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Vaccination of ewes for prevention of vertical transmission of Neospora caninum

R. M. O'HandleyParasite Biology, Epidemiology and Systematics Laboratory, Animal and Natural Resources Institute, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705.
Present address is the Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PEI, Canada, C1A 5L3.

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 PhD
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S. A. MorganParasite Biology, Epidemiology and Systematics Laboratory, Animal and Natural Resources Institute, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705.

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C. ParkerParasite Biology, Epidemiology and Systematics Laboratory, Animal and Natural Resources Institute, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705.

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M. C. JenkinsParasite Biology, Epidemiology and Systematics Laboratory, Animal and Natural Resources Institute, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705.

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J. P. DubeyParasite Biology, Epidemiology and Systematics Laboratory, Animal and Natural Resources Institute, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705.

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Abstract

Objective—To evaluate the immunologic response of a killed tachyzoite vaccine against Neospora caninum and its effectiveness in preventing vertical transmission of N caninum in sheep.

Animals—40 Dorset ewes seronegative for N caninum.

Procedure—Group-A ewes (n = 20) were vaccinated on days 1 and 126 with a killed N caninum tachyzoite preparation in a commercially available adjuvant. Group-B ewes (n = 20) were sham vaccinated. Blood samples were collected from ewes every 2 weeks and a recombinant ELISA (rELISA) was used to determine serum antibody titers against N caninum. During pregnancy, ewes were challenged with live N caninum tachyzoites. Precolostral serum was collected from lambs and tested for antibodies against N caninum by use of an indirect fluorescence antibody test and the rELISA. Tissue specimens from stillborn lambs or lambs that died within 2 weeks of birth were collected and examined for N caninum antigen and DNA by use of immunohistochemistry and polymerase chain reaction assay, respectively.

Results—Serum antibody titers against N caninum were significantly higher in group-A ewes, compared with group B ewes, following vaccination. Serum antibodies against N caninum were detected in 100% (33/33) of group-B lambs and 75% (18/24) of group-A lambs. In tissue specimens, N caninum DNA was detected in 9 of 11 group-B lambs and 0 of 10 group- A lambs. Histologically, N caninum tachyzoites were observed in 4 group-A lambs and 3 group-B lambs.

Conclusions and Clinical Relevance—The killed tachyzoite vaccine against N caninum stimulated a humoral immune response in sheep and provided partial protection against vertical transmission. (Am J Vet Res 2003;64:449–452)

Abstract

Objective—To evaluate the immunologic response of a killed tachyzoite vaccine against Neospora caninum and its effectiveness in preventing vertical transmission of N caninum in sheep.

Animals—40 Dorset ewes seronegative for N caninum.

Procedure—Group-A ewes (n = 20) were vaccinated on days 1 and 126 with a killed N caninum tachyzoite preparation in a commercially available adjuvant. Group-B ewes (n = 20) were sham vaccinated. Blood samples were collected from ewes every 2 weeks and a recombinant ELISA (rELISA) was used to determine serum antibody titers against N caninum. During pregnancy, ewes were challenged with live N caninum tachyzoites. Precolostral serum was collected from lambs and tested for antibodies against N caninum by use of an indirect fluorescence antibody test and the rELISA. Tissue specimens from stillborn lambs or lambs that died within 2 weeks of birth were collected and examined for N caninum antigen and DNA by use of immunohistochemistry and polymerase chain reaction assay, respectively.

Results—Serum antibody titers against N caninum were significantly higher in group-A ewes, compared with group B ewes, following vaccination. Serum antibodies against N caninum were detected in 100% (33/33) of group-B lambs and 75% (18/24) of group-A lambs. In tissue specimens, N caninum DNA was detected in 9 of 11 group-B lambs and 0 of 10 group- A lambs. Histologically, N caninum tachyzoites were observed in 4 group-A lambs and 3 group-B lambs.

Conclusions and Clinical Relevance—The killed tachyzoite vaccine against N caninum stimulated a humoral immune response in sheep and provided partial protection against vertical transmission. (Am J Vet Res 2003;64:449–452)