Towards environmental detection of Chagas disease vectors and pathogen

Background Accurate surveillance of triatomine household infestation is crucial for Chagas disease vector control. However, no gold standard detection method with high levels of sensitivity or specificity is currently available. Several intrinsic features of triatomine bug behaviour and the lifecycle of Trypanosoma (T.) cruzi lead to deposition of environmental DNA (eDNA) in infested houses. This study evaluated the use of FTA cards and cotton-tipped swabs as low-technology, cost-effective tools for simultaneous detection of T. cruzi and vector eDNA in the laboratory and field.

Methods/Principal Findings This study had two components: (1) laboratory evaluation and optimisation of QIAcard® FTA® classic cards to detect Rhodnius (R.) prolixus eDNA by altering five different environmental variables (darkness, triatomine number, temperature, feeding status and degradation at ambient temperature); (2) detection of R. prolixus and T. cruzi eDNA from cotton-tipped house wall swabs from an endemic region in Casanare Department, Colombia. eDNA was extracted from all specimens and amplified using a multiplex TaqMan qPCR assay targeting the R. prolixus 12S rRNA gene and T. cruzi satellite DNA region. R. prolixus eDNA from five 3rd/4th instar nymphs was successfully amplified from FTA cards after as little as 15 minutes of contact time under standard insectary conditions. Factors significantly increasing eDNA detection from FTA cards were increasing temperature from 21°C to 27-32°C, triatomine bug density from 1-25 bugs and recent blood-feeding. eDNA was detectable from FTA cards stored at room temperature for at least two weeks. In cotton-tipped swabs from the field, the sensitivity and specificity of R. prolixus eDNA detection was 60.6% (n=20/33) and 100% (n=33/33), respectively. T. cruzi eDNA was amplified from 93.9% (n=31/33) of infested houses.

Conclusions/Significance FTA cards are a highly sensitive tool for entomological surveillance of R. prolixus and exhibit little variability under different environmental conditions. Additionally, cotton-tipped swabs are a relatively sensitive tool for entomological and parasitological surveillance of R. prolixus and T. cruzi in situ, but more feasible due to low cost. Both methods could be utilised by citizen science initiatives to contribute to the control of Chagas disease in endemic communities.