Failure of dogs to shed oocysts after being fed bovine fetuses naturally infected by Neospora caninum

Neospora caninum is a protozoan that causes abortion in cattle. The dog has recently been identified as a definitive host for N. caninum. To verify if bovine fetuses can infect dogs, nine 2-4-month-old dogs were fed bovine fetuses naturally infected by N. caninum. None of the dogs excreted oocysts, seroconverted, had clinical signs or lesions compatible with N. caninum infection. Additional studies will be necessary to determine the natural mode of infection of dogs by N. caninum.     

Diagnosis and epidemiology of Neospora caninum-associated abortions in cattle]

Neospora caninum, a recently discovered protozoan parasite closely related to Toxoplasma gondii, has world-wide been recognized as an important cause of bovine abortion. N. caninum possesses a wide host range. The dog can be a definitive host for N. caninum. In cattle, the infection is transmitted transplacentally with high efficiency, while the majority of congenitally infected calves is clinically normal at birth and thereafter. Whether horizontal transmission occurs in cattle and whether this potential mode of transmission has epidemiological significance, remains to be elucidated. N. caninum-associated abortions can occur in epidemic or endemic form in a herd. The clinical symptoms of bovine neosporosis are confined to the occurrence of abortion, stillbirth and weak calves. Multifocal nonsuppurative encephalitis represents the most frequent pathohistological finding in N. caninum-associated abortions. The causative agent can be demonstrated by immunohistochemistry or polymerase chain reaction. Serological techniques can be used for indirect diagnosis. On the basis of the available diagnostic methods and the present knowledge about the epidemiology of the infection proposals are made regarding diagnosis, epidemiological assessment and prophylaxis of N. caninum-associated abortion problems in cattle herds.     

Studies on the role of the red fox (Vulpes vulpes) as a potential definitive host of Neospora caninum

Neospora (N.) caninum is a protozoan parasite which is regarded as a major cause of abortion in cattle. Dogs and coyotes are definitive hosts of N. caninum which may shed environmentally resistant stages, oocysts, in their feces. Epidemiological studies in Germany showed that the presence of dogs increased the risk of a bovine herd to be N. caninum-positive in a bulk-milk ELISA test. However, there were also N. caninum-positive herds where dogs were not kept together with cattle.This leads to the question whether canids other than dogs, e.g., foxes, might be involved in the horizontal transmission of N. caninum. Therefore, the aim of our examinations in wild animals was to find out whether there are indications for a sylvatic cycle with foxes as definitive hosts and deer, roe deer and wild mice samples contained structures which resembled those of coccidian oocysts. In 13 of these 65 samples coccidian DNA was detected using a 18S rRNA gene based polymerase chain reaction (PCR).The examination of the 65 samples in a N. caninum-specific PCR revealed no positive result. Hammondia (H.) heydorni-DNA was detected in two samples. In addition, brain samples from 528 foxes, 224 wild mice, 16 deer and roe deer as well as from 1 wild boar were examined for the presence of N. caninum DNA by real time PCR. All samples tested negative by PCR. In conclusion, our study yielded no evidence indicating that the examined animals were part of a sylvatic cycle for N. caninum.     

The role of the dog in the epidemiology of neosporosis in cattle

Neospora caninum is an intracellular protozoan parasite that was discovered in a dog in 1988. Since then, N. caninum has been demonstrated in a variety of animal species and it has been recognized as an important cause of abortion in cattle. An infection with N. caninum can be maintained in cattle herds for several generations by transplacental transmission from cow to calf. Recently, it was demonstrated that dogs can act as definitive hosts of N. caninum and therefore may be a source of infection for other species by shedding oocysts. Further evidence of a role of the dog in spreading the infection to cattle has been derived from epidemiological studies. The present state of knowledge is reviewed in this paper.     

Prevalence of antibodies to Neospora caninum in dogs from Amazon,Brazil

Neospora caninum is an important cause of abortion in dairy cattle worldwide. Dogs are important in the epidemiology of this parasite because they are the only hosts known to excrete N. caninum oocysts. Antibodies to N. caninum were assayed in serum samples from 157 dogs from Monte Negro, Rond?nia, Amazon, Brazil using the indirect fluorescent antibody test. Antibodies to N. caninum were found in 13 (8.3%) of dogs in titers of 1:50 in 1, 1:100 in 2, 1:200 in 5, 1:800 in 1, 1:1600 in 2, and 1:3200 in 2 dogs. These data indicate that N. caninum infection is prevalent even in remote areas of the Amazon.     

Recent advances in Neospora and neosporosis.

