Neosporosis and Abortion in Dairy Cattle
Neosporosis and Abortion in Dairy Cattle
Mark Anderson, Bradd
Barr, Joan Rowe, Karen Sverlow, Andrea Packham and Patricia Conrad
California Veterinary Diagnostic Laboratory and Department of Pathology,
School of Veterinary Medicine,
University of California Davis,
Davis, California, USA, 95617-1770.
E-mail to the Group at email@example.com
Fetal infections by the protozoa parasite, Neospora sp., is a newly recognized cause of abortion
and congenital infection in cattle. This infection is the most common cause of abortion seen in
many dairies throughout the world. Diagnosis of the infection is assisted by examinations of
aborted fetuses and serologic testing of cows. At the present time there is no treatment or
prevention for the infection and the life cycle of the parasite is not known. Cattle can be
chronically infected with Neospora and can pass the infection onto their offspring during
Neospora is a newly recognized genus that was first identified as a Toxoplasma-like protozoa in
dogs with encephalomyelitis and myositis (19) and later shown to be the same Neospora caninum
parasite isolated from a litter of puppies in the United States (18, 31, 34, 36). The genus
designation Neospora has since been applied to a similar protozoal parasite identified in livestock
(11, 66). In 1991, the first bovine Neospora isolates were obtained from aborted fetuses and have
been maintained in continuous cell culture (24). Whether the canine isolate (Neospora caninum)
and bovine isolate represent identical species is not certain. For the present, the infection in
livestock is most appropriately referred to as a Neospora species. Neospora have morphologic
similarities to Toxoplasma gondii, but can be antigenically differentiated by
immunohistochemistry (14). By light microscopy, Neospora can only be differentiated from
Toxoplasma in the tissue cyst stage when Neospora often have a thicker cyst wall. There are
distinct ultrastructural differences between Toxoplasma gondii and Neospora (14,49).
Infection due to Neospora has been reported in various species of livestock, including cattle (1-5,
10, 11, 14, 26, 27, 32, 35, 37, 40, 42, 45, 52-56, 59, 64, 65, 66, 67, 74, 75, 76), sheep (33,38),
goats (13,30), horses (41), and deer (74). Although only recently recognized, bovine neosporosis
has emerged as an important reproductive disease. Since its first association with an abortion
storm in 1987 in a dairy in New Mexico (66), there have been reports of Neospora abortions in
California and the Midwest which have confirmed this infection as a significant cause of abortion,
particularly among dairy cattle (1,5,11,53,64). Retrospective studies in California suggest that the
parasite has been endemic since at least 1985 (6). In California, 18 to 19% of all aborted bovine
fetuses submitted to the California Veterinary Diagnostic Laboratory System (CVDLS) are
diagnosed with this infection (5,11). In dairy cattle submissions from California, the proportion of
Neospora abortion is even higher, 24.4% (6).
Bovine neosporosis has a worldwide distribution and has been diagnosed in the United States
(48), Canada (*,17,48,52), Mexico (1), Britain (26,27,58,59), Netherlands (75), Denmark (2),
Australia (20,32,54), Israel (42), New Zealand (67), South Africa (43), Japan (*,56), and
Zimbabwe(*). Within the United States 32 states have reported cases including Alabama (48),
Arizona (*,53,76), California (3-11), Colorado (*,64), Georgia (48), Idaho (*), Illinois (*), Indiana
(35), Iowa (53, 76), Kansas (*), Maryland (*,40), Massachusetts (76), Michigan (*), Minnesota
(*, 53,76), Missouri (*,76), Montana (*), Nebraska (48,76), New Hampshire (*), New Mexico
(66), New York (*), North Dakota (*), Ohio (*), Oklahoma (*), South Dakota (53,76), Texas
(*,53,76), Utah (*), Vermont (*,76), Virginia (*,76), Washington (63,65), West Virginia (*), and
The pathogenic potential of bovine Neospora sp. has been confirmed by experimental infection of
pregnant cattle resulting in fetal death and in the birth of an in utero exposed or congenitally
infected calf (15). Neospora caninum from dogs also has been experimentally inoculated into
pregnant cattle and sheep resulting in transplacental fetal infection in a cow and abortion in sheep
At present, the only known natural route by which cattle become infected with Neospora is
transplacental infection of the fetus from the infected dam. The routes by which cattle may become
infected after birth are unknown, but the similarities of Neospora to other apicomplexan coccidia,
particularly Toxoplasma, suggests that postnatal infection may be acquired through oral ingestion
of coccidial oocysts shed from an unidentified carnivorous definitive host. Exogenous stages of
Neospora such as oocysts or sporocysts have not been identified. Tachyzoites and tissue cysts are
the life cycle stages of Neospora currently identified.
