Isolation of parapox viruses from man and animals: Cultivation and cellular changes in bovine fetal spleen cells

Abstract Maculopapular, pock-like lesions were detected repeatedly on hands and arms of students having contact with sheep or cattle. Pustular lesions were seen on the mammary gland and vulva of a goat. Biopsy samples of the lesions from 3 students and the goat were cultured on bovine fetal spleen (BFS) cells. Viruses were isolated from all samples. The viral isolates induced similar cytopathic changes in BFS cells. Slowly spreading plaque-like changes consisting of large, round cells developed in BFS monolayers. In a growth curve experiment involving the Shoe strain and BFS cells, virus infectivity increased 8 hr after inoculation. The major portion of the infectivity remained associated with the cell fraction. Maximal titers were found 36 hr after infection. Eosinophilic inclusions of varying size were detected in the cytoplasm 8–18 hr after infection of BFS cells. Later these inclusions enlarged, coalesced, stained basophilically, and remained attached to the pycnotic nuclei. Vacuoles created a ballooning appearance and separated the plasma membrane from the nucleus-viral inclusion complex by 24 hr after infection when the cells detached. Negatively stained preparations of purified virus of the isolates contained ovoid virions covered with diagonally woven bands. The long axis of the virions measured 220 and 250 nm and the short axis was 120–140 nm. These features are characteristic of the parapox virus genus which includes members that induce orf.