Serological tests for gambiense human African trypanosomiasis detect antibodies in cattle

Abstract

BackgroundSerological tests for gambiense human African trypanosomiasis (gHAT) detect antibodies to antigens on the cell surface of bloodstream trypanosomes. As trypanosomes that cause animal African trypanosomiasis (AAT) also express related antigens, we have evaluated two rapid diagnostic tests (RDTs) on cattle in trypanosomiasis endemic and non-endemic regions, to determine whether gHAT serological tests could also be used to screen for AAT.MethodsTwo RDTs, 1G RDT, made with native antigens, and p2G RDT, made with recombinant antigens, were tested on 121 cattle in a trypanosomiasis-free region, and on 312 cattle from a rhodesiense HAT and AAT endemic region. A subset of samples from the endemic region were also tested with two immune trypanolysis (TL) tests. The sensitivity of the tests was estimated by evaluating the result of the RDT on samples that were positive by both microscopy and internal transcribed spacer (ITS) PCR, whilst specificity was the result of the RDT on samples that were negative by ITS PCR and microscopy, and others from the non-endemic region.ResultsThe specificity of the p2G RDT on cattle from the non-endemic region was 97.5% (95% CI: 93.0–99.2%), compared to only 57.9% (95% CI: 48.9–66.3%) for 1G RDT. The specificities of 1G RDT, p2G RDT and TL on endemic control cattle were 14.6% (95% CI: 9.7–21.5%), 22.6% (95% CI: 16.4–30.3%) and 68.3% (95% CI: 59.6–75.9%), respectively. The sensitivities of the tests on trypanosome positive samples were 85.1% (95% CI: 79.1–89.7%), 89.1% (95% CI: 83.7–93.0%) and 59.3% (95% CI: 51.8–66.4%), respectively. Among the same samples, 51.7% were positive by both TL and the 1G RDT.ConclusionsThese serological tests detect cross-reacting antibodies in cattle. The p2G RDT based on recombinant antigens had a high specificity in a non-endemic region, while the 1G RDT had a lower specificity, suggesting cross-reactivity with other pathogens.Electronic supplementary materialThe online version of this article (10.1186/s13071-017-2487-8) contains supplementary material, which is available to authorized users.

Trypanosome infections in naturally infected horses and donkeys of three active sleeping sickness foci in the south of Chad

“…The sero-prevalence of 18.9% revealed here is too high since only 3 (1.04%) animals were found with T. b. gambiense infections. The low specificity of RDT is in line with observations by Matovu et al [31] reporting similar specificity in animals from AAT endemic region. It may result from the fact that the antigens used in RDTs could cross-react with epitopes of other trypanosome species, but are probably not predominant in these species [31].…”

Trypanosome infections in naturally infected horses and donkeys of three active sleeping sickness foci in the south of Chad

“…The sero-prevalence of 18.9% revealed here is too high since only 3 (1.04%) animals were found with T. b. gambiense infections. The low specificity of RDT is in line with observations by Matovu et al [31] reporting similar specificity in animals from AAT endemic region. It may results from the fact that the antigens used in RDTs could cross-react with epitopes of other trypanosome species, but are not probably predominant in these species [31].…”

“…The low specificity of RDT is in line with observations by Matovu et al [31] reporting similar specificity in animals from AAT endemic region. It may results from the fact that the antigens used in RDTs could cross-react with epitopes of other trypanosome species, but are not probably predominant in these species [31]. This is not surprising if we considered the high similarity reported at the genomic level between different trypanosome species [55,56].…”

“…This is not surprising if we considered the high similarity reported at the genomic level between different trypanosome species [55,56]. As already reported in cattle [31], the RDT used for specific identification of T. b. gambiense seems not convenient for horses and donkeys.…”

Infections With Extracellular Trypanosomes Require Control by Efficient Innate Immune Mechanisms and Can Result in the Destruction of the Mammalian Humoral Immune System

“…The reason for the persistence of this misconception about complement lysis of trypanosomes has probably to be attributed to the fact that in vitro antibody-mediated trypanolysis assays are being used as diagnostic tools for the detection of active infections. Indeed, when cultured or purified trypanosomes are incubated in vitro with high amounts of complement-rich guinea pig serum and plasma from infected individuals or animals, trypanosomes tend to lyse over time proportionate to the amount of antitrypanosome antibodies present in the donor serum (89). This phenomenon has been very clearly described in the 1970's in the correct context of the particular in vitro conditions for T. congolense and T. brucei, and the authors also immediately discussed the limitations of the observation with respect to the in vivo situation (90).…”