Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-008071, 2008 Aug; :1-31
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. We therefore conducted two types of studies for the awarded grant: 1) A cohort mortality study of 20,131 workers in poultry slaughtering/processing and a comparison group of 10,356 control workers in the seafood industry. These workers were identified from rosters of various unions of the United Food & Commercial Workers Union (UFCW) International. The rosters were from the Baltimore Meatcutters' Union, the Missouri Poultry Union, and a multi-state Union Pension Fund. Follow-up of these three cohorts has been completed, and we are in the process of analyzing the data, and some results are available. The results indicate that a total of 10 major cancer sites were observed to be occurring in excess in the cohort of poultry workers or in particular race/sex subgroup(s) of it. These are 1) cancers of the buccal & nasal cavities and pharynx; 2) esophagus; 3) rectum, recto-sigmoid junction, anus; 4) liver & intrahepatic bile ducts; 5) pancreas; 6) trachea, bronchus, and lung; 7) ovary; 8) brain; 9) tumors of the hemopoietic/lymphatic systems combined (including multiple myeloma, lymphoma, lymphoid leukemia, myeloid leukemia, monocytic leukemia, myelofibrosis); and 10) cancer of the gallbladder and extrahepatic ducts. These increased risks were not limited to cancers only but were also observed for neurologic diseases, cardiovascular diseases, and diseases of the urinary system. Two papers on cancer and noncancer mortality in the Baltimore cohort have been submitted for publication. We are preparing manuscripts for publication for the Missouri and Pension Fund cohorts separately and for all poultry cohorts combined. 2) A pilot case-cohort study of selected cancers within these three cohorts combined. The base population for the case-cohort study from which cases and controls were selected was defined as all subjects in the cohort study above, who were alive as of 01/01/1990 (N=43,904). The cases consist of the following cancer sites: cancers of the 1) lung, 2) buccal & nasal cavities & 5 pharynx, 3) esophagus, 4) rectum, recto-sigmoid junction & anus, 5) liver, 6) pancreas, 7) brain, 8) kidney, 9) bladder, and 10) tumors of the hemopoietic lymphatic systems. These cases were selected because they were identified in previous follow up of some of the studied cohorts to be occurring in excess in workers in poultry slaughtering/processing plants. As it turned out nearly all of these sites were also confirmed to be in excess in the study being reported on here. More detailed analyses are in progress, and to date we have results for cancers of the lung, pancreas, and liver. Specific jobs or tasks within the poultry industry were observed to be associated with each of these three cancers, especially tasks associated with exposure to oncogenic viruses and other transmissible agents, such as exposure to live animals and slaughtering activities in which exposure is highest. Also, exposure to fumes from the wrapping machine that contain carcinogenic benzene, polycyclic aromatic hydrocarbons (PAH) and phthalates was identified as another risk factor associated with excess occurrence of these three cancer types. Similarly exposure to PAH during smoking of meat was associated with excess cancer risk. In addition, we were able to confirm established occupational risk factors outside the meat and poultry industries and non-occupational risk factors for these cancer types. The findings of this study provide sufficient information that requires immediate steps to be taken to protect poultry workers during carrying out tasks that put them at risk of exposure to transmissible agents, which holds for virtually all workers, and to protect them from exposure to chemical carcinogens emitted during wrapping and smoking of meat. Protective measures may include engineering interventions, education, protective clothing and appropriate gloves, etc. Also, importantly the implication of these findings is that the general population may be at risk of developing cancer from exposure to live poultry or their products or from ingesting raw or inadequately cooked poultry products, or even from receiving vaccines contaminated with poultry oncogenic viruses such as ALSV. This may present a major public health problem and further studies are urgently needed to investigate this real possibility. Uniquely for the first time ever, we investigated a total of 185 causes of death. This many causes of death has not been previously investigated in any occupational mortality study published previously.