| Abstract |
Certain viruses naturally infect and cause cancer in chickens and turkeys. These include the retroviruses avian leucosis/sarcoma viruses (ALSV) and reticuloendothesiosis viruses (REV), and the herpesvirus Marek's disease virus (MDV). Infection is very common in birds destined for human consumption. Experimentally, cancer has been induced in primates infected with these viruses. These viruses have been shown to be capable of infecting human cells in vitro, and causing them to become cancerous. It has been shown that poultry workers and subjects in the general population are also commonly infected with these viruses. Human exposure to these viruses occur occupationally (workers in poultry slaughtering/processing plants and poultry farms, egg candlers, veterinarians, cooks, laboratory workers, etc.). The general population is also exposed through contact with live poultry, blood, secretions, raw meat, raw eggs and ingestion of raw or inadequately cooked poultry meat and eggs. Infection with ALSV also occurs through vaccination with live vaccines grown in chicken embryo cells such as measles, mumps and yellow fever vaccines. However, in spite of the scientific evidence accumulated thus far, definitive proof that can confirm beyond any doubt that these viruses cause cancer in humans is currently lacking. Two critical pieces of evidence are needed to incriminate these viruses as causing cancer in humans: (1) laboratory demonstration of ALSV integrated within the human genome, and (2) epidemiologic evidence of excess cancer occurrence in human exposed to these viruses. We have therefore been studying mortality in workers in poultry slaughtering/processing plants. These workers have the highest human exposure to these viruses, since they come into contact with thousands of chickens and turkeys daily at work and handle the internal organs, blood and secretions, and they get cuts and bruises in their skin that facilitate entry of microorganisms into their body. We reason that if these viruses cause cancer in humans, then it should be readily evident in workers in poultry slaughtering/processing plants. |
