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R. prolixus

R. prolixus is the primary Chagas disease vector in Venezuela and Colombia (Fig. 8.7), and was responsible for significant numbers of human infections before its recent eradication in Central America.3 Its epidemiological importance is due to its high degree of adaptability for living in human habitations, where it can build up very large colonies.73

Approximate current distribution of R. prolixus

Figure 8.7 Approximate current distribution of R. prolixus.

Source: Data updated from World Health Organization. Geographical distribution of arthropod- borne diseases and their principal vectors. WHO/VBC/89.967, Geneva; 1989.65 Artist: Linda Waller; Photographer: James Gathany (Centers for Disease Control and Prevention).

A single or multiple species?

As with T. infestans and T. dimidiata, there is uncertainty about R. prolixus being a single or multiple species, and whether the morphologically indistinguishable R. robustus is a sister taxa or subspecies. Slight morphological differences74 combined with the observation that the smaller R. prolixus often forms large domestic colonies, whereas R. robustus seems to be exclusively sylvatic, led to the use of “smaller size and domesticity” versus “larger size and nondomesticity” as a practical means to separate R. robustus from R. prolixus?5 Most importantly, it was also believed that domestication occurred only once and that all R. prolixus populations became reproductively isolated from their sylvatic counterparts.76

Mitochondrial DNA sequence analyses were crucial to confirming that R. prolixus and R. robustus are separate species, and that R. robustus comprises a species com- plex.77 However, the confirmation of R. prolixus and R. robustus as separate taxa does not remove the challenge to household level insecticide-based vector control efforts. Control efforts against R. prolixus, although quite successful in Central America, have been hampered in Venezuela and Colombia where sylvatic populations co-occur. In Venezuela challenges to vector control efforts were indicated by a study combining

cyt b and microsatellite data finding no difference between domestic and nearby sylvatic populations; however, there was evidence of past hybridization and introgres- sion.8 In Colombia, one study of four populations, three domestic and one sylvatic, reported genetic differentiation among all the populations, leaving the question of differentiation between geographically close domestic and sylvatic unresolved.78

Implications for control and future studies for R. prolixus

These findings indicate sylvatic R. prolixus populations are a perennial source of migrants to recolonize insecticide-treated area constituting real challenge to vector control. In light of the ease with which R. prolixus colonizes houses, suitable habitat inside houses through Ecohealth strategies, is the best option to diminish domestic populations.79

Further knowledge on the genetic structure of natural populations is likely to advance quickly, with 20 newly described microsatellite loci of R. prolixus8 Another important scientific accomplishment that will certainly revolutionize the field is publication of the R. prolixus genome,81 which at the very least will allow for the identification of many new nuclear markers.

 
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