with low abundance in the community (Magall´on-Gast´elum et al., 1998). Because the species of the Phyllosoma complex are sylvatic, invasion or re-invasion of the peridomicile by sylvatic populations is a permanent threat in the region under study (Magall´on-Gast´elum et al., 2001, 2004). Conversely, sylvatic specimens of T. barberi have not yet been observed in the wild environment. In the present work, an exhaustive entomological and serological survey was conducted to assess the distribution, densities, and colonization rates of both triatomine species in peridomestic habitats (outdoors) and investigate the status of the Trypanosoma cruzi transmission in a typical village of western Mexico.

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S.F. Breni`ere et al. / Acta Tropica 101 (2007) 249–257

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2. Materials and methods 2.1. Study area

The study was conducted in the region, “Valles de Ameca” in “Los Guerrero” village (20◦ 26 564 N, 103◦ 53 872 W), a rural community of the San Martin de Hidalgo municipality in Jalisco State, 90 km away from Guadalajara (Fig. 1a). This semi-arid region is characterized by a deciduous seasonal forest, which was cleared to provide land for cultures around the village.

Fig. 1. (a) The smaller map identifies the Jalisco state in Mexico whereas the main map shows the localization of the studied village of Los Guerrero. (b) A panoramic photograph of Los Guerrero village taken from the roof of a church (see Fig. 4 for the localization of the church).

Until recently, the land was composed of numerous plots surrounded by rock pile walls, but mechanized agriculture has progressively changed the landscape into large fields. The main crops are sugarcane (Saccharum officinarum), corn (Zea mays), and maguey tequilero (Agave tequilana). The minimum and maximum annual average temperatures are 20◦ C and 28 ◦ C, respectively. Mean annual rainfall ranges between 987.6 mm and 1349 mm and the dry season extends from October until June (data collected at: Inegi organization with the following URL: http://www.inegi.gov.mx/inegi/default.asp). Before the survey, the village was mapped and each dwelling was plotted. Seven hundred inhabitants were registered at the local health center. The village was composed of 314 dwellings of which 151 (48%) were closed because people were living and working in other places. One hundred inhabited dwellings were randomly selected and mapped during the study.

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2.2. Peridomicile and collection of triatomines

that distinguished between the two major phylogenetic lineages of T. cruzi. Slight modifications of the PCR procedures are as follows: samples were amplified in a PCR Master Mix reaction buffer (Promega, Madison, WI, USA) containing 10 pmol of each primer in a total reaction volume of 20–25 ␮l. The cycling was performed as previously described on a TC-312 Techne PCR devise system (Techne, Cambridge, UK). PCR products were loaded onto 3% agarose gels and visualized under UV illumination after ethidium bromide staining. The T. longipennis samples were selected from the different parts of the village (North, South, East, and West). Most of the infected T. barberi bugs were processed. The electrophoretic patterns were compared with those of the reference strains.

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The current peridomestic areas consist of private lands, all of which are surrounded by walls or fences enclosing different permanent structures, such as chicken coops, storage shelters or animal corrals and temporary structures as piles of wood, brick, tiles or various goods (Fig. 1b). From July to September 2003 (rainy season), a team of well-trained health workers, with the aid of entomologist, visited peridomiciles, described artificial ecotopes, and captured bugs. The search for bugs was manually conducted with flashlights, without repellent product, and the collected insects were placed in separate labeled plastic flasks and transported to the laboratory for morphological identification. All examined sites were numbered, characterized and localized on each household map. The mean time of search for bugs in each dwelling was 1 h and 15 ± 40 min.

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2.5. Presence of triatomine indoors Because a previous search for triatomines inside the houses in a similar village (Tepehuaje de Morelos) failed to demonstrate the presence of triatomines indoors (Magall´on-Gast´elum et al., 2006), the inhabitants were questioned on their own observations of triatomines in their house (indoors) and in the peridomicile (outdoors) areas while visiting their dwellings. Numbers of reported insects as well as their accurate location were recorded.

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2.3. Processing of triatomines The identification of triatomines (adults and nymphs) was performed according to the taxonomic keys of Lent and Wygodzinsky (1979). Sex and stages were also determined. Feces from each bug, obtained by abdominal pressure, were mixed with phosphate-buffered saline and examined for the presence of trypanosomatids by direct microscopical observation at 400× magnification. Then, bugs were dissected under a safety hood. The terminal part of the abdomen was cut and the abdominal contents (blood meal and intestinal part) were collected in a microtube. All samples were kept at −20 ◦ C until processing.

