Comparative studies of strains of infectious bovine rhinotracheitis virus isolated from latently infected calves

Three strains (479 C, 778 TL, 982 LE) of infectious bovine rhinotracheitis (IBR) virus isolated from latently infected calves were compared with the prototype strain of IBR virus (LA strain) in studies which included restriction endonuclease analysis, experimental infection, and reciprocal cross protection tests in cattle. From the restriction endonuclease analysis it appeared that the 3 "latent" viruses were derived from the same isolate, and that it differed slightly from the LA strain. However, latency does not seem to have affected the pathogenicity or the immunogenicity of the virus. This is demonstrated by the identical clinical and virologic response of calves subjected to experimental infection with the various strains under study, and by the finding that when the LA strain and a "latent" strain (982 LE) were tested in cross protection tests in cattle, they proved to be mutually protective.     

Immunizing efficacy of Toxoplasma gondii strains isolated from different hostsEfficacite d'immunisation par differentes souches de Toxoplasma gondii isolees de differents hotes

Studies were carried out to determine the fate of virulent Toxoplasma gondii challenge in immune animals. Toxoplasma strains isolated from human, swine, rabbit and cat hosts were used for the primary immunization of mice. Brains were removed at various intervals after the challenge and subinoculated into normal mice. Prior immunization with one of the nine toxoplasma strains enabled the mice either to eliminate or harbour the challenge organisms without loss of virulence. The outcome of challenge infection was dependent on the parasite strain used for the immunization and the time interval between challenge and subinoculation. Mice immunized with strain KSU isolated from a cat eliminated repeatedly administered challenge from 80% of animals. Strain S 162 isolated from a swine eliminated similar challenge from only 20% of animals. The results indicate that the extent of protection against virulent T. gondii can vary widely and is related to the immunogenicity of the original immunizing strain.     

Comparative study of various Chlamydia strains--preliminary study (author's transl)]

The chlamydia order comprises two species (Chlamydia trachomatis and Chlamydia psittaci) which are the only ones which can be rigorously differentiated with experimental criteria. However, the clinical study of chlamydia demonstrates the existence of various syndromes due to pathogenic agents. Some observations also seem to indicate the possibility of antigenic differences between isolated strains, during abortions, among small ruminants.We have entered upon a comparative study of various Chlamydia psittaci strains in order to look for objective criteria of differentiation of the strains extracted from small ruminants from those which were isolated from other animal species. Chlamydia taken from samples of ovine and caprine origin by direct isolation on embryonated egg or on cellular cultures were also compared by the following methods: seroneutralization on embryonated eggs and on cell cultures, characteristics of the plaques on cell cultures, crossed-immunofluorescence, toxic effects, lethal action on the foetus of the pregnant mouse, crossed-immunoelectrophoresis by agar gel (simple or double quantitative diffusion), electrophoresis by polyacrylamide gel.The use of those numerous techniques has enabled us to observe significant differences between those strains. However, it is not yet possible to propose a classification defining several groups. The specificity of these differences, especially between ovine and caprine strains, should become clear through the studies now in progress: in particular through the method using the interference of specific antigens compared on the one hand by serioimmunologic methods and, on the other hand, by tests setting an immunity to cellular mediation into action.     

The optimal time to stain for noncytopathic bovine virus diarrhea field sample virus using indirect fluorescent antibody technique

The use of an indirect fluorescent antibody (IFA) technique has been further explored to determine the optimum day(s) to stain for a noncytopathic bovine virus diarrhea virus from pooled and individual field samples. The IFA test further confirmed that under the experimental conditions of this study, somewhere between days 4 and 5 would be an optimum time to stain for a noncytopathic BVD virus which was present in tissues of suspected animals and diluted with minimal essential media.     

A study of cytopathic rotavirus strains isolated from calves with acute enteritis

Nine cytopathic bovine rotavirus strains were isolated in MA-104 cell cultures from fecal specimens of dairy calves suffering from diarrhea. Isolation of the virus was accomplished from three outbreaks which occurred on dairy farms located in Central and Southern Italy. Fecal suspensions were treated with a high concentration (1000 micrograms/ml) of trypsin, and inoculated into MA-104 cell cultures grown out in Eagle's minimum essential medium (MEM) containing 5 micrograms/ml of the enzyme. Cytopathic effects (CPE), characterized by intracytoplasmic inclusion bodies of different sizes and shapes, were observed on the 1st passage with five of the strains and on the 2nd (2 strains) or the 3rd (2 strains) passage for the others. The presence of trypsin and the use of MA-104 cells appeared to be essential for the occurrence of CPE, inasmuch as no CPE was detected when trypsin was omitted in the MA-104 cell system. Replication failed to occur when primary bovine embryo kidney cell cultures with or without trypsin were used. Electron microscopy revealed the presence of particles with a typical rotavirus morphology. In MA-104 cells, the titre of virus reached its maximum 48 hr after inoculation. Small, clear-cut plaques were produced by the isolates in MA-104 cells under the overlay of MEM containing carboxymethyl cellulose, trypsin and DEAE-dextran. The nine rotavirus strains were antigenically related, whereas the relationship to either the Nebraska or the Compton rotaviruses was quite weak.