Triatoma mexicana

Triatoma mexicana (Hemiptera: Reduviidae) in Guanajuato, Mexico: house infestation and seasonal variation

Paz María Salazar Schettino/+, José Santiago Rosales Piña, Gloria Rojas Wastavino, Margarita Cabrera Bravo, Mauro Vences Blanco, Jorge López Cárdenas*

Departamento de Microbiología y Parasitología, Facultad de Medicina, Universidad Nacional Autónoma de México, Edificio "A" 2º Piso, Ciudad Universitaria, Mexico DF *Laboratorio de Entomología Médica, Secretaría de Salud del Estado de Guanajuato, Guanajuato, Mexico

Triatoma mexicana was described by Herrich-Schaeffer in 1848. In 1940, a male specimen was found in Hidalgo. In 1970, this species was recorded in the state of Queretaro. Later, it was registered in Guanajuato and San Luis Potosi. In the present paper we performed an investigation in 545 dwellings from three counties in the state of Guanajuato, Mexico, from March 2003 to May 2004. The search and capture of triatomines were seasonally performed indoors and outdoors. Entomological indexes were calculated. The risk and no risk rela- tions between triatomine presence and housing construction materials were analyzed. Fourteen triatomines were collected indoors and 151 outdoors. The vectors were collected in houses built with either risky and non- risky materials. Adults go indoors but do not settle there, hence, no relationship was found between the build- ing materials and infestation of houses. Conventional interventions like house improvement or insecticide spraying are not efficient for the control of T. mexicana, because its developmental cycle is accomplished out- doors in the area surrounding the houses.

Key words: Triatoma mexicana - behavior - Chagas disease - Guanajuato

Currently, the subfamily Triatominae (Hemiptera: Reduviidae) is divided in six tribes, 19 genera and 137 species. In Mexico, the most important genera are Triatoma and Meccus. The most common is genus Triatoma with 19 species widely distributed, followed by Meccus with six species (previously in the Triatoma phyllosoma complex) (Galvao et al. 2003). Triatomine vectors have been reported in all Mexican states (Cruz- Reyes et al. 2006).

Triatoma mexicana was first described by Herrich- Schaeffer, in 1848, as Conorhinus mexicanus. Examples of T. mexicana have been scarcely captured in Metztitlan, Hidalgo, and in the neighboring state of Queretaro (Lent

& Wygodzinsky 1979). The geographical distribution was widened when this species was found in the bordering states of Guanajuato and San Luis Potosi. Natural infec- tion with T. cruzi in T. mexicana was reported for the first time in the state of San Luis, Potosi (Vidal-Acosta et al. 2000). López-Cardenas et al. (2005) extensively registered the presence and distribution of T. mexicana in Guanajuato.

Data on T. mexicana are scarce and mainly based on morphological description of males, and geographical distribution. The aim of this work is to acess the distri- bution, and developmental pattern (according to seasons)

Financial support: DGAPA (grant IN 238002)

+Corresponding author: pazmar@servidor.unam.mx Received 14 March 2007

Accepted 31 October 2007

of T. mexicana in the northeast of Guanajuato. Further- more, we describe indoor and outdoor ecotopes explored by this vector, as well as evaluate the influence of char- acteristics of the dwellings and the presence of T. mexicana. Additionally we aimed at estimating the ento- mological indexes in three counties of this state. All this in order to propose control measures to decrease the risk of T. cruzi natural transmission.

MATERTALS AND METHODS

Guanajuato is located in the center of the Mexican Republic. It is divided in 46 counties and eight Sanitary Jurisdictions. This research was carried out in the north- east, in the Sanitary Jurisdiction-2, San Miguel de Allende. We selected 545 dwellings in three counties as follows: Victoria (234), Santa Catarina (55), and Tierra Blanca (256). They were located at 20º42' and 21º13' N, 100º 02' and 100º 17' W. The altitude ranged between 1,593 and 1,844 m above sea level (INEGI 1997) (Fig- ure). These localities were chosen based on triatomine presence reported by the local vectors control person- nel, as well as on the publications by Vidal-Acosta et al. (2000) and López-Cárdenas et al. (2002). Collections were performed from March 2003 to May 2004. The vectors' personnel from the Sanitary Jurisdiction-2 were trained by our research team about Chagas disease and both worked together on the field.

