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Twenty-three susceptible newborn kittens were inoculated with feline panleukopenia virus on the day of birth and were sacrificed from 18 hr to 43 days postinoculation (DPI). Macroscopic lesions included thymic atrophy in animals examined at 4 to 14 DPI and cerebellar hypoplasia and degeneration in animals examined at 22 to 43 DPI. Clinical signs of ataxia were not observed in the four kittens with cerebellar lesions sacrificed at 22 to 43 days of age. Intranuclear inclusions were present in a variety of cell types in the organs examined from kittens that died or were sacrificed at 4 to 14 DPI. The most severely infected and depleted tissues were the thymus, spleen, mesenteric lymph nodes, and the cerebellum, whereas the bladder, testes, ovaries, and uterus were the least susceptible to panleukopenia virus infection. Specific fluorescence was demonstrated with panleukopenia antiglobulin conjugate in various cell types in tissues from 2 to 22 DPI and only in cerebellar Purkinje cells of kittens sacrificed at 29, 36, and 43 DPI. The virus replicated in the cells of all layers of blood vessels (endothelial, muscular, and connective tissue cells), suggesting that this is the route of dissemination of the agent throughout the body. Clinical findings, virology, hematology, and serology of this study on the pathogenesis of feline panleukopenia (FPL) in susceptible newborn kittens have been described in the preceding paper (5). This article characterizes the gross and histopathological changes and demonstrates the susceptibility of various cell types and spread of virus from portal of entry to various organs and tissues by the fluorescent-antibody (FA) technique. MATERIALS AND METHODS Histopathology. Tissue specimens were fixed in Formalin or Bouin's solution (10), or both. Paraffin sections were stained with hematoxylin and eosin (H & E). Attempts were made to collect sections from the nervous system of all animals at similar locations. These included a section through the cerebrum, in

Inoculation of susceptible newborn kittens with a large dose of panleukopenia virus caused subclinical infection in 19 of 23 cases. All infected kittens developed severe and prolonged leukopenia. Cell-free virus was present in the blood from 1 to 7 postinoculation days. The virus spread to all organs, regardless of the route of inoculation. The thymus, spleen, mesenteric lymph nodes, and the cerebellum were the

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The caliciviruses, as a proposed family Caliciviridae, have a distinct viπon morphology with cup-shaped depressions on a spherical capsid surface. The viruses have single-stranded RNA, which has a molecular weight about 2.6 × 10⁶ and is infectious. The RNA is covalently linked to a small protein. A single major polypeptide is found in the capsid. A sub-genomic RNA, molecular weight about 1 × 10⁶, coding for the capsid polypeptide is found in infected cells. Caliciviruses infecting swine, pinnipeds and cats have been characterized. Viruses which are morphologically identical to the known caliciviruses have been identified in human feces; these viruses have been shown to be associated with gastroenteritis, but they have not yet been propagated in the laboratory.

One of the crystal types induced in cell cultures by a new feline herpesvirus was identified as cholesterol by crystal structure, polarized light microscopy, and mass spectroscopy.

Experimental infection with infectious pancreatic necrosis virus (IPNV) was achieved in yearling rainbow trout (Salmo gairdneri) and 7-mo-old brook trout (Salvelinus fontinalis) by intraperitoneal inoculation and by water contact, respectively. Blood removed periodically from both groups of fish was fractionated and various blood components examined for virus. IPNV was recovered consistently from the plasma and mononuclear-enriched blood fractions of the rainbow trout from 1 to 19 d postinoculation (DPI) and also was detected in the mononuclear fraction on 33 DPI. In the brook trout virus was recovered from 3 to 40 DPI in the plasma and from 7 to 40 DPI in the mononuclear fraction. Thus a viremia appeared to be important in the early stages of experimental IPNV infection and infectious virus was found both free in the plasma and in association with an undetermined cell population present in the mononuclear component of blood.Key words: infectious pancreatic necrosis, blood, fish disease, Salmo gairdneri, Salvelinus fontinalis