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. 1999 Sep;6(5):765-7.
doi: 10.1128/CDLI.6.5.765-767.1999.

Serological evidence of human infection with the protozoan Neospora caninum

J Tranas  1 , R A Heinzen, L M Weiss, M M McAllister
Affiliations

Serological evidence of human infection with the protozoan Neospora caninum

J Tranas et al. Clin Diagn Lab Immunol. 1999 Sep.

Abstract

Neospora caninum is a protozoan parasite that is closely related to Toxoplasma gondii. Dogs are a definitive host. Prior to its discovery in 1988, N. caninum infection in animals was often mistakenly diagnosed as toxoplasmosis. Neosporosis in animals is characterized by encephalitis, abortion, and other conditions that clinically and pathologically resemble toxoplasmosis. The potential of N. caninum to infect humans is unknown. Therefore, evidence of human exposure to this parasite was sought by screening for antibodies in blood donors by indirect fluorescent antibody (IFA) tests and immunoblotting. Of 1,029 samples screened, 69 (6.7%) had titers of 1:100 by IFA testing. Fifty of the 69 (72%) sera that were positive for N. caninum were also negative for a closely related protozoan pathogen of humans, T. gondii. Immunoblot analysis confirmed the specificity of the positive sera for N. caninum antigens, with several sera recognizing multiple Neospora antigens with molecular masses similar to those of antigens recognized by monkey anti-N. caninum serum. An immunodominant antigen of approximately 35 kDa was observed with 12 sera. These data provide evidence of human exposure to N. caninum, although the antibody titers in healthy donors were low. The significance of human exposure to, and possible infection with, this parasite is unknown and warrants further study.

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Figures

FIG. 1
FIG. 1
IFA testing of human sera for reactivity against N. caninum. Slides were prepared with N. caninum tachyzoites as described in the text and treated with a 1:100 dilution of human sera. (A) Positive reactivity showing uniform peripheral staining of tachyzoites; (B) positive reactivity showing enhanced apical staining in addition to uniform peripheral staining of tachyzoites; (C) negative reactivity showing strong apical staining but no peripheral staining of tachyzoites.
FIG. 2
FIG. 2
Immunoblot analysis of reactivity of human sera against lysates of N. caninum (N), T. gondii (T), and Vero cells (V). The serum used to probe each blot is shown at the bottom. Strong bands of reactivity in the 35-kDa range are apparent with N. caninum lysates treated with either human serum sample. This reactivity is absent in lanes containing Vero cell or T. gondii lysates. Molecular masses are indicated in kilodaltons.
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