Occupational exposure to poultry and prevalence of antibodies against Marek's disease virus and avian leukosis retroviruses

A case-control study of occupational risk factors for pancreatic cancer in poultry plant workers: a random forest approach

BACKGROUND

Poultry plant workers are exposed to chemical carcinogens and oncogenic viruses in their work environment. Our objective was to identify jobs and workplaces related to poultries that could increase the pancreatic cancer risk.

METHODS

We conducted a case-control study within a defined cohort of poultry workers. We used a random forest algorithm to identify features that could increase pancreatic cancer in the poultry plant workers.

RESULTS

The mean age of participants was 59.49 years. The majority of the study participants were females (51.30%) and Whites (71.0%). The following workplaces and job tasks had an association with increased pancreatic cancer mortality: working in chicken and turkey plants, working in plants where food products were processed and canned, working in a place where poultry and animals where present, working as a hunter for game animals, working as a veterinarian in places had animals and different poultry birds, working in pet houses and working in places where birds were handled and killed. The accuracy and the area under the curve of the model were 72.3 and 71.50%.

CONCLUSION

Chicken and turkey plant workers could be at risk for pancreatic cancer mortality. We need to confirm the results in future studies.

Occupational risk factors in health of broiler-farm workers: A systematic review

The present study aimed to identify gaps in literature regarding occupational risks to broiler farming workers. A systematic review was performed in which inclusion criteria were workers in poultry farms. The search was done between May and June 2019 with online papers. Keywords were "poultry farmer," "poultry worker," and "poultry workers" as terms of an axis of a theoretical framework. Results indicated as predominant topics lung diseases, nasal mucosa or paranasal sinus contamination, and aflatoxicosis. The identified gaps in scientific publications are related to mitigation of occupational risks. Prevalent described risks are associated to exposure to chemicals gases, vapors and aerosols, biological hazards (micro-organisms), ergonomic risks, wrong working posture, excessive body movement and inadequate behaviors. Preventive policies about poultry farmer's health and safety needs to be adopted to reduce potentially dangerous risk factors and increase productivity.

Marek's disease herpesvirus serotype 1 in broiler breeder and layer chickens in Malaysia

Aim:

This study aimed to investigate the occurrence of Marek’s disease (MD) in five poultry farms in Malaysia using postmortem examination, histopathology, and polymerase chain reaction (PCR).

Materials and Methods:

Tissue samples were collected from 24 broiler breeder chickens from four commercial broiler breeder farms and six layer chickens from one layer farm. Gross and histopathological examinations and PCR amplification of the gene encoding for avian MD herpesvirus (MDV-1) were conducted.

Results:

Gross pathological changes including hepatomegaly, splenomegaly, lymphomatous lesion at the mesentery, oviduct atrophy, and follicular atresia with lymphomatous were observed, whereas diffuse multifocal whitish infiltration of the spleen, neoplastic infiltration in the liver, intrafollicular lymphoid infiltration of the bursa of Fabricius, and lymphomatous tumor at the mesentery were seen on histopathological examinations. Confirmation by PCR showed that a total of 16 (53.33%) samples were positive for avian MDV-1. Although the outbreak involved a much larger number of birds in the respective farms, our investigation was limited based on resource and time frame allocated for the study.

Conclusion:

The findings from this study help in emphasizing the potential threats of MDV to the poultry industry globally, in general, and in Malaysia, in particular. As the scope of the current study is limited, future studies focusing on MDV pathogenesis, typing, and causes of vaccine failures are recommended.

Excess lung cancer occurrence in poultry plants. Occupational risk factors: Findings for oncogenic viruses exposure and other occupational exposures