Neospora caninum has emerged as a major cause of abortion in cattle in many countries. This paper reviews recent advances in the life cycle and biology of Neospora with the emphasis on bovine neosporosis. The role of the recently discovered oocyst stage of N. caninum in the epidemiology of neosporosis is discussed. Progress made in serologic diagnosis of N. caninum infection is discussed. There is no vaccine for preventing Neospora-induced abortions in cattle or to prevent oocyst shedding in dogs.     

Outbreak of abortion associated with Neospora caninum infection in a beef herd

Abortion outbreaks caused by infection with Neospora caninum in beef cattle have not been well documented. Neospora caninum infection was confirmed in 4 fetuses that were aborted by cattle in a 350-head beef herd; an additional 58 cattle aborted during the next 2.5 months. Overall, 44.4% (157/354) of the cattle in the herd did not become pregnant or experienced fetal loss during this period. Initially, 81.3% (282/347) of the herd was seropositive for antibodies to N caninum, and seropositive cows were 6.2 times as likely to not be pregnant as were seronegative cows. Other potential causes of abortion were not identified in this herd. Following the outbreak, few cattle in the herd or in a second exposed herd seroconverted, but high antibody titers persisted in most seropositive cattle through the end of the calving season. Evidence of cow-to-fetus transmission of the organism was detected in > 82% of seropositive cows.     

Neospora abortions in dairy cattle: diagnosis, mode of transmission and control

AIM: To determine the contribution of Neospora caninum to abortions on a dairy farm in NSW (Australia), determine the mode of transmission and develop and trial a control option for infection. METHODS: Two whole herd bleeds were conducted 12 months apart and the association between serological status and abortion events were calculated for a number of bovine abortifacients. Family trees were constructed for N. caninum seropositive cattle in the herd. Some N. caninum seropositive cows were culled from the herd and no female offspring was retained from seropositive cows. RESULTS: At the first whole-herd bleed in December 2002 a seroprevalence of 10.2% for N. caninum infection was detected. Cows with N. caninum infection were 13 times more likely to abort than uninfected ones. Seventy-five percent of seropositive animals in the herd were related, suggesting a high degree of congenital infection/transmission. Only 15% of infections were likely to be postnatally acquired. Selective culling of seropositive cows and not breeding from them reduced the number of seropositive animals. Only one newly sero-converted cow was detected at the second whole-herd bleed 12 months later. CONCLUSIONS: Seroepidemiological approaches were able to establish a high degree of association between N. caninum infection and low-level abortion in the dairy herd. Vertical transmission of infection was the predominant mode of infection and hence control efforts aimed at selectively culling seropositive animals from the herd were highly successful in reducing the level of infection.     

Experimental infection of dogs (Canis familiaris) with sporulated oocysts of Neospora caninum

Neospora caninum is widely distributed in the world and this parasite is one of the major causes of abortion in cattle. Dogs and coyotes are definitive hosts of N. caninum and several species of domestic and wild animals are intermediate hosts. Dogs can become infected by the ingestion of tissues containing cysts and then excrete oocysts. It is not yet known whether sporulated oocysts are able to induce a patent infection in dogs, i.e. a shedding of N. caninum oocysts in feces. The objective of this study was to experimentally examine the infection of dogs by sporulated oocysts. The oocysts used in the experiment were obtained by feeding dogs with brain of buffaloes (Bubalus bubalis) positive for anti-N. caninum antibodies by indirect fluorescent antibody test (IFAT ≥200). Oocysts shed by these dogs were confirmed to be N. caninum by molecular methods and by bioassay in gerbils, and sporulated N. caninum oocysts were used for the oral infection of four dogs. The dogs were 8 weeks old and negative for antibodies to N. caninum and Toxoplasma gondii. Dogs 1 and 4 received an inoculum of 10,000 sporulated oocysts each; dog 2 an inoculum of 5000 sporulated oocysts and dog 3 received 1000 sporulated oocysts of N. caninum. The total feces excreted by these dogs were collected and examined daily for a period of 30 days. No oocysts were found in their feces. The dogs were monitored monthly for a 6-month period to observe a possible seroconversion and when this occurred the animals were eliminated from the experiment. Dogs 1 and 4 seroconverted 1 month after the infection with titer, in the IFAT, of 1600 and 800, respectively; the other two dogs presented no seroconvertion during the 6-month period. Dogs 1 and 2 were euthanized 180 days after infection and were examined for the detection of N. caninum in tissues (brain, muscle, lymph node, liver, lung, heart and bone marrow) by immunohistochemistry and PCR with negative results in both techniques. Bioassay in gerbils with brain of these dogs was also performed and again the results were negative. In conclusion, dogs infected with sporulated oocysts of N. caninum were not able to shed oocysts in feces. However, a higher dose of infection stimulated the production of antibodies against N. caninum in the dogs.     