The life cycle of Neospora is unknown, but attempts are being made to identify the definitive host
of bovine Neospora. Dogs, cats, rats and mice have been screened for Neospora coccidia following
experimental infection with bovine Neospora sp. (Conrad P and Barr B, unpublished data,
1992).Dogs, cats, and raccoons have been screened for N. caninum coccidia following
experimental infections with N. caninum, but no fecal oocysts identified as Neospora have been
identified in these species (48). Four species of birds (red tailed hawk, turkey vulture, barn owl,
and crow) have been inoculated with Neospora caninum infected mouse tissue with results that
suggest that these particular avian species are probably not definitive hosts for neosporosis
A significant method by which Neospora infections may be maintained within the herd is through
prenatal infection of fetuses which survive and become replacements that are chronically infected.
There is serologic evidence of congenital transmission of neosporosis in California dairies based
on the observation that the rate of seropositivity is not associated with the age of the cow, thus
indicating that the incidence of new, postnatal infection is low or nil (61).
Congenitally infected calves can have a chronic persistent infection which can be passed on
transplacentally to their offspring. In a survey of heifer calves in a known Neospora dairy herd, 25
calves with serologic evidence of congenital exposure were compared with 25 serologically
negative cohorts. The two groups were similar until pregnancy and calving. At the time of calving,
blood samples were obtained from the heifer and calf from 38 of the 50 heifers. All calves born to
heifers that had elevated Neospora titres as calves (evidence of congenital Neospora exposure)
also had elevated Neospora titres (20 of 20). Conversely all of the negative heifers had
serologically negative calves (18 of 18) (Mark Anderson and Jim Reynolds, unpublished data,
1995). In addition, there was no evidence of seroconversion to Neospora among the negative
heifers and the positive heifers retained serologic titres to Neospora. Ten of the calves were
purchased and necropsied, seven serologically positive calves from positive heifers, and three
serologically negative calves from negative heifers. All seven of the positive calves had histologic
lesions in the brain and spinal cord consistent with congenital Neospora infection and Neospora
protozoa were identified by immunohistochemistry in five of the seven calves. Neospora was
isolated from the tissues from two of these calves. The negative calves had no lesions or other
findings suggesting congenital Neospora infection.
These results suggest both that a chronic latent infection can occur with Neospora and, most
interestingly, that there is vertical transmission of this disease through generations of cattle.There
is a precedent to these observations in that vertical transmission of Toxoplasma gondii, a similar
parasite, has been observed in wild rats in the absence of the definitive host, members of the cat
Although congenital Neospora infections have been diagnosed in most domestic livestock, cattle
are the only livestock species in which there is sufficient information available concerning the
natural infection to describe its clinical features. There are no signs of clinical illness in cows that
abort due to Neospora infection. The aborted fetuses are usually autolysed with no gross lesions
and placentas are not retained. Abortions have been diagnosed in both heifers and cows from three
months gestation to term (5,11,40). Whether Neospora infection can cause reproductive problems
in the first trimester of gestation is unknown.A majority (78%) of Neospora abortions occur
between four and six months gestation and this pattern of mid-gestation abortion is distinctive
from other diagnosed causes of infectious abortion in dairy cattle which tend to occur later in
Although Neospora infections occur in both dairy and beef cattle, most reports attributing
significant numbers of abortions to this infection have been associated with dairy cattle,
particularly those in drylot dairies (1,3-8,10,11,53,64,66). This apparent disparity between beef
and dairy cattle is not thought to represent breed susceptibility as beef cattle are susceptible to
experimental infection (15) and both congenital infections and abortions due to Neospora have
been documented in beef breeds (*,35,37,40,63). It is possible that the environment of the drylot
dairy is more conducive to the spread and transmission of this disease. Cattle in drylot dairies are
densely populated and fed a variety of harvested feeds and commodities which are frequently
stored on or around the dairy prior to being mixed and fed. These feeding practices offer many
opportunities for fecal contamination of individual ration components which would then be mixed
and fed, efficiently exposing much of the herd. This pattern of increased exposure and disease
associated with intensive management mimics factors affecting the incidence of Toxoplasma
abortion in sheep flocks.
