Advances in diagnosis of livestock diseases

Abstract

Livestock ~1gricultnre is carried out to produce food and fi bre by the deliberate and controlled use of plants and
animals. It is11 manipulative ecology with its basic operational unit being the complex producl ion system influenced by
interactions, hetween biologic, climatic, economic, social and cultural factors. In recent years intens ificatit~n has
typified animal production. This trend has resuHcd in those diseases that manifest themselves primarily through a
decrease in production efficiency and that, in most cases arc endemic. The disease conditions often have a compte:(
multifactcraetiology that is intimately related to the production system. Secondly, emphasis has shifted from the
individual animal toward the population-a trend toward epidcmiolvgical considerations. The veterinarian and the
farmers are interestett in the frequency, distribution and determinants of health an<l disease (clinical or subclinical).
Orten times, productivity of the animal is used as a surrogate measure of health. Interest. is in optimizing health as
mertsurcd by productivity and not necessarily minimizing occurrence of disease. Diagnosis being the art of determining
the nature 'Jf a CftSO of disease amlllisiinguishing that disease from another, lms hecltuse oft he uniqueness oflivestock
production and managemenl, become very t:nmplkatcd requiring improvement in the methods for processing and
interpretation of diagnostic tcsis. This has called for thorou1.~h underst~mding of the intricate relationship among
nnimal characteristics, environmental factors, aetiologkal agent and disease in order to avoid mi~classiiicat.inn nflhe
population into healthy and diseased. The validity (Pn~cision, specificify and sensitivity and cui. .. off-values) of a test are
very cru('ial and ~vahtlltion of tests has become mandatory. There hlls, therefore, l>ecn developments in diagnosis
!·anging f;·0m clilii~al and/or :.>thin;}vett·rinary medicine, agent isola ticn (direct or indirect) lo epidemiologic?.!
t(!chniqnc<.,. T!Jc cntaiogue of diagnostic tests indudes micmscopic examination (hacmatological or CO(H'Ologic~l) iflJ!
ii'ro tissue a nd cell culture; in vh'O inocu!al.ion, xenod ia~nosis anll serological techniques (antibody andior antigen
(Jett~d;_on). Antigenlletcction has been strongly influenced by modern biotechnology which has culminated into the
polym~rase ch<~in reaction (PCR) and recombi~l?.ll t DNA and hybr idoma technoiogies. Landscape epidemiology and
uutri(ion stlalus (trace element levels) have increasingly found a role in the diagnosis p rocess, too. l>iseasc in livestock
comes ~bou l as a result of coincidence of many fac tors. Hence for diagnosis, there is need to in tegrate data from an
array of p r oced ures ranging from history, l~u·m ing system characteristics to laboratory findings. It is the inferenc.e
from the diagnostic tests rather than the observed test variable itself that is important.