Chickens so rarely get honorable places in history. Yet they do have at least one cool honor-- the species in which the first retrovirus was discovered!
Though RT wasnt discovered until the 1970s, way back in 1911, a fellow named Peyton Rous discovered that if he injected a healthy chicken with bits of chicken tumor, the healthy chicken got tumors. The idea that viruses could cause cancer was novel enough to win him a Nobel Prize in 1966! Sweet! Though he didnt know it at the time, Rous was studying alpharetroviruses.
Retroviruses are currently classified by phylogenetic analysis of RT genes. Obviously retroviruses have incredibly variable genomes, but their RTs remain stable enough that this analysis is possible. Theyre currently grouped into seven genuses, one of which is alpharetroviruses. Alphas, and Alpha-ERVs can only be found in birds... including our poor dear chickens.
The archetypical Alpha is Avian Leukosis Virus, the bane of chickens. ALV isnt exactly our buddy either. In the late 80s/early 90s, a subtype A ALV recombined with an endogenous ALV to create a subtype J, which caused a bit of a chicken epidemic. Big problem for chicken farms.
This also effects humans through our vaccine production. Turns out embryonic chickens arent just good for breakfast, theyre great little vaccine factories too! But unlike human ERVs, chicken ALV ERVs can still be pathogenic. There was a 'scare' in the late 1990s when RT activity was detected in MMR vaccines (*cue anti-vaxers* OMFG ALV CAUSES AUTISM!!111!!!1!). It is reasonable to assume alpharetroviruses wont know what to do with a human host, and the CDC explains why nicely:
Several factors, including a natural human resistance to infection with endogenous ALV, may explain the lack of transmission of these viruses to MMR vaccine recipients. However, few or no data are available on the ability of endogenous ALV to replicate in human cells. Resistance to endogenous ALV infection may, for instance, be attributed to the absence of a human cell-surface receptor for the virus as well as to other intracellular blocks for ALV replication. A tumor necrosis factor receptor-related protein, referred to as SEAR, has been recently identified as a receptor for endogenous ALV in turkey cells (22). Plasmid-encoded expression of SEAR in human 293 cells can confer susceptibility to infection by endogenous ALV, suggesting that human cells can support endogenous ALV replication if virus entry is achieved (22). Human serum can lyse ALV by complement activation (23); however, this protective mechanism has not been demonstrated for endogenous ALV and EAV particles.Translation: We dont have the receptor it needs to get in our cells. Its only got one key, and it doesnt fit any of our locks. Cant get in. However, we do have ways of getting rid of it. Oh, but dont let that SCIENCE nonsense get in the way of a bit of fear mongering!
If portions (genes) of animal viruses are introduced into humans, they have the potentials to interact differently with each individual's immune system and DNA, and cause disease. The presence of an avian leukosis virus (AVL), a retrovirus that infects birds, could be the reason approximately 1 in 1000 children will be diagnosed with leukemia by the age of 19.
Thus the CDC study mentioned above may not have presented an accurate assessment of viral presence, or long-term effects from the numerous ALV-associated offspring viruses. Considering that ALV can for example, easily capture the human erbB oncogene (59), and that erbB as well as the oncogene called myc are strongly associated with common forms of human breast cancer, it seems that the issue of ALV vaccine contamination would deserve a high level of attention
I recently acquired an empty vial of yellow fever vaccine and was startled at what was written on the label. "Avian leukosis free". Is this an admission that it one time the vaccine did contain avian leukosis?
Yellow fever vaccine was known to contain avian leukosis virus.* During World War II, batches of yellow fever vaccines were inadvertently also contaminated with hepatitis B virus. Current measles, mumps, rubella (MMR) vaccines contain low levels of reverse transcriptase, an enzyme associated with retroviruses. Both Salk and Sabin polio vaccines made from rhesus monkeys contained live monkey viruses called SV40, short for the fortieth monkey virus discovered. As Dr. Horowitz documents, polio vaccines may also have contained numerous other monkey viruses, some of which may have provided some building blocks for the emergence of HIV- 1 and human AIDS .
* Editor's note: This is the retrovirus that causes leukemia in chickens.
Chicken embryos (eggs) used in making vaccines against influenza, mumps, measles and yellow fever commonly contain the retrovirus, avian leukosis virus (ALV) which has the amazing ability to mutate into numerous other viruses by incorporating oncogenic gene segments into its own genome.
Some of these segments which can be easily incorporated include human oncogenes strongly associated with common forms of breast cancer. As well, ALV can incorporate itself directly into the human genome.