Erythroleukemia in Two Infant Chimpanzees Fed Milk from Cows Naturally Infected with the Bovine C-type Virus¹

Erythroleukemia and Pneumocystis carinii pneumonia were diagnosed in two of six infant chimpanzees (Pan troglodytes) fed from birth on unpasteurized milk from cows naturally infected with the bovine C-type virus. The chimpanzees died at 34 and 45 weeks of age after a 5 to 6-week illness characterized by lethargy, anorexia, leukocytosis, anemia, and progressive pneumonia. Blast cells and immature myeloid cells were prominent in bone marrow specimens and were present, although less conspicuous, in peripheral blood smears. At autopsy, both animals showed infiltration of neoplastic cells in the bone marrow, spleen, lymph nodes, and, to a much lesser extent, in the lungs, liver, and kidneys. Four chimpanzees in the milk-fed group and all six in the control group are alive and apparently healthy. The experimental chimpanzees were all housed together, but only the two affected animals received milk during the immediate neonatal period from cow BF044, our most reliable and abundant source of bovine C-type virus. Neither leukemia nor P. carinii pneumonia has been reported previously in chimpanzees. Electron microscopic and serological studies failed to demonstrate the presence of bovine C-type virus in either the milk-fed or control animals studied. However, the two leukemic chimpanzees died before their buffy-coat cells could be examined.