Association between seropositivity for Neospora caninum and reproductive performance of beef heifers in the Pantanal of Mato Grosso do Sul, Brazil

Abstract

Neospora caninum is an obligate intracellular parasite that can infect domestic and wild canids, ruminants, and horses. The purpose of this study was to evaluate the association between the presence of antibodies to N. caninum and reproductive loss in beef heifers in the South Pantanal region of Mato Grosso, Brazil. A total of 1098 heifers were evaluated from breeding to calving with regard to reproductive performance, and serology for neosporosis was assayed by indirect immunofluorescence reaction. The prevalence of N. caninum in cows that had failed to conceive was 22.13% higher than in those that had conceived (p > 0.0001), indicating a significant correlation between non-conception and presence of anti-N. caninum antibodies. The extraction rates for seropositive and seronegative heifers were 28.24 and 50.12%, respectively, with a statistically significant value (p > 0.0001) that showed a decrease of 44% in the extraction rate of seropositive animals. The results emphasize the importance of diagnosis for monitoring of neosporosis in primiparous cows, and indicators of seropositive females as a factor in strategies for culling the beef cattle herd.

Full text

www.cbpv.com.br/rbpv
Rev. Bras. Parasitol. Vet., Jaboticabal, v. 19, n. 2, p. 119-123, abr.-jun. 2010
*Corresponding author: Renato Andreotti
EMBRAPA-Gado de Corte, BR 262, Km 4, CP 154, CEP 79002-970,
Campo Grande - MS, Brasil;
e-mail: andreott@cnpgc.embrapa.br
Association between seropositivity for Neospora caninum
and reproductive performance of beef heifers in the
Pantanal of Mato Grosso do Sul, Brazil
Associação entre soropositividade para Neospora caninum e o desempenho reprodutivo
de novilhas de corte no Pantanal Sul-Mato-Grossense, Brasil
Renato Andreotti1*; Jacqueline Cavalcante Barros1; Anselmo Ranier Pereira2; Leandra Marla Oshiro3;
Rodrigo Casquero Cunha3; Leonardo Francisco Figueiredo Neto4
1Empresa Brasileira de Pesquisa Agropecuária – EMBRAPA-Gado de Corte
2Médico Veterinário Autônomo
3Universidade Federal do Mato Grosso do Sul – UFMS
4Departamento de Economia e Administração, Universidade Federal do Mato Grosso do Sul – UFMS
Received January 22, 2010
Accepted March 22, 2010
Abstract
Neospora caninum is an obligate intracellular parasite that can infect domestic and wild canids, ruminants, and
horses. e purpose of this study was to evaluate the association between the presence of antibodies to N. caninum
and reproductive loss in beef heifers in the South Pantanal region of Mato Grosso, Brazil. A total of 1098 heifers
were evaluated from breeding to calving with regard to reproductive performance, and serology for neosporosis was
assayed by indirect immunofluorescence reaction. e prevalence of N. caninum in cows that had failed to conceive
was 22.13% higher than in those that had conceived (p < 0.0001), indicating a significant correlation between
non-conception and presence of anti-N. caninum antibodies. e extraction rates for seropositive and seronegative
heifers were 28.24 and 50.12%, respectively, with a statistically significant value (p < 0.0001) that showed a decrease of
44% in the extraction rate of seropositive animals. e results emphasize the importance of diagnosis for monitoring
of neosporosis in primiparous cows, and indicators of seropositive females as a factor in strategies for culling the beef
cattle herd.
Keywords: Reproduction, bovine, diagnostic, abortion, Neospora caninum.
Resumo
Neospora caninum é um parasita intracelular obrigatório que pode infectar canídeos domésticos e selvagens,
ruminantes e equídeos. Neste trabalho estudou-se a associação entre soropositividade para Neospora caninum e perda
reprodutiva em novilhas de corte na região do Pantanal Sul-Mato-Grossense. Foram avaliadas 1098 novilhas da
estação de reprodução ao nascimento dos bezerros com relação ao desempenho reprodutivo e realizada a sorologia para
N. caninum através da reação de imunofluorescência indireta. A soroprevalência de N. caninum nas vacas que falhara
na concepção foi 22,13% maior que nas que conceberam (p < 0,0001), indicando que há uma correlação significativa
entre a não concepção e a presença de anticorpos anti-N. caninum. As taxas de desfrute para as novilhas soropositivas
e soronegativas para neosporose foram de 28,24 e 50,12%, respectivamente, mostrando uma redução de 44% na taxa
de desfrute de novilhas soropositivas para N. caninum. Ressalta-se a importância do monitoramento do diagnóstico da
neosporose em primíparas, e o indicador de fêmeas soropositivas como um fator nas estratégias de descarte no rebanho
bovino de corte.
