Effect of Neospora caninum on in vitro development of preimplantation stage bovine embryos and adherence to the zona pellucida

Neospora caninum is not transmissible via embryo transfer, but affects the quality of embryos in dairy cows

The aim of this study was to evaluate embryo transfer in cattle as a pathway of transmitting neosporosis and to quantitatively and qualitatively compare the embryo production from seropositive and seronegative donors. Superovulatory treatments were performed on eight Girolando donors (four seropositive and four seronegative for N. caninum), resulting in the recovery of ninety-one structures (embryos and non-fertilized structures). Embryos collected and classified as viable were transferred to seronegative recipients and analyzed by PCR to identify N. caninum. No difference was observed in the number of structures collected from seropositive and seronegative donors (40 and 51; P = 0.64). There was a significant difference in the percentages of freezable (25 % and 74 %, P = 0.04) and transferable (27.5 % and 78.4 %, P = 0.003) embryos. The recipients had similar pregnancy rates (60 % and 57.1 %, P = 0.97) and pregnancy loss (50 % and 43.8 %, P = 0.58). There was no change in the serological status of the recipients, and no protozoan DNA was identified in none of the samples. It was concluded that the embryo transfer technique is safe regarding the transmission of neosporosis; however, the quality of embryo production was compromised from donors seropositive for N. caninum.

Neospora caninum, A potential cause of reproductive failure in dairy cows from Northern Greece

Neospora caninum infection has been reported in a large number of intermediate hosts, such as ruminants, rabbits, mice, etc. but neosporosis has emerged as a serious disease in cattle and dogs worldwide. Abortions and other infertility issues have been reported in the infected cows, leading to great economic losses in farmers. The aim of our study was to assess N. caninum seroprevalence in dairy cattle from Northern Greece (region of Xanthi) by using the indirect fluorescent antibody technique. Blood samples were collected from 875 Holstein – Friesian dairy cows and tested for Neospora caninum antibodies. Among the cows that were studied, 184 (21.03%) were positive for N. caninum antibodies and concurrently their farms had a known previous history of infertility problems, such as abortions, increased number of artificial inseminations needed for conception, increased rate of returning to estrus and retention of fetal membranes.

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Neosporis is a common parasitosis in dairy cows.

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The number of abortions was significantly higher in seropositive cows.

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In seropositive cows the number of artificial inseminations was increased.

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The birth interval was much more longer in the N. caninum seropositive cows.

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Significant economic loss was observed in the infected farms.

Effect of using frozen-thawed bovine semen contaminated with lumpy skin disease virus on in vitro embryo production

Lumpy skin disease (LSD) is an important transboundary animal disease of cattle with significant economic impact because of the implications for international trade in live animals and animal products. LSD is caused by a Capripoxvirus, LSD virus (LSDV), and results in extensive hide and udder damage, fever and pneumonia. LSDV can be shed in semen of infected bulls for prolonged periods and transmitted venereally to cows at high doses. This study examined the effects of LSDV in frozen-thawed semen on in vitro embryo production parameters, including viral status of media and resulting embryos. Bovine oocytes were harvested from abattoir-collected ovaries and split into three experimental groups. After maturation, the oocytes were fertilized in vitro with frozen-thawed semen spiked with a high (HD) or a lower (LD) dose of LSDV, or with LSDV-free semen (control). Following day 7 and day 8 blastocyst evaluation, PCR and virus isolation were performed on all embryonic structures. After completing sufficient replicates to reach 1,000 inseminated oocytes, further in vitro fertilization (IVF) runs were performed to provide material for electron microscopy (EM) and embryo washing procedures. Overall, in vitro embryo yield was significantly reduced by the presence of LSDV in frozen-thawed semen, irrespective of viral dose. When semen with a lower viral dose was used, significantly lower oocyte cleavage rates were observed. LSDV could be detected in fertilization media and all embryo structures, when higher doses of LSDV were present in the frozen-thawed semen used for IVF. Electron microscopy demonstrated LSDV virions inside blastocysts. Following the International Embryo Transfer Society washing procedure resulted in embryos free of viral DNA; however, this may be attributable to a sampling dilution effect and should be interpreted with caution. Further research is required to better quantify the risk of LSDV transmission via assisted reproductive procedures.

