Nucleic acid hybridization:
This is a process by which a suitably labeled DNA or RNA from a known infectious agent is used to probe its complementary sequence unique to the pathogen (target) by hybridization process. Recent advances in DNA cloning and sequencing have greatly increased the usefulness of this technique in the diagnosis and epidemiology of diseases. It is now possible to make DNA and RNA probes of high specificity using isotopic and non-isotopic labels. The specific cDNA probes have been used with advantage to diagnose a number of viral, bacterial and parasitic diseases obviating the need for the isolation of the causative agent. Post- mortem samples can also be used to identify the pathogen involved in a particular disease. The use of non-radioactive labeled photobiotinylated cold probes is more adaptive for field situations. Cold probes have been used in diseases like blue-tongue and FMD. DNA probes have also been used to detect FMD virus nucleic acid sequences persisting in the oesopharyngeal fluids of bovines when infectious virus can not be isolated. Thus, nucleic acid probes could even be used to screen the animals for persistent virus infections.