Palavras-chave: Reprodução, bovinos, diagnóstico, aborto, Neospora caninum.
ISSN 0103-846X (impresso) / ISSN 1984-2961 (eletrônico)
Full Article

120 Andreotti, R. et al. Rev. Bras. Parasitol. Vet.
Introduction
Neospora caninum is an obligate intracellular parasite that until
1988 was confused with Toxoplasma gondii (LINDSAY; DUBEY;
McALLISTER, 1988). Dogs and coyotes are definitive hosts,
which eliminate parasite oocytes in their feces. After sporulation,
these oocytes are ingested by an intermediary host and form
tissular cysts (LINDSAY et al., 1999; McALLISTER et al., 1998;
GONDIM et al., 2004).
Neosporosis has emerged as an important disease in bovines
worldwide and is related to reproductive loss in these animals,
causing abortions and neonatal mortality (ANDERSON et al.,
1991; BARR et al., 1991; THORNTON; THOMPSON;
DUBEY, 1991; WOUDA et al., 1999). Establishing the diagnosis
of neosporosis is therefore important, as a step in re-breeding and
possibly switching dams according to their history of abortions
(DUBEY; SCHARES; ORTEGA-MORA, 2007).
Besides being associated with bovines, this protozoon has been
associated with the occurrence of sporadic disease in other animals
species, including sheep (DUBEY; SCHARES; ORTEGA-MORA,
2007), goats (BARR et al., 1992), and horses (MARSH et al.,
1996).
e serologic prevalence of N. caninum in beef cattle in
Canada, as obtained from random samples of confined animals, was
6.5% positive animals. Prevalence in blood samples from auction
animals was 9.0%. As opposed to this low seropositivity, a study
on the association between N. caninum infection and reproductive
performance found that 30% of the cattle selected for the study
were seropositive (HADDAD; DOHOO; VANLEEWEN,
2005). As for groups in which abortion had been documented
and no antibodies for other pathogens were found, between
17 and 45% of aborted fetuses were seropositive for N. caninum
(PITEL et al., 2001).
e presence of positive serology for N. caninum in beef cattle in
the State of Mato Grosso do Sul (MS), Brazil has been established
as 30% in heifers (ANDREOTTI et al., 2004) and 14.9% in cows
(OSHIRO et al., 2007). An association between seropositivity and
abortion was found in 69.8% of bovine herds (OSHIRO et al.,
2007). Seropositivity was 29.5% for anti-N. caninum antibodies
in embryo-receptor heifers of beef cattle raised extensively (PAZ;
LEITE; ROCHA, 2007).
Most abortions due to infection by Neospora are diagnosed
between 3 and 8 months of gestation, although abortions that
occur early in the pregnancy are more difficult to diagnose due to
a lack of fetal material necessary for analysis (INNES, 2007).
As for vertical transmission of N. caninum, infected heifers
that become healthy adults may transmit the agent to the fetus,
which is especially vulnerable, thereby maintaining the parasite
in the herd (ANDERSON et al., 1997; INNES et al., 2005).
Transplacental transmission has been reported in at least 36.8% of
neosporosis-positive heifers and may reach 100% in experimental
infections (THURMOND; HIETALA, 1996; WILLIAMS, et al.,
2000; INNES, et al., 2005; VIANA et al., 2008).
Here we studied the association between N. caninum antibodies
and reproductive loss in heifers of beef cattle of the south Pantanal
region of Mato Grosso State, Brazil. Our results allow us to measure
the bottleneck of the reproductive efficiency in these animals.
Material and Methods
1. Study area
e study was done in a farm located in the South Pantanal region
of Mato Grosso State, Brazil (20° 06’ 05” S and 56° 47’ 43” W). It
is an area of plains subjected to dry and flood seasons and suffers
periodic inundations. e climate is hot and rainy in the summer
and dry and pleasant in the winter, with average temperatures of
32 and 21 °C, respectively. e ground has low natural fertility
(CADAVID GARCIA, 1986).
e reproductive system on the farm is comprised of breeding,
rebreeding, and fattening. e areas dedicated to cattle have
cultivated pastures of marandu-grass (Brachiaria brizantha cv.
