|
Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 91, Num. 3, 1996, pp. 271-272
|
Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 91(1), May/June
1996
RESEARCH NOTE: Current Spread of Triatoma
infestans at the Expense of Triatoma sordida in
Bolivia
Francois Noireau/^+, Frederique Breniere*, Lucyla Cardozo**,
Marie France Bosseno*, Fernando Vargas, Carlos Peredo**, Marlon
Medinacelli**
Institut Francais de Recherche Scientifique pour le Developpement
en Cooperation (ORSTOM), Casilla Postal 9214, La Paz, Bolivia
*UMR CNRS/ORSTOM, BP 5045, 34032 Montpellier Cedex, France
**Centro Nacional de Enfermedades Tropicales (CENETROP), Casilla
Postal 2974, Santa Cruz, Bolivia
Code Number: OC96053
Size of Files:
Text: 6.3K
No associated graphics files
Key words: Triatoma infestans - Triatoma sordida -
distribution - Bolivia
Triatoma infestans is the most widespread synanthropic
species of Triatominae and the most important vector of Chagas
disease in South America. The progressive geographical expansion
of this species from its silvatic focus of origin in the
Cochabamba valley of Bolivia (JP Dujardin et al. 1987 J Med
Entomol 24: 40-45) was probably associated with human
migration into the continent (CJ Schofield 1988 Biosystematics
of haematophagous insects, p. 285-312. MW Service Oxford).
Triatoma sordida, a species associated with silvatic and
peridomestic habitats, is currently found in houses in some
rural areas of Bolivia, particularly in La Paz and Santa Cruz
departments (E De Muynck 1977 Bol Inform CENETROP 3: 41-
51, F Noireau et al. 1995 J Med Entomol 32: 594-598). The
analysis of the present distribution of T. sordida in
Bolivia, in comparison to 20 years ago data, gives a clear
indication of the reduction of the area within which this species
is found in houses and its substitution by T. infestans,
the most important vector of Chagas disease in this country.
Our first study area was the Yungas in the department of La
Paz. The Yungas are steep-sided valleys covered with subtropical
forest in the foothills of the Eastern Andean Cordillera. Both
T. infestans and T. sordida were reported more than
50 years ago in several main villages such as Chulumani, Coripata
and Coroico; T. sordida was the only triatomine species
collected in many houses in Chulumani and Villa La Fuente (S
Mazza 1942 Prensa Med Arg 29: 1-15). In spite of the
competitive superiority of T. infestans over T.
sordida in houses, probably due to its faster development
coupled with the greater accessibility to blood offered by man
and domestic animals, the coexistence of both species in this
region was likely to have been due to the relative human
stability in this period (E Juarez & EP de C Silva 1982 Rev
Saude Publ 16 (supl.): 1-36, Schofield 1988 loc. cit.,
ME Bar et al. 1994 Rev Saude Publ 28: 59-68). An
entomological survey performed 50 years later, in 1992, in the
small towns of Coroico, Coripata and Chulumani, as well as
villages situated in the valleys surrounding them, pointed out
the dispersal of T. infestans. 795 domestic triatomines
were collected and taxonomically identified by morphology (all
specimens) and genetics (confirmation of the taxonomic status for
nymphal instars by isozyme analysis). All specimens belonged to
T. infestans species except one 4th-instar nymph of the
T. sordida species. The spread of T. infestans and
the associated virtual disappearance of T. sordida from
houses had very likely occurred in association with the intense
human migratory flow from the endemic regions of Bolivia to the
Yungas during the 1950-1976 period (in the Yungas, the yearly
increasing rate of population was 3.62% compared to 2.05% for
Bolivia as a whole; Censo Nacional de Poblacion y vivienda,
Bolivia, 1992).
The Velasco province, located in the north of Santa Cruz
department, was the second study area. This province, which forms
part of the Chiquitania region, is made up of a mosaic of
woodlands and wooded savannas. Until recently T. sordida
was the only triatomine species reported to colonize houses in
this province (De Muynck 1977 loc. cit., J Salcedo et al.
1980 Bol Inform CENETROP 6: 2-10). An entomological survey
was performed in 1994 following the same process of taxonomic
identification as described above. It pointed out the rapid
penetration of T. infestans to this region during the last
15 years: among 26 investigated localities in the Velasco
Province, T. sordida was found as the only species
infesting houses in 18 localities (69%), while T.
infestans was collected in 8 other localities associated or
not with T. sordida. The few localities infested by T.
infestans are situated in areas which have recently
experienced substantial human migrations (during the 1976-1992
period, the yearly increasing rate of Velasco population was
3.50% compared to 2.11% for Bolivia as a whole; Censo Nacional
de Poblacion y vivienda, Bolivia, 1992). On the contrary,
isolated villages located off the lines of communication and
consequently less affected by migration are still free of T.
infestans. Nevertheless, such isolated villages may be
considered as being at risk to the short-term spread of T.
infestans. Such is the case in Tacoigo, located in the middle
of the area considered as free of T. infestans, one
specimen of this last species was recently collected in
association with 65 T. sordida. These surveys show that
in Bolivia as elsewhere T. infestans, when introduced into
new areas, quickly displaces T. sordida from human
dwellings.
Acknowledgments: to J Johnson for reviewing the
manuscript; to N Yaksic, J Telleria, J Ordonez and S Garcia H for
technical assistance.
Financial support from the UNDP/World Bank/WHO Special Programme
for Research and Training in Tropical Diseases (TDR).
^+Corresponding author. Fax: 591-2-39.1854
Received 21 September 1995
Accepted 29 January 1996
Copyright 1996 Fundacao Oswaldo Cruz
|