Case-Cohort Study of Cancers in Excess in Poultry Workers

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Johnson, Eric, S Certain retroviruses and herpesvirus naturally and commonly infect and cause cancer in chickens and turkeys. These viruses include some of the most potent cancer-causing agents known in animals. Human exposure to these agents is virtually universal, and occurs through: 1) contact with live poultry; 2) contact with their blood and raw meat and egg products; 3) through ingestion of raw or inadequately cooked poultry meat and eggs; 4) inoculation with vaccines manufactured by growing the vaccine virus in chicken embryos such as measles, mumps, influenza, and yellow-fever vaccines, that may contain exogenous and endogenous forms of these oncogenic viruses. 5) occupationally in jobs such as raising, slaughtering, processing, and sale of raw poultry products, veterinarians, poultry inspectors, cooks, laboratory scientists, etc.; It is known that the viruses can infect human cells in vitro and transform them into cancerous cells, and experimentally the viruses can infect and cause tumors in primates. Furthermore, serological tests in humans clearly indicate widespread infection of the general population with these viruses. However, definitive proof that the viruses cause cancer in humans is currently lacking partly because of the absence of analytic epidemiologic studies of cancer risk in exposed individuals. We hypothesize that if these viruses cause cancer in humans, it will be most readily evident in workers in poultry slaughtering & processing plants who have the highest human exposure to these agents. Accordingly, we conducted cancer mortality studies in three separate cohorts of these workers. The results indicate excess occurrence of 11 cancer sites. The proposed investigation is a case-cohort study of 7 of these sites to investigate the role of these viruses in their etiology, while controlling for and concurrently investigating the roles of other potential occupational and non-occupational carcinogenic exposures. The purpose of the proposed study is two-fold: 1) to assist in providing the critical epidemiologic evidence linking these viruses with cancer occurrence in humans through the study of this highly exposed group of workers; 2) To study cancer mortality in workers in poultry slaughtering & processing plants, who are exposed to not only oncogenic viruses at work (infectious disease is one of the priority areas identified by NIOSH in its Occupational Safety and Health Research program), but also to other occupational carcinogens, including polycyclic aromatic hydrocarbons, heterocyclic amines, nitrosamines, benzene, etc. This occupational group has not been studied before for cancer occurrence in spite of having these hazardous carcinogenic exposures.