DIAGNOSTIC NOTES

Diagnosis of swine abortionLarry D. Holler, DVM, PhD

Reproductive failure occurs in most if not all swine op-erations at some rate; however, the effects are per-ceived as significant only after measured production

rates decline below expected norms for the given operation. Asexpected, this level varies greatly among producers and pro-duction styles. Regardless of the management interventions,vaccination protocols, and diagnostic procedures implemented,there will always be some level of fetal wastage in swineherds. So both producers and practitioners often ask, "whybother with swine abortion / stillbirth diagnosis when the di-agnostic lab never seems to give me any useful information?"The answer to this question is difficult to explain to producerswho are experiencing financial losses associated with chronicabortion problems in their herds. It can be equally frustratingto explain to the practitioner who is diligently searching forsolutions to abortion problems and relies on the diagnosticlaboratory for timely answers and practical information. Abor-tion diagnosis rates for swine are traditionally very low,and alarge percentage of reproductive wastage is probably not asso-ciated with an infectious etiology. However, it is still recom-mended that complete diagnostic workups be routinelyperformed in cases of swine abortion / stillbirth in order toconfirm or rule out the common causes of infectious abortion

and to remain vigilant for emerging swine diseases.In this ar-ticle, I will outline the standard diagnostic protocol for swineabortion/stillbirth diagnostics at South Dakota State Univer-sity while briefly reviewing the common causes of infectiousabortion / stillbirth and examining the possible pitfalls in-volved in swine abortion diagnostics. Keep in mind that therewill be some variation of procedures among laboratories, andthis discussion is intended only as a general guideline. For adetailed discussion of specific aspects of reproductive failurein swine, the reader is encouraged to consult several of the ex-cellent references that are available in this area.1,2

Sample submissionThe quality of diagnostic service is usually directly related tothe quality and appropriateness of samples submitted to thediagnostic laboratory. The correct specimens must be collected,preserved, and submitted to the laboratory in a timely fashion.Avoidleaky obstetric sleeves and samples that have spent theFourth of July weekend in a UPStruck. If you are uncertainabout available means of shipping samples to the lab or howto properly package your samples, please contact your

Animal Disease Research and Diagnostic Lab, South Dakota StateUniversity,Brookings.South Dakota 57007

c

diagnostic laboratory prior to submission. Fill out submissionforms completely.Givea thorough history of the current prob-lem including the age of the animals affected (gilts versussows), how many animals are affected, vaccination status ofthe herd, recent additions, changes in feeding programs, envi-ronmental conditions, housing changes, and any previous orcurrent disease problems that have been recently diagnosed inthe herd. A complete history can often give the diagnosticianvaluable clues in finding a diagnosis.Unfortunately, the major-ity of submission forms are left nearly blank.

NecropsyWith swine abortions, it is usually convenient to submit entirechilled (not frozen) fetuses and placenta to the laboratory forevaluation. Weroutinely limit our investigation to three repre-sentative fetuses and all mummified fetuses from an affected

litter. Wedo not discourage submission of entire litters, as weoften gain some information by evaluating gestation ages, lit-ter size, numbers of mummified fetuses, and an estimate ofpostmortem condition. Necropsyprocedures vary, but as in allnecropsies, it is important for practitioners or diagnosticiansto develop a consistent protocol that they feel comfortablewith and that facilitates their ability to detect gross lesionsand collect appropriate samples. Gross lesions are infrequentlyobserved in porcine fetuses and when observed are often notspecific for a particular etiology. Nonspecific congestion andhemorrhage of visceral and cutaneous tissues combined withvariable amounts of blood-tinged fluid in the pleural, pericar-dial, and peritoneal cavity are common changes that very sel-dom correlate with a specific diagnosis. Without gross lesionsto guide our diagnostic efforts, we routinely collect a specificset of fetal tissues and rely on a predetermined battery oflaboratory tests to confirm or rule out specific etiologic agents.The battery of tests included in this workup should be con-stantly evaluated and updated as new technology develops andemerging disease agents are recognized.When the necropsy isperformed at the diagnostic laboratory, the pathologist cancollect appropriate samples for virologic, bacteriologic, andhistopathologic examination. When the necropsy is performedin the field, sample selection and submission become morecritical. Fresh tissues should include lung (bagged separately),liver, spleen, kidney, heart, tonsil, brain (bagged together),placenta (bagged separately), and any other tissue or organsthat you think may be required, Submit these in a securelypackaged and chilled container with ice packs. The same set oftissues can be fixed in 10%neutral buffered formalin. Fetal

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thoracic fluid and stomach contents are also required for acomplete diagnostic workup. Submit fluids in labeled glass orplastic tubes with secure lids. Syringes with attached needlesleak in transit and represent an unnecessary health threat tothe laboratory personnel handling the mail.