Marandu) and guinea-grass (Panicum maximum). e field system
is characterized by a low number of pastures and a defined season
for mating in which andrologic examination of the bulls is done and
separate handling is adopted for heifers and reproductive cows.
2. Sample collection
A total of 1098 Nelore heifers aging around 24 months and
with average weight of 259.14 kg were evaluated. e mating
season regime was artificial insemination with repeated bulls (1:35)
during the period of November 2007 and March 2008. Diagnosis
of gestation was based on a rectal palpation done around 60 days
after mating. Animals were followed during the reproductive
regime until the calves were one month of age.
Information about the herds was collected based on the
handling routine at the farm. We collected blood samples from
cows twice, once at the diagnosis of gestation, around 60 days
after mating, and again a month after delivery. Blood samples were
also collected from heifers when they were around one month
old. After identification, sera were kept in –20 °C until serologic
tests were done.
3. Indirect immunofluorescence reaction (RIFI)
Samples were examined by RIFI to detect the presence of
antibodies against N. caninum. e antigen was produced in cultures
of tachyzoites of N. caninum, strain NC-1 (DUBEY et al., 1988)
in Vero cells (OLIVEIRA et al., 2004). A commercial conjugate
anti-IgG bovine (Sigma) was used at a dilution of 1:10,000 and the
samples were tested at a dilution of 1:50 (PARÉ; THURMOND;
HIETALA, 1996). A positive and negative serum sample was
included in each slide.
4. Statistical analysis
To determine sample size we used the population proportion
estimate (n = (Zα/2)².0.25/E) according to Levine, Berenson e
Stephan (2000), with 95% of confidence and 3% error. A total
of 1098 primiparous Nelore heifers were analyzed.
For statistical analysis of prevalence results of the neosporosis
diagnosis in pregnant heifers, as well as of the abortion or conception
(birth) prevalence, we used 2 × 2 contingency tables as determined
by chi-square (χ2) test (SAMPAIO, 2007), using the statistical
program MedCalc® 8.0.0.0.

v. 19, n. 2, abr.-jun. 2010 Association between seropositivity for Neospora caninum and reproductive performance of beef heifers in the Pantanal 121
Results and Discussion
ere is no consensus for a cut-off value to be used as reference
for the diagnosis of neosporosis. Additionally, this value could be
affected by the animal age or disease stage, the strategy used for
diagnosis, and laboratory conditions (ALVAREZ-GARCIA et al.,
2003; Von BLUMRÖDER et al., 2004; DUBEY; SCHARES,
2006). Serological tests for the identification of infected animals may
require higher sensitivity and lower cut-off than suggested for the
diagnosis of bovine abortion. For these reasons we defined a cut-off
value that would provide greater sensitivity to the test (1:50).
Cow blood serum samples of the first and second collection by
RIFI showed similar results, with only three sera being converted
into positive in the second collection. erefore, we considered
the information from animals with two positive results for the
serological analysis in order to co-relate the results with births.
e diagnosis of gestation by palpation verified a total of
546 pregnant cows, which corresponded to 49.73% of the whole
herd. e diagnosis of gestation in the positive and negative
categories for N. caninum serology showed significant difference
(p < 0.0001) between groups (Table 1).
Loss of pregnancy was 15% higher in seropositive cows
(55.89%) as compared to loss in N. caninum seronegative cows
(40.88%), showing that in this bovine herd the presence of positive
N. caninum serology is a relevant factor for female reproduction.
It has been shown that a seropositive cow that suffers an abortion
has a 5.7 times greater risk of having an abortion in subsequent
gestations (THURMOND; HIETALA, 1997).
During the period between the beginning of the mating season
and the gestation diagnosis in cows negative for N. caninum,
we verified a loss of 40.88%, with an additional percentage of
9% of loss until birth. In cows positive for N. caninum, loss in
the first period was 55.89%, and in the second it was 15.87%.
e results revealed a higher impact of reproductive loss in both
categories between the beginning of the mating season and the
diagnosis of gestation.
Seroprevalence of N. caninum in cows that did not conceive was
22.13% higher than in those that conceived (p < 0.0001), which
indicates a significant correlation between not conceiving and the
presence of anti-N. caninum antibodies. ese results reveal that
the loss between the gestation diagnosis period and conception
in seropositive cows was 36%, while in seronegative cows it was
15.23%, indicating that positive serology for N. caninum affects
the conception ratio.
