Introduction
Bovine TB (BTB) caused by Mycobacterium bovis is a complex, transmissible, infectious disease. Cattle are the main hosts of the infection, but BTB also occurs in a wide range of domesticated and wild animals, and in humans.
The clinical and pathological manifestations, and immunological responses in this chronic disease differ substantially within and between species, the stage of the disease, the pathogenicity of the specific M. bovis strain, and environmental factors. In cattle, whether it is a recently infected herd, a herd with long-standing established infection with advanced and generalized, chronic cases, or a herd that has been subjected to eradication of BTB and elimination of most of the infected cattle for some time, the detection of all BTB-positive cattle is notoriously challenging.Because of the lack of sensitivity (Se) and specificity (Sp) of all the currently available diagnostic methods, there is not a single technique for individual animals to confirm a diagnosis of BTB with 100% certainty; all the tests are herd tests. Herein lies the challenge of controlling the disease, since the inability to reliably make a diagnosis in individual animals adds to the risk of infected animals remaining in herds in which attempts are being made to control and eradicate the disease, or to not detect its presence when the herd prevalence is low and/or unknown.
N. P. J. Kriek
Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
D. B. Areda
Department of Biological Sciences, Minnesota State University, Mankato, Mankato, MN, USA e-mail: demelash.areda@mnsu.edu
A. B. Dibaba (*)
Department of Pathobiology, College of Veterinary Medicine, Tuskegee University, Tuskegee, AL, USA
e-mail: adibaba@tuskegee.edu
© Springer Nature Switzerland AG 2019
A.
B. Dibaba et al. (eds.), Tuberculosis in Animals: An African Perspective, https://doi.org/10.1007/978-3-030-18690-6_9To successfully treat, control, and eradicate a disease, it is critical to make a correct diagnosis to allow the collection of information about the origin, presence, extent, distribution, species involved, and the sources of the infection on which to base the development and execution of successful control and eradication programs (van Soolingen et al. 1994; Ryan et al. 2006). These are the challenges faced by most of the African countries in which the disease remains uncontrolled, and its status unknown. The recent development of molecular techniques to address these issues is a great step forward, but the costs involved, the laboratory infrastructure required, and the availability of human resources with the necessary expertise to do the tests, remain scarce commodities in Africa.
To increase the likelihood of diagnosing BTB in infected animals and herds, it is prudent to use a combination of diagnostic methods. These include clinical signs and tests based on the delayed hypersensitivity reaction such as the tuberculin skin and gamma interferon (IFN-γ) tests; serology, postmortal, and histopathological examination, and microscopic examination of various clinical specimens likely to contain the organism, culture, and DNA-based molecular techniques. The Se and Sp of each one of these tests vary according to circumstances and species involved, and the limitations of each one should be taken into consideration when using them.
It is also important to keep in mind that only results of validated tests for specific species should be used for diagnostic purposes because of the marked differences in serological and immunological responses between species. When using unvalidated tests, culturing the organism is the only reliable method to confirm a diagnosis of BTB in species other than cattle and particularly in wildlife in which the disease is suspected.
Because of the complexity of many of the diagnostic methods, the variation in techniques used in laboratories and the observations of field staff when assessing tuberculin test reactions, it is critical that a system of quality control be instituted to monitor the various diagnostic procedures, be they field or laboratory based.Although BTB is considered to be one of the most important diseases of cattle and because of its zoonotic potential, the specificity and sensitivity of surprisingly few ante- and postmortal tests have been adequately assessed for the various species in which they are commonly used. These include the single intradermal skin test (SIT), single intradermal comparative cervical test (CCT), caudal fold skin test (CFT), the IFN-γ assay, enzyme-linked immunosorbent assay (ELISA), latex bead agglutination assay, multiplex immunoassay, fluorescence polarization assay, necropsy (including abattoir meat inspection), microscopic examination (including histopathology), culture, and the polymerase chain reaction (PCR) (Downs et al. 2017). The available tests that can be used to confirm the diagnosis of BTB in the various animal species are discussed in the following sections. It is not intended to deal with the detailed methodology of the techniques but only to outline the applicability, practicality, and reliability of each of the tests for surveillance and diagnostic purposes, with emphasis on the needs of the African countries.
9.2
More on the topic Introduction:
- 1 Introduction
- Introduction
- Introduction
- 19 Introduction
- Introduction
- Introduction
- INTRODUCTION
- Introduction
- Introduction
- Introduction
- Introduction
- Introduction: Hegel, Marx and the Dialectic
- INTRODUCTION: OVERVIEW OF COMPLICATIONS ASSOCIATED WITH HIV THERAPY