Brucellosis is a disease of socio-economic and zoonotic importance worldwide. In
animals it is associated with the ingestion of feed that is contaminated with cyetic
material from aborting herd-mates, while in humans it is associated with the
consumption of unpasteurised milk and dairy products from infected animals. It may
also be acquired from contact with infected material of animal origin by farmers,
veterinarians, and abattoir and laboratory workers. Brucellosis was first reported in
South Africa in the late nineteenth century. It is still present in the country today, with
reported annual losses of at least R 300 million, and a national annual incidence of
5 000 cases in humans. The global incidence of human brucellosis is about half a
million infections annually. As the incidence of human brucellosis is directly associated
with prevalence in animals, control of animal brucellosis is emphasised.
Veterinary control is compromised by the chronic nature and the variable incubation
period of the disease, with an estimated up to 15% of cattle in infected herds aborting
before sero-conversion. Latency, which involves about 5% of calves born from infected
dams, is also problematic as these infected animals often test seronegative, only to
seroconvert in the peri-parturient period, thus allowing opportunity for disease spread
within and between herds before diagnosis is made. In addition, the currently used
serological tests are at times unable to distinguish brucellosis from cross-reacting
antibodies from other infections or brucellosis vaccines.
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It was the objective of this study to investigate, under South African conditions, the
value of the brucellin skin test (BST) in improving the sensitivity and specificity of the
currently used serological tests. It has proved a valuable additional test in diagnosing
early and latent infections as well as in differentiating brucellosis from cross-reacting
organisms in unvaccinated cattle in Europe. The study also evaluated the benefit of
replacing some of the currently used serological assays with the fluorescence
polarisation assay (FPA). The FPA, a rapid and homogenous serological test with only
a few operational steps, has been validated and is in current use in Canada.
The study was carried out in Mpumalanga Province, on herds selected to reflect
prevailing South African farming conditions. These herds were divided into certified
Brucella abortus-negative herds (608 head) for the estimation of BST specificity, and
confirmed B. abortus-infected herds (845 head) for the estimation of BST sensitivity.
The results obtained indicated the BST had a specificity of 99.18%, and a relative
sensitivity of 42.86%. However, 65.38% of BST-positive animals were negative on
serology. When the high specificity is considered, together with the experiences of
other researchers who found that the skin test became positive earlier than serological
tests, these animals may be assumed infected. It is concluded that the BST is a
valuable addition to the panel of diagnostic tests currently used to identify infected herds
and individuals in South Africa. The FPA, with a relative sensitivity of 93.65% and a
specificity of 98.85%, can potentially be of use as a screening test under South African
conditions. / Dissertation (MSc)--University of Pretoria, 2012. / gm2014 / Veterinary Tropical Diseases / unrestricted
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:up/oai:repository.up.ac.za:2263/33370 |
| Date | January 2012 |
| Creators | Nyanhongo, Nhamo |
| Contributors | Michel, Anita Luise, nyanhongo@yahoo.com, Godfroid, Jacques |
| Publisher | University of Pretoria |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Rights | © 2012 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
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