Point source exposure of cattle to Neospora caninum consistent with periods of common housing and feeding and related to the introduction of a dog

Eight dairy herds with evidence of post-natal transmission of Neospora caninum were used to test the hypothesis of a point source exposure by a retrospective analysis of the housing and feeding of infected age-groups. The first N. caninum-associated abortion or birth of N. caninum-seropositive offspring from the post-natally infected age-group was considered as the first indication of the infection. In seven of the eight dairy herds, a point source exposure to N. caninum of the infected age-groups was found during a limited period of common housing and feeding. In all herds studied, the analysis indicated that the cattle had been infected shortly before the first abortions occurred. In all, except one herd, the post-natal infection was more directly related to housing than to feeding. Therefore, it appeared that the feed was contaminated in the feeding alley. In one herd, the total mixed ration was found to be the probable path of infection. In all farms studied, a new dog (young, adult dog or litter) had been introduced within a period of 1.5 years prior to the first indication of N. caninum infection in the cattle. As there was evidence in all herds of vertical transmission of neosporosis for years, it is hypothesized that the newly introduced dog was infected with N. caninum by materials from already infected cattle and subsequently transmitted the infection to other cattle by shedding of oocysts.     

Occurrence of Neospora caninum antibodies in sera from dogs of the city of São Paulo,Brazil

Neospora caninum is an important cause of abortion in dairy cattle worldwide. Dogs are important in the epidemiology of this parasite because they are the only hosts known to excrete N. caninum oocysts. In order to understand the prevalence of N. caninum in dogs, sera from 500 owned dogs and from over 600 feral street dogs from the city of S?o Paulo, Brazil were assayed for antibodies to N. caninum. Sera were examined by the Neospora agglutination test (NAT) using mouse-derived tachyzoites. Antibodies (> or =1:25) to N. caninum were found in nearly 10% (49/500) of owned dogs and in 25% (151/611) of stray dogs. NAT titers for owned dogs were 1:25 in 28 (5.6%) dogs, 1:50 in 20 (4%) dogs, and > or =1:500 in 1 (0.2%) dog. NAT titers for stray dogs were 1:25 in 79 (12.9%) dogs, 1:50 in 68 (11.1%) dogs, and > or =1:500 in 4 (0.6%) dogs. These data indicate that feral dogs may be important in the epidemiology of N. caninum infection.     

Control options for Neospora caninum infections 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.     

Shedding of Neospora caninum oocysts by dogs fed different tissues from naturally infected cattle

Neospora caninum is one of the most important causes of abortion in dairy cattle worldwide. The distribution of N. caninum in tissues of adult cattle is unknown and the parasite has not been demonstrated histologically in tissues of cows. In the present study the distribution of N. caninum in different tissues of adult cattle was evaluated by bioassays in dogs. Seventeen dogs (2-3 month-old) were fed different tissues of 4 naturally exposed adult cattle (indirect fluorescent antibody test N. caninum titer ≥ 400): 5 were fed with masseter; 5 with heart, 3 with liver, 4 with brain, and 3 pups were used as non-infected control. Two dogs fed masseter, 2 fed heart, 1 fed liver, and 3 fed brain shed oocysts, and all dogs presented no seroconvertion to N. caninum during the observation period of 4 weeks. The oocysts were confirmed as N. caninum based on the detection of N. caninum-specific DNA by PCR and sequencing. The results indicate that dogs can be infected by N. caninum with different tissues of infected cattle.     

Vertical and horizontal transmission of Neospora caninum in dairy herds in Québec

Neospora caninum is an important cause of abortion in dairy cattle. The objective of this observational study was to estimate the rate of vertical transmission of N. caninum in dairy herds in Québec and to investigate horizontal transmission in the same herds. The genealogy of cows from 23 dairy herds were examined. Prevalence of seropositive animals in herds studied varied from 4.3% to 61.8% (average, 21.9%). The overall rate of vertical transmission was estimated to be 44.4%, varying from 0% to 85.7%. Seven cases of horizontal transmission were identified in 6 of the 23 herds studied. Estimated vertical transmission rate varied from herd to herd, but appeared to be higher in herds with a high prevalence of seropositive animals. Although horizontal transmission was identified in 6 herds, it does not appear to be the major route of infection for N. caninum.     

Seroprevalence of Neospora caninum infection in dairy and beef cattle in Paraguay

Seroprevalence of Neospora caninum in 879 beef and dairy cattle in different locations of Paraguay was determined by an ELISA. In the survey, 262 (29.8%) cattle were positive to N. caninum, and animals with anti-Neospora antibody titre were observed in all the locations tested in the country. Serum samples taken from a herd that exhibited persistent abortion had the highest percentage of animals being positive to the parasite (17/30, 56.7%). In the same herd, abortion was significantly more likely in animals with high anti-Neospora antibody titre. Immunoblot analysis demonstrated that the banding pattern from positive Paraguayan cattle was similar to that seen with the positive control sample. In conclusion, N. caninum infection is present among Paraguayan beef and dairy cattle, and it may be an important cause of bovine abortion in Paraguay.     

