Elisa is a serologic test whose initials stand for:
Enzyme - Linked - Immuno - Sorbent - Assay

The production of serum (or vaccine) is comparable to the production of anti-flu vaccine. Specific sera are thus obtained against every virus.

Atibodies

The vaccine is placed in a special plastic dish, so that the antibodies contained in it will adhere to the "walls" of the recesses in the dish.

Sap

The sap of the plant undergoing analysis is then deposited; if any virus is present in the sap, its antigens will bond to the antibodies in the serum.

Conjugated Atibodies

After the sample is washed, another vaccine conjugated with an enzyme that changes colour in the presence of the virus antigen is added.

Substrate

A dyeing substrate is added to the antibody - antigen - antibody complex (possible only in the presence of a virus), which causes the solution to change colour, varying from transparent to yellow. The difference in colour is detected by a special computerized sensor; an infected sample will produce a coloured solution, a healthy sample will NOT.