Neospora infection has been identified throughout California in more than a third of the dairy
herds submitting aborted fetuses to the CVDLS (6,11). The herd prevalence of abortion due to this
infection can be quite variable. Rare sporadic cases may occur in some dairies with a nominal
abortion rate.However, explosive outbreaks of Neospora abortion may occur. A well-documented
example involved a group of 147 drylot dairy heifers in which 27 (18%) aborted during a six week
period and all fetuses examined (17) were diagnosed with Neospora infection (Jim Reynolds and
Mark Anderson, personal communication, Nov. 1993). In some instances, up to 5% of pregnant
cattle have aborted due to neosporosis within one to three months. Annual herd abortion rates up
to 30% have been reported in dairies with Neospora abortions and abortions may continue to occur
over a period of several years (*,1,64). Over a one year period of time, all aborted fetuses available
on 26 selected California dairies were collected and submitted to the CVDLS for diagnosis. A
total of 266 abortions were submitted, of which, 113 (42.5%) were confirmed Neospora abortions
from 19 (73%) dairies (8). In addition to abortion, fetal mummification has been associated with
Neospora outbreaks (*,64). Neospora abortions occur throughout the year, but there is possibly a
small increased risk of abortion during the late fall and winter (68).
Bovine fetal Neospora infection does not always produce fetal death resulting in abortion or
stillbirth. Fetal infection may result in the birth of live full-term congenitally affected calves
(13,14,27,32,35,37,40,57,63). Central nervous system infection and damage in these calves results
in highly variable clinical signs which are often limited to limb dysfunctions, ranging from mild
proprioceptive defects to complete paralysis. Microscopically there is a multifocal protozoal
encephalomyelitis which may be particularly localized in the spinal cord gray matter.
Calves may acquire a Neospora infection during gestation, but be born clinically normal except
that they have serologic and even histopathologic evidence of congenital infection. A consistent
finding in these calves is a high precolostral antibody titre to Neospora which is useful in
detecting in utero infection (13). In a survey of calves on a dairy with a history of Neospora
abortions, 67/189 newborn calves (35%) had serologic evidence of in utero Neospora infection,
with no evidence of increased morbidity or mortality in these calves (60). The apparent wide
variability in clinical presentation of these in utero exposed or congenitally infected calves may be
due to multiple factors, including the age and immune development of the fetus at the time of
exposure to Neospora, and the distribution of the lesions in the central nervous system.
Cows that abort a Neospora infected fetus can have additional infected fetuses in subsequent
pregnancies. The outcome of these subsequent pregnancies is variable, resulting in a congenitally
infected calf or possibly another abortion. Barr and colleagues identified five calves born to four
cows with Neospora abortions in the previous pregnancy. In all calves there was serologic and
histopathologic evidence of congenital infection (13). Repeat abortions can also occur, in a survey
of abortions in drylot dairies in California, two confirmed Neospora abortions were identified in
four of 41 cows in which information concerning other pregnancies was available (8). It is not
known whether these repeat transplacental infections are the result of a release of parasites from
tissue cysts in the dam or from reinfection of the dam from the environment. However, in bitches
naturally infected with Neospora caninum there is documented evidence of congenital infection in
successive litters of puppies (33) and there is experimental evidence of repeat transplacental
infection of Neospora caninum in mice that had one infectious exposure (23 ).
