Biologicals are generally produced using mammalian cell cultures, though such cells are easily infected by viruses. Once infected, a production batch can no longer be used, making it incumbent on biotechnology and pharmaceutical companies to repeatedly test for viral infections in their biologicals batches. In addition, mammalian cells contain viral DNA, which leads to the expression of intracellular virus-like particles. The intracellular particles must be monitored and production quantities should not be increased during production.
Transmission electron microscopy (TEM) plays a major role in the fast determination of viral family, after which the exact virus can be determined using qPCR. To determine the amount of virus-like particles in a batch and to monitor their evolution over time, TEM studies are the technology of choice. FEI product families with models used for biological production and viral load monitoring include the following: