Bovine Neospora abortion in north-eastern New South Wales

Using beef-breed semen in seropositive dams for the control of bovine neosporosis

A program for controlling bovine neosporosis based only on the use of beef semen, without culling seropositive animals, was evaluated in a closed dairy cattle herd over a 5-year period (2013-2017). The program was based on individual and periodic serological screenings to identify seropositive breeders. Seropositive cows were inseminated with beef-breed semen, thus excluding their descendants from the remount in order to prevent the vertical transmission of the disease. Seronegative animals, as well as heifers at first insemination, were tested before each insemination. Sera of 1097 cattle were examined by a commercial indirect ELISA for the detection of antibodies anti-Neospora caninum. To verify the difference in seropositivity values among years of sampling, statistical analysis through generalized estimation equations (GEEs) was performed, also considering the effects of age, lineages, and occurrence of abortion. A seroprevalence of 33.8% was found in the first screening. The prevalence and incidence of the infection within the herd decreased significantly in 2017 (P = 28.9%, I = 1.4%) (p-value = 0.0001). The family line investigation detected a higher risk of being seropositive for a cow born to a seropositive dam (p-value = 0.0001) than to a seronegative dam, decreasing both the apparently vertical and horizontal transmissions. The number of spontaneous abortions decreased after the first year of the study (23 in 2013 to 6 in 2017). Seropositive animals were associated with abortion events (p-value = 0.0001). Although an eradication of N. caninum was not achieved at the end of the study period, a significant reduction in prevalence and incidence of neosporosis in the herd and a reduction of the abortion rate was achieved with the application of this control plan in five years, without culling a high number of seropositive potential milk-producing animals.

Differential Gamma Interferon- and Tumor Necrosis Factor Alpha-Driven Cytokine Response Distinguishes Acute Infection of a Metatherian Host with Toxoplasma gondii and Neospora caninum

Toxoplasma gondii and Neospora caninum (both Apicomplexa) are closely related cyst-forming coccidian parasites that differ significantly in their host ranges and ability to cause disease. Unlike eutherian mammals, Australian marsupials (metatherian mammals) have long been thought to be highly susceptible to toxoplasmosis and neosporosis because of their historical isolation from the parasites. In this study, the carnivorous fat-tailed dunnart (Sminthopsis crassicaudata) was used as a disease model to investigate the immune response and susceptibility to infection of an Australian marsupial to T. gondii and N. caninum The disease outcome was more severe in N. caninum-infected dunnarts than in T. gondii-infected dunnarts, as shown by the severity of clinical and histopathological features of disease and higher tissue parasite burdens in the tissues evaluated. Transcriptome sequencing (RNA-seq) of spleens from infected dunnarts and mitogen-stimulated dunnart splenocytes was used to define the cytokine repertoires. Changes in mRNA expression during the time course of infection were measured using quantitative reverse transcription-PCR (qRT-PCR) for key Th1 (gamma interferon [IFN-γ] and tumor necrosis factor alpha [TNF-α]), Th2 (interleukin 4 [IL-4] and IL-6), and Th17 (IL-17A) cytokines. The results show qualitative differences in cytokine responses by the fat-tailed dunnart to infection with N. caninum and T. gondii Dunnarts infected with T. gondii were capable of mounting a more effective Th1 immune response than those infected with N. caninum, indicating the role of the immune response in the outcome scenarios of parasite infection in this marsupial mammal.

Neospora caninum and reproductive wastage in extensively managed Queensland beef herds

OBJECTIVE

To compare reproduction in extensively managed, tropically adapted beef cows that were either seropositive or seronegative to Neospora caninum.

DESIGN

Longitudinal study of cows within management groups.

METHODS

Compare pregnancy with weaning outcomes for 502 seropositive and 3255 seronegative cows in 25 management groups.

RESULTS

We found N. caninum in all herds, with an average of 20% of 2640 tested animals seropositive within management group; prevalence varied between 0% and 94%. At 7 of 10 sites assessed, there was evidence of horizontal transmission of N. caninum. There was no overall difference in pregnancy rate (79% vs 75%; P > 0.05), reproductive wastage after confirmed pregnancy diagnosis (11% vs 10%; P > 0.05) or weaning rate (67% vs 68%; P > 0.05) between seronegative and seropositive cows, respectively. In one herd where a combination of risk factors for N. caninum was present, a significant reduction in pregnancy rate occurred after the 6 months mating (85% vs 69%; P < 0.05). The fetal and calf losses observed were lowest in south-east Queensland (4.3% of 117 pregnancies), highest in north-west Queensland (15.5% of 413 pregnancies) and intermediate in north-east Queensland (10.2% of 1625 pregnancies). Other infectious agents that are known to cause reproductive wastage were endemic in many herds, though none appeared to cause significant fetal or calf loss in this study.

