Performance of high titre attenuated canine parvovirus vaccine in pups with maternally derived antibody.

The performance of live, attenuated, homologous, canine parvovirus vaccines was studied in 140 puppies aged from four to 11 weeks. In the presence of maternally derived antibody the ability of the vaccines to elicit a serological response, as determined by the haemagglutination inhibition test and a standardised ELISA, was found to be dose (infectious titre) related. An experimental vaccine containing 10(7.0) TCID50 of virus induced seroconversion rates of 95, 89, 82 and 44 per cent in dogs with haemagglutination inhibition antibody titres of less than or equal to 8, 16, 32 and greater than 32, respectively. The standardised ELISA appeared to be better than the haemagglutination inhibition test with respect to variability and subjectivity, especially when titres were low.

Safety of a temperature-sensitive vaccine strain of bovine viral diarrhea virus in pregnant cows.

Safety tests were conducted in 78 pregnant cows vaccinated with a commercial preparation of a temperature-sensitive vaccine strain of bovine viral diarrhea (BVD) virus. After vaccination, seroconversion was detected in 33 (97%) of 34 cattle that did not have antibodies against BVD virus. Overall, 43 (91%) of 47 cows with prevaccination titers less than or equal to 4 seroconverted. During the test period, cows did not become naturally infected with BVD virus, and BVD-associated reactions to the vaccine were not observed in vaccinated cows. Calves born to vaccinated cows did not have clinical signs of fetal BVD. Precolostral blood samples collected from the progeny of cows that were seronegative at vaccination were free of antibody against BVD virus. Bovine viral diarrhea virus was not isolated from the cattle evaluated in the present study.

The neurovirulence of human and animal rotaviruses in cercopithecus monkeys.

Cercopithecus monkeys were inoculated according to the specifications of neurovirulence safety test for live rubella virus vaccine with RIT 4237, a rotavirus vaccine candidate. RIT 4237 is a high passage level of the Nebraska Calf Diarrhoea Virus (NCDV). The histological findings in the first test indicated some involvement of the central nervous system. The same test was therefore repeated with RIT 4237, with a lower passage level of the NCDV strain, and with the 'Wa' strain, a human virus grown in tissue culture. Clinical signs and histological findings were concordant and demonstrated that all the viruses were moderately neurovirulent. As in the poliovirus neurovirulence test, the histological lesions depended mainly upon a correct inoculation in the lumbar cord. RIT 4237 was found to have the same degree of neurovirulence as the low-passage NCDV or as the 'Wa' strain.

Clinical evaluation of a temperature-sensitive bovine viral diarrhea vaccine strain.

A naturally occurring strain of bovine viral diarrhea (BVD) virus was chemically treated to produce a genetically stable, temperature-sensitive mutant, designated RIT 4350. The RIT 4350 strain had a restrictive growth temperature of 39.5 C, so that systemic replication or fetal infection was not detected after parenteral administration in cattle. The RIT 4350 strain was tested as a cell culture-adapted vaccine in healthy heifers, immunodepressed calves, and pregnant cows. In a pathogenicity test in 5 healthy heifers, vaccination with 10 times the field dose resulted in seroconversion, but produced no clinical signs of disease or leukopenia. In a pathogenicity test in immunodepressed calves, 7 test animals were treated with dexamethasone and inoculated with 10 times the field dose. The calves developed mild enteric signs, but virus isolation attempts were negative. Following vaccination, the immunodepressed vaccinated calves were challenge exposed with the Osloss strain of BVD virus; all these vaccinated calves remained healthy. Two of 68 postchallenge serum samples from vaccinated calves were positive for BVD virus, compared with 9 of 20 samples from control calves. In another pathogenicity test, 7 pregnant cows vaccinated with 4 times the field dose seroconverted, remained clinically healthy, and delivered healthy calves.

Protection studies in colostrum-deprived piglets of a bovine rotavirus vaccine candidate using human rotavirus strains for challenge.

Studies were performed to evaluate the potential use of the bovine RIT 4237 rotavirus strain as a vaccine candidate against infection with human rotaviruses. Initial experiments revealed that colostrum-deprived piglets were susceptible to infection with several human strains, except for those belonging to subgroup 1. Subsequently, different immunization procedures with RIT 4237 were studied in this animal model. It was found that a two-dose administration, either given intramuscularly (twice) or once intramuscularly and once intragastrically, was necessary to induce a significant serum antibody response. Finally, the protective effect of the latter vaccination schedules against subgroup 2 and 3 rotavirus strains of human origin was evaluated by artificial challenge. In both cases, prior administration of live RIT 4237 significantly decreased fecal shedding of the challenge virus when compared with control animals.

Recombinants of influenza virus type B as potential live vaccine candidates: RNA characterization and evaluation in man.