Certain viruses naturally infect and cause cancer in chickens and turkeys. Humans are widely exposed. The viruses cause cancer in primates, and transform human cells in vitro, but it is not known if they cause cancer in humans, mainly because of the lack of epidemiologic evidence. We conducted cohort mortality studies of workers in poultry slaughtering/processing plants across the United States, because they have the highest human exposures. An excess of lung cancer and other deaths was recorded in the poultry workers. Here, we report on a case-cohort study of the lung cancer deaths nested within these cohorts, that was conducted to provide epidemiologic evidence linking these viruses with human cancer occurrence, while adjusting for possible confounders, including workplace chemical carcinogens. We obtained interviews for 339 lung cancer deaths and 457 controls, selected from our combined cohorts of 30,411 poultry plant workers and 16,405 non-poultry workers, belonging to United Food & Commercial Workers unions. Data was analyzed by both logistic regression and Cox regression, adjusting for smoking and other confounders. Lung cancer risk was independently associated with tasks or work areas indicative of exposure to both poultry oncogenic viruses and to workplace chemical carcinogens. The study provides an incremental piece of evidence (epidemiologic), indirectly linking the oncogenic viruses of poultry with the occurrence of cancer in humans, and thus may have public health implications, but the limitations highlighted must be considered. Confirmatory studies, particularly molecular studies providing definitive proof of poultry oncogenic retrovirus integration in human DNA are needed, before the findings observed in this study can be put into proper perspective.

Review of Nonfoodborne Zoonotic and Potentially Zoonotic Poultry Diseases

Emerging and re-emerging diseases are continuously diagnosed in poultry species. A few of these diseases are known to cross the species barrier, thus posing a public health risk and an economic burden. We identified and synthesized global evidence for poultry nonfoodborne zoonoses to better understand these diseases in people who were exposed to different poultry-related characteristics (e.g., occupational or nonoccupational, operational types, poultry species, outbreak conditions, health status of flocks). This review builds on current knowledge on poultry zoonoses/potentially zoonotic agents transmitted via the nonfoodborne route. It also identifies research gaps and potential intervention points within the poultry industry to reduce zoonotic transmission by using various knowledge synthesis tools such as systematic review (SR) and qualitative (descriptive) and quantitative synthesis methods (i.e., meta-analysis). Overall, 1663 abstracts were screened and 156 relevant articles were selected for further review. Full articles (in English) were retrieved and critically appraised using routine SR methods. In total, eight known zoonotic diseases were reviewed: avian influenza (AI) virus (n = 85 articles), Newcastle disease virus (n = 8), West Nile virus (WNV, n = 2), avian Chlamydia (n = 24), Erysipelothrix rhusiopathiae (n = 3), methicillin-resistant Staphylococcus aureus (MRSA, n = 15), Ornithonyssus sylvarium (n = 4), and Microsporum gallinae (n = 3). In addition, articles on other viral poultry pathogens (n = 5) and poultry respiratory allergens derived from mites and fungi (n = 7) were reviewed. The level of investigations (e.g., exposure history, risk factor, clinical disease in epidemiologically linked poultry, molecular studies) to establish zoonotic linkages varied across disease agents and across studies. Based on the multiple outcome measures captured in this review, AI virus seems to be the poultry zoonotic pathogen that may have considerable and significant public health consequences; however, epidemiologic reports have only documented severe human cases clustered in Asia and not in North America. In contrast, avian Chlamydia and MRSA reports clustered mainly in Europe and less so in North America and other regions. Knowledge gaps in other zoonoses or other agents were identified, including potential direct (i.e., nonmosquito-borne) transmission of WNV from flocks to poultry workers, the public health and clinical significance of poultry-derived (livestock-associated) MRSA, the zoonotic significance of other viruses, and the role of poultry allergens in the pathophysiology of respiratory diseases of poultry workers. Across all pathogens reviewed, the use of personal protective equipment was commonly cited as the most important preventive measure to reduce the zoonotic spread of these diseases and the use of biosecurity measures to reduce horizontal transmission in flock populations. The studies also emphasized the need for flock monitoring and an integrated approach to prevention (i.e., veterinary-public health coordination with regard to diagnosis, and knowledge translation and education in the general population) to reduce zoonotic transmission.