CONCLUSION

Despite a high prevalence of N. caninum, there was no apparent effect on beef cattle reproduction, but there is potential to cause reproductive wastage if known risk factors to neosporosis are in effect.

What is the global economic impact of Neospora caninum in cattle - the billion dollar question

Neospora caninum is regarded as one of the most important infectious causes of abortions in cattle worldwide, yet the global economic impact of the infection has not been established. A systematic review of the economic impact of N. caninum infections/abortions was conducted, searching PubMed with the terms 'cattle' and 'Neospora'. This yielded 769 publications and the abstracts were screened for economically relevant information (e.g. abortion prevalence and risk, serological prevalence). Further analysis was restricted to countries with at least five relevant publications. In total, 99 studies (12.9%) from 10 countries contained data from the beef industry (25 papers (25.3%)) and 72 papers (72.8%) from the dairy industry (with the remaining two papers (2.0%) describing general abortion statistics). The total annual cost of N. caninum infections/abortions was estimated to range from a median US $1.1 million in the New Zealand beef industry to an estimated median total of US $546.3 million impact per annum in the US dairy population. The estimate for the total median N. caninum-related losses exceeded US $1.298 billion per annum, ranging as high as US $2.380 billion. Nearly two-thirds of the losses were incurred by the dairy industry (US $842.9 million). Annual losses on individual dairy farms were estimated to reach a median of US $1,600.00, while on beef farms these costs amounted to just US $150.00. Pregnant cows and heifers were estimated to incur, on average, a loss due to N. caninum of less than US $20.00 for dairy and less than US $5.00 for beef. These loss estimates, however, rose to ∼US $110.00 and US $40.00, respectively, for N. caninum-infected pregnant dairy and beef cows. This estimate of global losses due to N. caninum, with the identification of clear target markets (countries, as well as cattle industries), should provide an incentive to develop treatment options and/or vaccines.

Australian dingoes are definitive hosts of Neospora caninum

To provide objective data on the potential role of dingoes (Canis lupus dingo) in the life cycle of Neospora caninum in Australia, the production of N. caninum oocysts by experimentally infected canids was investigated. Three dingo pups raised in captivity and three domestic dogs were fed tissue from calves infected with an Australian isolate of N. caninum, Nc-Nowra. Oocysts of N. caninum, confirmed by species-specific PCR, were shed in low numbers by one dingo pup at 12-14 days p.i. The remaining animals did not shed oocysts. Furthermore, the blood from two out of three dingoes tested positive for DNA of N. caninum using PCR tests at 14 and 28 days p.i. Oocyst shedding from the intestinal tract of a dingo demonstrates that dingoes are definitive hosts of N. caninum and horizontal transmission of N. caninum from dingoes to farm animals and wildlife may occur in Australia.

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.

If control of Neospora caninum infection is technically feasible does it make economic sense?

Recent work on Neospora caninum, a protozoan parasite that causes abortions in dairy cattle has focused on a number of different control options. Modelling has suggested the most effective options for control but the present paper argues that the most effective option might not necessarily be optimal from an economic point of view. Decision trees, using published quantitative data, were constructed to choose between four different control strategies. The costs of these interventions, such as 'test and cull', therapeutic treatment with a pharmaceutical, vaccination or "doing nothing" were compared, and modelled, in the first instance, on the New Zealand and Australian dairy situation. It is argued however, that the relative costs in other countries might be similar and that only the availability of a registered vaccine will change the decision tree outcomes, as does the within-herd prevalence of N. caninum infection. To "do nothing" emerged as the optimal economic choice for N. caninum infections/abortions up to a within-herd prevalence of 18%, when viewed over a 1-year horizon, or 21% when costs were calculated over a 5 years horizon. For a higher (>or=21%) within-herd prevalence of N. caninum infection vaccination provided the best (i.e. most economic) strategy. Despite being the most efficacious solutions, 'test and cull' or therapeutic treatment never provided a viable economic alternative to vaccination or "doing nothing". Decision tree analysis thus provided clear outcomes in terms of economically optimal strategies. The same approach is likely to be applicable to other countries and the beef industry, with only minor changes expected in the relationships of decisions versus within-herd prevalence of N. caninum infection.

Diagnosis of bovine neosporosis

The protozoan parasite Neospora caninum is a major cause of abortion in cattle. The diagnosis of neosporosis-associated mortality and abortion in cattle is difficult. In the present paper we review histologic, serologic, immunohistochemical, and molecular methods for dignosis of bovine neosporosis. Although not a routine method of diagnosis, methods to isolate viable N. caninum from bovine tissues are also reviewed.

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.

Neospora caninum: Serological follow-up in dairy cows during pregnancy

We conducted a longitudinal study to follow-up the anti-Neospora caninum serologic status in 30 initially seropositive and 83 initially seronegative cows during their pregnancy. Study cows were blood-sampled every other month during pregnancy until parturition. Blood serum samples were screened for anti-N. caninum antibodies by ELISA. Cows that seroconverted were re-tested by immunoblot as a confirmation test. Among 30 seropositive cows, 28 cows remained seropositive during the whole pregnancy, whereas 2 cows transiently tested negative at least once during pregnancy. Among 83 seronegative cows, 82 cows remained seronegative and 1 cow tested positive three times during the sixth, eighth and last month of pregnancy. As only 2 out of 30 seropositive animals and 1 out of 83 animals changed their serologic status during pregnancy, the study results indicate that there is only a minor temporal instability of anti-N. caninum antibody reactivity in adult cattle.

Recent advances in understanding the epidemiology of Neospora caninum in cattle

INTRODUCTION

Neospora caninum is the most frequently diagnosed cause of cattle abortion in New Zealand and is an important pathogen worldwide. The parasite has been found in aborted bovine foetuses and in puppies with neurological disease. Recent developments have provided new insights into the epidemiology of the disease that are reviewed in this article.

TRANSMISSION

Transplacental infection is of major importance in the spread of N. caninum overseas. Most congenital infections result in the birth of apparently healthy calves. Seroepidemiological studies indicate introduced point-source infections are also likely, as do investigations of abortion outbreaks in cattle herds attributed to N. caninum. Horizontal transmission is an important determinant of the stability of infection prevalence in a herd. Two potential sources of horizontal transmission that have recently been reported are: via a canine definitive host and; cow-to-calf transmission through pooled colostrum or milk. Transmission parameters for the organism have been estimated using mathematical modeling, to explore the epidemiology and options for control of N. caninum infection in dairy cattle in the absence of precise epidemiological data. LIFE-CYCLE: Seroepidemiologic studies, combined with the knowledge that dogs can be a definitive host, provide evidence supporting a dog-cattle life-cycle. The importance of dogs in the epidemiology of bovine neosporosis is not yet clear. It is likely that N. caninum oocysts in dog faeces could serve as a source of infection for cattle and recent studies have shown that the canine and bovine isolatesflare the same organism. Infection of cattle orally exposed to oocysts has been demonstrated experimentally but not in nature. It is not known if other wild carnivores may serve as definitive hosts of N. caninum.

CONCLUSION

Despite active research for over a decade, very little is known about the mechanisms of transmission of N. caninum. Vertical transmission is well documented but horizontal spread and the pathogenesis of abortion from this disease need further investigation. It is evident that, even with a very high probability of vertical transmission, some form of horizontal transmission is required for the disease to persist in a herd.

Prevalence of Neospora caninum infection in dairy cows and its consequences for reproductive management

This study was carried out to determine the prevalence of neosporosis in an area of intensive dairy production, in Portugal. Sera samples were obtained in a random basis from 114 cows in 49 herds (group A), and from 1237 cows in 36 herds with a history of abortion outbreaks (group B). All sera samples were tested for neosporosis by direct agglutination test (DAT). Additionally, attempts to isolate Neospora caninum in 42 aborted bovine fetuses from 38 dairy herds (group C) were carried out, utilizing a bioassay with immuno-depressed Swiss Webster mice. Parasitological confirmation was done by indirect fluorescent antibody test (IFAT). The prevalence of neosporosis in the group A was 28%. Group B had a significantly (P < 0.001) higher prevalence (46%) and Neospora caninum was isolated in 36% of the aborted fetuses (group C). These results indicate that neosporosis, a disease only recently (2001) diagnosed in Portugal, has a high prevalence in the country, particularly in populations with a story of abortion. Thus, neosporosis should systematically be considered in the differential diagnosis of abortion. In the context of embryo transfers, the importance of selecting Neospora-free embryo recipients is discussed, as well as the pertinence of assessing the Neospora status of traded and imported cattle.

Genetic Susceptibility to Neospora caninum Infection in Holstein Cattle in Ontario

Neospora caninum has been reported to be an important cause of endemic fetal loss and occasional abortion epidemics in cattle around the world. This study examined 12,016 sera collected from 9723 Holstein cows on 125 herds across Ontario in 1998, 1999, and 2000. An enzyme-linked immunosorbent assay was used to examine the sera for antibodies to N. caninum. The overall prevalence of N. caninum antibodies in the cattle was 11.2% and the prevalence in individual herds varied from 0 to 70.4%. Among 3109 daughter-dam pairs, 619 positive dams had 252 positive daughters, giving a detected vertical transmission rate of 40.7%. In contrast, there were only 6.7% positive daughters from negative dams (167 of 2490). Pedigree edits left 8031 cows with 1463 sires for estimation of heritability. Five genetic models (sire model, animal model, sire-dam model, a sire-maternal grandsire model, and a maternal effects model) with fixed effects of bleeding year-month, age of the animals, and herd were fitted to the data. The estimated heritability of susceptibility to N. caninum ranged between 0.084 and 0.124. The sire-maternal grandsire model and the maternal effects model provided better fit than the other models because the maternal genetic variance was much greater than the direct genetic variance. To reduce the incidence of N. caninum infection, more emphasis should be placed on management practices than on genetic selection.

Reproductive Losses due to Neospora caninum in a Beef Herd in Argentina

Reproductive losses in a beef herd of 857 heifers with a pregnancy rate of 86.3% are described. After pregnancy testing, 69 abortions were seen during a 3 month period. Before calving season, three heifers had delivered pre-mature non-viable calves. Serum samples from 58 of 69 aborted heifers were available for serological tests. In order to compare the seroprevalence in non-aborted vs. aborted heifers, 214 pregnant animals were bleed during the abortion storm. In addition, blood samples were collected from two heifers with pre-mature calves and from 16 heifers with their calves prior to colostrum intake. All available serum samples were tested for Neospora caninum antibodies using an indirect fluorescence antibody test (IFAT). Fifty-nine of 290 (20.3%) evaluated heifers were seropositive. Heifers that aborted and heifers with pre-mature calves were more likely to be seropositive than pregnant heifers and heifers with normal calves [odds ratio (OR), 12.01; 95% CI, 6.18-23.30]. Vaginal mucus from four aborted heifers, and samples from two aborted foetuses and three pre-mature calves were available. Laboratory tests for Tritrichomonas foetus, bacterial and viral isolation, and histological examination were performed. Culture from vaginal mucus and foetal samples were negative. Histological lesions consistent with neosporosis and positive immunohistochemistry (IHC) to N. caninum were found in one aborted foetus and in one pre-mature calf. It is the first description of reproductive losses because of N. caninum in beef herds in Argentina.

The effect of the dam-calf relationship on serostatus to Neospora caninum on 20 Costa Rican dairy farms

An epidemiological study was conducted on 20 dairy herds previously diagnosed as seropositive for Neospora caninum. The number of females per farm varies from 41 to 296. All females present on the farms were bled once in the period of July and August 2000. A total of 3002 females were bled. An indirect ELISA was used to determine the serostatus of the animals. The analysis of the data was performed in four steps: (1) descriptive statistics about the serological status and general characteristics of the cattle; (2) calculation of vertical and horizontal transmission; (3) an univariate analysis and, (4) a multivariate logistic regression analysis with herd as random effect. The within-herd seroprevalence varied between 25.0% (34/136) and 70.5% (203/288). Seven hundred and forty-seven dam-daughter pairs were available, involving daughters of any age. Daughters in the specific age-class of 2- and 3-years old had a higher seroprevalence (P<0.01) compared with younger and older age-classes. The risk of being seropositive when being born to a mother that tested seropositive (prevalence ratio (PR)) was 2.8-fold increased which coincides with a 5.3-fold increased odds. The probability of horizontal infection amounts to 0.22. The probability of a seropositive offspring due to vertical transmission was 0.64 (attributable fraction among exposed (AFexp)). The multivariate logistic regression showed a significant 6.0-fold increased odds for being seropositive when born from a seropositive mother. Also the within-herd seroprevalence level was significantly associated with the serostatus of the daughters. In the specific conditions of the dairy herds involved in this study, the serostatus of the cows should be not used as a predictor of the serostatus of daughters due to the increased probability of horizontal transmission.

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.

Risk of abortion associated with Neospora caninum during different lactations and evidence of congenital transmission in dairy cows

OBJECTIVE

To examine the relationship between exposure to Neospora caninum and abortion in dairy cows during their first, second, third, and fourth or later lactations and to establish the main mode of transmission in female calves from birth until their first pregnancy was terminated by abortion or parturition.

DESIGN

Prospective observational study.

ANIMALS

460 Holstein cows and 79 female calves.

PROCEDURE

Cows were classified as seropositive or seronegative to N caninum within 7 days after calving; incidence of abortion was compared between groups during different lactations. Blood samples were collected from female calves before ingestion of colostrum and every 6 months until their first pregnancy was terminated by abortion or parturition; number of seropositive calves was compared between seropositive and seronegative dams.

RESULTS

During the first pregnancy of their second lactation, risk of abortion for seropositive cows was 2.8 times that of seronegative cows. Among 10 calves born to seropositive cows, 4 were classified as seropositive at birth and thereafter. Among 69 calves born to seronegative cows, all were classified as seronegative at birth; 67 calves remained seronegative thereafter.

CONCLUSIONS AND CLINICAL RELEVANCE

Exposure to N caninum alone was not significantly associated with abortion in cows during the first, third, and fourth or later lactations. Seropositive cows that have aborted previously may have subsequent abortions attributable to N caninum. Congenital infection was the main mode of N caninum transmission in a cohort of female calves.

Prevalence of antibodies to Neospora caninum in Korean native beef cattle

A total of 438 sera from Korean native beef cattle in 9 provinces were tested for Neospora caninum antibodies using an immunofluorescent antibody test (IFAT). Eighteen (4.1%) cattle were positive by IFAT. The titers ranged from 1:200 (10 animals), 1:400 (5 animals), 1:800 (2 animals) to 1:1,600 (1 animal). Although the seroprevalence was slightly higher in Chungnam (8.9%), this was not significantly different from those noted in Kyunggi, Kangwon, Kyungbuk, Kyungnam, and Cheju provinces. Sera obtained from beef cattle in the provinces of Chungbuk, Jeonbuk and Jeonnam were all negative. Neospora positive sera were also tested for anti-Toxoplasma gondii antibodies using a commercial latex agglutination test (LAT). Antibody to T. gondii was detected in only 1 (5.6%) of 18 N. caninum positive sera. These results indicate that N. caninum and T. gondii infection are present at a low level in the Korean native beef cattle.

Characterisation of the first Australian isolate of Neospora caninum from cattle

OBJECTIVE

To isolate Neospora caninum from a congenitally infected calf.

PROCEDURE

A calf was obtained from a N. caninum infected dam maintained in a dairy herd of Holstein-Friesian cattle located on the south coast of NSW near Nowra. The calf was euthanased and samples collected for serology and pathology. Samples of brain and spinal cord of the calf were homogenised and injected into immunocompromised mice in an attempt to recover protozoa by in vivo culture. Sequential passage of brain homogenate through IFNgammaPKO mice was performed and tissue culture flasks were inoculated with brain homogenate. Parasites were identified by electron microscopy and DNA sequencing. The antigen profile of the isolate was analysed using Western blotting. Pathogenicity was examined in BALB/c mice and transmission of the parasite during pregnancy was examined in Qs mice.

RESULTS

The calf was seropositive for N. caninum and histopathological examination of sections of cerebrum identified lesions consistent with a very mild infection with N. caninum. The parasites isolated using tissue culture were identified as N. caninum, based on the sequence of the ribosomal DNA and electron microscopy. The antigen profile of the new isolate was similar to that of the NC-Liverpool isolate, but quite different from that of Toxoplasma gondii. In BALB/c mice inoculated with the new isolate, severe clinical signs developed in only three of ten infected mice, compared with six of ten mice infected with NC-Liverpool. Mild to moderate nonsuppurative encephalitis was observed in BALB/c mice infected with the new isolate, compared with mice infected with NC-Liverpool, that developed severe nonsuppurative encephalitis. Transplacental transmission of the isolate arising from an acute infection during pregnancy occurred in about 87% of pups.

CONCLUSION

This is the first isolation of bovine Neospora caninum in Australia. This isolate, called NC-Nowra, appears to be a less virulent form and may prove to be a suitable candidate for vaccine development.

Control options forNeospora caninuminfections in cattle — current state of knowledge

This article reviews control options for Neospora caninum infection and abortion in cattle, drawing on published literature and the authors' own research in this field. Apart from the successful use of embryo transfer to prevent congenital infection in calves born to infected cows, there are currently no accepted control methods for the prevention of abortions in cattle. The epidemiological data at hand suggest that concomitant infections with bovine pestivirus increase the risk of abortion significantly and that these infections, for which effective vaccines exist, should therefore be controlled. While vertical transmission appears to be the major route of infection in cattle, there is also a role for postnatal transmission, involving a definitive host. Presently, the control of dogs and their access to bovine tissues, particularly potentially infected placentae and other foetal tissues, appear to be the most prudent control methods. There are some indications that vaccination against N. caninum may aid in the prevention of abortions. Suggestions for control options are limited by our current lack of actual experiences with control strategies. Further practical fieldwork is needed in this area.

Factors associated with Neospora caninum serostatus in cattle of 20 specialised Costa Rican dairy herds

Twenty-five specialised Costa Rican dairy farms (located in the Poás area) were used to determine neosporosis seroprevalence and the association of seropositivity with environmental and management factors. The farms involved were selected intentionally and all of them use VAMPP 5.1 (Veterinary Automated Management and Production Control Programme) as management-information system. Holstein-Friesian, Jersey and crosses between them were the most-frequent breeds in these herds. The number of females per farm varied from 41 to 296. Our cross-sectional study had two phases. In the first phase, we determined the presence or absence of seropositivity at herd level. For the second phase, all females in 20 seropositive farms were bled. Serum samples were tested for antibodies to Neospora caninum using an indirect enzyme-linked immunosorbent assay (ELISA). A questionnaire with factors mentioned in the literature was administered to the farmers. Logistic regression (LR with herd as random effect) was used to assess the relationships of the serostatus at the individual level with characteristics of the cows and environmental factors. In the first phase all herds had >20% seropositive females; therefore, all herds were eligible for the second phase. In the second phase, the overall prevalence was 39.7% (1191/3002), and within-herd prevalences were between 25.0 and 70.5%. Age 3-6 years, parity < or =2 of the dam of the cow, Jersey breed and lack of purposive sampling to diagnose abortive infectious disease were associated with positive serostatus; other management and environmental factors did not show significant associations. The lack of association between management and environmental factors with serostatus might be because all farms were exposed to a considerable number of potential factors. That all herds of this study were seropositive for neosporosis and the within-herd prevalence was considerable raises questions about how far the infection is spread in other dairy areas of Costa Rica.

Prevalence ofNeosporaantibodies in beef cattle in New Zealand

AIM

To estimate the prevalence of Neospora infection in a sample of New Zealand beef cattle.

METHODS

The prevalence of Neospora caninum infection in New Zealand beef cattle was estimated by collecting blood at slaughter from 499 beef cattle from 40 different farms at 2 slaughter plants in the North Island and 1 in the lower South Island . Sera were tested using an ELISA against Neospora tachyzoite antigen.

RESULTS

The prevalence of seropositive cattle was 2.5% (n=120), 3.6% (n=166) and 2.3% (n=213) at the plants surveyed, the overall prevalence being 2.8%. The serologically positive cattle came from 9 farms, 3 of which had more than 1 positive animal. The highest prevalence recorded amongst animals from 1 farm was 4/13 (31%), in a group of young steers.

CONCLUSION

Neosporosis appears to be present at a lower level in the New Zealand beef cattle population than in the New Zealand dairy cattle population. Nevertheless, from the high seroprevalence evident amongst young cattle on 1 farm, we suggest that Neospora may be a cause of infertility in beef cattle in this country.

A European perspective on Neospora caninum

Since the identification of Neospora caninum in 1984 as a parasite separate from Toxoplasma gondii by Bjerkas et al., and its subsequent characterization and classification in 1988 by Dubey and co-workers, this parasite has attracted increasing attention, primarily as an important causative agent of abortion in cattle and neuromuscular disease in dogs, but also as a complementary model system to T. gondii for investigating the basic biology of intracellular parasitism. During November 11-14, 1999, the COST 820 Annual meeting (Vaccines against coccidioses) took place in Interlaken, Switzerland. Almost half of the papers presented at that meeting were on N. caninum and neosporosis, reflecting the increasing awareness of the importance of this parasite on part of the scientific community in Europe. On the occasion of the meeting, participants in this COST Action involved in Neospora research in Europe were asked to participate in this invited review in order to document the growing interest in N. caninum and the disease it causes. Thus, this paper is a unique collection of contributions provided by several European experts in the field. It is comprised of 10 reviews or original papers on different aspects of Neospora research including epidemiology, immunology, application and development of serological tools, and molecular characterisation of the parasite currently carried out throughout Europe. In addition, two distinguished invited speakers from overseas (Milton McAllister and John Ellis) provided valuable contributions. This invited review demonstrates that the COST 820 Action has brought together scientists from all over Europe and other parts of the world, and has laid the basis for many fruitful collaborations. The studies described here will contribute in assessing the relevance of neosporosis as a potential risk factor not only for animals, but also for human health.

Neospora caninum infections in Australia and New Zealand

OBJECTIVE

To review the current state of knowledge of Neospora caninum infections with particular reference to Australia and New Zealand.

PROCEDURE

Several databases were searched electronically including Medline, Current Contents, Vet CD using several key words (Neospora caninum, neosporosis, abortion, cattle, dogs) and authors names. References in original articles were also traced and use made of the author's own original research in the field.

CONCLUSION

N caninum is recognised worldwide and is also widespread, in particular in dairy cattle, in Australia and New Zealand. It has been reported in both countries retrospectively (in dogs) from the early 1970s. Abortion storms in dairy herds appear to be the most common feature. Recent reports indicate that the dog is the definitive host, in which the sexual cycle is completed. Further studies are however required to establish important aspects of the epidemiology, such as mode of transmission. In the absence of an effective vaccine, the most effective control strategy is selective culling of infected animals and the prevention of access of dogs to expelled placentas and foetuses and, possibly, to raw beef.

Seroprevalence of Neospora caninum infection following an abortion outbreak in a dairy cattle herd

OBJECTIVE

To investigate the seroprevalence of Neospora caninum infection in a commercial dairy cattle herd, 15 months after detection of an abortion outbreak.

PROCEDURE

Sera from the whole herd (n = 266) were examined for N caninum antibodies by indirect fluorescent antibody test (IFAT) and immunoblot analysis. Herd records were reviewed to collate serological results with abortion history, proximity to calving, and pedigree data.