Prevalence and risk factors associated with anti-Neospora caninum antibodies in dairy herds in the central region of Minas Gerais State, Brazil

Neospora caninum is one of the parasites that frequently causes reproductive loses in cattle herds all over the world. Surveys have shown a high prevalence of the parasite in herds; in certain locations, 90% to 100% of dairy holdings are positives according serological tests. The aim of this study was to estimate the prevalence and risk factors associated with the increased number of seropositive dairy cattle in the central region of Minas Gerais, the largest milk producer state in Brazil. Samples were collected from 151 dairy herds and from 2915 lactating cows, and were evaluated by an indirect ELISA assay. According to results, animal prevalence was 21.9% (CI 95%: 18.9 to 24.9%), while the herd prevalence it was 98.5% (CI 95%: 97.0 to 99.9%). Poisson regression estimate the herd risk factors associated with the increased number of cases. An increased number of positive animals was related to the previous history of abortion and the presence of dogs. The use of individual natural colostrum feeding and reproductive techniques such as embryo transfer and in vitro fertilization are associated with a reduced number of seropositive animals in the herd. In conclusion, Neospora caninum is overspread across the dairy herds of the region, and it may be causing major economic losses for dairy farmers. The use of reproduction techniques, the access of dogs to the herds and the management of calf colostrum are important issues to be considered in the control of the disease.

Effect of vaccination of cattle with the low virulence Nc-Spain 1H isolate of Neospora caninum against a heterologous challenge in early and mid-gestation

Live vaccines have emerged as one of the most potentially cost-effective measures for the control of bovine neosporosis. Previous studies have shown that Nc-Spain 1H is a naturally attenuated isolate of Neospora caninum and that immunisation with live Nc-Spain 1H tachyzoites generated a protective immune response in mice. The aim of this study was to evaluate the safety and efficacy of immunisation in cattle. N. caninum-seronegative heifers were immunised subcutaneously twice with 10⁷ live Nc-Spain 1H tachyzoites prior to artificial insemination. No adverse reactions or negative effects on reproductive parameters were recorded following immunisation. In immunised and non-challenged heifers, no foetal deaths were observed, and none of the calves was congenitally infected. The efficacy against N. caninum-associated foetal death and vertical transmission was determined after challenge with high doses of the Nc-1 isolate at 70 and 135 days of gestation, respectively. After the challenge in early gestation, the immunisation induced a protection of 50% against foetal death. In addition, the microsatellite analysis performed in PCR-positive tissue samples from foetuses that died after challenge infection showed that the profiles corresponded to the challenge isolate Nc-1. A degree of protection against vertical transmission was observed after challenge at mid-gestation; calves from immunised heifers showed significantly lower pre-colostral Neospora-specific antibody titres than calves from the non-immunised/challenge group (P < 0.05). Strong antibody and interferon gamma responses were induced in the immunised heifers. This study indicates that the immunisation before pregnancy with the Nc-Spain 1H vaccine isolate appeared to be safe and reduced the occurrence of N. caninum-associated abortion and vertical transmission in experimentally infected cattle. In light of these encouraging results, the next step for testing this live attenuated candidate should be the assessment of its efficacy and safety in naturally infected cattle.

Epidemiology and control of neosporosis and Neospora caninum

Neospora caninum is a protozoan parasite of animals. Until 1988, it was misidentified as Toxoplasma gondii. Since its first recognition in dogs in 1984 and the description of the new genus and species Neospora caninum in 1988, neosporosis has emerged as a serious disease of cattle and dogs worldwide. Abortions and neonatal mortality are a major problem in livestock operations, and neosporosis is a major cause of abortion in cattle. Although antibodies to N. caninum have been reported, the parasite has not been detected in human tissues. Thus, the zoonotic potential is uncertain. This review is focused mainly on the epidemiology and control of neosporosis in cattle, but worldwide seroprevalences of N. caninum in animals and humans are tabulated. The role of wildlife in the life cycle of N. caninum and strategies for the control of neosporosis in cattle are discussed.

Intrauterine Neospora caninum inoculation of heifers and cows using contaminated semen with different numbers of tachyzoites

OBJECTIVE

To investigate the potential of different Neospora caninum tachyzoite doses to infect heifers (experiment 1) and cows (experiment 2) when administered in utero by artificial insemination via contaminated semen.

METHODS

In experiment 1, five groups of 5, 7, 8, 9, and 5 cyclic heifers were hormonally synchronized and artificially inseminated with semen containing 0 (A, controls), 10(2) (B), 5 x 10(3) (C), 5 x 10(4) (D), and 5 x 10(5) (E) live N. caninum NC-1 isolate-tachyzoites, respectively. Experimental infection was followed for 100 days. Parasitaemia and specific serum IgG, and interferon-gamma (IFN-gamma) responses were studied. In experiment 2, four groups of 9, 10, 9, and 9 adult multiparous cows with confirmed infertility problems of diverse aethiology were hormonally synchronized and artificially inseminated with semen containing 0 (a, controls), 10(2) (b), 5 x 10(3) (c), and 5 x 10(5) (d) live N. caninum NC-1 isolate-tachyzoites, respectively. Experimental infection was followed for 63 days. Parasitaemia and specific serum IgG responses were studied.