Two recombinants (R22 and R75) of the attenuated B/USSR/69 strain Bright and the virulent B/Hong Kong/5/72 and one recombinant (R5) of Bright and the virulent B/Hong Kong /8/73 were selected for genotypic and phenotypic caracterization. All three recombinants had the growth property of the attenuated parent Brigit. Analysis of their RNA's by polyacrylamide gel electrophoresis revealed that, the strains R22 and R75 had derived all their genes from Brigit, those coding for haemagglutinin excepted. These recombinants were clinically evaluated and found to be attenuated and immunogenic. The recombinant R5 which derived, besides the bene coding for the haemagglutinin, several other genes from B/Hong Kong/8/73 was only partly attenuated since it induced influenza-like symptoms in one out of three volunteers. It is concluded that the strain Brigit can be used as a donor of genes for the attenuation of the B/Hong Kong/5/72 virus and that recombinants of influenza type B can be identified, like influenza type A recombinants, by their RNA pattern.

Genotypic characterization and clinical evaluation of an influenza A/Texas/1/77 (H3N2)-like recombinant: RIT 4199.

The RIT 4199 (H3N2) strain was obtained by recombination of PR/8/34 (H0N1) and A/Alaska/5/77 (H3N2) isolates. Its genetic composition was determined by RNA-RNA hybridization and by identification by gel electrophoresis of the double-standard RNA formed. The RIT 4199 was inoculated intranasally to 27 seronegative volunteers at a dose of 10(7.3)EID50. The results show that it is suitable for live vaccine strain.

Properties of A/Victoria/3/75 recombinants: development of an attenuated strain RIT 4050.

An attenuated Influenza A strain, RIT 4050, has been selected among the inhibitor resistant variants of a range of H3N2 recombinants of A/PR/8/34 and A/Victoria/3/75. The criterion used for the selection of the vaccine strain was the homology rate of the viral RNA of the recombinant with the complementary RNA of A/PR/8/34 as determined by an RNA-RNA hybridization technique. Safety has been assessed by administering the vaccine by the nasal route to double seronegative volunteers. Incidence and nature of post-vaccinal symptoms was low and mild as in healthy seropositive volunteers. The excretion pattern of the strain was investigated. Volunteers shed virus for one day after vaccination and the titre of the virus was low. Eight reisolates of RIT 4050 were characterized and found similar to the original vaccine strain offered to the volunteers.

RNAs of influenza virus recombinants derived from parents of known virulence for man.

Extensive use of recombinants made from A/PR/8/34 (H0N1) and wild, virulent H3N2 viruses as live influenza vaccines has provided a number of viruses of defined virulence for man. Clinical symptoms produced by these strains have ranged from febrile influenza to local coryzal symptoms or nil. A study was therefore made of the extent to which the PR8 genome had been incorporated into that of a number of the recombinants. By RNA--RNA hybridization it seemed that recombinants which had 55 per cent of greater homology with the PR8 parent were likely to conform an acceptable standard of attenuation. Those with lesser homology were frequently, but not always, clinically virulent. The technique seemed potentially useful, therefore, for screening PR8 live vaccine recombinants in vitro before giving them to volunteers.

Laboratory characteristics of an attenuated influenza type A (H3N2) virus ('Alice' strain).

The Alice strain of live attenuated influenza virus was obtained by selection of a gamma inhibitor-resistant strain from a virus recombinant between A/PR/8/34 (HON1) and A/England/42/72 (H3N2). Its behaviour in vitro and in vivo was studied. Three marker systems were investigated: resistance to serum inhibitors, growth capacity at high temperature and low sensitivity to amantadine hydrochloride. In ferrets the strain was found to be attenuated and immunogenic. Passages in man, animals and eggs have not affected its resistance to gamma inhibitors.

Local and systemic response after simultaneous intranasal inoculation of temperature-sensitive mutants of parainfluenza 3, IBR and bovine adenovirus 3.

Triple seronegative calves were exposed by the nasal route to three (ts) mutants of bovine respiratory viruses (PI3, IBR, Adeno3). After a single exposure, they responded with significant levels of serum antibodies to the three viruses. Nasal antibodies were demonstrated for PI3 and adenovirus antigens. The failure to demonstrate nasal antibodies to IBR may be due to lack of sensitivity of the procedure used. When reexposed six weeks later, calves had sharp increases in levels of serum antibodies and developed a secondary type response at the local level for all three viruses. The persistence of the local antibodies was much longer after reexposure than after primary inoculation. This study indicates that the simultaneous application of these three (ts) viruses by the respiratory route is perfectly safe and affords a long lasting immunity towards homologous respiratory infections.

Inoculation of hamsters with a temperature sensitive (ts) mutant of parainfluenza 3 virus.

The multiplication pattern of a temperature-sensitive (ts) mutant of bovine parainfluenza 3 virus was studied in hamsters and compared with that of a virulent virus strain. The ts mutant was recovered regularly from the nasal mucosa and not from the lungs, whereas the virulent virus multiplied in the lungs as well as in the nasal mucosa.The serological response induced by the mutant was comparable to that obtained after inoculation of the virulent virus.This ts mutant may be a potential candidate for a live intranasal vaccine against bovine parainfluenza 3 infection.