Using PCR to Detect Viral Agents in Animal Sera

The polymerase chain reaction (PCR) first described in 1985 is a simple, rapid and powerful method of amplifying specific DNA or RNA sequences. PCR is used in a wide variety of fields including molecular biology, medical science, biotechnology, microbiology, the food industry, genetics, gene cloning and virology.

How can PCR reduce risk in the use of animal-derived products for culture?

PCR is especially suited for detecting the presence of nucleic acid targets of specific organisms in biological material. Viruses have unique DNA or RNA sequences. By testing for the presence or absence of a unique sequence in a sample, PCR can be used as one of the methods to determine if a sample contains a nucleic acid target of a specific virus or other contaminating organism.

Despite its capacity for generating relatively large numbers of copies of DNA or RNA sequences, PCR does have limitations that should be considered when screening sera or other biological substances for the presence of viral materials. Because PCR detects the absence or presence of a nucleic acid target, it will amplify nucleic acids from both viable and non-viable material, without distinguishing between the two.

Overcoming the inability of PCR to assess viability using cell culture

A strategy for overcoming the inability of PCR to distinguish between viable and non-viable viral material is to pass the sample through a virus-susceptible cell line prior to PCR testing. Multiple passages of cells in culture will amplify low levels of viable virus material, thus increasing the sensitivity of the assay. Furthermore, the cell culture passages will diminish non-viable virus material via dilution. The greater the number of cell culture passages, the more likely a positive PCR result will be due to viable viral material.

Although all materials we use are rigorously pre-screened according to strict federal regulations, low levels of extraneous agents may exist that are below the threshold of detection by current test methodology. These levels can be detected by PCR, but because of the limitations of this technique, it cannot be determined whether the detected nucleic acids are from viable or non-viable viral material.

We offer the SER-TAIN^™ gamma irradiation process, which has been shown to significantly inactivate many biological contaminants. This validated process provides greater assurance that any existing low levels of microbes will be inactivated, minimizing the risks associated with animal-derived components. The SER-TAIN^™ process also helps to ensure that any viral nucleic acid sequences detected by PCR are from non-viable viral material.