Non-cancer mortality in workers in the meat and delicatessen departments of supermarkets (1950-2006)

We studied non-cancer mortality in 10,701 workers in the meat and delicatessen departments of supermarkets because they have increased exposure to a variety of microorganisms that infect and cause disease in food animals such as cattle, pigs, sheep, and poultry, to which subjects in the general population are also exposed, albeit to a lesser degree. These workers were also exposed to fumes from the wrapping machine. Standardized mortality ratios were estimated in the cohort as a whole and in race/sex subgroups, using the US population for comparison. Study subjects were followed up from January 1950 to December 2006. Significantly increased deaths from diabetes, ischemic heart disease, pulmonary embolism, chronic bronchitis, peritonitis, intracranial and intraspinal abscess, other bacterial diseases, and significantly decreased deaths from diffuse diseases of connective tissue, functional diseases of the heart, intracerebral hemorrhage, occlusion/stenosis of the precerebral and cerebral arteries, and various types of accidents were observed in certain race/sex subgroups or in the cohort as a whole. The observed increased risks of several infectious conditions suggest that the increased occupational exposure to microorganisms may be responsible for at least some of the observed excess deaths, while exposure to fumes may also contribute to the excess of chronic bronchitis. The findings are important not only for supermarket workers and other workers in the meat and poultry industries, but also because the general population is exposed to these microorganisms found in food animals and their products. Nested case-control studies within cohorts that include both workers in supermarkets and other sectors of the meat and poultry industries, are now needed to examine specific risks from occupational exposures while adequately controlling for confounding factors, so that the role of these infectious agents in the occurrence of these diseases in workers and in general population subjects can be adequately assessed.

Cancer mortality in the meat and delicatessen departments of supermarkets (1950-2006)

Meat cutters and meat wrappers in the meat department of supermarkets are exposed to oncogenic viruses present in raw meat from cattle, pigs, sheep, and poultry, and their products (unpasteurized milk and raw eggs). Up to the mid 1970s, meat wrappers were also exposed to carcinogens present in fumes emitted from the machine used to wrap meat. Because of this we studied cancer mortality in a cohort of 10,701 workers in the meat and delicatessen departments of supermarkets, and we report here the findings after the third follow-up. Standardized mortality ratios (SMR) were estimated in the cohort as a whole and in race/sex subgroups, using the US population for comparison. Study subjects were followed up from January 1950 to December 2006. Significantly increased SMRs of 1.3 (95% CI, 1.2-1.5), and 2.7 (95% CI, 1.2-5.3) were recorded for cancers of the lung, and tonsils/oropharynx, respectively, in the entire cohort, affecting nearly all race/sex subgroups. SMRs of 4.6 (95% CI, 1.0-13.6) for cancer of the floor of the mouth, and 2.8 (95% CI, 1.3-5.3) for cancer of the gall bladder and biliary tract were recorded only in White male meatcutters. Significantly decreased SMRs were observed for a few cancers. It is not known if the observed excess of cancers is a result of occupational exposures. However, substantial evidence points to fumes from the wrapping machine as a possible candidate for explaining the excess in female meat wrappers. Nested case-control studies that can examine risks from occupational exposures in greater detail, and adequately control for confounding factors are now needed, to permit specifically investigate the role of the oncogenic viruses, fumes and non-occupational risk factors in the occurrence of these cancers. The findings are important, not only occupationally but also because the general population may also experience these exposures, albeit to a lesser degree.

Lack of evidence that avian oncogenic viruses are infectious for humans: a review

