Transcript Ecologia silvestre dos triatomíneos

Wild Triatoma infestans, a potential
threat that needs to be monitored
François Noireau
UR 016, IRD, Montpellier, France
IIBISMED, Facultad de Medicina, UMSS, Cochabamba, Bolivia
Triatoma infestans still remains the most important vector of Chagas
disease in the Southern Cone countries
The expected success of large-scale control campaigns relied on its
almost exclusively domestic nature, precluding the recolonization of
treated areas by insects from sylvatic environment
Current evidence that wild populations are much more widespread
than previously thought
Known distributional range of wild
Triatoma infestans in Bolivia
Highland foci
Inter-Andean Dry Forest
1,600 - 2,800 m asl
Lowland foci
Gran Chaco
< 500 m asl
Existence of wild T. infestans in periurban environments
Cochabamba
(> 500,000 inhabitants):
soaring urbanization near
wild vectors refuges
Chromatic plasticity displayed by wild T. infestans
Dark morph
Common morph
“Mataral” morph
The different morphs of wild T. infestans
Name
Distinguishing
morphoch romatic traits
Area of endemism
Habitat
Host-feeding
T. cruzi infection rates
Common morph
"Mataral" morph
Dark morph
-
Large size
Markings on the
conne xivum
Overall dark coloration
Markings on the
conne xivum
Inter-Andean D ry
Forest (>2,000 m asl)
Inter-Andean D ry Forest,
SE Cochaba mba
(~1,700 m asl)
Gran Chaco
(<500 m asl)
Rupico lous
Rupico lous
Arboreal
Small mammals
Small mammals
Probably birds
High
High
Low
Natural ecotopes of Andean wild T. infestans
Rocky outcrops
Cliffs
Fallen rocks
Bioecological traits of a wild Andean
T. infestans population
Cochabamba valley, 2,700 m asl, rocky outcrops
•
30% of the rocky refuges contained
infestans
•
> 90% of nymphal instars
•
One generation of triatomines per year
•
Hosts and T. cruzi reservoirs: rodents
and marsupials
•
T. cruzi infection in vectors > 60% (TcI)
T.
Bioecological traits of the Chacoan
“dark morph” T. infestans
Tita, 350 m asl
•
Natural ecotopes of T. infestans “dark
morph”: hollow trees, cotorra nests
(Myiopsitta monachus ) and bromelias
•
10% of the emergent trees contained
infestans
•
> 90% of nymphal instars
•
Host: parrot (Amazona aestiva)*
•
T. cruzi infection in vectors < 3%
* Ceballos et al. 2009
T.
The origin of T. infestans as a species
•
First hypothesis: Chacoan origin of
T.
infestans:
based
on
the
occurrence, in the Chaco, of the
other species with which T. infestans
is closely related
•
Second hypothesis: Andean origin of
T. infestans: allozymes, genome size
and nuclear rDNA favor this
hypothesis
The origin of T. infestans domestic populations
Traditional speculation
Step 1: domestication of wild guinea
pigs by Andean tribes about 5,000 BC
Step 2: dispersal of domestic vectors in
association with human migrations
The origin of T. infestans domestic populations
New speculation
During the Inca period, maize
production and storage in the
Cochabamba valley
Step 1: transport and distribution
of maize hosting the associated
fauna (wild rodents and insects)
through the Inca Empire
Step 2: dispersal of domestic
vectors in association with human
migrations
Key question: threat represented
populations of T. infestans
by
wild
Can wild populations of T. infestans recolonize insecticide-
treated villages and thus jeopardize control efforts?
Several observations support the epidemiological
risk represented by the wild T. infestans
1. Concerning the apparent distribution of T. infestans
1
2
1. Maximum distribution reached during the 1970’s (Gorla 2002)
2. Current distribution (Schofield et al. 2006)
Records of wild T. infestans
Domestic T. infestans persist in areas where occur wild vectors
2. Concerning the genetic and morphochromatic
variability observed in T. infestans
Various haplotypes (COI and Cytb genes) are shared by
both domestic and sylvatic Andean populations
The distinct "Mataral form”, found in sylvatic
environment in the southeastern Cochabamba
department, is also colonizing houses of the
same region
3. Concerning the process of domestication of T. infestans
T. infestans was, without any doubt, the triatomine
species that displayed the most successfully completed
process of domestication
It is difficult to give credit to the hypothesis that wild forms
of T. infestans would since then have become restricted to
their natural habitat
Genetic diversity and dispersal ability in wild T. infestans
at high altitude: collecting sites
Cochabamba valley, 2,700 m asl
Northern hill
Western hill
Rocky outcrops
Large block of rocks
Houses
Southern hill
Genetic diversity of wild T. infestans based on
the mitochondrial CytB gene
 46 T. infestans characterized
 T. infestans collected in the sylvatic
sites (3 hills and large outcrops)
display genetic variation (7 hapl.)
Northern hill
Western hill
Large outcrops
C
Houses
Southern hill
 T. infestans from the houses
display only one haplotype (C)
also detected in wild triatomines
 Two sylvatic haplotypes (A & C)
were found in domestic bugs from
the region of Sucre*
* Giordano et al. 2005
Domestic triatomines from Cochabamba and Sucre
display haplotypes also detected in sylvatic bugs
Dispersal ability
Microsatellite loci used to detect gene flow between neighboring collecting sites
(< 1 km2)
Northern hill
Western
hill
T. infestans disperses over
continuous land cover (high
significant Fst values)
Large PD rocks
Southern
hill
T. infestans does not disperse
over land cover disrupted by
man made activities
T. infestans does not disperse by flying at high altitude
Current hypotheses
Evidences do not support a continued flow of T. infestans
between sylvatic refuges and domestic environments
In the Andes, the crepuscular coldness restricts flight dispersal and may
hamper the process of domestic intrusion by wild T. infestans
In the Chaco, the emergent trees are become scarce in the vicinity of the
villages. Consequently, the T. infestans "dark morph" would persist in
preserved and remote wooded areas
Finally, only unusual circumstances would generate a transfer
of T. infestans from the natural to the domestic environment
Agradecimientos:
PNCH: Mirko Rojas
FAN Santa Cruz: Teresa Gutierrez
IIBISMED Cochabamba: Team of Lineth Garcia
ETS Cochabamba: Roberto Rodriguez
IOC FIOCRUZ Rio de Janeiro: Teams of José Jurberg and Ana Maria Jansen
IRD Montpellier: Team of Pierre Kengne
Obrigado