Group discussion: epidemiological, social, and control determinants of Chagas disease in Central America and Mexico

Abstract

The existence of Chagas disease in Central Americawas reported for the first time in El Salvador in 1913,four years after its discovery in Brazil. At that time onlyTriatoma dimidiata was known as a vector, but two yearslater, in the same country, Rhodnius prolixus was dis-covered, which is a more efficient vector and now con-sidered to be an introduced species in the area.Several epidemiological and clinical studies haveshown that, with the exception of Belize, the disease isendemic in all Central American countries and in cer-tain areas has become a serious public health problem.This led the health authorities of the countries to launchthe Central American Initiative for the control of Chagasdisease in 1997. Since that date, several actions havetaken place, aiming to eliminate R. prolixus from theregion, lower vectorial transmission by T. dimidiata , andcontrol transmission by blood transfusion.Summary of the discussion of Dr Ponce paperDr Zeledon - I would like to add two important epi-demiological facts related to the situation in Nicaragua:the recent finding of R. pallescens in the DepartmentRio San Juan, on the border with Costa Rica, and the pres-ence, in some departments of the northeast and south-east of the country, of T. ryckmani.The presence of a species of Rhodnius in Rio SanJuan, led the Ministry of Health personnel to spray 2000houses with insecticide convinced it was R. prolixus untilit was realized that the species present in the area wasactually R. pallescens . The latter has been found mainlyin the peridomiciles but in at least four houses somenymphs were also found indoors, suggesting an initia-tion of colonization of those houses. A serological sur-vey in school children yielded 6.7% of positive tests and inspite of the occasional finding of T. dimidiata, R. pal-lescens seem to be an important vector in the area. On theCosta Rican side, R. pallescens is only a visitor of housesand the seroprevalence there, also in school children, islow (0.24%). In both sides across the border, R. pallescenshas been found in palm trees (Attalea butyracea).In relation to T. ryckmani, the species is becoming afrequent visitor inside and outside houses where adultsare attracted to lights. In Guatemala, the species has beenfound living in bromeliads of the genus Tillandsia insemiarid regions of the country and in a few instances itis able to colonize human dwellings. The bromeliadswhere this bug breeds, are used locally for decorationsand are also exported abroad and this could become amechanism for dissemination of the insect.Another aspect worth mentioning is in reference toenvironmental management methods for the control ofT. dimidiata as was recommended in a technical work-shop on the species held in San Salvador in 2002. A pi-lot project was implemented in Costa Rica by modify-ing the environment around a group of houses in orderto destroy the peridomestic habitats and make difficultthe colonization of the bug in those areas, with very prom-ising results.Going back to the hypothesis that R. prolixus is anexotic species in Central America, the idea originated in1995 in the ECLAT meeting of Santo Domingo de losColorados, Ecuador. After the meeting, Dr Ponce wasable to transmit the idea of a possible elimination of thespecies to the Minister of Health of Honduras who mean-while was able to convince the health authorities of theother countries to include this premise as an objectiveof the Central American Initiative for the control ofChagas diseases, which was created, also at the requestof Honduran authorities, two years later. This is a goodexample of a scientist transferring knowledge and ad-vising a politician, leading to the political will of con-verting it into action.Dr Ponce - It is possible that R. prolixus could dis-appear from Central America within the next two years.Dr Silveira - It is unacceptable as an aim of the Cen-tral American Initiative just the reduction of the infesta-tion by T. dimidiata. Reduction to which level? Does itcorrespond to the control of the domiciliary transmis-sion or just to the interruption of transmission? In thecase of autochthonous vectors the “possible” level ofcontrol of the vector is the elimination of its intrado-miciliary colonies avoiding its re-colonization throughcommon entomological surveillance actions.Dr Ponce - I agree.Dr Silveira - Was the protocol for interventions onR. pallescens in Panama, proposed by a team during aninternational evaluation in that country, finally applied?Dr Ponce - Not yet due to changes in personnel inthe country but is being considered at present.