One of the main symptoms of seropositivity in bovines is
abortion, which may occur due to activation of tachyzoites and their
migration to the uterus (DUBEY; SCHARES; ORTEGA-MORA,
2007). us, the association between positive serology for
N. caninum and abortion during the reproductive season, when
compared to negative cows, can confirm the presence of this
disease in this herd. e positive serology suggests the existence
of antibody production from tachyzoites and the presence of at
least the latent form, bradyzoites, which remains in the host for
the rest of its life.
e prevalence of N. caninum in calves in relation to heifers
is shown in Table 2. e highest prevalence of seropositive calves
among those born from N. caninum seropositive heifers was
statistically significant (p < 0.0001), suggesting the occurrence of
vertical transmission of neospora between the mother and calves,
although it was not possible to determine the ratio of vertical
transmission in this herd.
ere were 38.4% more N. caninum seropositive calves born
from seropositive cows as compared to seropositive calves born
from seronegative cows. However, in this study, blood collection
from calves was performed during the first month after birth, which
affected the results due to the transmission of immunoglobulin
through the colostrum, so it was not possible to verify the immune
response in these calves. It is noteworthy that in the conditions
found in the field we assume that calves usually feed from their
own mothers. Vianna et al. (2008) found positive serology of
36.8% in fetuses from N. caninum seropositive cows.
A total of 29.12% of calves positive for N. caninum serology
from negative cows show an infection ratio from the environment
that suggests a careful analysis. In endemic conditions, the oocytes
may be found in the pastures and in the water. e definitive host
and other native species of the region favor the maintenance of the
agent in the environment. is combined with a lack of control
of the disease on the farm and the discarding of the carcasses of
dead animals in the field favor the persistence of the risk factors
associated with contamination.
e extraction rates of heifers that were either seropositive or
seronegative for N. caninum were 28.24 and 50.12%, respectively,
which shows a reduction of 21.88% in the extraction rate of
N. caninum seropositive heifers (p < 0.0001). When compared with
weaning and natality indexes of beef cattle herds that are raised
in native pastures in the Pantanal, which are considered low in
relation to dense and covered tropical regions of the country, the
values for N. caninum seropositive heifers are close to 50 and 58%,
as found by Brasil (1978) and Cadavid Garcia (1981, 1986).
When the extraction rate of N. caninum seropositive heifers
is considered, we observe a strong reduction capable of causing
impact in the reproductive system, to a degree that varies according
to the age of the female.
In Brazilian bovine herds a discard system that considers the
N. caninum serology of the animal is not in place. In this study
we found that cows seropositive for N. caninum are 1.44 times
more prone to lose calves than are seronegative cows. e risk of
abortion for cows infected with N. caninum was 1.7, and 3 to 7 times
higher in seropositive cows as compared to seronegative cows
(THURMOND; HIETALA, 1997).
Due to differences in the effect of risk factors associated with
abortion in beef and dairy cattle observed in different regions and
handling conditions, control strategies should be diversified and
adopted based on the cost/benefit analysis for the reproductive
system. In this case, the parameters to be considered are the
production system, the handling conditions, the prevalence of
the disease in the herd, the predominant transmission route, the
existence of biosecurity measures in the propriety, and the effects of
infection calculated in the productive and reproductive performance
(DUBEY; SCHARES; ORTEGA-MORA, 2007).
Our results show that the reproduction of N. caninum
seropositive primiparous cows has an impact of 44% in relation
to seronegative heifers, which suggests the need for controlling

122 Andreotti, R. et al. Rev. Bras. Parasitol. Vet.
the herds in the Pantanal region. e existence of flooding areas
and wild animals, especially canids, should be further investigated
to evaluate whether they are risk factors for this disease.
Losses during gestation may be the consequence of misdiagnosis
of gestation, abortion, absorption of the embryo, or occurrence of
infectious diseases that affect reproduction. Presence of neosporosis
in this animal category in the system of beef cattle in the Pantanal
contributes for a lower extraction rate of the herd. us, developing
measures for the control of neosporosis in this animal category
is very important.
In beef cattle herds of the Pantanal of South Mato Grosso,
presence of N. caninum seropositive heifers causes a significant
impact on reproduction, with a reduction of 21.88% in the
extraction rate of the herd. us, we would like to highlight the
importance of performing evaluations and procedures to control
this disease in the herd, of establishing a control mechanism for
buying and introducing new animals, and of the use of serology
for N. caninum as an indication for the discarding of animals in
bovine herds.
Acknowledgments
e authors would like to express their thanks for the funding
of this project, which was provided by the Universal proposal of
CNPq.
