Contact with hospital, drugs, and chemicals as aetiological factors in leukaemia.

45 adults with acute leukaemia or chronic myeloid leukaemia and a control group of patients from the same hospital were asked about the people they had close social contact with before their illness, and about their use of drugs and chemicals. 18 (40%) leukaemia and 6 (13%) control patients had close social contact with hospital personnel or leukaemia patients. 8 (18%) leukaemia patients, but no control patients, had been in close contact with haemotological ward personnel. These differences were statistically significant. 9 (20%) leukaemia and 4 (9%) control patients lived in the same house as healthy persons working in a hospital. No conclusion could be drawn from differences between the two groups in their use of drugs, since the possibility that they were used to treat initial symptoms of leukaemia could not be excluded. Exposure to chemicals, including weed-killers and agricultural insecticides containing a benzene-ring known to be leukaemogenic, was about the same in the two groups.

Proviral sequences of baboon endogenous type C RNA virus in DNA of human leukaemic tissues.

Hybridisation of RNA from a baboon endogenous type C RNA virus to DNA from tissues of leukaemic patients indicates that a virus of this type is horizontally transmitted among humans. DNA from several patients with leukaemia hybridised 70% of the hybridisable RNA from baboon endogenous type C RNA virus (BaEV) and yielded hybrids of high tm, whereas DNA from normal human tissues hybridised only 23% of the BaEV RNA, and the tm of these hybrids was lower.

Leukemia of BALB/c mice induced by cellfree filtrate from transplantable Thurzo--Svec rat leukemia.

Leukemia was produced in adult BALB/c mice inoculated with cellfree filtrate derived from cells of transplantable Thurzo-Svec rat leukemia. The leukemogenic activity of 20% filtrates was 10(8) ID 50 per ml. Leukemia induced in mice with rat materials was serially transplantable by cellfree filtrates of leukemic tissues and plasma to the same strain of mice.

[The incidence of lymphosarcoma (leukaemia) and feline leukaemia virus (FeLV) in cats in the Netherlands (author's transl)]. / Het voorkomen van lymfosarcoom/leukemie en katten-leukemievirus (FeLV) bij de kat in Nederland

Seven different groups of cats were examined to study the incidence and distribution of feline leukaemia virus (FeLV) in the Netherlands. The indirect fluorescent antibody (IFA) technique was used to detect FeLV antigen. Of the cats with lymphosarcoma (leukaemia), 73.2 per cent and of those with infectious peritonitis, 32.4 per cent were found to be positive for FeLV antigen. Of the sixty-six cats with other tumours, only one, a cat with carcinoma of the mammary gland; was positive for FeLV antigen. Of 557 cats with various lesions, forty-two (7.5 percent) were positive for FeLV antigen. The IFA-test was found to be a useful adjunct in establishing the correct diagnosis. Of all stud cats which had been in contact with FeLV-positive cats, 24.7 percent were positive for FeLV antigen, wheras all those which had not been in contact with these cats, were negative. There was a marked difference between the proportions of FeLV-positive cats in the groups of clinically normal cats which had (20.6 per cent) and which had not (0.4 per cent) been in contact with FeLV-positive cats. Follow-up studies showed that 67.8 percent of the clinically normal, FeLV-positive cats had died from or been sacrificed because of FeLV-associated diseases within twenty months.

Different hematological diseases induced by type C viruses chemically activated from embryo cells of different mouse strains.

Type C RNA viruses can be induced by certain chemicals from cells of many mouse strains. Both C58 and BALB/c cells have been shown to contain endogenous viruses that are designated N-tropic because they grow preferentially in cells of NIH Swiss mouse origin. While demonstrating many similar biological and immunological properties, the C58-induced virus is around 10-fold more infectious per physical particle than the N-tropic virus of BALB/c cells. In the present studies, inoculation of these viruses into newborn NIH Swiss mice led to the development of diseases associated with splenomegaly and lymphadenopathy at similar frequency in each group. The disease induced by C58-MuLV was histophathologically diagnosed as lymphoblastic leukemia and was highly malignant following transplantation into newborn mice. The histopathological appearance of spleens from BALB/c virus-affected animals was distinguishable, demonstrating instead myeloid metaplasia or myelogenous leukemia. These findings provide evidence that different endogenous mouse type C viruses can induce distinct diseases in the same mouse strain. Furthermore, they implicate the N-tropic virus endogenous to C58 cells as a major factor in the development of lymphoblastic leukemia that occurs at high frequency in that strain.

Leukaemia and lymphoma patients interlinked by prior social contact.

Patients with either leukemia or lymphoma were asked if they had close personal associations with other patients before the onset of disease. Iinitial interviews indicated that several patients could be interlinked into social clusters. Tumour-registry records were used to contact each patient (or a surviving relative) diagnosed during the years 1964-73 in three areas of West Virginia. Close personal associations, antedating the onset of disease in 1 or both individuals of each linkage pair, were detected in 14 of 23 (61%), 14 of 22 (68%), and 6 of 8 (75%) patients from these three areas during this ten-year period. In addition, among 28 randomly selected patients with Hodgkin's disease from various parts of the United States, 10 (36%) had direct or indirect close personal associations with 17 other patients with leukemia or lymphoma. Patients with leukemia or lymphoma frequently are interlinked by prior close personal associations to other patients with these diseases.