| The major infectious causes of reproductive failure in pigs include porcine reproductive and respiratory syndrome virus, porcine parvovirus, pseudorabies virus, Japanese B encephalitis virus, classical swine fever (hog cholera) virus,
Leptospira
spp
, and
Brucella
suis
. |
|
Porcine Reproductive and Respiratory Syndrome (PRRS): |
| PRRS is caused by an arterivirus. It is the most important disease of pigs in the USA and is of major importance throughout most of the world. Most PRRS strains do not cross the placenta until after 90 days of gestation. Consequently, most abortions are near the end of gestation. Affected litters contain fresh and autolyzed dead pigs, weak infected pigs, and healthy, uninfected pigs that often develop respiratory disease within a few days of birth. The sows are often anorectic
and feverish a few days before aborting. Concurrent respiratory disease and increased numbers of bacterial infections in the herd are common. Hemorrhage in the umbilical cord, when present, is the only gross lesion associated with PRRS abortions. Not all fetuses are infected, so multiple fetuses should be sampled. Viral antigen is most consistently present in the fetal thymus and in fluid collected from the fetal thoracic cavity. PCR testing of pooled thoracic fluid from 3-5
fetuses is the most reliable means of diagnosis. Herd management is important in control and prevention. Inactivated and modified live virus vaccines are available. (See also
Porcine Reproductive and Respiratory Syndrome: Introduction .) |
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Porcine Parvovirus: |
| Porcine parvovirus is ubiquitous in pigs in the USA and most of the world. Almost all females are naturally infected before their second pregnancy, and immunity is lifelong. Consequently, it is a disease of first parity pigs. Fetal infection before 70 days of gestation can result in death of the fetus. Not all fetuses are infected at the same time, and death at different stages of pregnancy is typical. Some fetuses survive and are born alive but persistently infected. Most
fetuses infected after 70 days of gestation mount an immune response, clear the virus, and are healthy at birth. Infected litters are carried to term. Litters with dead fetuses of varying sizes, including mummified fetuses, along with stillborn and healthy pigs born to first parity sows are the hallmark of porcine parvovirus. Diagnosis is by fluorescent antibody testing, virus isolation using lung from mummified fetuses, or demonstration of precolostral antibody in stillborn
pigs. Boars shed virus by varying routes, including semen, for a couple of weeks after acute infection and can introduce the virus into a herd. Effective inactivated vaccines are available. |
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|
Pseudorabies (Aujeszky’s Disease, Porcine Herpesvirus 1): |
| Pseudorabies is a cause of CNS and respiratory diseases. Infection results in latency, and seropositive animals are considered infected. Infection early in pregnancy can result in embryonic death and resorption of the fetuses. Infection later in pregnancy can result in abortion and birth of stillborn and weak pigs. Mummification can occur but is uncommon. There are no gross lesions in most aborted pigs, but a few have pinpoint white foci of necrosis in the liver and tonsils.
Diagnosis is by virus isolation or fluorescent antibody staining. Gene-deleted vaccines that allow serologic differentiation of vaccinated and naturally infected pigs are available and effective. There is a federal eradication program in the USA, and future outbreaks will probably be controlled by slaughter of infected pigs. State and federal authorities should be consulted before vaccinating. (See also
Pseudorabies: Introduction.) |
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|
Japanese B Encephalitis Virus: |
| Japanese B encephalitis is an arthropod-borne disease that causes reproductive failure in pigs and encephalitis in humans. Infected litters can contain dead pigs of various sizes (including mummies), stillborn pigs, weak pigs, and pigs with CNS signs. Hydrocephalus and subcutaneous edema are the most common gross lesions. Pigs are the primary amplifying host for the virus and are vaccinated not only to prevent reproductive failure, but also to prevent human infection. |
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|
Classical Swine Fever (Hog Cholera): |
| Classical swine fever is caused by a pestivirus that has been eradicated from the USA but is a serious problem throughout much of the world. With highly virulent strains that cause serious maternal illness, abortion is common. With strains of moderate or low virulence, birth of mummified and stillborn pigs, weak pigs, and persistently infected pigs are more common. Fluorescent antibody staining and virus isolation are used for diagnosis. Both killed and modified live vaccines
are available, but their use in the USA is prohibited. (See also
Classical Swine Fever: Introduction.) |
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|
Leptospirosis: |
|
Leptospira
interrogans
(especially serovar
pomona
) is a major cause of reproductive failure in swine. Although acute leptospirosis occurs in adult swine, most cases are asymptomatic. Abortion occurs 1-4 wk after infection, so the abortuses are autolyzed. Mummification, maceration, stillbirths, and weak pigs are also seen. Diagnosis is based on demonstration of leptospires in fetal tissues or stomach contents. Vaccination with a multivalent bacterin every 6 mo helps prevent the disease. The carrier state can be
eliminated by administration of streptomycin at 25 mg/kg. A similar dosage can be given to pregnant sows during an outbreak to control abortions. (See also
Leptospirosis: Introduction .) |
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Brucellosis: |
| Brucellosis in swine (
Brucella
suis
) has become rare in the USA as a result of state and federal control programs. Infected sows can abort at any stage of gestation, and abortions are not always accompanied by illness. Abortion is probably due to endometritis and fetal infection. There are few fetal or placental lesions, although some fetuses may be autolyzed. Diagnosis is by serology and isolation from the placenta and fetal tissues. No treatment has been uniformly effective. Control is based on test
and slaughter. Brucellosis is one of the few venereal diseases recognized in swine.
B
suis
causes a serious zoonotic disease. (See also
Brucellosis in Large Animals: Introduction.) |
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| Other Infectious Causes of Abortion: |
| Porcine circovirus 2 (PCV-2) has been associated with abortion and increased stillborn pigs in gilts. Affected pigs had signs of congestive heart failure and myocarditis. The importance of PCV-2 as a cause of reproductive failure remains to be determined. Pigs with foot-and-mouth disease (
Foot-and-mouth Disease: Introduction) and African swine fever (
African Swine Fever: Introduction) often abort, but they and their herdmates also have clinical signs of those diseases.
Enteroviruses and encephalomyocarditis virus have been reported to cause fetal losses in pigs, but they are not considered economically important. Blue eye paramyxovirus is an important cause of abortion, stillbirths, and mummified fetuses in parts of Mexico. Bacteria that cause sporadic abortions include
Staphylococcus
aureus
,
Streptococcus
spp
,
Erysipelothrix
rhusiopathiae
,
Salmonella
spp
,
Pasteurella
multocida
,
Arcanobacterium (Actinomyces)
pyogenes
,
Listeria
monocytogenes
, and
Escherichia
coli
. |
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