Viral titer

Viral titer is a quantitative measurement used in virology, which calculates the concentration of viruses in a solution. It is often expressed as viral particles, or infectious particles per unit volume, and is used in various applications such as vaccine manufacturing.

Definition

A viral titer is the concentration of a solution as determined by the highest dilution of the solution that still yields a detectable level of infection. The titer is usually expressed as the reciprocal of the dilution that yields infection in 50% of the inoculated hosts; this measure is known as the TCID50 (Tissue Culture Infective Dose).

Methods of Determination

There are several methods to determine the viral titer. These include:

• Plaque assay: This is the most common method used to measure the number of viruses in a sample. In this method, viruses are allowed to infect a layer of cells, which are then covered with a semi-solid medium to prevent the virus from spreading indiscriminately. The virus can only infect neighboring cells, forming a plaque or clear area. Each plaque represents a single virus; therefore, counting the number of plaques allows the calculation of the viral titer.

• Endpoint dilution assay: This method involves infecting cells with different dilutions of the virus. The highest dilution that still causes an infection is the endpoint, and this is used to calculate the viral titer.

• Quantitative PCR: This method uses the polymerase chain reaction to amplify the viral DNA or RNA. The amount of amplified product is proportional to the amount of virus in the original sample, allowing the calculation of the viral titer.

Applications

Viral titers are used in various applications, including:

• Vaccine production: The viral titer is crucial in vaccine production to ensure that the vaccine has the correct amount of virus to stimulate an immune response without causing disease.

• Gene therapy: In gene therapy, viral vectors are often used to deliver genes to cells. The viral titer must be determined to ensure that the correct amount of virus is used.

• Virology research: Viral titers are often used in virology research to study the effects of viruses on cells and organisms.

See Also

• Virology
• Vaccine
• Gene therapy
• Plaque assay
• Endpoint dilution assay
• Quantitative PCR

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