Interruption of Chagas disease transmission in the Andean Countries: Colombia

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Abstract
From a total population of 360 million people living in areas endemic for Chagas disease, it is estimated that at least 100 million are exposed to the risk of infection, and that 16 to 18 million are currently infected with the causative agent, Trypa- nosoma cruzi. According to estimates in 1991 by the World Health Organization, approximately 500,000 people become infected each year in the absence of control programmes, and 300,000 out of this number are children. The mortality rate can reach 5 to 15% during the initial acute phase of the infection. In Colombia, the first case of Chagas disease was reported in 1929. Since then, numerous stud- ies have contributed to our epidemiological knowl- edge (Marinkelle 1975), and it is now estimated that there are 1,3 million infected people in the country, with a further 3,6 million people consid- ered at risk since they live in regions known to harbour the domestic insect vectors. Fig. 1 shows the vectorial transmission areas in Colombia, with estimates of their different risk levels. Twenty species of triatomine vectors have been reported in Colombia. The most important in epi- demiological terms are those that live in close as- sociation with humans, living in cracks and crev- ices of rural dwellings and emerging at night to suck the blood of the sleeping occupants. Rhodnius prolixus, is the main domestic vector in Colombia, followed in importance by Triatoma dimidata and T. maculata. Other species such as R. robustus, R. brethesi, R. pallescens and T. venosa are generally silvatic in habit, rarely coming in contact with hu- mans and so of lesser epidemiological significance (D'Alessandro et al. 1981). The importance of each species as a vector of T. cruzi depends on several factors, such as geographical distribution, density of domestic or peridomestic populations, prefer- ence for feeding on humans or other domestic ver- tebrates, feeding frequency, susceptibility to the infection, and capacity to produce the infective metacyclic trypomastigote forms of T. cruzi. All these factors, taken as a whole, are important for the implementation of vector control programmes and epidemiological surveillance of Chagas dis- ease transmission. The insect vectors probably account for over 90% of transmission of T.cruzi to humans, but transmission can also occur via blood transfusion from infected donors. This is also important in Colombia where an average of 450,000 blood- units/year are used, and the prevalence of the in- fection in blood donors ranges from an average of 3.3% in endemic areas, to 1.3% in non-endemic areas.