A technique developed originally by Louis Pasteur in the 1880's. Similar to selective breeding and can be used to create an attenuated strain of a virus to develop vaccines or increase the virulence of a viral strain to create epidemics.

Basically, you infect a series of host organisms with a virus. Each time you give the virus some time to incubate and then you infect the next host with the incubated virus. The virus may mutate repeatedly into a form that is resistant to a wide variety of host immune system defenses or a weaker strain may result.

Pasteur produced an early rabies vaccine by using serial passage to transmit the virus until an attenuated developed which could be used to stimulate an immune response without causing a pathological infection.

Scientists have observed that non-virulent forms of HIV can give rise to virulent strains after serial passage is used on primates.

External links

• Brief mention of Pasteur's work with rabies serial passage (http://www.fas.org/ahead/docs/rabies.htm)
• abstract of report about serial passage in baboons giving rise to a virulent strain (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12477812&dopt=Abstract)