Mem Inst Oswaldo Cruz, Rio de
Janeiro, Vol. 97(1) 2002, pp. 43-46
Triatomines Involved in Domestic
and Wild Trypanosoma cruzi Transmission in Concepción, Corrientes,
Argentina
María Esther Bar/+, Miryam
Pieri Damborsky, Elena Beatriz Oscherov, Alicia María Francisca Milano,
Gilberto Avalos, Cristina Wisnivesky-Colli*
Cátedra de Artrópodos, Facultad
de Ciencias Exactas y Naturales y Agrimensura, Universidad Nacional del Nordeste,
Av. Libertad 5470 (3400) Corrientes, Argentina *Unidad de Ecología de
Reservorios y Vectores de Parásitos, Departamento de Ciencias Biológicas,
Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos
Aires, Argentina
+Corresponding author. Fax: +54-3783-473930. E-mail: mebar@exa.unne.edu.ar
Received 5 March 2001
Accepted 23 August 2001
Code Number: oc02006
An entomological and serological survey was
performed in three localities of the Department of Concepción, Province
of Corrientes, Argentina in 1998 and 1999, to identify triatomines species involved
in domestic and wild transmission of Chagas disease. Triatomines were collected
by man/hour capture in 32 houses randomly selected and 44 nearby outdoor ecotopes.
Trypanosoma cruzi infection
in triatomines was assessed by direct microscopic observation (400x) of feces
and polymerase chain reaction. Serological techniques used for people were Indirect
Hemagglutination Test and Indirect Fluorescent Test. Triatomines were collected
in 28.1% of the houses and 31.8% of the wild biotopes. Triatoma
infestans (Klug 1834) was exclusively
found indoors and T. cruzi infected
60% of them. Triatoma sordida
(Stål 1859) was mainly found in extradomestic ecotopes where trypanosome
infection rate reached 12.7%. Serological study of 98 local people showed that
29.6% were seroreactive; most of their houses were closed to wild biotopes colonized
by T. sordida.
Results indicate that there is an active T.
infestans mediated transmission of Chagas
disease in this zone that yields important human prevalence and that the populations
of T. sordida
in wild biotopes not only sustain the wild T.
cruzi cycle but also represent an actual
risk for people living in the area.
Key words: Triatoma infestans - Triatoma sordida
- infestation - infection -seroprevalence - Argentina
In rural areas of Corrientes Province, Triatoma
infestans (Klug 1834) is mainly found indoors and is also present in peridomestic
premises (Bar et al. 1992, 1996b, 1997).
T. sordida (Stål 1859) colonizes
wild biotopes (Bar et al. 1996a) as well as artificial ecotopes in peridomestic
areas, sometimes coexisting with T. infestans and even established inside
a rural house (Bar et al. 1992, 1996b). In Corrientes city it frequently invades
houses and a large colony was captured in an urban ecotope (Bar et al. 1993).
Although intradomestic colonies of T. infestans
have been eliminated from some areas of Corrientes province, T. sordida
may replace it as a domestic vector. Integration of extradomestic triatomines
to domestic transmission cycles has been occasionally reported in Minas Gerais,
Brazil (Diotaiuti et al. 1993).
Anthropic environmental modification, mainly
the replacement of natural forest by cultivated land, harvesting of wood and
uncontrolled grazing may produce a concentration of wild mammals and triatomines
in the peridomicile, generating local transmission cycles of Trypanosoma
cruzi. Those foci can provide invading vectors to the domicile that can
eventually carry trypanosomes (Wisnivesky-Colli et al. 1993). The peridomicile
may represent a transition environment for triatomines coming from the wild
and facilitate their domiciliation process (Gajate et al. 1996).
An important flood affected Corrientes Province
in 1998, as a consequence of the El Niño phenomenon, which made the owners
of the dwellings leave them temporarily. Most of the houses were rebuilt afterwards.
This entire situation contributed to the increase
of the environmental disturbance.
In order to increase our knowledge on the ecology
of domestic and wild triatomines, an entomological and serological survey was
carried out in rural settlements of the Department of Concepción, Corrientes.
MATERIALS AND METHODS
Study area - The study area was situated
in the localities of Santa Rosa, Colonia Tabay and Colonia Tata Cuá of
the Department of Concepción, Corrientes, Argentina (27º to 28ºS
and 57º to 58ºW). Biogeographically the area belongs to the oriental
district of the Chaco region (Cabrera & Willink 1973).
Socioeconomic characteristics - Most of
the houses were built with materials obtained from the environment. Wood walls
and sheet metal or cardboard roofs were observed in 62.5% of the households,
the remainder had mud stick walls and thatched roofs. Similar materials were
used to built the storerooms and kitchens.
Domestic animals were present in 97% of the households,
of which 80.5% were dogs, 55% cats and 53% hens.
Peridomestic ecotopes were open structures made
with sticks or wood, partially covered or not by a roof, 5-20 m far from the
domiciles.
The main activities are agricultural production
directed to the family subsistence and temporary employment in cattle rearing
or in the sawmills.
Field work - Houses were selected at random
and nearby outdoor premises like hen and pigeon houses, pens, kennels and wild
biotopes (piled trunks, palms, bird nests) were examined. Triatomines were collected
by man/hour capture (Wisnivesky-Colli et al. 1987) using dislodging substances
("Neopynamin": tetramethrin 0.2%). The study was carried out during
four seasons: spring (1998) and summer, autumn and winter (1999), after the
"El Niño" phenomenon.
Laboratory work - Triatomines were taxonomically
determined and classified by sex and instars (Lent & Wygodzinsky 1979, Carcavallo
et al. 1997). Trypanosome infection in collected triatomines was initially assessed
by direct microscopic observation of feces (400x). Observed parasites were identified
as T. cruzi by PCR of DNA from feces dried on Whatman paper no.1 (Russomando
et al. 1996). One pair of specific TCZ primers were used (Mozer et al. 1989).