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2.4. PCR-based assay for parasite typing in blood meals

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The collected blood meals (10–200 ␮l) were diluted with PBS to a final volume of 200 ␮l, and DNA extracted with a QIAamp® DNA Mini kit according to the manufacturer’s instructions (Qiagen, Courtaboeuf, France). The DNA elution was performed in 50 ␮l of DNase-free water regardless of the blood meal volume. The detection and identification of parasites were performed using the mini-exon multiplex PCR previously described. With this technique, we amplified intergenic parts of mini-exon genes with primers TC1OF, TC2OF, TC3OF, TROF and MEOF allowing for the indentificaiton of major groups of T. cruzi and Trypanosoma rangeli (Fern´andez et al., 2001). A portion of the blood meal was also analyzed by mini-exon PCR according to Souto et al. (1996) with TC1, TC2 and TC primers

2.6. Entomological indices and result analyses Entomological indices were calculated according to the definition proposed by WHO (1991), but applied to peridomectic units. Peridomiciliary infestation (number of infested peridomiciles/number of investigated peridomiciles × 100) was positive when the presence of at least one triatomine was detected. The crowding index is the number of captured triatomines/number of peridomiciles with triatomines. The infection prevalence (number of triatomine with flagellates/number of triatomines examined × 100) was calculated for the entire village and for each species separately. The colonization index was the number of peridomiciles with Triatoma sp. nymphs/number of peridomiciles with Triatoma sp.) × 100. The MapInfo Professional Version 7.0 software was used to visualize the spatial distribution of the triatomines by peridomestic unit and capture site over the entire village. Statistical analyses were performed using the Statistix software. The Kolmogorov–Smirnov test was used to examine whether a variable fit a normal distribution. The correlation between two quantitative variables was estimated by computing Pearson correlation statistics. The association between current peridomestic infestation by triatomines

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and the householders’ triatomine observations was tested by a Chi-squared test. 2.7. IgG antibodies anti-T. cruzi

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Three hundred and forty-five children, teenagers and adults were T. cruzi treatment-naive and lived in Los Guerrero. The adults were volunteers and consent was obtained from each individual or their guardian. Specific anti-T. cruzi IgG was assessed in four assays. Two commercial assays were applied, the indirect hemagglutination and the ELISA tests (Chagastest HAI, Chagastest ELISA, Weiner laboratorios Rosario, Argentina). Another Elisa test using a Mexican strain as an antigen source (total extract from epimastigote forms) was processed according to Sanchez et al. (2001) and the recombinant Tc 24 protein of T. cruzi was also tested (Guevara et al., 1995). A serum sample was considered seropositive to T. cruzi when at least three of the four tests were reactive.

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Fig. 2. Stage structure of triatomine populations of T. longipennis and T. barberi species collected manually in 100 peridomestic habitats in Los Guerrero village (Jalisco state) in July and September 2003.

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(X2 = 20.74, 5 d.f., P < 0.0009). The T. longipennis population was younger than T. barberi (Fig. 2).

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3. Results

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One thousand, eight hundred and twenty-one triatomines were collected in peridomestic structures in 60 out of 100 visited habitats. T. longipennis was the most prevalent species (93.2% of adults) and T. barberi was the second most prevalent (6.6%). One male of T. picturata and one female of T. pallidipennis were also collected. Another male presented with morphological hybrid characters between T. longipennis and T. picturata: the connexivum structure bore specific shaped marks in the posterior portion of each segment like T. longipennis while the overall pronotum was black with an orange-red hind lobe like T. picturata. The female to male ratio was not significantly different from unity in T. barberi (X2 = 1.35, 1 d.f., P > 0.05) but was highly biased towards males for T. longipennis (X2 = 40.6, 1 d.f., P < 10−4 ). The nymphs of the phyllosoma complex cannot be distinguished on morphological grounds. As T. longipennis was the almost exclusive species found in the current village, the nymphs were all considered to be of the T. longipennis species. One thousand, two hundred and seventy-five nymphs were collected (75%). Conversely, T. barberi, a species belonging to the protracta complex, has nymphs easily differentiated from those belonging to the phyllosoma complex and 62.5% of T. barberi collected insects were nymphs. The stage structure of the two species was significantly different