References
ALVAREZ-GARCIA, G. et al. Influence of age and purpose for testing
on the cut-off selection of serological methods in bovine neosporosis.
Veterinary Research, v. 34, n. 3, p. 341-352. 2003.
ANDERSON, M. L. et al. Evidence of vertical transmission of
Neospora sp. infection in dairy cattle. Journal of the American Veterinary
Medicine Association, v. 210, n. 8, p. 1169-1172, 1997.
ANDERSON, M. L. et al. Neospora-like protozoan infection as a major
cause of abortion in California dairy cattle. Journal of the American
Veterinary Medicine Association, v. 198, n. 2, p. 241-244, 1991.
ANDREOTTI, R. et al. Evidence of Neospora caninum in beef cattle and
dogs in the state of Mato Grosso do Sul, Center-Western Region, Brazil.
[Evidência de Neospora caninum em gado de corte e em cães no estado
de Mato Grosso do Sul, região centro-oeste, Brasil.] Revista Brasileira
de Parasitologia Veterinária, v. 13, n. 3, p. 129-131, 2004.
BARR, B. C. et al. Neospora-like protozoal infections associated with
bovine abortions. Veterinary Pathology, v. 28, n. 2, p. 110-116,
1991.
BARR, B. C. et al. Neospora-like protozoal infections associated with
abortion in goats. Journal of Veterinary Diagnostic Investigation,
v. 4, n. 3, p. 365-367, 1992.
BRASIL. Ministério do Interior. Estudo de desenvolvimento integrado
da bacia do Alto Paraguai: relatório de pré-diagnóstico. Brasília, DF,
1978. 506 p.
CADAVID GARCIA, E. A. Estimativa dos custos de produção da
pecuária de corte do Pantanal Matogrossense. Corumbá: Embrapa-
UEPAE, 1981. 75 p. (Circular Técnica, 5).
CADAVID GARCIA, E. A. Estudo técnico-econômico da pecuária
bovina de corte do Pantanal Mato-grossense. Corumbá: Embrapa -
CPAP, 1986. 150 p. (Documentos, 4).
DUBEY, J. P.; SCHARES, G. Diagnosis of bovine neosporosis.
Veterinary Parasitology, v. 141, n. 1-2, p. 1-34, 2006.
DUBEY, J. P.; SCHARES, G.; ORTEGA-MORA, L. M. Epidemiology
e control of neosporosis and Neospora caninum. Clinical Microbiology
Reviews, v. 20, n. 2, p. 323-367, 2007.
DUBEY, J.P. et al. Newly recognized fatal protozoan disease of dogs.
Journal of the American Veterinary Medical Association, v. 192, n. 9,
p. 1269-1285, 1988.
GONDIM, L. F. et al. Coyotes (Canis latrans) are definitive hosts of
Neospora caninum. International Journal for Parasitology, v. 34, n. 2,
p. 159-161, 2004.
HADDAD J. P.; DOHOO I. R.; VANLEEWEN J. A. A review of
Neospora caninum in dairy and beef cattle - a Canadian perspective.
Canadian Veterinary Journal, v. 46, n. 3, p. 230-243, 2005.
INNES, E. A. et al. e host-parasite relationship in bovine neosporosis.
Veterinary Immunology and Immunopathology, v. 108, n. 1-2,
p. 29-36, 2005.
INNES, E. A.e host-parasite relationship in pregnant cattle infected
with Neospora caninum. Parasitology, v. 134, p. 1903-1910, 2007.
LEVINE, D. M.; BERENSON, M. L.; STEPHAN, D. Estatística:
teoria e aplicações. Rio de Janeiro: LTC, 2000. 811 p.
Table 1. Association between N. caninum seroprevalence in heifers, reproductive status, and conception.
Heifers Reproductive status Conception Extraction rate
Pregnant (%) Not pregnant (%) Conceived Did not conceive
Seropositive 303 (44.11) 384 (55.89) 194 493 28.24%
Seronegative 243 (59.12) 168 (40.88) 206 205 50.12%
Total 546 (49.73) 552 (50.27) 400 698 36.43%
χ2
g = 22.607 (p < 0.0001) e χ2
c = 52.233 (p < 0.0001), in which χ2
g is the relation between reproductive status and N. caninum seroprevalence and χ2
c is the relation
between conception and N. caninum seroprevalence.
Table 2. Seroprevalence of anti-Neospora caninum antibodies as de-
termined by RIFI in calves born from Neospora caninum seropositive
or seronegative heifers.