Human blood was collected from voluntary residents
by venipuncture. Diagnosis of Chagas disease infection was performed combining
Indirect Hemagglutination Test and Indirect Fluorescent Test. Individuals were
considered positive if they were simultaneously reactive in both tests at serum
dilution ³ 1:32. Of 163 residents in this area,
98 people were studied, considering a previous estimated 30% prevalence of infection
and a 90% confidence interval.
RESULTS
Entomological survey - From a total of
32 houses and 44 outdoor biotopes searched, triatomines were found in 28.1 and
31.8% respectively. T. cruzi infection was recorded in 60% of T. infestans
and in 12.7% of T. sordida individuals.
Total triatomines collected according to stages,
species and seasons are recorded in Table I.
Winter - Eight houses and nine peridomestic
premises were searched but no triatomine was found. Two out of three wild biotopes
were infested by T. sordida nymphs (N = 9) and Psammolestes coreodes
adults (N = 3). None of them was infected by T. cruzi.
Spring - Seven houses were searched and
three were infested by T. infestans (N = 19). One out of three collected
adults was infected by T. cruzi. Entomological searches were performed
in seven peridomestic premises and three wild biotopes. The 12.5% of captured
triatomines were infected. One infected T. sordida female was found in
a pigpen. In two wild biotopes we collected 29 T. sordida, mainly nymphs
of fifth instar.
Summer - In three infested houses from
seven examined, we found 28 T. infestans bugs including T. cruzi
infected adults. Hatched T. sordida eggs were found inside a bed. In
one peridomicile, numerous fecal streaks of triatomines were recorded.
In 75% of eight examined wild biotopes a total
of 27 T. sordida insects were collected. T. cruzi was detected
in 17.4% of collected wild triatomines.
Autumn - Ten houses resulted to be not
infested by live triatomines, however hatched eggs were found in two of them.
All of the ten peridomiciles examined rendered negative results.
T. sordida nymphs (N = 13) were collected
in two wild biotopes and T. cruzi infection was confirmed in 1fifth instar
nymph.
Serological survey - We studied men and
women from 1-96 years old that were permanent residents of both infested and
non-infested dwellings. The overall prevalence rate of infection by T. cruzi
in the analyzed population was 29.6% (Table
II). Our data documented a seroprevalence of 12.2% in children up to 10
years old. Meanwhile the infection rate observed in the following age group
was approximately four times greater. Half of all people older than 30 years
(9/18) were seroreactive. No significative difference was observed between sexes
(c2 = 0,36, p = 0,56).
DISCUSSION
The study area has undergone a strong environmental
impact due to man-made practices like replacement of natural vegetation by citrus
crops, Pinus sp. and Eucaliptus sp. forestation and timber extraction.
Although the 1998 flood destroyed primitive mud-bricked
dwellings and new wooden houses were built instead, colonies of T. infestans
were present indoors. The finding of eggs, first instar nymphs and adults in
these new houses indicated a recent infestation. The insects could have arrived
from the old houses with clothes and furnitures or from neighboring ecotopes.
A high proportion of wild biotopes was infested
and harbored infected vectors. This fact was not observed in peridomestic areas,
which is in concordance with those results verified in other localities (Bar
et al. 1996b). The epidemiological situation in peridomestic areas is not similar
to other Argentinian and Brazilian regions where the levels of peridomicilies
infestation are very high (Diotaiuti et al. 1994, Gajate et al. 1996).
At a settlement in Colonia Tabay, located near
those wild foci, we observed a high domiciliary colonization of infected T.
infestans. Besides, T. sordida was frequently found in the wild environment
and showed a high natural infection index by T. cruzi. Under those circumstances,
interaction among wild and domestic cycles may be possible and mediated by an
interchange of parasites between mammals and vectors in their respective habitats.
In Concepción the infestation index was similar to the one in Empedrado
(Bar et al. 1997) and lower than those of other areas of the province of Corrientes
(Bar et al. 1992, 1996b).
In spite of the insecticidal action carried out
in the past, neither the rural health agents nor the Chagas Provincial Service
followed any systematic actions. It could be concluded that these campaigns
did not have enough success considering the infection and infestation results
obtained in this study. A systematic residual insecticide spraying program should
be applied in order to control the recovery of the vector population.
Peridomestic habitat lacked adequate structural
conditions to facilitate triatomine colonization. Nevertheless the question
about the ability of T. sordida to replace T. infestans inside
houses still remains.
The highest densities of T. sordida, the
most important wild vector in the studied area, were registered in spring and
summer, when mainly older nymphs and adults were collected. The small number
of collected females could result from early dispersion after molting probably
to colonize other biotopes.
This is the first citation of T. sordida
and P. coreodes in the Department of Concepcion and involves a widening
of their present geographic distribution.
The seropositivity rate among the age group of
higher transmission risk (0-10 years old) was similar to that reported for San
Miguel (Bar et al. 1996b). However, the seroreactivity obtained in the remaining
age groups revealed that humans in Concepcion show the highest rates in relation
with populations from other localities (Bar et al. 1992, 1996b, 1997). The serological
increasing trend was similar to those from highly endemic areas located in the
western dry area of the Chaco region (Wisnivesky-Colli et al. 1989).
The infection profile of the inhabitants suggests
the existence of a strong past and a moderate present transmission of T.
cruzi. This control probably reflects the anti vectorial activities of the
Southern Cone Initiative to eliminate T. infestans (Schofield & Dias
1999), and call special attention to the necessity to continuous this program,
under the risk to revert the actual situation to the original one, with high
indexes of transmission.
REFERENCES