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The ADDL Diagnostic Forum introduces a new feature entitled "Diagnostic Profiles" in this issue.  The intent will be to suggest a panel of diagnostics which will be appropriate and helpful in defining the cause of non-specific disease syndromes.  Practitioners are often presented with patients having clinical signs which fall into a general category of disease that may represent one of a number of specific conditions and may result from various etiologies.  Approaching a differential diagnosis simultaneously with multiple testing modalities should expedite determination of a definitive diagnosis.  This approach will provide the most useful, timely and complete information needed for consideration in therapeutic and disease control decisions.

  As we introduce Diagnostic Profiles, let's consider abortion as an example of a timely "syndrome".  Abortion in all species, including small animals, horses and food animals, may be caused by both infectious and non-infectious factors.  A multifaceted approach is necessary for diagnostic investigation into this type of syndrome and, even then, the underlying cause may remain unknown.  Successful diagnosis of a specific etiology is achieved about 50% of the time.

  When an aborted fetus, preferably accompanied by the placenta and serum from the dam, is submitted to ADDL, multiple laboratories become involved in searching for the cause of the problem.  The protocol starts with a necropsy and then proceeds with the array of tests that are listed on the ADDL web site.  The reported success rate for  determining a specific diagnosis is over four times greater when the fetus, placenta and serum are submitted than when only fetal tissues are submitted for laboratory examination.

  If submission of the entire fetus to ADDL is not possible, then performing the necropsy in the field and submitting specimens is the next best approach.  Gross lesions in aborted fetuses are rare, non-specific and often limited to diffuse congestion and excessive fluid within body cavities.  When observed, gross lesions are most common in lung and placenta.  Microscopic lesions are most often observed in lung, placenta, heart, brain, liver or kidney.  Consequently, a routine set of tissues, both fixed and fresh, should be collected for ancillary laboratory testing.  These are detailed in the following tables.

Infectious etiologies of abortion include viruses, bacteria, fungi, protozoa and Mycoplasma.  Some of these agents are easy to isolate or demonstrate by traditional methods while others are not.  Molecular diagnostic techniques are now employed to demonstrate the presence of those agents that cannot be readily isolated.

  Certain abortifacient agents have historically posed a problem for laboratory diagnosis.  Agents such as Leptospira sp. and Brucella sp. require extended incubation time.  Agents such as Coxiella burnetii and Chlamydophila abortus pose a health risk to laboratory technicians.  Protozoal agents such as Neospora sp. and Toxoplasma gondii cannot be cultured.  Employing the polymerase chain reaction (PCR) method provides a rapid, safe and accurate means of demonstrating these agents.

  Fresh tissues to be submitted should include placenta, stomach/abomasal content, lung, kidney, spleen, heart and brain.  These tissues are used for culture of bacteria and fungi as well as virus isolation and molecular diagnostics.  Packing fresh chilled (NOT frozen) tissues separately in a well-chilled insulated container and shipment  via an overnight delivery service is recommended for best diagnostic results.

  Tissues for histopathology should include placenta, brain, eyelids, thymus, lung, heart, liver, spleen, kidney, skeletal muscle, abomasums (stomach), small and large intestine.  For best results, specimens submitted for histopathology should be no thicker than 0.5 cm and should be fixed in 10 times their volume of 10% neutral buffered formalin.

  Diagnosis of abortion can be aided by examination of serum samples from the dam or body fluids collected from the pericardial, thoracic or abdominal cavities of the fetus.  Serology from the dam is more valuable if baseline levels from the herd are established from samples collected at the time of pregnancy diagnosis.  Negative serology has value in that it eliminates some agents from the differential list.

  Noninfectious abortion may be caused by physical, nutritional, toxic and genetic factors.  History and clinical signs observed in the dam may be most suggestive of a diagnosis of noninfectious abortion.  Chemical testing of ocular fluid for nitrate levels is a means of diagnosing nitrate induced abortion.  Fetal hepatic selenium levels can be measured in cases of abortion suspected to be caused by selenium deficiency.

  The following tables detail the elements of diagnostic panels for the most common causes for abortion in livestock.  The array of laboratory tests included provide the most efficient approach to determining the cause of an abortion and, once determined, control measures can be initiated.

-by Drs. Bill Wigle and Steve Lenz, ADDL Pathologists

 

 

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