Gallid herpesvirus 2 (GaHV-2) causes malignant lymphomas in chickens (Marek's disease, MD). Although MD is controlled through vaccination efforts, field isolates of GaHV-2 have increased in virulence worldwide and even cause MD in vaccinated chickens. GaHV-2 strains are classified into four categories (mild, virulent, very virulent and very virulent +) based on the virulence exhibited in experi...

The experiments reported in this paper indicate that a pure culture of a virulent Type I pneumococcus as transferred under ordinary conditions is made up of individuals which are not identical in virulence for animals,-in bile solubility, or in their power to multiply under unfavorable conditions. By mechanical analysis alone no avirulent strains were obtained from the virulent strain, but one,...

The nucleotide sequences of the fusion (F) and haemagglutinin-neuraminidase (HN) glycoprotein genes of the extremely avirulent Newcastle disease virus (NDV) strain Ulster have been determined by sequencing cDNA clones derived from viral genomic RNA. Open reading frames, assumed to encode the F0 and HN0 glycoprotein precursors, were 553 and 616 amino acids long, respectively. Comparisons of the ...

The ability of virulent strains of Aeromonas salmonicida to resist the bactericidal activity of serum was quantitated. The A. salmonicida strains tested included virulent strains, mutants lacking the major surface A-protein, and mutants lacking A-protein and having a modified lipopolysaccharide structure. The sera evaluated included normal human, rabbit, and trout sera, immune trout serum, and ...

The ecology of virulent strains of Rhodococcus equi on horse farms is likely to influence the prevalence and severity of R. equi pneumonia in foals. This study examined the association between the ecology of virulent R. equi and the epidemiology of R. equi pneumonia by collecting air and soil samples over two breeding seasons (28 farm-year combinations) on Thoroughbred breeding farms with diffe...

The pathogenicity of different birnavirus strains to turbot was determined by challenge experiments. The reference strains of IPNV (Sp, Ab and VR-299) were not pathogenic for turbot (Scophthalmus maximus). The Norwegian serotype (N1) and two selected birnavirus strains isolated from turbot and related to the Ab serotype of IPNV (TB-306 and TB-390) were virulent to different degrees for turbot a...

Toxoplasma gondii is an obligate intracellular protozoan parasite responsible for a common infection of the central nervous system. Interferon (IFN) γ is the key cytokine of host defence against T. gondii. However, T. gondii strains differ in virulence and T. gondii factors determining virulence are still poorly understood. In astrocytes IFN γ primarily induces immunity-related GTPases (IRGs), ...

Based on nucleotide sequence analysis of the hemagglutinin (HA) gene from the virulent and avirulent A/chicken/Pennsylvania/83 influenza viruses, it was previously postulated that acquisition of virulence was associated with a point mutation that resulted in loss of a glycosylation site. Since there are two potential glycosylation sites in this region of the HA molecule and since all Asn-Xaa-Th...

In vivo infection studies in Japanese flounder (Paralichthys olivaceus) demonstrated that the number of viable cells of the virulent strain (NUF251) of Edwardsiella tarda increased gradually in kidney and hepato-pancreas after intraperitoneal injection, but the low virulent strain (NUF194) did not. To gain insight into the virulence factors of E. tarda, in vitro responses of Japanese flounder (...