Vector mapping and bloodmeal metabarcoding demonstrate risk of urban Chagas disease transmission in Caracas, Venezuela

Abstract

Chagas disease is a significant public health risk in rural and semi-rural areas of Venezuela. Triatomine infection by the aetiological agent Trypanosoma cruzi is also observed in the Metropolitan District of Caracas (MDC), where foodborne T. cruzi outbreaks occasionally occur but active vector-to-human transmission (infection during triatomine bloodmeal) is considered absent. Citizen science-based domiciliary triatomine collection carried out between 2007 and 2013 in the MDC has advanced understanding of urban T. cruzi prevalence patterns and represents an important public awareness-building tool. The present study reports on the extension of this triatomine collection program from 2014 to 2019 and uses mitochondrial metabarcoding to assess feeding behavior in a subset of specimens. The combined, thirteen-year dataset (n = 4872) shows a high rate of T. cruzi infection (75.2%) and a predominance of Panstrongylus geniculatus (99.01%) among triatomines collected in domiciliary areas by MDC inhabitants. Collection also involved nymphal stages of P. geniculatus in 18 of 32 MDC parishes. Other collected species included Triatoma nigromaculata, Triatoma maculata, Rhodnius prolixus, and Panstrongylus rufotuberculatus. Liquid intestinal content indicative of bloodmeal was observed in 53.4% of analyzed specimens. Dissection pools representing 108 such visually blooded P. geniculatus specimens predominantly tested positive for human cytochrome b DNA (22 of 24 pools). Additional bloodmeal sources detected via metabarcoding analysis included key sylvatic T. cruzi reservoirs (opossum and armadillo), rodents, and various other synanthropic and domesticated animals. Results suggest a porous sylvatic-domiciliary transmission interface and ongoing adaptation of P. geniculatus to the urban ecotope. Although P. geniculatus defecation traits greatly limit the possibility of active T. cruzi transmission for any individual biting event, the cumulation of this low risk across a vast metropolitan population warrants further investigation. Efforts to prevent triatomine contact with human food sources also clearly require greater attention to protect Venezuela's capital from Chagas disease.

Fig 1

A. Numbers of triatomine specimens obtained from each MDC parish for the collection period 2007–2019. Fill color in the choropleth map represents the total number of specimens obtained per parish, increasing from lighter to darker blues. No specimens were obtained from Catedral parish (#6, white fill). A total of 4872 specimens were obtained across 31 parishes. B. Rates of natural T. cruzi infection in triatomine specimens from each MDC parish for the collection period 2007–2019. Fill color in the choropleth map represents the rate of T. cruzi infection (by microscopy) per parish, increasing from lighter to darker blues. Infection occurred in all parishes from which triatomine specimens were obtained. The analyzed sample set represents 3845 specimens. C. Rates of observing liquid material (potential bloodmeal) in triatomine intestinal content from each MDC parish for the collection period 2007–2019. Fill color in the choropleth map represents visually blooded triatomine occurrence per parish, increasing from lighter to darker blues. The visually blooded condition occurred in all parishes from which triatomine specimens were obtained. The analyzed sample set represents 4422 specimens. A random subset of visually blooded specimens from Petare (#32), Baruta (#23), and Sucre (#22) feature in bloodmeal barcoding analysis. The country map at bottom was created using 1:10 m cultural vectors from https://www.naturalearthdata.com. MDC maps above contain information from OpenStreetMap and OpenStreetMap Foundation, which is made available under the Open Database License. Specifically, parish boundaries were plotted using administrative level 7 lines downloaded with the OpenStreetMap Overpass API [42].

Fig 2. Monthly triatomine yield for the MDC collection period 2007–2019.

Line color indicates collection year. Media attention to an oral Chagas disease outbreak in May 2010 may help explain the high collection numbers of May and June 2010.

Fig 3. Annual rates of natural T. cruzi infection and observations of blood-like intestinal content in male and female triatomine specimens for the MDC collection period 2007–2019.

Blue color indicates the rate of T. cruzi infection among 3845 specimens analyzed. Red color indicates the rate at which blood-like intestinal content was observed among 4422 specimens analyzed. Circles and squares indicate values for females and males, respectively.

Fig 4. Vertebrate DNA sources identified in 108 pooled P. geniculatus bloodmeals from Petare, Baruta, and Sucre parishes for the MDC collection period 2009–2016.

Points in the map indicate the geographical origin of the 108 samples contributing to the 24 dissection pools used in cytb analysis. Point fill color indicates pool membership. Pools composed of T. cruzi-positive samples are outlined in black. Arrows indicate pools presenting cytb DNA from the T. cruzi reservoir species D. marsupialis and D. novemcinctus. Numbers in parentheses indicate the number of pools in which the corresponding vertebrate blood source was detected. The map base layer represents Scene ID LC80040532015120LGN01 from the Landsat 8 OLI/TIRS C1 Level-1 dataset–courtesy of the U.S. Geological Survey.