Imperfect Poultry Vax

Chickens immunized against Marek’s disease virus are apt to spread more-virulent versions of the pathogen, a study shows.

Jul 27, 2015
Amanda B. Keener


The controversial theory that vaccination against some viruses clears the way for their more-virulent relatives has garnered new support. According to a study published today (July 27) in PLOS Biology, inoculating chickens with a live Marek’s disease virus (MDV) vaccine can lengthen the disease transmission period, allowing stronger strains of the virus to reach unvaccinated birds, effectively increasing the virus’s fitness.

Unlike most human vaccines, the MDV vaccine reduces symptoms of disease, but does not prevent infection or viral shedding, making it what scientists call a “leaky” or “imperfect” vaccine. “Our research demonstrates that the use of leaky vaccines can promote the evolution of nastier ‘hot’ viral strains that put unvaccinated individuals at greater risk,” study coauthor Venugopal Nair, the head of the Avian Viral Diseases program at the Pirbright Institute in the U.K., said in a statement.

Nair and his colleagues infected unimmunized or MDV-immunized chickens with more virulent strains of the virus and found that the immunized birds shed more virus during their prolonged illness compared to unvaccinated birds, which all died within two weeks of infection.

“By keeping infected birds alive, vaccination substantially enhances the transmission success and hence spread of virus strains too lethal to persist in unvaccinated populations, which would therefore have been removed by natural selection in the pre-vaccine era,” Nair and his colleagues wrote in their paper.

Although the study did not show that vaccination caused MDV to mutate into more virulent forms, Nair said that the prolonged infection period within immunized chickens could give the virus more time to morph.

“Though, as far as I am aware, there is no direct evidence that this has actually happened in the field, it is a plausible risk that needs to be taken into account in designing vaccines,” Philip Minor, head of the National Institute of Biological Standards and Control’s Division of Virology, who was not involved in the work, said in a statement e-mailed to reporters. “These risks are already carefully considered . . . in implementing new human vaccine programs.”

September 2018

The Muscle Issue

The dynamic tissue reveals its secrets


Sponsored Product Updates

StemExpress LeukopakâNow Available in Frozen Format

StemExpress LeukopakâNow Available in Frozen Format

StemExpress, a Folsom, California based leading supplier of human biospecimens, announces the release of frozen Peripheral Blood Leukopaks. Leukopaks provide an enriched source of peripheral blood mononuclear cells (PBMCs) with low granulocyte and red blood cells that can be used in a variety of downstream cell-based applications.

New Antifade Mounting Media from Vector Laboratories Enhances Immunofluorescence Applications

New Antifade Mounting Media from Vector Laboratories Enhances Immunofluorescence Applications

Vector Laboratories, a leader in the development and manufacture of labeling and detection reagents for biomedical research, introduces VECTASHIELD® Vibrance™ – antifade mounting media that delivers significant improvements to the immunofluorescence workflow.

Enabling Genomics-Guided Precision Medicine

Enabling Genomics-Guided Precision Medicine

Download this eBook from Qiagen to learn more about the promise of precision medicine and how QCITM Interpret can help deliver better care with better knowledge.

Best Practices for Sample Preparation and Lipid Extraction from Various Samples

Best Practices for Sample Preparation and Lipid Extraction from Various Samples

Download this white paper from Bertin Technologies to learn how to extract and analyze lipid samples from various models!