Inoculation of Balb/c mice with live attenuated tachyzoites protects against a lethal challenge of Neospora caninum.
Neospora caninum tachyzoites attenuated through passage in tissue culture were tested for their ability to induce protective immunity against a lethal challenge dose of parasites. Balb/c mice were each inoculated with either 1x10(6) live virulent tachyzoites (Group 1) or 1x10(6) live attenuated tachyzoites (Group 2), while (Group 3) received a control inoculum. All mice were each challenged 28 days later with 5x10(6) virulent parasites. Histopathological lesions in the brains including necrosis and microgliosis were observed following post-mortem on day 28 post-challenge (p.c.) in 71% of Group 1 and 56% of Group 2. Immunohistochemistry (IHC) of these lesions showed tachyzoites and Neospora antigens to be associated with moderate brain lesions in 17% of Group 1, while in 11% of Group 2 N. caninum tissue cysts were detected, but these were not associated with lesions, Parasite DNA was detected by PCR in the brains of 86% of mice in Group 1 and 56% of mice in Group 2. Following challenge the mice in Group 3 showed high morbidity and 100% mortality within 17 days p.c. Positive IHC for N. caninum was seen in 88% of the Group 3 mice and parasite DNA was detected in all brain samples. This study shows that it is possible to protect against a lethal challenge of N. caninum through inoculation with attenuated or virulent tachyzoites. However, more severe pathology developed in mice initially inoculated with virulent parasites following a secondary challenge, compared to mice initially inoculated with attenuated parasites.
Bartley
P M
PM
Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik EH26 0PZ, Scotland, UK. paul.bartley@moredun.ac.uk
Wright
S
S
Chianini
F
F
Buxton
D
D
Innes
E A
EA
D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood; D000953:Antigens, Protozoan / Q000032:analysis / Q000378:metabolism; D001835:Body Weight; D001921:Brain / Q000469:parasitology / Q000473:pathology; D001927:Brain Diseases / Q000276:immunology / Q000469:parasitology*; D003048:Coccidiosis / Q000276:immunology* / Q000401:mortality / Q000469:parasitology / Q000517:prevention & control; D016054:DNA, Protozoan / Q000032:analysis; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D004195:Disease Models, Animal; D005260:Female; D007114:Immunization / Q000379:methods; D051379:Mice; D008807:Mice, Inbred BALB C; D018688:Neospora / Q000276:immunology* / Q000472:pathogenicity; D016052:Protozoan Vaccines / Q000008:administration & dosage / Q000276:immunology*; D013997:Time Factors; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000276:immunology*
D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D016054:DNA, Protozoan; D021903:DNA, Ribosomal Spacer; D016052:Protozoan Vaccines; D014613:Vaccines, Attenuated