Chickens may be infected with three different oncogenic viruses: avian leukosis virus (ALV), reticuloendotheliosis virus (REV), and Marek's disease herpesvirus (MDV). Several epidemiological studies have suggested a link between these viruses and different types of cancer in people working in poultry processing plants and with multiple sclerosis. In this article, we analyze the epidemiological evidence that these viruses are causative agents for human cancer, followed by description of the relevant key characteristics of ALV, REV, and MDV. Finally, we discuss the biological evidence or lack thereof that avian tumor viruses are involved in the etiology of human cancer and multiple sclerosis (MS). The recent primary epidemiologic articles that we reviewed as examples were only hypothesis-generating studies examining massive numbers of risk factors for associations with various imprecise, non-viral-specific outcomes. The studies lacked precise evidence of exposure to the relevant viruses and the statistical methods failed to adjust for the large risks of false-positive claims. ALV subgroups A-D and J have been eradicated in the United States from the pure lines down to the parent stocks by the breeder companies, which have greatly reduced the incidence of infection in layer flocks and broilers. As a consequence, potential exposure of humans to these viruses has greatly diminished. Infection of humans working in processing plants with ALV-A and ALV-B is unlikely, because broilers are generally resistant to infection with these two subgroups. Moreover, these viruses enter cells by specific receptors present on chicken, but not on mammalian, cells. Infection of mammalian cell cultures or animals with ALV-A, ALV-B, and ALV-J has not been reported. Moreover, humans vaccinated with exogenous or endogenous ALV-contaminated vaccines against yellow fever, measles, and mumps did not become antibody- or virus-positive for ALV. The risks for human infection with REV are similarly limited. First of all, REV also has been eradicated from pure lines down to parent stock by breeder companies in the United States. Broilers can still become infected with REV through infection with fowl pox virus containing REV. However, there is no indication that REV can infect human cells. Low levels of antibodies to ALV and REV in human sera have been reported by a few groups. Absorption of sera with chicken antigens reduced the antibody titers, and there was no clear association with contacts with poultry. Possible cross-reactions with human endogenous or exogenous retroviruses were not considered in these publications. MDV is typically associated with infection of chickens, and almost all experimental data show that MDV cannot infect mammalian cells or animals, including nonhuman primates. One study reports the presence of MDV gD DNA in human sera, but this finding could not be confirmed by another group. A Medline search of the term "gene expression in human cancers" was negative for publications with avian retroviruses or MDV. In conclusion, there is no indication that avian oncogenic viruses are involved in human cancer or MS or even able to infect and replicate in humans.

Detection of antibodies against Turkey astrovirus in humans

Astroviruses are a leading cause of gastroenteritis in mammals and birds worldwide. Although historically thought to be species-specific, increasing evidence suggests that astroviruses may cross species barriers. In this report, we used enzyme-linked immunosorbent assays to screen sera from three distinct human cohorts involved in influenza studies in Memphis, TN or Chapel Hill, NC, and Midwestern poultry abattoir workers for antibodies to turkey astrovirus type 2 (TAstV-2). Surprisingly, 26% of one cohort’s population was TAstV-2 positive as compared to 0 and 8.9% in the other cohorts. This cohort was composed of people with exposure to turkeys in the Midwestern United States including abattoir workers, turkey growers, and non-occupationally exposed participants. The odds of testing positive for antibodies against turkey astrovirus among abattoir workers were approximately 3 times higher than the other groups. These studies suggest that people with contact to turkeys can develop serological responses to turkey astrovirus. Further work is needed to determine if these exposures result in virus replication and/or clinical disease.

A cohort mortality study of workers in a soup manufacturing plant

There has been no study of disease risk or exposures in workers in soup manufacturing plants. These workers may have hazardous exposures to biological and chemical cancer-causing agents at the workplace. The authors report here on mortality in 1,779 workers from a plant in Baltimore, Maryland. Standardized mortality ratios (SMRs) were estimated using the US population for comparison. Significantly increased mortality was observed for cancer of the floor of the mouth, colon cancer, epilepsy, and chronic nephritis in certain groups. Significantly decreased SMRs were observed for some causes. The findings are important, given the complete absence of data on this occupational group. It is not known whether the associations observed are related to occupational or nonoccupational exposures, or due to chance. The findings do, however, indicate that further studies of this occupational group are warranted.

Occupational exposure assessment using antibody levels: exposure to avian leukosis/sarcoma viruses in the poultry industry

Avian leukosis/sarcoma viruses (ALSV) infect and cause cancers in chickens. Poultry workers are exposed to ALSV and other infectious agents in the workplace. This study examines if industrial hygiene assessment of antibody levels in poultry workers can identify risky job tasks at the higher exposure risk to an infectious agent, i.e., ALSV. We compared ALSV antibody levels in poultry workers and control subjects. Occupational and demographical factors were examined for an association with the exposure risk in poultry workers. We found that the antibody levels were significantly higher in poultry workers than in control subjects. Job category and age together were significantly associated with the antibody levels in workers. Certain job tasks were identified with significantly higher antibody levels as compared to others, implying that recommendations should be made to protect workers at these jobs. The findings of this study indicate that the measurement of antibody levels in workers can be useful for industrial hygiene assessment of exposure to infectious agents.

