Animal viruses of economic importance: genetic variation, persistence, and prospects for their control

Therapeutic potential of plant photosensitizers

Many bioactive phytochemicals have been shown in recent years to be photosensitizers, i.e. their toxic activities against viruses, micro-organisms, insects or cells are dependent on or are augmented by light of certain wavelengths. These activities are often selective, and this has led to the concept of therapeutic prospects in the control of infectious diseases, pests and cancer. Reaction mechanisms commonly involve singlet oxygen and radicals, which are thought to cause photodamage to membranes or macromolecules. The main classes of plant photosensitizers reviewed here are polyyines (acetylenes, thiophenes and related compounds); furanyl compounds; beta-carbolines and other alkaloids; and complex quinones. We propose that within each group of phytochemicals there are several representatives that merit further study for therapeutic abilities in appropriate animal models.

Properties of the immunosuppressive factor induced by murine cytomegalovirus

Murine cytomegalovirus infection of spleen cultures induced the production of a small (less than 10,000 molecular weight) immunosuppressive factor (VISF), which suppressed concanavalin-A mitogenesis in fresh mouse spleen cells, and in fresh human peripheral blood leukocytes. The factor did not affect the growth of two murine T-cell lines or of mouse fibroblasts. A similar factor was also found in the serum of infected mice, at the time of maximum immune suppression. The properties of VISF indicate that the mechanism of MCMV immune suppression is different from that caused by several other viruses which are important in human and veterinary medicine.

The efficacy of amantadine and other antiviral compounds against two salmonid viruses in vitro

Various compounds, with known clinical efficacy against human viruses, were evaluated for their ability to inhibit the growth of infectious hematopoietic necrosis virus (IHNV, a rhabdovirus), and infectious pancreatic necrosis virus (IPNV, a birnavirus), in rainbow trout cell cultures. Amantadine inhibited the plaque forming ability of IHNV, at concentrations which did not affect cell growth or morphology, although it was not active against IPNV. Metisazone and bis-benzimidazole were also effective against IHNV; but they were slightly cytotoxic. Ribavirin, as expected, was active against IPNV, but was also equally effective against IHNV, although it was cytotoxic. Several other compounds were also tested but they were not inhibitory to either virus. The attraction of amantadine is the fact that relatively easy administration should be feasible.

Characterization of a murine cytomegalovirus-induced immunosuppressive factor

Murine cytomegalovirus infection in spleen cultures resulted in the production of a soluble factor, VISF (virus-induced suppressive factor), which inhibited concanavalin A mitogenesis in fresh spleen cells. Its production was specific for MCMV, since infection of spleen cultures by Sindbis virus, or bacteriophages PM 2 and T 4, and the phagocytosis of latex beads, all failed to elicit VISF. Maximum appearance of the factor occurred within 24 hours p.i. in spleen cultures, and its source was identified as the population of spleen cells which adhered to a plastic culture dish within two hours at 37 degrees C. Non-adherent cells did not produce the factor. Its production was not inhibited by indomethacin. VISF could be concentrated by ultrafiltration on a YM 2 membrane filter, and it was readily fractionated by chromatography on sephadex G-25. In relation to peptides of known molecular weight it appeared to be smaller than 1,400 daltons. Its ability to suppress concanavalin A mitogenesis was largely removed by digestion with proteinase K. Thus VISF appears to be a relatively small peptide or peptide-containing substance. It was purified further by HPLC.