Comparison of diagnostic techniques during subclinical single infections of trypanosomiasis in goats

Trypanosomosis in small ruminants maintained by low riverine tsetse population in central Nigeria

The prevalence of trypanosomosis was investigated over a 12-month period, among small ruminants grazing in known sleeping sickness endemic area of central Nigeria and under light riverine tsetse challenge. Analysis of the data from 304 Yankassa sheep and 239 West African DwarfxRed Sokoto goats indicated high mean prevalence (27.62%, confidence limits Cl: 0.232, 0.312). Interspecies difference between sheep (38.16%; 0.382, Cl: 0.332, 0.432) and goats (14.23%; 0.142, Cl: 0.102, 0.182) was highly significant (P<0.001). Infections were also significantly higher (P<0.05) with agro-pastoral (extensive) management, during the dry season and in adults compared to intensively managed animals, the wet season and young animals, respectively. Trypanosoma vivax was the predominant parasite encountered and accounted for over 49% of the infections. T. congolense and mixed populations were diagnosed at approximately 15% each while T. brucei were absent in caprines. The implications of these findings in the epidemiology of the diseases in both man and domestic animals is discussed.

Evaluation of a simple PCR technique for the diagnosis of Trypanosoma vivax infection in the serum of cattle in comparison to parasitological techniques and antigen-enzyme-linked immuno sorbent assay

Polymerase chain reaction (PCR) with specific oligonucleotides for the amplification of Trypanosoma vivax DNA has been developed by Masiga et al. (1992) to detect the presence of T. vivax DNA in biting flies. The aim of this experiment was to evaluate the efficacy of this technique when applied directly on cattle serum, without DNA purification, to detect infection. The sensitivity of this PCR technique was compared with parasitological techniques, namely haematocrit centrifuge technique (HCT) and buffy coat method (BCM), and with the antigen-enzyme-linked immunosorbent assay (Ag-ELISA) for T. vivax developed by Nantulya and Lindqvist (1989). Blood and serum samples were collected from four calves experimentally infected with a stock of T. vivax from French Guyana (IL4007). During the first 51 days of infection, a total of 164 samples were collected and processed using the four tests. Mean percentages of positive results were 68% with HCT, 59% with BCM, 4% with Ag-ELISA and 64% with PCR. Parasitological and PCR techniques yielded approximately the same sensitivities. PCR was able to detect active infection in serum samples when parasitaemia was over 10(3) trypanosomes/ml. With this isolate of T. vivax the Ag-ELISA was not found to be sensitive enough to be used as a diagnostic tool. The sensitivity of this PCR technique is not greater than parasitological techniques but it allows delayed processing of the samples and gives a highly species-specific diagnosis. This simple PCR technique should be evaluated for field diagnosis because it makes retrospective epidemiological survey using serum banks possible. Moreover, it can be substituted to parasitological techniques when immediate examination is not feasible.

Comparison between six parasitological methods for diagnosis of Trypanosoma evansi in the subtropical area of Argentina

In a total of 165 blood samples from horses in the Province of Formosa (Argentina), the diagnosis for equine trypanosomiasis (T. evansi) was made using Giemsa-stained smears (GSS), wet blood films (WBF), Strout's concentration method (SCM), haematocrit centrifuge technique (HCT), buffy coat method (BCM) and mouse inoculation of blood (MBI). Trypanosoma evansi was demonstrated in 52 samples. Mouse inoculation gave a sensitivity of 88.2%; HCT 71.1%; BCM 63.4%; WBF 53.8%; SCM 46.1% and GSS 45.6%. No single method alone was totally effective. The haematocrit centrifuge technique, mouse inoculation of blood and Giemsa-stained smears were proposed as the most effective diagnostic combination.

Small ruminant trypanosomiasis in Guyana--a preliminary report

Trypanosomes identified as Trypanosoma vivax were found infecting nine sheep (4.6%) and one goat (1.3%) on four of 11 farms surveyed on coastal Guyana. Animals sampled on another farm situated in the Rupununi savannahs gave negative results. Haematological techniques preferred for studies of this nature were the haematocrit centrifuge technique (HCT) and the thick blood smear technique.

Recent studies of the biology of Trypanosoma vivax

Recent biological investigations of the African trypanosomes have been moving away from their previous preoccupation with the phenomenon of antigenic variation. The feeling has arisen that antigenic variation, as demonstrated by the Trypanozoon and Nannomonas subgenera of trypanosomes, is too extensive, the number of serodemes too large and the coexistence of different species in many areas too complicated, to allow any immunoprophylaxis based on antibodies to variable antigens. This is, of course, not to rule out possible biochemical intervention in the biosynthesis or export of VSG molecules by trypanosomes. However, in the case of T. vivax, more information is required concerning antigenic variation and coat structure in this organism before these avenues of investigation are discarded. Ways of improving the yield of mature metacyclic trypanosomes in vitro must be found, so that the contribution of metacyclic variable antigens to the induction of immunity in T. vivax infection can be elucidated. The number of bloodstream VATs must be determined (perhaps by genetic rather than serological means), as there is evidence both for VAT exhaustion contributing to the self-cure of infected hosts, and for a possible limit to the number of VATs which can be expressed in infections in Africa. In South America nothing is known of the number of serodemes of T. vivax which exist, although such knowledge is obviously required, especially if immunity to bloodstream variants is the more important mechanism of inducing immunity to this trypanosome and true cyclical transmission is rare in, or absent from, that subcontinent. Further, in a fragile organism, with a coat of suspect integrity, the method of VSG packing and the relative exposure of underlying surface molecules seems to hold out even more hope for an immunological intervention based on cell surface but invariant molecules than is the case with T. brucei or T. congolense, although this is being attempted with the latter species. In T. brucei infections the appearance of the non-dividing stumpy population acts as a stimulus to the induction of humoral immune responses. In ruminants, antibody responses to T. vivax, at least as judged from lysis tests, lag behind the appearance of the different VATs by some days. It would be important to determine, therefore, whether, if late bloodstream forms could be induced more frequently in the ruminant, the speed of anti-VAT responses could be enhanced. Whilst self-cure appears to be relatively common in T. vivax infections, it is unlikely that it results in sterile immunity.(ABSTRACT TRUNCATED AT 400 WORDS)