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The peridomiciliar infestation by T. longipennis species was predominant (60%) and spread throughout the village (Fig. 3a). T. barberi infestation was less important (16%; Fig. 3b). The colonization indices were 93.3% (T. longipennis) and 75% (T. barberi). The crowding index was 28.3 ± 32.2 for T. longipennis and 7.5 ± 5.9 for T. barberi. Within the 100 visited peridomiciles, 369 sites were investigated for the presence of triatomines, 118 sites were positive, 31.2% and 5.4% of the sites had at least one T. longipennis and T. barberi organism, respectively. Moreover, 85% of the sites infested by T. barberi were also co-infested with the T. longipennis species. The number of bugs collected at a single site ranged from 1 to 318 specimens. The population size of T. barberi was small (<25 bugs) while the T. longipennis populations ranged from 1 to 325 specimens. The population abundance of T. longipennis did not fit a normal distribution (Kolmogorov-Smirnov statistic, Z = 3.834, P < 10−3 ). Sites with small colonies (1–15 bugs) were very abundant (77.4% of observations), while sites with very large colonies of triatomines (5 populations ≥60 bugs) were rarely observed. The spatial and quantitative distributions of the triatomines per capture site are depicted in Fig. 4.

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3.1. Field collections of triatomines and morphological identification

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3.2. Infestation, colonization and crowding indexes and spatial distribution of triatomines in the village

3.3. Colonization and dissemination Nymphs were collected in the majority of infested sites and were the predominant observed form of both species. T. longipennis nymphs were spread over the

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with 1 or 2 T. longipennis were observed throughout the entire village, 47.4% of the organisms were adults of either sex and the other 52.6% was comprised by organisms in the nymph stage. 3.4. Presence of triatomines indoors Forty percent of the inhabitants reported having previously seen triatomines in their house (indoors) and 31.6% in their peridomicile areas (95 inhabitants interviewed). A significant association was observed between the current infestation of the peridomicile and the observation of triatomine indoors (X2 = 12.3, 1 d.f., P = 0.0005), but not outdoors (X2 = 1.83, 1 d.f., P = 0.18). Moreover, in 50% of the indoor positive reports, the observation was recent (less than 6 months) and the bugs were discovered in the bedroom and frequently close to the bed.

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entire village (data not shown). The proportion of T. longipennis nymphs increased according to the size of the population collected in a single site. The proportion of nymphs was 52.6% in sites with 1 or 2 bugs and reached 78.3% in sites >50 bugs. Small colonies of triatomines were frequently observed and the proportion of sites with 1 or 2 bugs reached 38% for T. longipennis and 50% for T. barberi (Fig. 5). The sites

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Fig. 3. Peridomiciliar infestation by T. longipennis (a) and T. barberi (b) as a result of active manual research of triatomines during the day in 100 habitats in Los Guerrero village.

Fig. 4. Number of triatomines per site (ecotope) in the Los Guerrero village. Each circle represents a positive peridomiciliar capture site infested by T. longipennis. The size of each collected population is proportional to the circle size. Arrows indicate the five sites with the largest triatomine populations.

Fig. 5. Histograms presenting the percentage of infested sites with different numbers of insects 1 and 2, 3–15, 16–50 and >50) of the two species T. longipennis and T. barberi that were found in Los Guerrero village.

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Table 1 Microscopical evaluation of Trypanosoma cruzi infection of triatomine stages

No. positivea

Infection rate

No. examined

Nymphal instars 1st 2nd 3rd 4th 5th

29 122 225 221 230

1 15 68 88 128

3.5% 12.3% 30.2% 39.8% 55.6%

2 7 14 17 34

Adults Male Female

243 110

164 77

67.5% 70.0%

24 16

1180

541

45.8%

114

Total

Infection rate

0 1 4 7 14

nc 14.3% 28.6% 41.2% 41.2%

15 11

62.5% 68.7%

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45.6%

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nc = No calculated because of sample size. a No. of specimens with flagellate.

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No. examined

T. barberi

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T. longipennis

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Fig. 6. Ethidium bromide stained 3% agarose gel containing mini-exon PCR products—(lanes 1–10) DNAs extracted from triatomine blood meals; (lanes 12–14) DNAs of T. cruzi reference strains Gamba cl 1 (DTU 1), Sc43 cl 1 (DTU 2d), Can III cl 3 (DTU 2a); (lane 15) DNA of T. rangeli reference strain RGB; (lanes 11 and 16) small Fragment molecular weigh marker (Eurogentec, Seraing, Belgium).

