Bovine leukosis and human cancer

Exposure to animals and selected risk factors among Canadian farm residents with Hodgkin's disease, multiple myeloma, or soft tissue sarcoma

Exposures to farm animals has been associated with certain rare cancers. Simultaneously, using the same methodology and control group, we conducted a six-province incident, population-based study of Hodgkin's disease (HD), multiple myeloma (MM), and soft tissue sarcoma (STS). Farm residence or work was reported by 38% (n = 119) of HD, 45% (n = 178) of MM, 43% (n = 156) of STS cases and 45% (n = 673) of controls. We conducted conditional logistic regression analyses and report odds ratios (OR(adj)) and 95% confidence intervals. After adjustment for covariates, exposure to farm animals had minimal effect on risk. The independent risk factors after adjustment for covariates were a family history of cancer (MM, STS), occupational uranium exposure (HD), professional driving (MM), and personal previous cancer (MM) or shingles (HD, MM).

Canadian male farm residents, pesticide safety handling practices, exposure to animals and non-Hodgkin's lymphoma (NHL)

BACKGROUND

A majority of published studies indicate that farmers have an elevated risk of developing non-Hodgkin's lymphoma (NHL) compared to other workers.

METHODS

We evaluated accidental exposure to pesticides, the use of personal protective equipment, and exposure to animals among male farm residents in a Canadian population-based, multi-centre, NHL-control questionnaire study.

RESULTS

In a multivariate model, the following variables had statistically significant adjusted odds ratios (OR) using 95% confidence intervals (95% CI) (a) higher risk: having more than 13 head of swine, raising bison, elk or ostriches, a personal history of cancer, > 4 and < or = 15 years of farm residence and occupational exposure to diesel fuel and exhaust; (b) lower risk: raising cattle and a personal history of measles.

CONCLUSIONS

Future multidisciplinary studies of NHL should include a comprehensive review of exposure to animals in sufficient detail to assess etiological mechanisms to explain the putative associations between exposure to farm animals and NHL.

Food animal and poultry retroviruses and human health

In summary, studies reported to date have largely failed to demonstrate human infection with animal and poultry retroviruses or an association between human diseases and these viruses. A number of studies, most of them serologic, have attempted to demonstrate human infection with these viruses. The lack of antibodies in apparently exposed groups of persons suggests an absence of infection. However, another possible explanation is that humans may be immunologically unresponsive to infection with these viruses. Although attempts to infect normal human cells in vitro with many of these viruses have not been reported, BLV and BIV appear to grow poorly or not at all. On the other hand, ALSV subgroup D infect and transform human cells in vitro. However, the production of infectious virus in vitro has been low or nonexistent. This may explain the absence of antibodies in human populations. Furthermore, many of the methods used to detect infection, either directly or indirectly, have either low sensitivity or problems with specificity. Several epidemiologic studies have tried to show a relationship between human and animal leukemia or lymphoma. In many of these studies the actual exposure to retroviruses is unknown and exposure to animals may merely represent exposure to other risk factors that are more important but were either not considered or are undefined; alternatively, a common exposure may be responsible for malignancy in humans and animals with no interspecies relationship. Based on the reported studies, these viruses appear unlikely to be responsible for any significant occurrence of human disease, particularly lymphoid malignancies. Although a definitive statement of no risk to human health is probably unwarranted, the evidence to date indicates that the risk is low and perhaps nonexistent. Thus, no specific public health recommendations regarding retrovirus-infected animals or poultry are warranted at this time.

Farming and mortality from non-Hodgkin's lymphoma: a case-control study

A case-control study of non-Hodgkin's lymphoma (NHL) and its subtypes among males was conducted using computerized mortality listings from the State of Wisconsin for the years 1968-1974. Age, year of death, race, county of usual residence, marital status, and usual occupation were abstracted for the 774 records of male deaths due to NHL and a matched series of deaths due to other causes. The frequency of farming occupation among NHL cases was compared to the frequency among controls, and odds ratios (OR) were calculated. Farming was more common among cases than among controls (OR = 1.22). The association of NHL with farming occupation was greater among decedents under 65 years of age (OR = 1.7) than among those who were older. The younger decedents were at higher risk of reticulum-cell sarcoma (OR = 2.7) than of other cell types. The strength of the association increased over the 9-year study period. County levels of selected agricultural characteristics were used as surrogate measures of farming exposures in residence counties of farmers and were summarized by factor analysis. Major findings were of elevated risk among younger farmers for reticulum-cell sarcoma in counties high in summary measures of general agricultural activity (OR = 3.2), of small grain acreage and acres treated with insecticides (OR = 6.6), and of wheat acreage (OR = 4.4). Given the limitations of the data, further investigation of non-Hodgkin's lymphoma in farmers is warranted.

The zoonotic potential of bovine leukemia virus

Many workers have investigated the possibility that bovine leukemia virus (BLV) might be transmissible to man. The epidemiological studies were designed to examine for associations between human leukemia and a rural environment, cattle farming, veterinary activities, or bovine leukosis. The serological studies were used to test serum samples from human cancer patients and from persons with potential occupational exposure to BLV, among others, for evidence of BLV antibodies. All these studies are critically reviewed. It is concluded that there is no epidemiological or serological evidence from human studies to indicate that BLV can infect man.