What is it?

Neospora caninum is a recently discovered parasitic protozoan which affects a variety of large and small animal species.  It has emerged as a major cause of bovine abortion in many countries, including the United States.  Since its identification as an abortifacient agent in cattle, Neospora caninum has been associated with sporadic abortions, enzootic abortions, and abortion storms.  Affected bovine fetuses range in gestational age from 3 months to 9 months, with the majority of the cases occurring between the 5th and 7th month of gestation.  Prospective and retrospective studies from California have indicated that 20-45% of all bovine abortions in dry lot dairies in California were attributed to neosporosis.  Other reports included acute point source and endemic bovine abortions from California and the midwestern United States.  Although there is little information on neosporosis-associated bovine abortions in the eastern United States, a recent study    indicates that N. caninum is an important bovine abortifacient in the state of Pennsylvania as well.

How is it diagnosed?

Presently, the definitive diagnosis of this condition requires a thorough gross and histologic post-mortem examination of the aborted fetus.  In affected fetuses, the microscopic N. caninum organisms are sporadically located in a variety of tissues, with the brain and heart most commonly affected.  Histologically, varying degrees of organ inflammation are associated with the organism.  Currently, the most reliable, specific and sensitive method of detection of the organisms is the utilization of immunohistochemical staining procedures.  Although this procedure is currently the diagnostic procedure of choice for the detection of N. caninum, the procedure is time consuming, relatively expensive and is subject to limitations (reliance on thin tissue samples for the presence of sporadically located organisms). 

The polymerase chain reaction (PCR) procedure greatly amplifies specific genetic material, DNA or RNA, so that it can be detected even when present in only minute amounts.   This highly sensitive method requires knowledge of the sequence of the genetic material to be amplified.  This information has become available in the last few years and several PCR techniques for N. caninum have been reported using different genetic sequences.  PCR for N. caninum has been shown to be highly sensitive and specific under experimental conditions.  These techniques have not yet been applied under field conditions for diagnostics. 

Currently available serologic testing for N. caninum consists of an indirect florescent antibody test.  This technique is expensive and relatively insensitive.  It is not performed by PADLS but is done at a collaborating laboratory.  Due to cost, inconvenience and questions about sensitivity, the test is not widely used.   Interpretation of serologic data is therefore lacking.  Correlation of antibody status with active disease versus exposure with no disease has not yet been established for cattle herds under Pennsylvania management systems. 

A sensitive and specific commercially available enzyme linked immunosorbency assay (ELISA) test is available.  The ELISA test has a lower cost per sample and is designed for large scale screening.  This new test will make it possible to economically generate serologic data about N. caninum in cattle herds.   Appropriate incorporation of serologic testing into routine diagnostics for bovine abortion first requires evaluation of the test in conjunction with findings of currently run tests.

The development of reliable polymerase chain reaction (PCR) procedure, with its greater sensitivity and specificity (versus immunohistochemical staining procedure), and a commercially available ELISA serology test, with lower cost and greater ease of use (versus current IFA test), would greatly enhance the ability to accurately diagnose Neospora caninum-induced abortion in cattle.  Use of these tests will allow more accurate characterization of the incidence, prevalence, location, and pathogenesis of this condition in Pennsylvania dairy herds.

Our objectives for the future:

To develop a polymerase chain reaction (PCR) technique to identify Neospora caninum in fetal tissue samples submitted for diagnosis of abortion in cattle.

To characterize serologic response to N. caninum measured by a commercial enzyme linked immunosorbency assay (ELSA) test on an individual and herd basis for diagnosis of abortion in cattle.

To validate the use of PCR and ELISA for N. caninum as routine diagnostic tests for the Pennsylvania Animal Diagnostic Laboratory System (PADLS). 

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