HistopathologrHistologicexamination of fetal tissue is usually an unreward-ing process in swine abortion diagnostics.Wecan, however, oc-casionally find evidence of focal inflammation or perhaps afetal pneumonia that signals the likelihood of an infectiousprocess.Absenceof histologic lesions does not preclude findingan etiologic diagnosis. Significant lesions can be obscured bypostmortem autolysis; therefore, the faster the samples arepreserved, the greater the chance of observing microscopicchanges. We routinely attempt histologic examination in allcases that submit suitable tissues for evaluation.

BacteriologyDetermine which tissues are suitable for bacterial isolation in

swine abortion cases based on the previous successes of thediagnostic laboratory. Potential bacterial etiologies includeActinobacillus rossii, Actinobacillus spp; Streptococcus spp,Erysipelothrix spp, Actinomyces pyogenes,Pasteurella spp, Sal-monella spp, Bacillus spp, Escherichia col~ and various otherbacterial organisms.3,4Fetal stomach contents and lung are ourtissues of choice for routine bacterial isolation. If we isolate a

moderate to heavy growth of a particular bacterial organismin relatively pure culture from stomach contents and lung,and we find histologic evidence of inflammation (i.e., fetalpneumonia or placentitis), we become suspicious that this or-ganism may be involved in the abortion case.If we are unableto establish any other likely cause of abortion in the case, wewill make presumptive diagnosis of bacterial abortion basedon this evidence. Implicating a common bacterial organism,even isolated in pure culture, is difficult without some otherevidence of infectious disease (i.e., inflammation on histo-pathology, sick sows,etc.). The majority of bacterial abortionsare sporadic. Occasional organisms such as Streptococcus suisand Erysipelothrix spp that cause systemic disease in affectedherds can be associated with abortion outbreaks. As a generalrule, a diagnosis of bacterial abortion is uncommon in swine.

Leptospirosis caused by various serovars of LeptosPira inter-roganshas long been recognized as a potential swine pathogenin this country. Many herds will test serologically positive forthis organism, probably reflecting widespread vaccine use.Occasionalacute and chronic cases of leptospirosis are associ-ated with late-term abortions, stillborn and weakborn pigs,and early embryonic death. Diagnosisof LeptosPira infectionis often difficult. Occasional affected pigs will have a mildfibrinous peritonitis and pleuritis with swollen and congestedlivers and kidneys. Evidence of inflammation in affectedpiglets is inconsistent. For diagnosis, we routinely rely on

immunofluorescent staining of the organism in homogenatesof kidney and lung. False positives associated with nonspecificfluorescence are occasionally a problem with this test. Equallydisconcerting to the diagnostician is the possibility of false-negative tests associated with poor sample quality. Demon-strating organisms with typical morphology and movement ispossible with dark-field microscopy;however, caution must betaken to distinguish actual organisms from look-alike artifacts.Isolating the organism is difficult, tedious, and unsuitable forroutine diagnostic testing in most situations. Detecting el-evated antibody titers (~1 :1600) in affected sows can provideevidence for infection; however, the vaccination status of theherd and the clinical picture should be considered before im-plicating Leptospira spp based solely on serology results.

VirologyViral agents associated with swine abortions include thosethat cause systemic disease in the sow,indirectly affecting thefetus, and those that primarily directly affect the fetus. Ex-amples of the first category include pseudorabies virus (PRV),transmissible gastroenteritis (TGE), swine influenza virus(SIV), and porcine reproductive and respiratory syndromevirus (PRRSV).Examples of the second group include porcineparvovirus (PPV) and enteroviruses (PEV) and potentially,encephalomyocarditis virus (EMCV).When you are suspiciousof a particular viral etiology in swine abortions, it's importantto keepthis distinctionin mind.Forexample,diagnosingPRRSfrom fetal tissues is routinely unrewarding. Producers andpractitioners are often suspicious of PRRSin older pigs on afarm and are often frustrated when we are unable to isolate

or identify the virus from an abortion case from the samepremises. Unfortunately, the pathogenesis of this virus inreproductive disease is largely still unknown. Additional re-search may hopefully unravel this mystery and leave the diag-nostician with a more sensitive set of tools to diagnose thisproblem. Currently, diagnosis of PRRSVis basedprimarilyonserologic evidence of the virus in the sow and clinical anddiagnostic evidence of respiratory disease in young pigs on thesame premises?