Serologic evidence of avian metapneumovirus infection among adults occupationally exposed to Turkeys

Genetically similar, the avian metapneumovirus (aMPV) and the human MPV (hMPV) are the only viruses in the Metapneumovirus genus. Previous research demonstrated the ability of hMPV to cause clinical disease in turkeys. In this controlled, cross-sectional, seroepidemiological study, we examined the hypothesis that aMPV might infect humans. We enrolled 95 adults occupationally exposed to turkeys and 82 nonexposed controls. Sera from study participants were examined for antibodies against aMPV and hMPV. Both in bivariate (OR=3.2; 95% CI: 1.1-9.2) and in multivariate modelling adjusting for antibody to hMPV (OR=4.1; 95% CI: 1.3-13.1), meat-processing workers were found to have an increased odds of previous infection with aMPV compared to controls. While hMPV antibody cross-reactivity is evident, these data suggest that occupational exposure to turkeys is a risk factor for human infection with aMPV. More studies are needed to validate these findings, to identify modes of aMPV transmission, and to determine risk factors associated with infection.

Cancer mortality in workers employed in cattle, pigs, and sheep slaughtering and processing plants

OBJECTIVES

We studied mortality in two separate cohorts of workers in abattoirs (N=4996) and meat processing plants (N=3642) belonging to a meatcutters' union, because they were exposed to viruses that cause cancer in food animals, and also to chemical carcinogens at work.

METHODS

Standardized mortality ratios (SMRs) and proportional mortality ratios (PMRs) were estimated for each cohort as a whole and in subgroups defined by race and sex, using the US general population mortality rates for comparison. Study subjects were followed up from January 1950 to December 2006, during which time over 60% of them died.

RESULTS

An excess of deaths from cancers of the base of the tongue, esophagus, lung, skin, bone and bladder, lymphoid leukemia, and benign tumors of the thyroid and other endocrine glands, and possibly Hodgkin's disease, was observed in abattoir and meat processing workers. Significantly lower SMRs were recorded for cancer of the thymus, mediastinum, pleura, etc., breast cancer, and non-Hodgkin's lymphoma.

CONCLUSION

This study confirms the excess occurrence of cancer in workers in abattoirs and meat processing plants, butchers, and meatcutters, previously reported in this cohort and other similar cohorts worldwide. Large nested case-control studies are now needed to examine which specific occupational and non-occupational exposures are responsible for the excess. There is now sufficient evidence for steps to be taken to protect workers from carcinogenic exposures at the workplace. There are also serious implications for the general population which may also be exposed to some of these viruses.

Non-cancer mortality in poultry slaughtering/processing plant workers belonging to a union pension fund

BACKGROUND

The role of the biological environment in the occurrence of many chronic human diseases has been little studied. Humans are commonly exposed to transmissible agents that infect and cause a wide variety of subacute and chronic diseases in chickens and turkeys. The objective of this study is to investigate whether these agents cause similar diseases in humans, by studying workers in poultry slaughtering and processing plants who have one of the highest human exposures to these agents.

METHODS

Mortality in poultry workers was compared with that in the United States general population through the estimation of standardized mortality ratios.

RESULTS

Excess mortality from infectious and parasitic diseases was observed in the poultry workers. In addition, excess occurrences of deaths involving several sites of the cardiovascular, neurological, endocrine, gastrointestinal and reproductive systems, were observed, although the numbers involved were few in some instances.

CONCLUSION

The results indicate that poultry workers are at increased risk of dying from certain causes of death, including infections. This is consistent with other reports. Although it is possible that occupational exposure to transmissible agents present in poultry may be one of the causes of the excess occurrence of some of these diseases, other factors that were not considered because of the nature of the study design, could be equally important. Also, the small number of deaths involved in some instances calls for caution in interpreting the results. However, the study is important, as it has succeeded in newly identified areas that need further research, and which may have implications not only for workers, but also for the general population.

