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