Porcine parvovirus (PPV) is our most common cause of diag-nosed porcine abortion.4 When we diagnose ppy, we usuallyare looking at a herd with minimal or no vaccination proce-dures for PPVor herds that occasionally have gilts abort thatare immunologically naive to ppv.The stage of gestation whenthe virus infection occurs will determine the clinical presenta-tion with parvovirus abortion (i.e., embryonic deaths, mum-mies,weakborn, or stillborn piglets).Fluorescent antibody (FA)techniques (primarily on lung tissue from mummified fetusesand virus isolation procedures from aborted or stillborn pig-lets) are generally reliable in diagnosing ppv. Pseudorabies israpidly becoming a regional problem. For diagnosis, FAtech-niques and virus isolation are our standard techniques. For theremainingviral pathogens(PEY,EMCV,and potential new viral

30 Swine Health and Production- November and December, 1994

pathogens) we rely on virus isolation procedures, recognizingthat our overall success rate will be low.

SerologySerology is often used as a diagnostic tool in diagnosing por-cine abortion. The porcine fetus is generally considered atleast partially immunocompetent by 70 days of gestation. De-tecting elevated levels of immunoglobulin in fetal fluid ofaborted fetuses past 70 days of age suggests an infectiousabortion.4 With PPV,an indirect FAprocedure is frequentlyused to detect antibody in fetal fluids to this agent. Maternalserology is often beneficial for making a presumptive diagno-sis of some causes of abortion if proper caution is used wheninterpreting the results. The majority of mature pigs have sub-stantial antibody titers to PPV whether by vaccination orexposure.The vaccination status of the herd for agents such asleptospirosis, PRY,and PRRSVmust also be considered wheninterpreting results. Contact your diagnostic laboratory andfind out what tests are available and what criteria they usefor interpretation.

Noninfectious causes ofabortion

Noninfectious causes of reproductive wastage and abortion inswine account for the majority of economic losses in mosttypical swine production units. This type of wastage is oftenmultifactorial, nearly always sporadic, and frequently diffi-cult to diagnose. Carbon monoxide toxicosis associated withgestating sows in heated confinement buildings is a commoncause of abortion in the upper midwest.4 Clinical signs areusually not observed in affected sows.Tissues from aborted orstillborn piglets are bright red if postmortem autolysis isminimal. Levels of carboxyhemoglobin in sow blood is oftenelevated 15%-25%.Other environmental factors such as the

effects of ambient temperature and length of daylight (suchas in the fall abortion syndrome) are much more difficult tocharacterize. Likewise,factors that alter hormonal regulationof pregnancy maintenance and result in abortion are alsopoorly understood. The role of low levels of various mycotox-ins in feedstuffs and imbalances in micronutrients in swine

abortion is also poorly characterized.

Summary)

Swine abortion diagnosis is a challenging yet often unreward-ing process. Frequently, we as diagnosticians only succeed intelling the practitioner and producer what the problem isn't.Although this can be useful information, it often fails to de-fine what an appropriate intervention strategy may be tominimize additional losses.In order to maximize this diagnos-tic process, it becomes important for the diagnostician, practi-tioner, and producer to work effectively together, sharinginformation and defining strategies to improve swine abortiondiagnosis.

References

1. Dial GD, Marsh WE, Polson DD,Vaillancourt ]P: ReproductiveFailure: Differential Diagnosis. In Leman AD, Straw BE, Mengeling WL,et aL (eds): Diseases of Swine, 7th edition. Ames, Iowa: Iowa StateUniversity Press, 1992.

2. Christianson WT: Stillbirth, mummies, abortions, and earlyembryonic death. In Tubbs RC,Leman AD (eds): Vet GUn N Am-FoodAnim Pract-Swine Repro. 8:3, Philadelphia, Pennsylvania: WB.Saunders Co., 1992.

3. Kirkbride, CA (ed): Laboratory Diagnosis of Livestock Abortion, 3rdedition. Ames, Iowa: Iowa State University Press, 1990.

4. Kirkbride, CA.Managing an outbreak of livestock abortion-3:Diagnosis and control of porcine abortion. VetMed 1985;]une:80-84.

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