Update of cancer and non-cancer mortality in the Missouri poultry cohort

BACKGROUND

workers in poultry slaughtering and processing plants have one of the highest human exposures to transmissible agents that cause cancer and other diseases in chickens and turkeys, and also have other occupational carcinogenic exposures. The general population is also exposed to these transmissible agents.

METHODS

we investigated mortality in workers who belong to a poultry union in Missouri, and estimated standardized mortality ratios.

RESULTS

significantly increased mortality was observed for some leukemias, benign neoplasms, thyroid diseases, bacterial infections, and schizophrenic disorders. The risk of breast cancer and several non-cancer conditions was significantly depressed.

CONCLUSION

the findings add to the growing evidence suggesting that workers occupationally exposed to transmissible agents and carcinogens in the poultry industry, are at increased risk of dying from certain chronic diseases, including cancer.

Cancer mortality in poultry slaughtering/processing plant workers belonging to a union pension fund

BACKGROUND

The role of zoonotic biological agents in human cancer occurrence has been little studied. Humans are commonly exposed to viruses that naturally infect and cause cancer in food animals such as poultry that constitute part of the biological environment. It is not known if these viruses cause cancer in humans.

OBJECTIVE

To study cancer mortality in the largest cohort to date, of 20,132 workers in poultry slaughtering and processing plants, a group with the highest human exposures to these viruses.

METHODS

Mortality in poultry workers was compared with that in the US general population through the estimation of standardized mortality ratios.

RESULTS

Significantly increased risks were observed in the cohort as a whole or in subgroups, for several cancer sites, viz: cancers of the buccal cavity and pharynx; pancreas; trachea/bronchus/lung; brain; cervix; lymphoid leukemia; monocytic leukemia; and tumors of the hemopoietic and lymphatic systems. Elevated SMRs that were not statistically significant were observed for cancers of the liver, nasopharynx, myelofibrosis, and myeloma. New sites observed to be significantly in excess in this study were cancers of the cervix and penis.

CONCLUSION

This large study provides evidence that a human group with high exposure to poultry oncogenic viruses has increased risk of dying from several cancers. Other occupational carcinogenic exposures could be of importance in explaining some of the findings, such as fumes from wrapping machines. These findings may have implications for public health amongst persons in the general population who may also be exposed to these viruses. What is needed now are epidemiologic studies that can demonstrate whether the excess of specific cancers can be attributed to specific occupational exposures while adequately controlling for other potential occupational and non-occupational carcinogenic exposures.

Mortality in workers in poultry slaughtering/processing plants: the Missouri poultry cohort study

BACKGROUND

Subjects who work in poultry slaughtering and processing plants have one of the highest human exposures to viruses that cause cancer in chickens and turkeys. It is not known whether these viruses cause cancer in humans also. Epidemiological studies investigating this issue are scarce.

AIMS AND METHODS

Mortality was studied during the period 1969-90 in a cohort of 7700 subjects who worked in poultry slaughtering and processing plants and were members of a local poultry union in the State of Missouri.

RESULTS AND CONCLUSIONS

Statistically significant excess risks of non-malignant respiratory diseases, accidents, and symptoms, senility, and ill-defined conditions, and increased but not statistically significant excesses for some cancers were observed in particular race/sex groups. Most of these results were based on small numbers of deaths, and in many cases were evident only in particular subgroups of the cohort. Because of this and the multiple comparisons made, chance could not be ruled out in explaining the findings. Furthermore, the cohort is young, with only 6% deceased at the end of follow up. Further follow up of this cohort is required before a reliable assessment of the potential risk associated with these viruses can be made.

Detection of avian oncogenic Marek's disease herpesvirus DNA in human sera

The avian herpesvirus Marek's disease virus (MDV) has a worldwide distribution and is responsible for T-lymphoma in chickens. The question as to whether MDV poses a public health hazard to humans was first raised when the virus was isolated in 1967. However, no irrefutable results have been obtained in immunological and virological studies. We used a nested-PCR to detect MDV DNA in human serum samples. A total of 202 serum samples from individuals exposed and not exposed to poultry was tested by nested-PCR for a target sequence located in the MDV gD gene. The assay system was specific and sensitive, making it possible to detect a single copy of the target sequence. Forty-one (20%) of the 202 serum samples tested positive for MDV DNA. The prevalence of MDV DNA was not significantly different in the group exposed to poultry and the group not exposed to poultry. There was also no difference due to age or sex. Alignment of the 41 gD sequences amplified from human sera with eight gD sequences amplified from MDV-infected chicken sera showed a maximum nucleotide divergence of 1.65%. However, four 'hot-spot' mutation sites were identified, defining four groups. Interestingly, two groups contained only human MDV-gD sequences. The status of the MDV genome detected in human blood is discussed.