RESULTS

The seroprevalence of N caninum infection was 24% (63/266) for IFAT titre > or = 160, 29% (78/266) for immunoblot positive (+ve), and 31% (82/266) for IFAT > or = 160 and/or immunoblot +ve; 94% (59/63) of animals with IFAT > or = 160 were immunoblot +ve. The association between seropositivity (IFAT > or = 160 and/or immunoblot +ve) and history of abortion was highly significant (P < 0.001); the seroprevalence was 86% (18/21) in aborting cows, compared with 30% (50/164) in non-aborting animals. The abortion rate for seropositive cows was 26% (18/68) compared with 3% (3/117) for seronegative animals. IFAT titres of infected cows were higher within 2 months of calving than at other times (P < 0.001). The association between seropositivity in dams and daughters was highly significant (P = 0.009).

CONCLUSIONS

The abortions were associated with N caninum infection and there was evidence of reactivation of latent infection close to calving and congenital transmission of infection. Immunodominant antigens identified by immunoblots may prove useful for improved diagnostic tests.

Estimation of vertical and horizontal transmission parameters of Neospora caninum infections in dairy cattle

Transmission parameters of Neospora caninum infections in dairy cattle were determined in six herds with a history of Neospora-associated abortions, using an antibody-detection ELISA to detect evidence of infection. A total of 124 seropositive dams and their calves were tested at calving to estimate vertical transmission, and 154 seronegative heifers were monitored prospectively from birth for evidence of post-natal infection. The probability of vertical transmission was very high; 95.2% (95% confidence interval: 89.8%, 98.2%) of the seropositive dams produced calves that were seropositive prior to consumption of colostrum. In the prospective study, three heifers seroconverted, by 1, 8 and 16 months of age, and the overall incidence rate of seroconversion was 1.9 per 100 heifer-years at risk, ranging from 0 to 4.1 per 100 heifer-years at risk within herds. If heifers with inconclusive ELISA results were included in the analysis, the incidence rate of seroconversion was 3.8 per 100 heifer-years at risk, ranging from 0 to 8.3 per 100 heifer-years at risk within herds. This study showed that vertical transmission was the major route involved in the spread of N. caninum in these herds, and that there was only a low detectable level of horizontal transmission. However, further studies are needed to provide parasitological evidence of infection in those heifers that seroconverted.

Development of a single tube nested polymerase chain reaction assay for the detection of Neospora caninum DNA

Sensitive detection techniques are required to study the life cycle of Neospora caninum and to diagnose infections. In this study, we describe the development of a PCR assay for N. caninum based on two successive amplification steps within a single tube. This technique, called single tube nested PCR, was sensitive to a single copy of target sequence, and able to amplify parasite DNA from biological specimens such as formalin-fixed, paraffin-embedded tissues of naturally infected dogs and cattle. An internal standard (or PCR MIMIC) is also described. This assay should prove useful in the study of the biology of N. caninum.

Mathematical models of Neospora caninum infection in dairy cattle: transmission and options for control

The transmission and control of Neospora caninum infection in dairy cattle was examined using deterministic and stochastic models. Parameter estimates were derived from recent studies conducted in the UK and from the published literature. Three routes of transmission were considered: maternal vertical transmission with a high probability (0.95), horizontal transmission from infected cattle within the herd, and horizontal transmission from an independent external source. Putative infection via pooled colostrum was used as an example of within-herd horizontal transmission, and the recent finding that the dog is a definitive host of N. caninum supported the inclusion of an external independent source of infection. The predicted amount of horizontal transmission required to maintain infection at levels commonly observed in field studies in the UK and elsewhere, was consistent with that observed in studies of post-natal seroconversion (0.85-9.0 per 100 cow-years). A stochastic version of the model was used to simulate the spread of infection in herds of 100 cattle, with a mean infection prevalence similar to that observed in UK studies (around 20%). The distributions of infected and uninfected cattle corresponded closely to Normal distributions, with S.D.s of 6.3 and 7.0, respectively. Control measures were considered by altering birth, death and horizontal transmission parameters. A policy of annual culling of infected cattle very rapidly reduced the prevalence of infection, and was shown to be the most effective method of control in the short term. Not breeding replacements from infected cattle was also effective in the short term, particularly in herds with a higher turnover of cattle. However, the long-term effectiveness of these measures depended on the amount and source of horizontal infection. If the level of within-herd transmission was above a critical threshold, then a combination of reducing within-herd, and blocking external sources of transmission was required to permanently eliminate infection.