Heifers Calves Prevalence
Seropositive Seronegative
Seropositive 131 63 67.53%
Seronegative 60 146 29.12%
Total 191 209 47.75%
χ2
b = 57.518, where χ2
b is the relation between serologic diagnosis of
N. caninum among calves and their mothers, with degree of significance
(p < 0.0001). Serologic exam: RIFI (1:50).

v. 19, n. 2, abr.-jun. 2010 Association between seropositivity for Neospora caninum and reproductive performance of beef heifers in the Pantanal 123
LINDSAY, D. S.; DUBEY, J. P.; McALLISTER, M. M. Neospora
caninum and the potential for parasite transmission. Compendium on
Continuing Education for the Practicing Veterinarian, v. 21, n. 4,
p. 317-321, 1999.
MARSH, A. E. et al. Neosporosis as a cause of equine protozoal
myeloencephalitis. Journal of the American Veterinary Medical
Association, v. 209, n. 11, p. 1907-1913, 1996.
McALLISTER, M. M. et al. Dogs are definitive hosts of Neospora
caninum. Internacional Journal for Parasitology, v. 28, n. 9,
p. 1473-1478, 1998.
OLIVEIRA, J. M. et al. Prevalence of anti-Neospora caninum antibodies in
dogs in the urban area of Campo Grande, MS, Brazil. Revista Brasileira
Parasitologia Veterinária, v. 13, n. 4, p. 155-158, 2004.
OSHIRO, L. M. et al. Prevalence of anti-Neospora caninum antibodies
in cattle from the state of Mato Grosso do Sul, Brazil. Revista Brasileira
de Parasitologia Veterinária, v. 16, n. 3, p. 133-138, 2007.
PARÉ, J.; THURMOND, M. C.; HIETALA, S. K. Congenital Neospora
caninum infection in dairy cattle and associated calfhood mortality.
Canadian Journal of Veterinary Research, v. 60, n. 2, p. 133-139,
1996.
PAZ, G. F.; LEITE, R. C.; ROCHA, M. A. Associação entre sorologia
para Neospora caninum e taxa de prenhez em vacas receptoras de embriões.
Arquivo Brasileiro de Medicina Veterinária e Zootecnia, v. 59, n. 5,
p. 1323-1325, 2007.
PITEL, P. H. et al. Neosporosis in bovine dairy herds from the west
of France: detection of Neospora caninum DNA in aborted fetuses,
seroepidemiology of N. caninum in cattle and dogs.Veterinary
Parasitology, v. 102, n. 4, p. 269-277, 2001.
SAMPAIO, I. B. M. Estatística aplicada à experimentação animal.
3. ed. Belo Horizonte: Fundação de Estudo e Pesquisa em Medicina
Veterinária e Zootecnia, 2007.
THORNTON, R. N.; THOMPSON, E. J.; DUBEY, J. P. Neospora
abortion in New Zealand cattle. New Zealand Veterinary Journal, v. 39,
n. 4, p. 129-133, 1991.
THURMOND, M. C.; HIETALA, S. K. Effect of congenitally acquired
Neospora caninum infection on risk of abortion and subsequent abortions
in dairy cattle. American Journal of Veterinary Research, v. 58, n. 12,
p. 1381-1385, 1997.
THURMOND, M.C.; HIETALA, S. K. Culling associated with Neospora
caninum infection in dairy cows. American Journal of Veterinary
Research, v. 57, n. 11, p. 1559-1562, 1996.
VIANNA, L. C. et al. Incidence and transplacental transmission of
Neospora caninum in primiparous females from Bos indicus slaughtered
in Presidente Prudente, São Paulo, Brazil. Semina: Ciências Agrárias,
v. 29, n. 2, p. 387-392, 2008.
Von BLUMRÖDER, D. et al. Comparison and standartisation of
serological methods for the diagnosis of Neospora caninum infection in
bovines. Veterinary Parasitology, v. 120, n. 1-2, p. 11-22, 2004.
WILLIAMS, D. J. L. et al. Neospora caninum associated abortion in
cattle: the time of experimentally-induced parasitaemia during gestation
determines foetal survival. Parasitology, v. 121, p. 347-358, 2000,
(parte 4).
WOUDA, W. et al. Seroepidemiological evidence for a relationship
between Neospora caninum infections in dogs and cattle. International
Journal of Parasitology, v. 29, n. 10, p. 1677-1682, 1999.