3.5. T. cruzi infection of triatomines and determination of parasite species and subgroup by mini-exon gene polymorphism

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Feces of 1180 T. longipennis and 114 T. barberi were microscopically examined (Table 1). The overall infection prevalence was 46% and was similar for the two species (X2 = 1.81, 4 d.f., P > 0.05; first instar were not included in the test and all adults were grouped). For both species, the infection increased sequentially between the first instar (3.2%) and the fifth (53.8%) and reached 68% in adults. No significant differences were observed between infected males and females (X2 = 0.04, 1 d.f.,

P > 0.05; X2 = 0.03, 1 d.f., P > 0.05). Positive bugs were discovered in most of the infested peridomiciles and were spread throughout the entire village. Blood meals of 89 specimens of T. longipennis (51 adults and 38 nymphs) and 43 of T. barberi (22 adults and 21 nymphs) with parasite positive feces were analyzed by mini-exon multiplex PCR-based typing for direct detection of T. rangeli and T. cruzi subgroups. Fig. 6 shows the PCR profiles observed for a run of 10 blood meals and DNA of 4 reference strains. All the PCR positive samples (78% of the processed samples), except one, showed a major 200 bp band of variable intensity and a weak band of 180 bp. This pattern was identical to that of the Gamba

Table 2 Seroprevalence of T. cruzi infection in Los Guerrero village Number of patients

Registered at the health center Tested for T. cruzi antibodies Negative serology Positive serology

Age groups (years) <5

5–9

10–19

20–39

40–59

>60

Total

63 35 34 1

81 59 59 0

132 103 102 1

193 115 115 0

137 74 72 2

94 53 90 4

700 439 431 8

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3.6. Human seroprevalence of Trypanosoma cruzi Of the 700 residents registered at the Health Center, 439 were examined for antibodies (Table 2). The serological survey included more than 40% of the residents in each age group. The overall seropositivity of T. cruzi infection was 1.8%. Among the eight seropositive cases, five of them were positive for all the assays and three were negative only for the Tc24 recombinant test. Two children were seropositive for T. cruzi (2 and 14 years old) whereas their mothers were seronegative. They were born in the village and had no history of blood transfusion. All other positive cases were adults born in the municipality without any record of blood transfusion.

2002; Enger et al., 2004). Here, T. longipennis dominated throughout the entire village whereas in the state of Colima, situated on the Pacific coast, T. longipennis coexists in a sympatric manner with T. pallidipennis another species of the phyllosoma complex (Espinoza-Gomez et al., 2002). Moreover, in the Central part of Mexico (State of Morelos), T. pallidipennis is the dominant species in the villages (Bautista et al., 1999). According to several reports and our own observations in Nayarit and Jalisco states, the geographical distribution of the phyllosoma complex species in households (domestic environment in a broad sense) correlates with the most abundant species found in the respective sylvatic environments (EspinozaGomez et al., 2002; Magall´on-Gast´elum et al., 2001, 2004; Bautista et al., 1999). In fact, the geographical distribution of the phyllosoma complex species in the domestic environment would be the result of the colonization of the sylvatic populations present in the natural surrounding environment. Consequently, vector control strategies should be adapted to this epidemiologic situation. In the current study, we showed that T. longipennis is able to develop very large colonies at a single site of capture (ecotope) in the peridomicile area. These sites can be regarded as places of multiplication of the triatomines since they include all the developmental stages. They also highlight their remarkable ability to adapt to peridomiciliar environments. Further, we noted that in 40% of the positive sites, only one or two triatomines (adults or nymphs) were observed. These insects are moving probably to the search of food and/or microenvironment favourable to their installation. From the current results, we think that the multiplication foci could be an important source of dispersing, adult insects or nymphs, moving mainly by walk in the peridomiciliar area and reaching from time to time indoors. Nevertheless, the current infestation of indoors in Los Guerrero has yet to be specifically measured. In previous work, the active search of triatomines by experimented collectors gave negative result in a neighboring village (Magall´onGast´elum et al., 2006). Also, an alternative method of triatomine collection by the inhabitant could be proposed. The T. barberi species is the second most abundant species found in peridomicile areas of Los Guerrero. This species forms small populations currently colonizing the area since all developmental stages can be observed. T. barberi is largely distributed throughout Mexico and sympatric collections of the phyllosoma complex species have been previously reported (Magall´on-Gast´elum et al., 1998; Enger et al., 2004). Here, colonization of the peridomicile by T. barberi suggests a possible role of T.

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cl1 strain (T. cruzi I group). Out of the 29 PCR negative samples, 11 were positive with the second PCR-based diagnosis exhibiting the typical 350 bp-band of the T. cruzi I group. The only pattern that differed from the others was composed of 3 bands, the 200 and 180 bp bands were identical to Gamba cl1 and one at 380 bp. When the primers of the mini-exon multiplex were applied separately with this sample, the 200 bp and 180 bp bands were amplified only with the TC1OF-MEOF primers and the 380 bp with TC2OF-MEOF primers, but the PCRbased diagnosis according to Souto et al. (1996) gives one 350 bp band specific for the T. cruzi I group.