Herd-specific and age-specific seroprevalence of Neospora caninum in 14 British dairy herds

All the cattle in 14 dairy herds in England were tested for Neospora caninum-specific antibodies with a commercial ELISA. Three of the herds had had sporadic abortions, eight had had endemic abortions and three had had epidemic abortions associated with N caninum before the study. Of 4295 cattle tested, 17.1 per cent were seropositive and the herd-specific prevalence ranged from 7.3 per cent to 44.8 per cent. No significant effect of either herd size (P = 0.988), endemic (P = 0.869) or epidemic (P = 0.138) patterns of abortion on herd-specific prevalence was found by using logistic regression analysis. There was no evidence in any herd of a significant increase in prevalence with age; the prevalence in seven-to 12-month-old cattle was not significantly different (P > 0.400) from the prevalence in older cattle, except that there was a significantly lower prevalence (P = 0.017) in 13-to 24-month-old cattle. The results of this study are consistent with vertical transmission being the major route of N caninum transmission in these herds.

Herd-based diagnosis of Neospora caninum-induced endemic and epidemic abortion in cows and evidence for congenital and postnatal transmission

Aborting and nonaborting cows and their dams or daughters were studied to determine if herd abortion problems were associated with the presence of Neospora caninum antibodies and to estimate when aborting cows may have acquired the infection. Cows were sampled from 20 herds that had experienced an abortion epidemic presumed to have been caused by N. caninum and from 2 herds experiencing endemic abortion. Seroprevalence for 14 herds experiencing an epidemic ranged from 7% to 70%, as estimated by enzyme-linked immunosorbent assay. A strong association between seropositivity and abortion was found for only 5 of 14 herds with a presumed diagnosis of N. caninum abortion (P < or = 0.015, lower 95% confidence interval of odds ratio > or = 1.2), indicating N. caninum may be overdiagnosed as the cause of an abortion epidemic in some herds. No association was found between dam and daughter seropositivity for herds experiencing an epidemic (P > or = 0.17), suggesting that most cows aborting during an epidemic were infected postnatally. For the 2 herds with endemic abortion (A, B), odds of an aborting cow having N. caninum antibodies were 3.4-fold (herd A) and 7.0-fold (herd B) higher than odds for nonaborting cows (P < or = 0.05). Cows that aborted a fetus infected with N. caninum were more likely to have had a previous seropositive daughter than were nonaborting seronegative cows (P < or = 0.0025), suggesting that infection had been acquired before conception of the aborted fetus.

A review of Neospora caninum and neosporosis

Neospora caninum is a recently recognized protozoan parasite of animals, which until 1988 was misidentified as Toxoplasma gondii. Its life cycle is unknown. Transplacental transmission is the only recognized mode of transmission. It has a wide host range, but its zoonotic potential is unknown. Neosporosis is a major cause of abortion in cattle in many countries. It is also an important cause of neuromuscular paralysis in dogs. This paper reviews information on parasite structure, life cycle, biology, clinical signs, diagnosis, treatment and control.

Experimental neosporosis in pregnant ewes and their offspring

Six groups of six pregnant ewes each were inoculated with 170,000 or 1,700,000 tachyzoites of Neospora caninum on gestation day 65, 90, or 120. All ewes seroconverted, and none showed signs of illness other than abortion. Regardless of the inoculum dose, all ewes inoculated on gestation day 65 aborted; ewes inoculated on gestation day 90 aborted, gave birth to weak lambs, or gave birth to clinically normal lambs; and all ewes inoculated on gestation day 120 gave birth to clinically normal lambs. Using an immunohistological procedure that stains bradyzoites, we observed protozoal cysts in brains of 11 of 29 (38%) aborted fetuses, in one of four (25%) weak lambs, and in seven of 18 (39%) clinically normal lambs. Cysts were not observed in extraneural tissues from two clinically normal lambs that had cysts in the brain. No evidence of infection was observed in tissues of five ewes examined using an immunohistological procedure that stains N. caninum tachyzoites and bradyzoites. Multifocal nonsuppurative encephalitis was observed in 46 of 51 (90%) aborted, weak, or clinically normal lambs. Cerebral necrosis, dystrophic mineralization, and meningitis were also commonly identified in live and aborted lambs (even when severely autolyzed). Nonsuppurative, necrotizing placentitis was observed in 15 of 17 (88%) placentas. Nonsuppurative myositis was common in fetuses but not in live lambs. Inflammation occurred less frequently in liver and lung. Clinical and pathological features of neosporosis in sheep closely resemble those of bovine neosporosis and ovine toxoplasmosis. Although abortion caused by naturally occurring neosporosis in sheep has not been reported, diagnosticians should carefully distinguish between neosporosis and toxoplasmosis in cases of ovine protozoal abortion unless future investigations exclude the likelihood of naturally acquired neosporosis in sheep.

Evidence suggesting a point source exposure in an outbreak of bovine abortion due to neosporosis

A Holstein dairy farm suffered an abortion outbreak due to neosporosis. Abortion losses were > 18%. Cows with the highest Neospora antibody titers were at the greatest risk of aborting. Mummified fetuses were found after the 43rd day of the outbreak. The epidemic curve was suggestive of a point source exposure, which is consistent with the hypothesis that Neospora can be spread by a definitive host.