Evaluation of Diagnostic Tests for Trypanosoma evansi in Experimentally Infected Pigs and Subsequent Use in Field Surveys in North Vietnam and Thailand

Abstract

This study is concerned with the evaluation of established diagnostic tests for diagnosis of Trypanosoma evansi in pigs. The immune trypanolysis test (TL), card agglutination test (CATT), latex agglutination test (LATEX), enzyme-linked immunosorbent assay (ELISA), microhaematocrit centrifugation technique (MHCT) and mouse inoculation (MI) tests were initially evaluated in experimentally infected fattening pigs. All infected pigs were confirmed parasitologically positive with both MHCT and MI. Results of the serological assays indicated that the TL could be a reference test for the presence of RoTat 1.2 antibodies in pigs. The results of the CATT and LATEX were inconsistent with the TL while the ELISA results correlated with the TL results. The four serological assays were subsequently used in two field surveys in Vietnam and Thailand. Results of the two agglutination assays (CATT and LATEX) were not consistent and did not correlate with TL results. The ELISA at percentage positivity of 22 appeared to have good ability to discriminate between seropositive and seronegative animals. Of the 437 samples collected at smallholder pig premises in northern Vietnam, no positive pigs were detected with the TL test. In Thailand, 77 samples were collected from five farrowing farms with a history of surra. Two parasitologically positive sows were found and on each farm seropositive sows were detected.

Serological tests for gambiense human African trypanosomiasis detect antibodies in cattle

“…This would be expected, since TL detects antibodies that are specific to the VATs in the test [ 11 ], in this case only anti-VSG LiTat 1.3 and anti-VSG LiTat 1.5 antibodies. A similar difference between TL tests and other screening tests has been reported in other studies [ 47 ]. The difference in sensitivity between the 1G RDT and TL could be because the VSGs used to develop the 1G RDT are detached from trypanosomes, exposing epitopes that in the live parasites used in the TL test, would not be available to detect antibodies against them [ 52 ].…”

Molecular identification of Trypanosoma brucei gambiense in naturally infected pigs, dogs and small ruminants confirms domestic animals as potential reservoirs for sleeping sickness in Chad

“…We cannot rule out the fact that some positive RDTs could result from crossreactions with epitopes of other trypanosome species [29]. In fact, sera from animals infected with either T. congolense, T. b. brucei or T. evansi have been shown to cross-react with antigens used in the RDT and the card agglutination test for gambiense human African trypanosomiasis [18,43,61]. Moreover, sera from both T. b. gambiense and T. b. rhodesiense patients have induced cross-reactions with a large number of trypanosome antigens including VSG LiTat 1.3 and VSG LiTat 1.5 [1].…”

Evaluation of an Indirect-ELISA Test forTrypanosoma evansiInfection (Surra) in Buffaloes and Its Application to a Serological Survey in Thailand

“…Standardization and validation methods have been developed [ 12 – 15 ]. ELISA T. evansi , initially used on camels [ 16 ], has been adapted to other species such as horses [ 17 , 18 ], buffaloes [ 19 ], cattle [ 20 ], and pigs [ 21 ]. However, the local development of serological tests, including parasite production, mean population responses, and selection of control sera is necessary to cope with the variability in response that may exist between parasite stocks and hosts from different geographic areas [ 13 , 22 ].…”