Cancer in veterinarians

OBJECTIVES

Veterinarians come into contact with several potentially carcinogenic exposures in the course of their occupation. These exposures include radiation, anaesthetic gases, pesticides (particularly insecticides), and zoonotic organisms. This review aims to summarise what is known about the carcinogenic risks in this profession.

METHODS

The levels of exposure to potential carcinogens in the veterinary profession are examined and evidence is reviewed for carcinogenesis of these substances in humans at doses similar to those experienced by veterinarians. The few published studies of cancer in veterinarians are also summarised.

RESULTS

Veterinarians have considerable potential for exposure to several known and potential carcinogens. Risks may be posed by work in clinics with poorly maintained x ray equipment, by use of insecticides, and from contact with carcinogenic zoonotic organisms. The few studies available suggest that veterinarians have increased mortality from lymphohaematopoietic cancers, melanoma, and possibly colon cancer.

CONCLUSIONS

The exposures examined in this review are not unique to the veterinary profession, and, as a consequence, information gathered on the carcinogenic risks of these exposures has implications for many other occupations such as veterinary nurses, animal handlers, and some farmers, as well as dentists, radiographers, and anaesthetists.

Evidence of avian leukosis virus subgroup E and endogenous avian virus in measles and mumps vaccines derived from chicken cells: investigation of transmission to vaccine recipients

Reverse transcriptase (RT) activity has been detected recently in all chicken cell-derived measles and mumps vaccines. A study of a vaccine manufactured in Europe indicated that the RT is associated with particles containing endogenous avian retrovirus (EAV-0) RNA and originates from the chicken embryonic fibroblasts (CEF) used as a substrate for propagation of the vaccine. We investigated the origin of RT in measles and mumps vaccines from a U.S. manufacturer and confirm the presence of RT and EAV RNA. Additionally, we provide new evidence for the presence of avian leukosis virus (ALV) in both CEF supernatants and vaccines. ALV pol sequences were first identified in particle-associated RNA by amplification with degenerate retroviral pol primers. ALV RNA sequences from both the gag and env regions were also detected. Analysis of hypervariable region 2 of env revealed a subgroup E sequence, an endogenous-type ALV. Both CEF- and vaccine-derived RT activity could be blocked by antibodies to ALV RT. Release of ALV-like virus particles from uninoculated CEF was also documented by electron microscopy. Nonetheless, infectivity studies on susceptible 15B1 chicken cells gave no evidence of infectious ALV, which is consistent with the phenotypes of the ev loci identified in the CEF. PCR analysis of ALV and EAV proviral sequences in peripheral blood mononuclear cells from 33 children after measles and mumps vaccination yielded negative results. Our data indicate that the sources of RT activity in all RT-positive measles and mumps vaccines may not be similar and depend on the particular endogenous retroviral loci present in the chicken cell substrate used. The present data do not support transmission of either ALV or EAV to recipients of the U.S.-made vaccine and provide reassurance for current immunization policies.

On the need to assess cancer risk in populations environmentally and occupationally exposed to virus and chemical agents in developing countries

Evidence exists that exposure to poultry oncogenic viruses may produce elevated cancer mortality in human populations, particularly excesses of cancer of lung and excesses of cancer of lymphopoietic tissues. To date, this potential risk is unknown in populations from the developing countries. This paper suggests the need to assess cancer risk in populations of developing countries with reported environmental exposure to chicken meat products and eggs; the need to assess risk of cancer in populations inoculated with vaccines from infected chicken embryos; and the need to assess risk of cancer in occupational populations highly exposed to poultry oncogenic viruses, and with potential concurrent exposure to chemical agents known or suspected to be carcinogens.