RESULTS

In experiment 1, parasitaemia was detected in 1, 2, and 3 heifers from groups B, C, and D, respectively, between 9 and 23 days after insemination. Persistent specific serum antibody responses were detected in 2 and 3 heifers from groups D and E, respectively. Transient specific serum antibody responses were detected in 2, 1 and 1 heifers from groups C, D, and E, respectively. In addition, 1 heifer from group B showed a serum-specific antibody level higher than cut off value at 21 days post-insemination. Heifers seroconverted between 23 and 47 days after insemination. Specific IFN-gamma levels were detected in 1, 4, 6, and 3 heifers from groups B, C, D, and E, respectively, between 9 and 55 days after insemination. Pregnancy rate in the control group (60%) was higher than those observed in inoculated heifers (0-42.9%). Pregnancy rates in inoculated heifers were lower when the tachyzoite dose was increased (B 42.9%, C 12.5%, D 11.1%, and E 0%). In experiment 2, no Neospora DNA in blood nor specific serum IgG to N. caninum were detected in any of the cows studied, except in one cow inoculated with 5 x 10(5) tachyzoites (group d) which showed a relative index x100 (RIPC) values of 9.4, 18.9, and 18.1 at 42, 56, and 63 days after insemination, respectively.

CONCLUSIONS

This study provides evidence that the intrauterine infection via contaminated semen using 5 x 10(4) and 5 x 10(5) tachyzoites caused persistent serum-specific antibody responses in some heifers. On the basis of serological data, a dose-response effect was also observed. In addition, N. caninum would be a probable cause of early foetal death in inoculated heifers. In contrast, results obtained in a similar experiment with cows showing confirmed infertility indicate that higher doses, such as of 5 x 10(5) tachyzoites, were necessary to induce seroconversion in at least one animal.

ESTUDO MORFOLÓGICO DE EMBRIÕES BOVINOS FERTILIZADOS IN VITRO EXPOSTOS EXPERIMENTALMENTE À NEOSPORA CANINUM

RESUMO Durante a última década, a infecção por Neospora caninum tem emergido como uma importante doença reprodutiva em bovinos e, em vários países, tem sido diagnosticada como principal causa de aborto. Tendo em vista a importância dessa doença esse trabalho teve como objetivo avaliar morfologicamente embriões bovinos produzidos in vitro infectados experimentalmente por N. caninum. Os embriões foram produzidos in vitro a partir de oócitos colhidos de ovários de bovinos provenientes de abatedouro. Foram separados em grupo controle, mantido somente com meio HTF e grupo infectado com 10 mL de N. caninum. Os embriões foram avaliados após 48 e 96h em microscópio óptico invertido. Os embriões do grupo controle não apresentaram alterações morfológicas. No grupo infectado foi verificado o aparecimento de grânulos escuros no citoplasma, bloqueio da clivagem e ruptura da zona pelúcida (ZP). Em alguns casos, observou-se estruturas semelhantes a taquizoitos de N. caninum no interior da ZP. Esses resultados sugerem que, de alguma maneira há a interação do patógeno com o embrião, talvez em um processo inicial de ligação com a ZP, promovendo posteriormente sua entrada. Esses estudos tornam-se relevantes quando se leva em consideração a possível transmissão da N. caninum por técnicas conceptivas artificiais.

Pathogenesis of bovine neosporosis

The protozoan parasite Neospora caninum is a major pathogen of cattle and dogs, being a significant cause of abortion in cattle in many countries. It is one of the most efficiently transmitted parasites, with up to 90% of cattle infected in some herds. The pathogenesis of abortion due to Neospora is complex and only partially understood. Losses occur after a primary infection during pregnancy but more commonly as the result of recrudescence of a persistent infection during pregnancy. Parasitaemia is followed by invasion of the placenta and fetus. It is suggested that abortion occurs when primary parasite-induced placental damage jeopardises fetal survival directly or causes release of maternal prostaglandins that in turn cause luteolysis and abortion. Fetal damage may also occur due to primary tissue damage caused by the multiplication of N. caninum in the fetus or due to insufficient oxygen/nutrition, secondary to placental damage. In addition, maternal immune expulsion of the fetus may occur associated with maternal placental inflammation and the release of maternal pro-inflammatory cytokines in the placenta. Thus N. caninum is a primary pathogen capable of causing abortion either through maternal placental inflammation, maternal and fetal placental necrosis, fetal damage, or a combination of all three. The question of how N. caninum kills the fetus exposes the complex and finely balanced biological processes that have evolved to permit bovine and other mammalian pregnancies to occur. Defining these immunological mechanisms will shed light on potential methods of control of bovine neosporosis and enrich our understanding of the continuity of mammalian and protozoal survival.