The local climate is mild dry and warm, with 400 - 700 mm annual rainfall, with the heaviest precipitation reported in August and the lowest in March. Tempera-

ture range from 16 to 20ºC. Vegetation is bush-like, con-

sisting of palo vidrioso (Bursera sp.), garambullos (Myrtillocactus sp.), pitayos (Stenocereus sp.) and

mezquites (Prosopis sp.). In the agricultural area, corn

(Zea mays) and beans (Phaseolus vulgaris) are grown.

The household heads were fully informed of the pur- pose of this research, and were asked to sign a consent letter. In addition, they were interviewed to gain informa- tion on vectors and characteristic of dwellings. The build- ing material from the roof, walls and floor was classified as risky or non risky (Table I) (García de la Torre 1998).

The search for triatomines was carried out indoors (on walls, floors, beds, and wood piles) and outdoors (in the henhouse, pigsty, stone walls, wood stick piles, and plants) through man/hour method. The search and cap- ture of triatomines were carried out seasonally along the year. Taxonomic identification of adults was achieved with the triatomine keys of Lent & Wygodzinsky (1979).

Three entomological indexes were obtained: infes- tation index (houses positive for triatomine/number of investigated houses X 100), colonization index (houses

with triatomine nymphs/number of houses positive to

Mexico, expanded area, state of Guanajuato, and states where T. mexicana

has been reported.

TABLE I

Classification of construction material of the houses surveyed in the three counties in Guanajuato, Mexico, from March 2003 to May 2004

Roof Wall Floor Risk

Roof tile Stone Soil

Cardboard sheet Cardboard Sheet Stone

Wood Carrizo/bamboo Adobe

Without risk

Brick Flattened adobe Brick

Cement Flattened and regular brick Cement Tin plate, galvanized, Flattened and plastered block Mosaic

zinco

Brick and plaster Floor tile Block

Cement

triatomine X 100) and natural infection index (positive triatomine for T. cruzi/number of examined triatomine X 100). The last index was obtained from the exam of the intestinal content of bugs diluted in saline solution to determine T. cruzi infection rate (Silveira et al. 1984)

Statistical analysis - Data were processed with SPSS

V.10 software. A percentage descriptive analysis of the geo- graphical distribution, the collected samples and develop-

mental stages (according to season and site of capture), was performed. We analyzed risk and non-risk relations between the presence of triatomines and the construction materials, using 2 test, and 95% coefficient intervals.

RESULTS

From 545 houses, 43 were positive for triatomines, and 165 specimens of T. mexicana in different developmental stages were collected. When comparing triatomine captures among counties, significant differ- ence was detected for any comparison, except between Santa Catarina and Tierra Blanca (p > 0.05). Fourteen (8.0%) triatomines were collected indoors, and 151 (92%) outdoors (p < 0.05) (Table II). Eggs were not found. The highest number of samples was from Victoria County, mostly composed of adults. The highest number of triatomines was collected during spring and summer (p < 0.05); no statistically difference (p > 0.05) was found between collections performed during summer and autumn. When comparing among seasons, all depicted statistical differences (p < 0.05).The highest number of nymphs was found in the autumn. A few insects were collected in the winter. Males were more abundant than females (p < 0.05), and adults were more frequently caught than nymphs (p < 0.05) (Table III).

The main indoor vector ecotope was the bedroom walls. The patio, outdoor wall and under the stone of walls

were the main vector ecotopes outside the houses (Table IV). Table V shows results from infested houses: 22/234 (9%) (p < 0.05) were detected in Victoria, 10/55 (18%)

(p > 0.05) in Santa Catarina, and 11/256 (4.3%) (p > 0.05) in Tierra Blanca. This Table also shows the results of different associations (dwellings with and without risk

material, and presence or absence of triatomines) in the three counties, which showed to be significantly differ- ent (p < 0.05). The CI95% was calculated in the all dif-

ferent associations.

The infestation index in Victoria County was 9.4%, 18.1% in Santa Catarina, and 4.2% in Tierra Blanca. The

colonization index was 36.3% in Victoria and Tierra Blanca counties, and 20.0% in Santa Catarina. The natu- ral infection index was 2.6% in Victoria, 2.0% in Santa

Catarina, and 4.7% in Tierra Blanca.

DTSCUSSTON

House infestation index and seasonal variation of abun- dance of T. mexicana

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