Risk factors for canine neosporosis in farm and kennel dogs in southern Italy

Neosporosis by Neospora caninum causes losses to livestock production through abortion in cattle while, in dogs, it induces neuromuscolar disease. This study investigated neosporosis seroprevalence associated risk factors (including the seropositivity to leishmaniosis) in dogs of southern Italy, determined the prevalence of N. caninum oocyst shedding and examined the relationship between seroprevalence of neosporosis in farm dogs and cattle. Using an inhibition ELISA, 20.9% of 306 dogs had percent inhibition values >10 (indicative of exposure) and farm dogs had a significantly (p<0.001) higher seroprevalence than dogs in a rescue kennel. Whilst N. caninum seroprevalence was associated with increasing age in dogs (p< or =0.01) there was no association between seropositivity for N. caninum and for Leishmania infantum. Oocysts of N. caninum were not detected in faecal samples from 230 dogs including 160 farm dogs. The results indicated that neosporosis infection is common in southern Italy both in dogs and in cattle and that dogs at higher risk of exposure are free-ranging ones living in farms. The lack of correlation between canine seroprevalence for N. caninum and L. infantum assumes a particular significance in an endemic area for leishmaniosis.     

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.     

Detection of Neospora caninum in semen of bulls

In cattle, transplacental infection is the main route of Neospora caninum transmission, but postnatal transmission by the oral uptake of sporozoite-containing oocysts shed by dogs may also be possible. Other routes of horizontal transmission, such as the venereal route, have not been investigated. In this study, we evaluated the presence of N. caninum DNA by a nested-PCR in fresh non-extended semen and frozen extended semen straws of five Holstein-Friesian bulls with naturally-acquired neosporosis. The infection status was assessed by an immunofluorescent antibody test (IFAT) and confirmed by immunoblotting (IB). Because of inhibitory components of semen, a protocol was developed to purify N. caninum DNA from bovine semen. Sporadically, N. caninum DNA was detected in non-extended fresh semen samples and frozen extended semen straws of the five seropositive bulls. In all positive samples, specific DNA was consistently found in the cell fraction of semen and not in seminal plasma. The parasite mean load in positive fresh semen samples determined by a real-time PCR was low oscillating between 1 and 2.8 parasites/ml of semen (maximum parasite load detected in one sample was 7.5 parasites/ml of semen). In parallel, another three similar but uninfected bulls acted as controls and no N. caninum DNA was amplified in any of their fresh and straw semen samples assayed. Whether venereal transmission plays a role in the spread of bovine neosporosis needs to be determined.     

Infection by Neospora caninum associated with bovine herpesvirus 1 and bovine viral diarrhea virus in cattle from Minas Gerais State, Brazil

Neospora caninum is a canine parasite which is considered a significant cause of bovine abortion. Two cattle herd groups were serologically studied with the objective of studying the prevalence of infection by N. caninum associated with BHV1 and BVDV infections. In group I, 15 dairy herds (476 samples) naturally infected by the three infectious agents were analyzed,. In group II, three dairy herds (100 samples) of cows vaccinated for two viruses were analyzed, in order to determine the infection prevalence by N. caninum. In the first group, an infection prevalence of 12.61, 34 and 28.3% was determined for N. caninum BHV1 and BVDV, respectively. In the second group, a seropositive prevalence of 46, 85 and 76%, respectively, was determined for N. caninum, BVH1 and BVDV. In the first group, the virus and N. caninum had shown in the first group 4.41% positive samples in association with BVH1, 3.15% with BVDV, and 8.41% with BVH1 and BVDV.     

A review of Neospora caninum in dairy and beef cattle--a Canadian perspective

Neospora caninum is one of the most important causes of abortion in cows. The occurrence of N. caninum infection in beef and dairy cattle has been reported worldwide, and in most provinces in Canada. The objective of this review is to summarize our current understanding of N. caninum in dairy and beef cattle for Canadian bovine practitioners. The review covers the life cycle of the agent, its mechanisms of transmission, clinical signs, and tests for diagnosing the infection. Data on the prevalence of the infection in Canadian dairy and beef cattle are reviewed and briefly compared with estimates from other parts of the world. Most importantly for Canadian bovine practitioners, the impacts of the infection, risk factors for its occurrence, and methods of control are also discussed. By reviewing the scientific literature on N. caninum from a Canadian perspective, culling decisions based on the interpretation of diagnostic tests are more effectively made in the control of N. caninum-associated disease.