4. Discussion

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We previously stated that, in the occidental part of Mexico, the invasion of bugs from the peridomicile to indoor areas represents a significant transmission risk (Breni`ere et al., 2004; Magall´on-Gast´elum et al., 2006). Indeed, the large serological survey of the population of Los Guerrero that was performed showed eight cases of seropositivity (1.8% seroprevalence rate) including two children with permanent residence in the village. These results support the hypothesis that this region is endemic and past and present transmission of T. cruzi infection occurs. In Mexico, early entomological works highlight the large geographical distribution of the different triatomine species (Espinoza-Gomez et al., 2002; Bautista et al., 1999; Ramsey et al., 2000), but basic entomological studies aimed at measuring vectorial micro-distribution and population density associated with the evaluation of infection prevalence are scarce. The present study confirms the magnitude of the peridomiciliar colonization by T. longipennis. Indeed 60% of the dwellings in Los Guerrero are infested with T. longipennis, a rate significantly higher than that described in previous reports (Espinoza-Gomez et al.,

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brasiliensis, which can develop into large colonies in Brazil (Sarquis et al., 2006). In the studied area, vector control of peridomestic populations by means of insecticides should be effective, but re-infestation by sylvatic populations must be considered. Alternative and/or combined methods of control reducing hiding sites of triatomines, thereby inhibiting their ability to colonize must be incremented. Long-term control likely relies on the improvement of peridomiciliary management. Moreover, similar studies in other areas are necessary to assess the impact of the biodiversity in Mexico over the transmission of Chagas disease to establish suitable control strategies. Acknowledgements

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We thank the authorities of the San Martin de Hidalgo municipality for providing fieldwork facilities and specifically, Dr. Carmen Amalia Garza Aguila. This investigation received financial support from the Pan American Health Organization, Research and Training in Tropical Diseases (TDR), Grant ID A30442 and the “Institut de Recherche pour le D´eveloppement” (IRD).

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barberi in the transmission of Chagas disease in this region. Indeed, intradomiciliary specimens have been previously collected in Jalisco and according to the current results, the indoor insects should originate from peridomiciliar populations. Moreover, T. barberi is able to colonize the domestic environment; small colonies have been observed by our team in 1999 in two villages of the Oaxaca state (10–14% indoor infestation for 92 visited households) (unpublished data). The infection rates of the two species are very high (45% for both) reaching that of Triatoma infestans, the main domiciliary vector in South America (WHO, 1991; Gurtler et al., 1998; Breni`ere et al., 1999). The multiplex PCR based-typing of T. cruzi strains confirms that the flagellate observed in the feces are true T. cruzi belonged to T. cruzi I and not T. rangeli, a non pathogenic human parasite. This result corroborates the predominance of T. cruzi I in Mexico (Bosseno et al., 2002). The recent analysis of blood meals of triatomines captured in Los Guerrero showed that rats (Rattus rattus) are the principal sources of blood meals for the two species (Bosseno et al., 2006). Indeed, this rodent probably plays a principal reservoir role to maintain such an important rate of infection in triatomines. The consequence of T. cruzi I on the pathology is unknown, but Mexican strains which develop successful infection in murine experimental models have highly variable virulence and pathogenicity (Espinoza et al., 1998). Therefore, more studies on genetic heterogeneity and biological characteristics of the Mexican strains are necessary to better understand their clinical consequences. According to the seroprevalence estimates in Mexico, the village of Los Guerrero presents a seroprevalence rate reaching the average value of the rural population (Guzman-Bracho, 2001). The current study provides an entomological reference in a village with a medium level of endemicity. The principal features are as follows: (i) high indices of infestation and colonization of the peridomicile by the principal (T. longipennis) and secondary (T. barberi) organisms, (ii) large distribution of the principal species throughout the entire village, (iii) formation of large colonies by T. longipennis (successful adaptation), (iv) capacity of dispersion of the different stages, (v) high infection rates of the two principal species of T. cruzi I strains. The present study clearly shows that methods of control in the peridomiciliar area must be applied to reduce the number of triatomines. Indeed, the peridomiciliar area was described as the origin and principal source of reinfestation after chemical control methods in the case of T. infestans infestation in Argentina (Cecere et al., 2002) and also designed as a risk factor when infested by wild species, such as T.

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