Potential as an aerosol vaccine of an improved Newcastle disease vaccine derived from the LaSota strain—I. In vitro studies

After mutagenic treatment of the LaSota strain, cold-adapted mutants were selected by serial passages in eggs at 26°C.One of these mutants, RIT 4030, was attenuated for S.P.F. day-old chickens vaccinated by aerosol.In vitro studies were performed to define the properties which differentiate this mutant from the parental LaSota strain.

1. 1. The strain RIT 4030 bears a ts mutation which reduces its multiplication at 41°C.

2. 2. The strain RIT 4030 has modified infectivity properties in CEF and behaves like a “host-range” mutant.

The correlation between these mutations and the reduced pathogenicity of this strain for chickens is discussed.     

Intranasal vaccination against upper respiratory tract disease (U.R.D.) in the cat—II. Results of field studies under enzootic conditions in The Netherlands with a combined vaccine containing live attenuated calici- and herpesvirus

A live vaccine containing attenuated calici- and herpesviruses was tested in field studies in the Netherlands.This vaccine is administered intranasally. Cats may show local transient reactions in the week following vaccination. The experiments were conducted in three types of infected premises: boarding catteries, homes for stray cats and breeding colonies. In the boarding catteries the vaccine was instilled intranasally at least one week before admission. If this was impossible—like it is in homes for stray cats—the animals were vaccinated at the day of admission and then quarantined for at least 24 hr.In the four boarding catteries 290 cats were vaccinated. Local reations were observed in 25 animals (less than 9%). Five cats (less than 2%) showed clinical symptoms of the disease in spite of vaccination. However these cases were all in the same cattery which also housed stray cats.In three homes for stray cats 257 animals were vaccinated. The percentage of local reactions was much higher (49%) due to suppressed infections and secondary bacterial invaders. Clinical disease was seen in 13 cats (5%). However eight of these cats were in one cattery where some of the requirements of the experiment—c.q. quarantine—could not be met.Prevention of the disease in infected breeding colonies was difficult to achieve because infected parent animals are known to shed virulent virus during rehousing and parturition.The following vaccination program was very successful: parent animals are vaccinated intranasally prior to mating and the pregnant queens again on the day of parturition. The kittens are then vaccinated intranasally at an age of 8–10 days old. With this program the percentage of healthy kittens that could be sold was as high as 98%. This compares to 66% in a previous vaccination program where the queens were given an intramuscular vaccine and the kittens received either several intramuscular vaccinations or one intranasal vaccination on the age of six days.The CH vaccine is available on the Dutch market for one year. The results obtained by veterinary practitioners confirm the good results obtained in the field studies.     

Characterization of shiga toxin-producing Escherichia coli strains isolated from calves in Poland

Fecal samples from 67 3–5-months-old calves with diarrhea were screened for the presence of shiga toxin-producing Escherichia coli (STEC). Several accessory virulence factors genes were also tested. Among 192 E.coli isolates tested, 15 (7.6%) were found to harbour the shiga toxin 1 or 2 (stx1 or stx2) genes. The stx2-carrying samples were further subtyped by PCR for the stx2c, stx2d, and stx2e toxin variants. It was shown that stx2-positive bacteria mainly possessed the stx2c shiga toxin type gene. The enterohemolysin (hlyA) and intimin (eae) genes were found in seven (46.7%) STEC strains whereas the cytotoxic necrotizin factor 1 and 2 or the P fimbrial genes were detected in two isolates only. This study confirmed that calves are a reservoir of STEC strains (with all pathogenicity genes) that may be virulent for humans.     

Characterization of Salmonella isolates from beef cattle, broiler chickens and human sources on Prince Edward Island

Non-typhoid Salmonella serovars remain a potential threat to human health, and beef cattle and broiler chickens are possible sources of these organisms on Prince Edward Island (PEI). In this study, the ceca of beef cattle belonging to fasted and non-fasted groups, and broiler chickens were examined for Salmonella at the time of slaughter. The characteristics of the isolates, including antimicrobial resistance patterns and virulence genes, were studied along with the isolates obtained from cases of human salmonellosis on PEI during the study period (1996–97). The prevalence of Salmonella in beef cattle was 4.6% (11/240). The rate was significantly higher in fasted cattle (7.46%), than in non-fasted cattle (0.94%). The prevalence rate in chickens was 32.5% (39/120). In beef cattle, Salmonella typhimurium phage type (PT) or definitive type (DT) 104 which was resistant to ampicillin, chloramphenicol, streptomycin, sulfisoxazole and tetracycline, was the most predominant type (64%). In chickens, S. heidelberg, with resistance to gentamicin, streptomycin and sulfisoxazole, predominated. Of 26 isolates from humans, the most common serovar was S. typhimurium, including a multidrug-resistant strain of DT104. Examination by PCR revealed presence of the virulence gene invA in all serovars, and the spvC gene in all S. typhimurium isolates, of both beef cattle and human origin. Among the other serovars the latter gene was found in 7 human isolates, but in none of the chicken or beef isolates. All but 3 of the spvC-positive isolates possessed a 90 kilobasepair (kbp) plasmid suggesting that the 3 isolates had the spvC gene on their chromosome. These findings were confirmed by plasmid DNA isolation using 3 different protocols and by sequence analysis of the spvC-PCR product.     

Therapeutic effect of anti-TNF-α antibody and levofloxacin (LVFX) in a mouse model of enterohemorrhagic Escherichia coli O157 infection

The ability of an anti-TNF-α antibody to confer protection against enterohaemorrhagic Escherichia coli (EHEC) O157 was investigated in germfree IQI mice. The use of an antibiotic levofloxacin (LVFX) alone or with the antibody was also studied. Protection included an increase in survival rate. Treatment with the anti-TNF-α antibody inhibited the histological signs associated with EHEC infection but did not prevent the colonization of EHEC or production of Shiga toxin (Stx). No clinical signs were observed and EHEC was completely eliminated in the mouse model receiving both anti-TNF-α antibody and LVFX. Anti-TNF-α antibody suppressed inflammatory cytokine response in the mouse kidney and brain by EHEC infection.     

An enzyme-linked immunosorbent assay using canine coronavirus-infected CRFK cells as antigen for detection of anti-coronavirus antibody in cat

From the reasons that canine coronavirus (CCV) grows more efficiently than feline coronavirus in a cell culture and they are mutually related in their antigenicities, an enzyme-linked immunosorbent assay (ELISA) using CCV-infected feline kidney (CRFK) cells as substrate antigens was developed for detection of anti-coronavirus antibodies in cats. It was indispensable for generating coronavirus-specific ELISA antibody activities that the sample was applied to the mock-infected, normal CRFK cells in parallel with the CCV-infected cells and then the optical density values given by the mock-infected cell antigen were subtracted from those given by the virus-infected cell antigen. On the basis of ELISA antibody titers obtained in sera from the cats experimentally infected with CCV and from the spontaneous feline infectious peritonitis (FIP) cases, the ELISA described in the present study was found to be applicable as a simple and easy serologic test which was able to detect anti-coronavirus antibodies as efficiently as the indirect immunofluorescence assay with homologous FIP virus.