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Neosporosis: |
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Neospora
caninum
is found worldwide and is the most common cause of abortion in dairy cattle in many parts of the USA.
Neospora
abortion is less common in beef cattle, but it is still economically significant. Abortion can occur any time after 3 mo of gestation, but is most common between 4 and 6 mo of gestation.
Neospora
can be associated with sporadic abortions or abortion storms, and repeat abortions in cows have been reported. Some infected calves survive and are born with paralysis or proprioceptive deficits. Dogs are the definitive host for
Neospora
and can be the source of infection. The role of wild canids is unknown. Cows are not clinically ill, and placental retention is not common. The fetus is usually autolyzed and rarely has gross lesions. Microscopically, nonsuppurative inflammation is common in the brain, heart, and skeletal muscles. Organisms can be identified in these tissues and the kidneys by immunohistochemical staining. Many late gestation fetuses have precolostral antibodies. Infected calves may be
born alive and clinically normal. They remain infected for years and possibly for life. During pregnancy,
Neospora
organisms can become activated and infect the fetus. This is thought to be the most common source of infection. There is no treatment. Strict hygiene to prevent fecal contamination of feed by dogs may aid in prevention. A commercial vaccine is available. See also
Neosporosis: Introduction. |
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Bovine Viral Diarrhea (BVD): |
| In several surveys, BVD was the most commonly diagnosed virus in bovine abortion cases. The pathology of BVD in the developing fetus is complex. Infection of the fetus before 125 days of gestation can cause fetal death and abortion, resorption, mummification, developmental abnormalities, or fetal immunotolerance and persistent infection. After 125 days of gestation, BVD may cause abortion, or the fetal immune response may clear the virus. Diagnosis is by identification of BVD
virus by isolation, immunologic staining, PCR, or detection of precolostral antibodies in aborted calves. The virus is present in a wide variety of tissues, but the spleen is the tissue of choice. Rising antibody titers to BVD in aborting animals or herdmates is diagnostic of recent infection. BVD virus is immunosuppressive and is found in many fetuses infected by other agents. Outbreaks of abortions by organisms that normally cause sporadic abortion should raise suspicion of
possible concurrent BVD virus infection. Prevention should focus on removal of persistently infected cattle and herd vaccination. See also
Bovine Viral Diarrhea and Mucosal Disease Complex. |
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Infectious Bovine Rhinotracheitis (IBR, Bovine Herpesvirus 1): |
| IBR is a major cause of viral abortion in the USA, with abortion rates of 5-60% in nonvaccinated herds. The virus is widespread and can recrudesce; therefore, any cow with a positive IBR titer is a possible carrier. The virus is carried to the placenta in WBC; over the next 2 wk to 4 mo, it causes a placentitis, then infects the fetus and kills it in 24 hr. Abortion can occur any time but usually is from 4 mo to term. Autolysis is consistently present. Occasionally there are
small foci of necrosis in the liver, but in a large majority of cases there are no gross lesions in the placenta or fetus. Microscopically, small foci of necrosis with minimal inflammation are consistently present in the liver. Necrotizing vasculitis is common in the placenta. Diagnosis can be made by immunologic staining of the kidney and adrenal glands. IBR virus can be isolated from ~50% of infected fetuses (most successfully from the placenta). In most cases, maternal titers
have peaked by the time of abortion. In abortion storms, rising titers can often be demonstrated in herdmates. Control is by herd vaccination; intranasal, modified live virus, and killed vaccines are available. See also
Bovine Herpesvirus 1. |
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Leptospirosis: |
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Leptospira
interrogans
, serovars
grippotyphosa
,
pomona
,
hardjo
,
canicola
, and
icterohaemorrhagiae
usually cause abortions in the last trimester, 2-6 wk after maternal infection. Although dams may show clinical signs of leptospirosis, most abortions are in otherwise healthy cattle. Abortion rates vary from 5-40% or more. The leptospires cause a diffuse placentitis with avascular, light tan cotyledons and edematous, yellowish intercotyledonary areas. The fetus usually dies 1-2 days before expulsion and therefore is autolyzed. Occasionally calves are born alive but
weak. There are no specific lesions, but placenta and fetus should be submitted to the laboratory for fluorescent antibody staining or PCR testing for
Leptospira
.
