Phenotypic characterisation of a Neospora caninum temperature-sensitive strain in normal and immunodeficient mice.
The in vivo persistence, immunogenicity and pathogenicity of a recently described temperature-sensitive (ts) strain from Neospora caninum, NCts-8, was investigated in normal and immunodeficient mice. Groups of BALB/c and SCID/Bg mice were infected s.c. with 5 x 10(6) wild-type NC-1, control NCts-8 (pass 0) or NCts-8 tachyzoites prepared at four in vitro passage levels (pass 7, 13, 21 and 28). For persistence and immunogenicity studies, BALB/c mice were bled and sacrificed at 4, 6 or 8 weeks p.i. Sera were analysed by IFAT and brain tissues examined for lesions by histology and tested for parasite presence by PCR. For pathogenicity studies, SCID/Bg mice were monitored by clinical signs and survival time. Results from parasite persistence experiments demonstrated microscopic lesions and PCR positive brain tissues in NC-1 infected mice. In contrast, brain tissues from NCts8-infected groups were consistently negative by histology and PCR. Based on IFAT titres, all parasite strains were immunogenic, although parasite-specific IgG levels were lower in the NCts-8 infected groups. Results from pathogenicity studies in SCID/Bg mice demonstrated a significantly (P < 0.0001) longer mean survival time in NCts-8 vs NC-1 infected groups. In addition, there was no significant difference in mean survival time between control NCts-8 and experimental passage NCts-8 infected mice. Collectively, these studies demonstrate that the NCts-8 strain maintains a stable phenotype following multiple passages in vitro, and possesses an attenuated, shorter persistence phenotype in vivo compared with the parental wild-type NC-1.
Dreier
K J
KJ
Animal Health Biological Discovery and Drug Safety Evaluation (RLK), Pfizer Central Research, Pfizer Inc., Groton, CT 06340, USA.
Stewarter
L W
LW
Kerlin
R L
RL
Ritter
D M
DM
Brake
D A
DA
D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood; D001921:Brain / Q000473:pathology; D003048:Coccidiosis / Q000469:parasitology*; D016054:DNA, Protozoan / Q000032:analysis; D051379:Mice; D008807:Mice, Inbred BALB C; D016513:Mice, SCID; D018688:Neospora / Q000235:genetics / Q000276:immunology / Q000472:pathogenicity / Q000502:physiology*; D010641:Phenotype; D016133:Polymerase Chain Reaction; D013696:Temperature; D014774:Virulence
D000913:Antibodies, Protozoan; D016054:DNA, Protozoan