Isolation and characterization of a bovine isolate of Neospora caninum with low virulence.
Neospora caninum tachyzoites were isolated from the brain of an asymptomatic naturally infected calf with precolostral-specific antibodies. The new isolate, named Nc-Spain 1H, was identified as a member of the N. caninum species based on its internal transcribed spacer 1 (ITS-1) sequence and was genetically characterized using microsatellite markers. Multilocus analysis showed that Nc-Spain 1H was genetically different from other N. caninum isolates. We compared the in vitro tachyzoite yield and viability rate of the Nc-Spain 1H and Nc-1 isolates in a plaque assay. The lower tachyzoite yields displayed by Nc-Spain 1H were complemented with a significantly lower viability rate. Moreover, in an in vitro tachyzoite-bradyzoite stage conversion assay, the percentage of Nc-Spain 1H bradyzoite conversion was similar to that of the cystogenic isolate Nc-Liv, with the exception that Nc-Spain 1H produced only intermediate bradyzoites. The pathogenicity of Nc-Spain 1H was examined in BALB/c mice, and the results demonstrated that Nc-Spain 1H failed to induce clinical signs or mortality and that no parasite DNA was detected in the brain during the chronic stage of infection. In a pregnant mouse model, Nc-1 infection resulted in high transplacental transmission, leading to a high neonatal mortality rate over time. In contrast, the offspring survival rate from Nc-Spain 1H-infected dams was almost 100%, and N. caninum DNA was detected in only one pup. These data show that Nc-Spain 1H appears to be a low virulence isolate and may be a suitable candidate for live vaccine development.
Rojo-Montejo
Silvia
S
SALUVET, Animal Health Department, Faculty of Veterinary Sciences, Complutense University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain.
Collantes-Fernández
Esther
E
Regidor-Cerrillo
Javier
J
Alvarez-García
Gema
G
Marugan-Hernández
Virginia
V
Pedraza-Díaz
Susana
S
Blanco-Murcia
Javier
J
Prenafeta
Antonio
A
Ortega-Mora
Luis Miguel
LM
D000704:Analysis of Variance; D000818:Animals; D000913:Antibodies, Protozoan / Q000235:genetics / Q000276:immunology*; D002417:Cattle; D002418:Cattle Diseases / Q000469:parasitology*; D003048:Coccidiosis / Q000469:parasitology / Q000662:veterinary*; D005260:Female; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D018895:Microsatellite Repeats; D018688:Neospora / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity*; D016133:Polymerase Chain Reaction / Q000662:veterinary; D018709:Statistics, Nonparametric; D010948:Viral Plaque Assay; D014774:Virulence / Q000235:genetics / Q000276:immunology
D000913:Antibodies, Protozoan