BIOTECHNOLOGY LEARNING CURVES SERIES: Introduction to Vaccines Production (Part 4)

Viral Vaccine: Candling & Marking of Eggs

The process for the production of viral vaccine and bacterial vaccine are very different due to the nature of the microbes used.Viral vaccine which is based on viruses needs viable cells (living cells) to survive and propagate meanwhile bacterial vaccine needs only growth nutrient to grow on. Hence, in producing viral vaccine, we need to have incubated eggs (usually SPF- Specific Pathogen Free). SPF means that the eggs are free from 26 common diseases and pathogens. One of the main step in preparing the eggs for vaccine production is eggs candling.

On 7^th day, the eggs will undergo the candling process where the eggs are being observed under the light. The infertile or dead eggs are discarded and the fertile eggs are put in to the incubator for another 3days. The eggs can be differentiated under the light based on the characteristics as follows:

Infertile egg : no embryo

Dead egg : contain embryo but no blood vessel

Fertile egg : contain both embryo and blood vessel

On 10^th day, the eggs will go through the marking process. The eggs are observed under the lamp and the staff will mark the air sack, drilling point and the position of the eye of the embryo. This is an important procedure as it helps in the drilling, inoculation and harvesting procedures later. The marked drilling point indicates the position on the egg shell to be drilled and inoculated while the air sack marked will indicate the position of the shell that can be discarded during the harvesting process. The eye marking are to avoid the inoculation of the virus onto the eye of the embyo which will eventually cause hemorrhagic behavior in the embryo and cause the allantoic fluid to become reddish.