Ray M. Dutcher

PEDIGREE STUDIES IN BOVINE LYMPHOSARCOMA

As early as 1897, European veterinarians’ reported the occurrence of lymphosarcoma in cow families in which both a dam and a daughter were affected. Early in the 20th Century, German workers2 noticed a higher incidence of the condition in some breeds than in others and late? reported on a familial incidence of lymphosarcoma. However, as lymphosarcoma became more widely recognized, gradually less importance seemed to be placed on its hereditary aspects. In the United States, Karlson4 studied the familial aggregation of lymphosarcoma cases in cattle herds in Minnesota. He reported on a Milking Shorthorn herd of 25 animals in which five cases of lymphosarcoma had occurred within a six-month period. Two of the affected animals were half-sisters; the relationship of the other affected animals was not mentioned but there may have been relationships. He also reported on an Aberdeen-Angus herd of 100 head in which three lymphosarcoma cases had been diagnosed. Two of these cases were in full sisters and one was in a daughter of one of the sisters. Finally, he described a Jersey herd in which six cases of lymphosarcoma occurred in a single family during a ten-year period. In 1962 Larson5 reported on additional Minnesota cattle herds in which lyniphosarcoma occurred in related animals. Familial aggregations of lymphosarcoma cases were also reported by Starr and Young6 who studied a Holstein family in which a normal cow produced two affected daughters, an affected granddaughter, and an affected grandson; and a Guernsey family in which four successive female generations succumbed to lymphosarcoma. In Denmark, Bendixen’ observed that lymphosarconia (“leukosis enzootica bovis”) occurred with greater frequency in the daughters of affected cows than in the daughters of unaffected cows. Our pedigree studies were undertaken in an attempt to elucidate some of the factors involved in the multiple occurrence of lymphosarcoma in certain dairy cattle herds in Pennsylvania and surrounding states.

OCCURRENCE OF LYMPHOCYTOSIS IN DAIRY CATTLE HERDS WITH HIGH INCIDENCE OF LYMPHOSARCOMA

European veterinarians were the first to suggest a relationship between bovine lymphosarcoma and the occurrence of lymphocytosis in the peripheral blood of clinically normal cattle in herds where cases of lymphosarcoma had appeared.’S2 p 9 v 4 They believe that lymphosarcoma is a slowly advancing, horizontally transmitted, infectious disease (“leucosis enzootica bovis”), and that the lymphocytosis represents subclinical infection. In Denmark, for purposes of herd evaluation, a “Leukosis Key” (TABLE l ) , based upon total lymphocyte counts, is used to classify clinically healthy cattle from “leucosis” herds into normal, suspect, and positive groups. This work was undertaken to study the occurrence and significance of lymphocytosis in multiple-case lymphosarcoma herdst in the eastern United States. Fur purposes of comparison, it was necessary to establish values for absolute lymphocyte counts in a statistically valid sampling of cattle of various ages from “normal”

ETIOLOGICAL STUDIES ON BOVINE LYMPHOSARCOMA

herds of the four major dairy breeds.

Evidence in support of a virus etiology for bovine leukemia

European workers believe that the incidence of lymphosarcoma, or “leukosis” t of cattle, has increased since World War I1 in the cattle populations of Denmark, Sweden, and Germany. They also believe that “leukosis” is a slowly advancing infectious disease with a long incubation period in which the initial sign is an increase in the absolute lymphocyte An infectious etiology for lymphosarcoma has also been suggested by Goetze et al. 1956’; by the reported isolation of a virus from “leukosis” cattle by Thorell, 1957,’O Montemagno et ul., 1957,11 and Papparella, 195912; by the cattle transmission experiments of Rosenberger, 196lS; and by the recent reports of McKercher, 1962,13-14 Jarrett, 1962,16 and Sorenson, 1962.I6-l7 However, proof that an infectious agent is involved in the etiology of bovine lymphosarcoma is still lacking. Our group has recently reported on attempts to characterize lymphosarcoma with regard to clinical manifestations, pathologic alterations and familial distribution of cases in high incidence herds.18 Analysis of pedigree data from cattle with lymphosarcoma in multiple-case herds indicates that the disease occurs in related animals. Such a familial aggregation of cases is suggestive of genetic susceptibility to lymphosarcoma and/or vertical transmission of an infectious agent. We have been attempting to exploit the clinical, hematological, and epidemiological data in developing criteria for the selection of cattle to be used in etiological studies of lymphosarcoma. Cattle are considered to be “normal” or “noninfected” 1 if they: 1. Show no clinical signs of lymphosarcoma. 2. Are derived from herds with no past history of lymphosarcoma. 3. Are derived from herds not showing generalized lymphocytosis on re-

Observations on a heifer with cutaneous lymphosarcoma

Virus‐like particles resembling the C‐type particles of murine leukemia were detected in tissue biopsies and more frequently in thin sections of pellets following density gradient centrifugation of milk from leukemic cows and cows in a high incidence leukemic herd. These particles had a buoyant density in potassium citrate and sucrose gradients of 1.15 to 1.16 Gm/cc. Fractions in which the particles were found contained both DNA and RNA, with RNA in higher concentration. Virus interference assays on tissue cultures derived from leukemic and leukemia‐free cattle yielded equivocal results. Bone marrow cultures were uniformly resistant to challenge with vesicular stomatitis virus. Interferon was identified in the supernatant fluid of two resistant cultures. Immunofluorescence studies with anti‐Rauscher virus globulin and a globulin from a leukemic calf suggested possible antigenic similarity when the fluorescent globulins were used to stain tissue cultures derived from leukemic cattle.

Comparative aspects of bovine leukemia.

Cutaneous lesions are exceedingly rare in cattle with lymphosarcoma in the United States. Such cases are of particular interest because of a widely held belief, on epidemiologic grounds, that the etiology and pathogenesis of “skin leucosis” differs from the more typical adult form of the disease. Except for cutaneous lesions, a 20‐month‐old grade Holstein heifer originating on a Pennsylvania farm showed the clinical configuration, pathological alterations and laboratory findings commonly observed in cattle with generalized lymphosarcoma. It is, therefore, difficult to accept the view that the etiology and pathogenesis of lymphosarcoma in this animal with skin manifestations (one of many possible expressions of the disease) was fundamentally different from other forms of lymphosarcoma.

Comparative Studies on Monolayer and Suspension Cell Cultures from a Transplantable Rat Mammary Carcinoma Containing C-Type Virus Particles

The discovery of particles resembling mouse leukemia virus in cows milk from a herd with a high incidence of leukemia and in lymph node cells of leukemic cattle and the finding of similar viruslike particles in human leukemic plasma and in pasteurized market milk are disquieting developments calling for intensive investigation to determine the biologic significance of the particles. The features of bovine leukemia are reviewed, and experiments are described which suggest the presence of a “resistance factor” in leukemic milk.

Electron Microscopic Studies on Tissue Cultured Cells and Density Gradient Fractions of a Transplantable Rat Mammary Carcinoma

Attempts to establish monolayer cell cultures from an X-irradiation-induced transplantable rat mammary carcinoma were successful only on a short-term basis (3 to 4 passages). However, suspension cell

Virus-Like Particles in Cow's Milk From a Herd With a High Incidence of Lymphosarcoma

Mature and immature C-type particles were observed in the extracellular spaces and in vesicles as well as budding from tumor cells and cell cultures derived from a transplanted X-irradiation induced r