Panstrongylus geniculatus and four other species of triatomine bug involved in the Trypanosoma cruzi enzootic cycle: High risk factors for Chagas' disease transmission in the Metropolitan District of Caracas, Venezuela

Abstract

Background: Chagas' disease is caused by the protozoan Trypanosoma cruzi and is autochthonous to the Americas. Its distribution depends on triatomine bugs that are responsible for the transmission of the disease. In 2005, we reported the presence of Panstrongylus geniculatus as a risk for Chagas' disease transmission in Caracas and neighboring areas. Three massive oral outbreaks occurred in the following years. Here we report the results of a 7-year study on triatomine species found in the Metropolitan District of Caracas (MDC), Venezuela. Methods: Triatomine species collected by inhabitants of Caracas during 7 years were analyzed for parasite infection and blood meal. Triatomines were found in 31 of the 32 parishes surveyed. Traitomines were examined for the presence of blood and parasites in the digestive tract. Molecular techniques were used for the typing of parasites. Results: A total of 3551 triatomines were captured from 31 of the 32 parishes surveyed. The vast majority of these were identified as P. geniculatus (98.96%), followed by Triatoma nigromaculata (0.59%), Triatoma maculata (0.39%) and Rhodnius prolixus (0.06%). Triatomines were always most abundant between April and June, and 2010 showed the highest number. We found that 54% of the specimens were females, 42.5% males and 3.5% nymphs. Overall, 75.2% of the insects were naturally infected with T. cruzi and 48.7% had fed on blood. Analysis of the adult forms showed that 60% of the females and 31.9 % of the males had blood in their stomachs, and 77.5% of the females and 73.3% of the males were naturally infected with T. cruzi. Nearly all, 99.6% of the T. cruzi isolates analyzed belonged to the TcI genotype. Conclusions: Blood-fed triatomine bugs infected with T. cruzi were distributed throughout Caracas. Four different species of triatomines were identified of which P. geniculatus was by far the most predominant. Our previous report of Eratyrus mucronatus raises the number of triatomine species in the MDC to 5. Dramatic modifications to the surrounding natural habitats have led to the establishment of a T. cruzi urban enzootic cycle, resulting in a high risk for Chagas' disease transmission in this capital city.