Intrauterine Neospora caninum inoculation of heifers

Here, we studied the potential of Neospora caninum tachyzoites to infect heifers when administered in utero by artificial insemination via contaminated semen. Eighteen primiparous cyclic heifers were hormonally synchronized and artificially inseminated. Nine of them, which were inseminated with semen containing 10(7) live N. caninum NC-1 isolate-tachyzoites, reacted with seroconversion and a specific IFN-gamma response. Moreover, N. caninum DNA was demonstrated by a nested-PCR in the blood of all nine heifers and in brain, lungs, liver and uterine horn of several of them. In contrast, nine heifers inseminated with tachyzoite-free semen developed no antibody or IFN-gamma responses, and no parasite DNA was detected in blood or organs. At necropsy, viable embryos were detected in one and six of the infected and non-infected heifers, respectively. No specific Neospora DNA was detected in any of the embryos. This study provides evidence that intrauterine inoculation via contaminated semen cause N. caninum infection in cattle.

Observations on the fertilization and development of preimplantation bovine embryos in vitro in the presence of Tritrichomonas foetus

Tritrichomonas foetus, a world-wide distributed parasitic protozoan is a cause of infertility and abortion. There is no documented information on the susceptibility of bovine embryos to the parasite. To determine the effect of T. foetus on fertilization and embryonic development of preimplantation bovine embryos, we added approximately 10(4)/ml or 10(6)/ml T. foetus (Belfast strain) to sperm cells and oocytes prior to in vitro fertilization (IVF) or to presumptive zygotes 24 h post-fertilization. Light and scanning electron microscopy (SEM) revealed that exposure of oocytes or embryos at any stage of development to T. foetus caused rapid adhesion of the trichomonads to the embryonic intact zona pellucida (ZP) and to trophoblastic cells of hatched blastocysts. Treatment of contaminated embryos with 0.25% trypsin for 3 min did not render them free from T. foetus. Motile parasites were not observed after 18 h incubation in IVF medium, or after 72 h in synthetic oviductal fluid (SOF) embryo culture medium. The percentages of cleaved zygotes, blastocysts and hatched embryos resulting from culture of experimental and uninfected control groups of embryos were not different (P > 0.05). Tritrichomonas foetus was not detected in embryonic cells of ZP-intact or hatched embryos when examined by transmission electron microscopy (TEM). In conclusion, T. foetus has no detrimental effect on the fertilization and development of IVF embryos and the potential risk of transmission of trichomonosis is unlikely, due to the limited survival of the parasite in IVF culture conditions.

Review of Neospora caninum and neosporosis in animals

Neospora caninum is a coccidian parasite of animals. It is a major pathogen for cattle and dogs and it occasionally causes clinical infections in horses, goats, sheep, and deer. Domestic dogs are the only known definitive hosts for N. caninum. It is one of the most efficiently transmitted parasite of cattle and up to 90% of cattle in some herds are infected. Transplacental transmission is considered the major route of transmission of N. caninum in cattle. Neospora caninum is a major cause of abortion in cattle in many countries. To elicit protective immunity against abortion in cows that already harbor a latent infection is a major problem. This paper reviews information on biology, diagnosis, epidemiology and control of neosporosis in animals.

Evaluation of a single serological screening of dairy herds for Neospora caninum antibodies

Twenty-one dairy herds with a history of Neospora caninum-associated abortions were used for a longitudinal serological study. A total of 1,676 animals were blood sampled 3 times and used to evaluate a single serological screening for N. caninum antibodies. The results of the first serological screening were compared with the results based on three consecutive samples, whereby two or more positive or negative test results per animal were considered to determine its serological status as positive or negative, respectively. In both test regimes 95.3% of the animals had the same interpretation, of which 33.9% were seropositive, and 61.3% seronegative. Relative sensitivity of one-time sampling compared to three consecutive samplings was 94.7%, while relative specificity was 95.6%. Relative specificity differed between herds. Predictive values positive and negative of one-time sampling were 92.4 and 97%, respectively. The agreement between one-time sampling and three consecutive samplings, kappa, was 0.90. For evaluation of discrepant results age distribution and pedigree data were used to provide clues regarding likelihood of transmission. Age clustering of seropositive animals was interpreted to indicate a point source infection. Daughter-mother relationships were used for the interpretation of congenital infections. The proportion of congenital infection decreased with increasing parity of the mother. Seropositive heifers had 80% congenitally infected offspring, while in older cows 66% of the offspring was congenitally infected, possibly due an increased immunity to transplacental infection with age. It is concluded that a single serological screening of a whole herd in connection with an analysis of age distribution and pedigree data is a rapid and valid method to interpret the serologic status of individual animals and to study the mode of transmission of N. caninum.