The confirmation of a suspect Neospora infection will require the assistance of a veterinary
diagnostic laboratory. The preferred samples in cases of abortion include one or more aborted
fetuses submitted with placenta and sera from the dam. The aborted fetus is usually autolysed with
serosanguinous fluid accumulation in body cavities. Rarely there are subtle gross lesions,
consisting of pale white foci in the skeletal muscles or the heart. Histologic lesions consist of
widespread nonsuppurative infiltrates. The most diagnostically significant lesions are found in the
brain and consist of scattered foci of nonsuppurative cellular infiltrates with occasional foci of
necrosis. Protozoa are not usually seen on routinely stained slides. Other histologic lesions that are
consistently found include nonsuppurative epicarditis and/or myocarditis, focal nonsuppurative
myositis and nonsuppurative portal hepatitis, frequently with focal hepatic necrosis. The
presumptive diagnosis of protozoal infection can usually be made on the basis of histologic
lesions. Immunohistochemistry using antibodies to Neospora caninum (45) or the bovine
Neospora isolate (14,15) is an effective method to identify Neospora in fetal tissues and establish a
definitive diagnosis. Recently, a monoclonal antibody against Neospora caninum has been
developed which can also be used to detect infection in aborted fetuses (22). Neospora
immunohistochemistry is most successful on sections of fetal brain, although the parasites are also
frequently present in the lung, kidney, and skeletal muscle (Mark Anderson, unpublished data,
1994). Immunohistochemistry has been successfully employed to diagnose Neospora infections in
mummified fetuses although the autolytic state of these fetuses diminishes the diagnostic
The definitive diagnosis of Neospora infection in fullterm calves can be difficult due to the patchy
distribution of lesions and low numbers of parasites that may be present (14). The most
characteristic lesions are in the spinal cord, consisting of a multifocal nonsuppurative myelitis. In
some cases thick-walled tissue cysts may be present within neurons. However, these tissue cysts
are extremely rare in many in utero exposed calves, making it difficult to establish a diagnosis on
the basis of Neospora immunohistochemistry alone. Neospora serology, utilizing an indirect
fluorescent antibody (IFA) test, has proven effective in detecting elevated Neospora antibodies in
the serum of congenitally infected or in utero exposed calves (14,25). In addition, the Neospora
IFA test may be useful in establishing the diagnosis in aborted fetuses, since infected fetuses six
months or more in gestation may have elevated Neospora antibody titres (16). However, just as
with Toxoplasma infections, a negative fetal Neospora IFA titre does not rule out the possibility of
The use of Neospora IFA for serodiagnosis of Neospora infection in adult cows requires caution in
interpretation because some cows aborting a Neospora infected fetus may not have significantly
elevated titres. In one study, 22% of known infected cows that aborted a positive fetus had
Neospora IFA titres that were within two dilutions of titres in presumed noninfected cattle (25). In
addition, within 2-5 months following abortion, the previously elevated titres in cows aborting a
Neospora infected fetus may drop to levels similar to noninfected cattle (25). Laboratories using
this or any other serologic test for Neospora must establish appropriate cut off titres using
standardized sera and should attempt to confirm their positive results by the identification of
parasites in aborted fetuses.
An enzyme-linked immunosorbent assay (ELISA) for detection of Neospora antibodies has been
recently developed (62). The ELISA test is being used for routine diagnostic testing at the
California Veterinary Diagnostic Laboratory as part of the bovine abortion serologic panel. This
new procedure is an improvement in serologic testing for Neospora because the test is rapid,
inexpensive and consistent with excellent sensitivity (88.6%) and specificity (96.5%). Cutoff
values have been established for the ELISA by which the probability of infection can be estimated
in cattle. In addition to its use in individual abortion cases, the test can be used to estimate
seroprevalence of Neospora infection within a herd by testing 30 to 50 cows in the herd at least
two months postpartum. The test is also useful in investigating the causes of recent abortion
storms. The Neospora ELISA values of cows that had aborted can be compared with a group of
pregnant herdmates. The number of pregnant cows tested should be twice that of aborting cows
At present, the only clearly established method of Neospora transmission in herds is through
prenatal infections. Cattle that are chronically infected pass the infection transplacentally to their
fetus. Although various antimicrobial agents have been tested against Neospora caninum in vitro
there is currently no known method whereby an infected cow can be cleared of the infection
(46,47,50). Therefore, control of the infection in the herd would need to be focused on reducing the
level of latent infection in cows in the herd and to limit introduction of infected cattle into the herd
Culling decisions concerning cows that have a Neospora abortion should be made with the
knowledge that repeat abortions or repeat congenital infections might occur in these animals.
Currently there is insufficient information concerning the future reproductive performance of these
cows by which to establish economic estimates to guide culling.
There are no proven methods available to prevent postnatal infection because there is insufficient
information on the biology of this parasite, including the life cycle, on which to base specific
recommendations. However, it is prudent to remove all potentially infected tissues, such as
aborted fetuses and placentas from the environment, that might serve as a source of infection for
susceptible hosts. In addition, fecal contamination of feed and water sources by other animals
should be minimized.It is apparent that fecal contamination of the environment or feeds of cattle is
extremely common since virtually all cattle are infected with Sarcocystis cruzi through ingestion of
coccidia from a canidae definitive host. As is the case with toxoplasmosis, development of an
effective Neospora vaccine will be difficult.
Sound Reproductive Health Management Program
Detection in Tie-stall and Free-Stall Environments
Approach to Reproductive Programs in Dairy Herds
Applied Dairy Science Course - University of Alberta:
Managing Reproduction in
Alberta Dairy Management Fact Sheet:
Getting Cows Bred -
1. Preparing cows for high conception rates
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results from submissions to California Veterinary Diagnostic Laboratory, 1995.