Lineage-specific rapid diagnostic tests can resolve Trypanosoma cruzi TcII/V/VI ecological and epidemiological associations in the Argentine Chaco

Abstract

Background Trypanosoma cruzi, the protozoan agent of Chagas disease, is comprised of at least 6 genetic lineages (TcI-TcVI). Their geographical distribution, clinical associations and reservoir hosts are not fully elucidated, as genotyping is hampered due to the difficulty in isolating representative populations of organisms. Lineage-specific serological techniques may address these issues. Methods Trypanosoma cruzi lineage-specific serological assays were performed on human, canine, feline and armadillo sera from the Gran Chaco in northern Argentina, a region of ongoing transmission. Synthetic peptides representing lineage-specific epitopes of the trypomastigote small surface antigen (TSSA) were used in ELISA, and the TcII/V/VI shared epitope peptide (TSSApep-II/V/VI) was used in the Chagas Sero K-SeT rapid diagnostic test (RDT). Results Chagas Sero K-SeT RDT, using Protein G to detect human and canine IgG, was at least as sensitive as TSSApep-II/V/VI ELISA using specific secondary antibodies. For sera from humans TSSApep-II/V/VI seroprevalence by Chagas Sero K-SeT was 273/393 (69.5%), for dogs 48/73 (65.8%) and for armadillos 1/7 (14.3%); by ELISA for cats 5/19 (26.3%). The seroprevalence for humans was similar to that for Bolivian patients, amongst whom we previously observed an association of TSSApep-II/V/VI seropositivity with severity of cardiomyopathy. In humans, prevalence of TSSApep-II/V/VI recognition was associated with locality, and with increasing and decreasing age within the Qom and Creole populations, respectively. For dogs TSSApep-II/V/VI recognition was associated with being born before community-wide insecticide spraying (P = 0.05) and with Qom household (P < 0.001). Conclusions We show here that Chagas Sero K-SeT RDT can replace ELISA for TSSApep-II/V/VI serology of humans and dogs; for humans there were statistically significant associations between a positive Chagas Sero K-SeT RDT and being resident in Area IV, and for dogs association with Qom household or with being born before the mass spraying campaign; we also show that with cats the TcII/V/VI epitope can be detected by ELISA. We assessed the lineage distribution in an unprecedented 83% of the human T. cruzi-seropositive population. These results form the basis for more detailed studies, enabling rapid in-the-field surveillance of the distribution and clustering of these lineages among humans and mammalian reservoirs of T. cruzi infection.

A lineage-specific rapid diagnostic test (Chagas Sero K-SeT) identifies Brazilian Trypanosoma cruzi II/V/VI reservoir hosts among diverse mammalian orders

“…Armadillos, especially D. novemcinctus, have been reported as natural hosts of TcIII throughout South America [11,40,41], thus the absence of TcII/V/VI infections from all 49 armadillos was not surprising. Although Chagas Sero K-SeT was shown to be able to detect infection in armadillo [20], positive test line intensity was weak; Protein A may be more appropriate than Protein G for binding of armadillo IgG, as others have reported [42], and which we observed here. No armadillo-specific conjugate was available for ELISA; this also encourages further deployment of Protein A for these important reservoirs hosts.…”

“…Regarding the latter point, the application of serology based on lineage-specific antigens has great potential for resolving the cryptic ecological cycles and the discovery of novel reservoir hosts of this parasite. Applications of T. cruzi lineage-specific serology to naturally-infected animals are with dogs [17,26], primates [18] and sympatric dogs, cats, and armadillo [20]. We have applied Chagas Sero K-SeT to exploit the capacity of Protein G to recognise TSSApep-II/V/VI specific IgG from a range of mammalian Orders.…”

“…This novel, low cost, lateral flow immunochromatographic rapid test was developed with Coris BioConcept, and employs TSSApep-II/V/VI as the coated antigen, and colloidal goldlabelled Protein G as the detection molecule for specific IgG, as previously described [19,20]. Following application of the serum sample on the sample zone (wide green line, Fig 2) then buffer in the buffer window, reactions were considered positive if at 15 minutes incubation a band was observed at the antigen line, in conjunction with an integral test validation line.…”

Glycosylation of Trypanosoma cruzi TcI antigen reveals recognition by chagasic sera

“…Availability of gTSSA-I serology enables parallel investigation of clinical status associated with TcI infection, and serological detection of sporadic TcII/V/VI and TcI co-infections, which occur in some Bolivian and Brazilian endemic foci 40 , 41 . As with application of TSSA-II/V/VI serology to sylvatic mammals 20 , 21 , 23 , 42 , 43 , gTSSA-I can be deployed for resolution of TcI domestic and sylvatic transmission cycles, and for discovery of reservoir hosts. Thus, expression of L. tarentolae recombinant antigens representing epitopes specific to each of the T. cruzi lineages, may facilitate comprehensive epidemiological investigations.…”

“…Furthermore, TcII/V/VI serology, adaptable to rapid diagnostic test (RDT) format, demonstrated that among Bolivian patients stratified by severity of cardiomyopathy, TcII/V/VI seropositives were five-fold more prevalent in the severe versus no evidence of cardiomyopathy groups 22 . RDTs also identified TcII/V/VI seropositive sympatric humans and dogs in the Argentine Chaco 23 .…”