Histopathology can provide a strong framework to establish the real causality of a clinical problem.
J. Segalés
To establish an accurate disease diagnosis is compulsory to counteract a given clinical problem in any animal species. In all cases, the clinical examination of the patient/s is the corner stone for further developments in terms of diagnosis approach.
Sudden disease outbreaks represent significant challenges for both farmers and veterinarians, who must identify and counteract the causes of the problem to restore normality. Under these circumstances, the swine veterinarian becomes an investigator, since he/she must assess multiple elements that may contribute to disease causality in a complex scenario involving aspects related with environment, nutrition, biosecurity, epidemiology, presence of multiple pathogens and human-pig interaction.
Population-wide diseases tend to be of infectious or nutritional (toxicities or deficiencies) origin. The first diagnostic approach always includes thorough clinical and epidemiological investigations by the veterinarian. If the clinical outcome implies mortality or severely affected pigs, necropsy of some of them (those considered representative of the condition) should provide some clues about the cause, or at least allow ruling out certain aetiologies.
Necropsy should be performed in an orderly manner, with a systematic approach and being complete.
Presence of lesions might not provide specific causes in most cases but allows orientation about them or narrowing down the differential diagnostic list
As an example, gross pneumonia patterns offer a set of aetiological possibilities, although in several cases it is needed to go beyond and use additional (laboratory) tests.
Laboratory analyses: all that glitters is not gold!
Different analytical approaches help identify potential pathogens (viruses, bacteria, parasites, fungi) or toxins involved in a clinical problem. The most frequently used nowadays involve molecular biology tests such as polymerase chain reaction (PCR) and its variations (qualitative, quantitative, for DNA or RNA). The big advantage of this technique is its sensitivity (able to detect minimal amounts of pathogen genome or gen codifying for a toxin), but this is also its drawback, since the mere detection of a pathogen or toxin in an endemic scenario is not enough to establish an unequivocal etiological diagnostic.
Other laboratory techniques such as bacterial isolation (including antibiogram) are extremely useful, since allow establishing an etiological diagnostic and offer a putative successful treatment. Antibody detection techniques, on the other hand, are excellent monitoring tools, but offer poor diagnostic possibilities since presence of such antibodies depends on vaccination and/or infection status as well as maternally derived immunity.
Stay tuned for the second part.
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