Although maternal titers are probably waning by the time of abortion, an initial titer of >1:800 may be suspicious. Approximately one-third of cows aborting because of
L
hardjo
have titers of <1:100 at the time of abortion. The dam’s urine can be cultured or examined for leptospires within 2 wk of abortion. For control, sources of infection (such as feed or water contaminated by dogs, rats, or wildlife) should be identified and eliminated. Cattle may be lifelong carriers of
L
hardjo
and are a source of infection for herd additions. Vaccination with a 5-way bacterin is recommended every 6 mo. Leptospirosis is zoonotic, and urine and milk of dams may be infective for up to 3 mo. (See also
Leptospirosis: Introduction.) |
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Brucellosis: |
| Brucellosis (Bang’s disease) is a threat in most countries where cattle are raised. In the USA, active control programs, including test, slaughter, and heifer vaccination, have greatly decreased its incidence. Brucellosis causes abortions in the second half of gestation (usually ~7 mo), and ~80% of unvaccinated cows in later gestation will abort if exposed to
Brucella
abortus
. The organisms enter via mucous membranes and invade the udder, lymph nodes, and uterus, causing a placentitis, which may be acute or chronic. Abortion or stillbirth occurs 2 wk to 5 mo after initial infection. Affected cotyledons may be normal to necrotic, and red or yellow. The intercotyledonary area is focally thickened with a wet, leathery appearance. The fetus may be normal or autolytic with bronchopneumonia. Diagnosis can be made by maternal serology combined
with fluorescent antibody staining of placenta and fetus or isolation of
B
abortus
from placenta, fetus, or uterine discharge. Prevention is by calfhood vaccination of heifers. |
| Brucellosis is a serious zoonosis and a reportable disease, and the appropriate authorities should be contacted. (See also
Brucellosis in Large Animals: Introduction .) |
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Mycotic Abortion: |
| Fungal placentitis due to
Aspergillus
sp
(septic fungi, 60-80% of cases), or to
Mucor
sp
,
Absidia
, or
Rhizopus
sp
(nonseptate fungi) is an important cause of bovine sporadic abortion. Abortions occur from 4 mo to term and are most common in winter. It is believed the fungi gain entry through the oral or respiratory tracts and travel hematogenously to the placenta. Placentitis is severe and necrotizing. Cotyledons are enlarged and necrotic with turned-in margins. The intercotyledonary area is thickened and leathery. Adventitious placentation is common. The fetus seldom is
autolyzed, although it may be dehydrated; ~30% have gray ringworm-like skin lesions principally involving the head and shoulders. The diagnosis is based on the presence of fungal hyphae associated with necrotizing placentitis, dermatitis, or pneumonia. Fungi can also be isolated from the stomach contents, placenta, and skin lesions. Isolation must be correlated with microscopic and gross lesions to rule out post-abortion contamination. |
| For control, moldy feed should be avoided. (See also
Mycotoxicoses: Introduction.) |
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Arcanobacterium pyogenes: |
|
Arcanobacterium (Actinomyces)
pyogenes
causes sporadic abortion at any stage of pregnancy. Rarely, the incidence in a herd may reach epizootic levels. The bacterium is present in the nasopharynx of many normal cows and in abscesses. It is not normally present, even as a contaminant, in fetuses or fetal membranes, and isolation is almost always significant. It gains entry to the bloodstream and causes an endometritis and placentitis, which is diffuse with a reddish brown to brown color. The fetus is usually
autolyzed, with fibrinous pericarditis, pleuritis, or peritonitis possible. |
| Bronchopneumonia may be evident on histopathology, but
A
pyogenes
is best cultured from placenta or abomasal contents. Abortion is usually sporadic, and no effective bacterin is available. |
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Trichomoniasis: |
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Tritrichomonas (Trichomonas)
foetus
infection causes a venereal disease that usually results in infertility but occasionally causes abortion in the first half of gestation. Placentitis is relatively mild with hemorrhagic cotyledons and thickened intercotyledonary areas covered with flocculent exudate. The placenta is often retained, and there may be pyometra. The fetus has no specific lesions, although
T
foetus
can be found in abomasal contents, placental fluids, and uterine discharges. Trichomoniasis can be prevented by artificial insemination using noninfected bulls. (See also
Trichomoniasis: Introduction.) |
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Campylobacteriosis: |
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Campylobacter
fetus
venerealis
causes venereal disease that usually results in infertility but occasionally causes abortion between 5 and 8 mo of gestation.
C
fetus
fetus
and
C
jejuni
are transmitted by ingestion and subsequent hematogenous spread to the placenta. Both cause sporadic abortions, usually in the last half of gestation. The fetus can be fresh with partially expanded lungs or severely autolyzed. Mild fibrinous pleuritis and peritonitis may be noted, as well as bronchopneumonia. Placentitis is mild with hemorrhagic cotyledons and an edematous intercotyledonary area.
Campylobacter
spp
can be identified by darkfield examination of abomasal contents or culture of placenta or abomasal contents. Isolation and identification of the species involved is important if vaccination is to be instituted. Venereal campylobacteriosis can be controlled by artificial insemination and vaccination. (See also
Bovine Genital Campylobacteriosis: Introduction.)
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Listeriosis: |
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Listeria
monocytogenes
can cause placentitis and fetal septicemia. Abortions are usually sporadic but may affect 10-20% of a herd. Abortion is at any stage of gestation, and the dam may have fever and anorexia before the abortion; retained placenta is common. The fetus is retained for 2-3 days after death, so autolysis may be extensive. Fibrinous polyserositis and white necrotic foci in the liver and/or cotyledons are common. Diagnosis is by culture of
Listeria
from fetus or placenta. There is no available bacterin. Listeriosis is a reportable disease in many areas and is a serious zoonosis with spread possible through improperly pasteurized milk. (See also
Listeriosis: Introduction.) |
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Chlamydophilosis (Chlamydiosis): |
|
Chlamydophila
abortus
(
Chlamydia
psittaci
serotype 1), the cause of enzootic abortion of ewes, causes sporadic abortion in cattle. Most abortions occur near the end of the last trimester, but they can occur earlier. Placental lesions consist of thickening and yellow-brown exudate adhered to the cotyledons and intercotyledonary areas. Histologically, placentitis is consistently present, and pneumonia and hepatitis can be found in some cases.
C
abortus
can be identified by examination of stained smears of the placenta or by ELISA, fluorescent antibody staining, PCR, or isolation in embryonated chicken eggs or cell culture. Organisms can often be identified in the lungs and liver, but not as consistently as in the placenta. There are no vaccines for cattle, although they are produced for sheep (see
enzootic abortion of ewes, below). The bacterium is zoonotic, occasionally producing life-threatening disease and abortion in pregnant women. |
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Ureaplasma
diversum
Infection: |
|
Ureaplasma
diversum
is a common inhabitant of the vagina and prepuce of cattle that also causes abortions. Abortions are usually single, but severe outbreaks occur on occasion. Most fetuses are aborted in the third trimester and are well preserved. The cows are not sick, but retained placentas are common. The intercotyledonary areas are usually thickened and sometimes contain areas of fibrin deposition and hemorrhage. There are no gross lesions in the fetus. Microscopically, there is
nonsuppurative placentitis and pneumonia characterized by accumulations of lymphocytes around bronchi and by diffuse alveolitis. Diagnosis is by isolation of
U
diversum
from the placenta, lungs, and/or abomasal contents. |
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Epizootic Bovine Abortion (Foothill Abortion): |
| Epizootic bovine abortion (EBA) is localized to the foothill region surrounding the Sacramento/San Joaquin Valley and the Eastern Sierra Nevada range of California and parts of Nevada, although disease clusters may exist in neighboring states. EBA usually causes a protracted abortion storm affecting primarily heifers or cows recently introduced to the geographic region; however, abortion can occur 3-5 mo after leaving the endemic area. Abortion is usually in the last trimester,
and rates may be as high as 60%. The animals abort without illness, and the fetus is seldom autolyzed. While the etiologic agent has not been definitively determined, the vector appears to be the argasid tick
Ornithodoros
coriaceus
. The aborted fetus may have hepatomegaly, splenomegaly, and generalized lymphomegaly. Microscopically, there is marked lymphoid hyperplasia in the spleen and lymph nodes and granulomatous inflammation in most organs. Fetal IgG is increased. Cows seldom abort in subsequent pregnancies, and heifers are often exposed to endemic areas before breeding age in an effort to prevent abortions. |
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| Other Causes of Abortion: |
| Bluetongue virus and Akabane virus (where present) cause abortion and fetal anomalies. Parainfluenza-3 virus causes abortion in experimentally inoculated seronegative cattle, but is seldom, if ever, diagnosed in field cases of abortion. Occasionally,
Salmonella
spp
cause abortion storms. The cows are usually sick and the fetuses and placentas are autolyzed and emphysematous. Salmonellae can be isolated from the abomasal contents and fetal tissues.
Mycoplasma
spp
,
Histophilus
somni
(
Haemophilus
somnus
), and a wide variety of other bacteria can also cause sporadic abortions in cattle. |
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;)
;)