W. Wouda

Seroepidemiological evidence for a relationship between Neospora caninum infections in dogs and cattle.

Dogs from dairy farms with a known prevalence of Neospora caninum antibodies in the cattle were examined for the presence of N. caninum antibodies using an ELISA. Data of farm dogs were compared with those of dogs examined at a university clinic, which originated mainly in urban areas. Of the 152 farm dogs, 36 (23.6%) were seropositive to N. caninum, which was significantly higher than the proportion of seropositives in the clinic dog population (19 of 344, 5.5%). Seroprevalence was significantly higher (P = 0.01) in female dogs than in male dogs. Seroprevalence in dogs increased with age, indicating postnatal infection. Seropositivity to N. caninum in farm dogs was strongly correlated with a high prevalence of N. caninum antibodies in the cattle. At farms where no dogs were present, the seroprevalence to N. caninum in the cattle was significantly lower (P = 0.0002) than in farms where dogs were present. These findings suggest that there is a relationship between N. caninum infection of farm dogs and cattle. Since dogs have been shown to be definitive hosts of N. caninum, cattle may be infected by exposure to canine oocysts. Further research is needed to find out whether and how dogs may acquire the infection from cattle.

Risk factors for neospora caninum-associated abortion storms in dairy herds in The Netherlands (1995 to 1997)

A 2 to 1 matched case control study design was used to analyze herd level risk factors for Neospora caninum-associated abortion storms in 47 dairy herds. Data were obtained using a questionnaire regarding the state of affairs at the farms over the 2 years prior to the abortion storm. The questionnaire included 120 variables considered to be potential risk factors for either introduction of infection or recrudescence of chronic infection. The relationship between risk factors and case control pairs was analyzed by conditional logistic regression using a three-steps procedure. In addition, cross sectional serology was used to assess the possible role of concomitant infections. The main factors that were significant in the analysis and that were considered to have potential biological relevance were the presence of dogs, the presence of poultry, and the feeding of moldy maize-silage during summer. For both the presence of dogs and the presence of poultry on the farms, a linear relationship was found between the number of animals and the assessed risk for an abortion storm. These findings suggest a possible role of these species in the transmission of N. caninum. Further evidence for such a role of dogs was the significant association between the presence of dogs and the presence of seropositive cattle in the control herds. The feeding of moldy fodder is considered to be a factor which may induce recrudescence of a latent N. caninum-infection by mycotoxins causing immune suppression. We also found some evidence for a possible influence of management practices around calving and a high prevalence of retained afterbirths. No significant association was found for herd level prevalence of antibodies to bovine viral diarrhea virus, bovine herpesvirus 1, Leptospira hardjo or Salmonella dublin.

Abortion risk in progeny of cows after a neospora caninum epidemic

A study was done of the descendants of cows from 4 dairy herds in which there had been N. caninum abortion outbreaks. Precolostral antibodies to N. caninum were demonstrated in 34 of 50 (68%) F1 calves and in 14 of 17 (82%) F2 calves from cows that aborted during the outbreaks. In 214 F1 progeny, N. caninum seroprevalence was nearly 50%, and there was a significant association between serostatus of the offspring and serostatus of dams. These observations indicated that congenital infection was an important mode of transmission after abortion outbreaks in these herds. A total of 52 abortions was recorded in 293 pregnancies of F1 progeny cows (1 to 3 pregnancies per animal). It was found that seropositive F1 cows had a three-fold increased abortion risk compared with seronegative F1 cows. In 2 of 10 abortions in seronegative cows evidence for N. caninum infection was found, suggesting that a low level of postnatal infection may also have occurred. It is concluded that N. caninum-infected calves should not be used as replacement stock, to decrease the future risk of abortion in dairy herds.

Characteristics of neospora caninum-associated abortion storms in dairy herds in The Netherlands (1995 to1997)

Abortion storms in 50 dairy herds in The Netherlands were reported in which there was a strong association with Neospora caninum-infection. The duration of the abortion storms ranged from 6 to 65 d (mean 41.5 d). The cumulative proportion of aborting cows ranged from 0.11 to 0.57 (mean 0.26) of the animals at risk. An apparent seasonal influence was noted as most abortion storms occurred during the summer and early autumn. The prevalence of antibodies to N. caninum in 50 herds which had had an abortion storm was compared with that of 100 control herds which had no history of an abortion storm. Seroprevalence was estimated by testing a 20% cross sectional herd sample using a tachyzoite lysate-based ELISA method. Seroprevalence in case herds (range 17 to 87%, mean 51.5%) was significantly higher than that in control herds (range 0 to 53%, mean 13.9%). For most herds the seroprevalence levels were equal across all age groups, which suggests that the infection had been perpetuated by vertical transmission. In these herds, the abortion storms appeared to be induced by factors causing recrudescence of a N. caninum-infection in chronically infected animals rather than being the result of a recent introduction. In 6 case herds the seroprevalence in the dairy cows was significantly higher than in the young stock, which may have been attributable to superimposed postnatal infection.

Evidence of post-natal transmission of Neospora caninum in Dutch dairy herds

Eighteen dairy herds with neosporosis-associated abortions were analysed for antibodies against Neospora caninum. Blood samples of all cows, heifers and calves were collected on the same day for each farm. A total of 2430 heads of cattle were examined. For each herd, the seropositive and seronegative animals were plotted against month of birth. Analysis of seroprevalence in relation to age showed an equal distribution of seropositives in all age-groups in 10 herds. In contrast, in eight herds an age-group could be identified which had a significantly higher seroprevalence than the other animals in the herd. Most seropositive animals in the high seroprevalence age-groups had either seronegative dams or seronegative offspring, whereas there was a strong relationship between the serostatus of dams and offspring in the other animals in the herd. Aborting animals were mainly part of the high seroprevalence age-group. These findings strongly indicate a post-natal infection of the animals in the high seroprevalence age-groups, probably due to a point source exposure to N. caninum.

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.

A high rate of seroconversion for Neospora caninum in a dairy herd without an obvious increased incidence of abortions

The purpose of this paper is to investigate the high rate of seroconversion for Neospora caninum in a dairy herd. Forty-five of 95 (47%) of the seronegative animals seroconverted within a period of 6 months. Seropositive animals were not equally distributed among age-groups. A high seroprevalence age-group of 8-30 months was housed together during a period of 4 months, indicating a point source infection within this period. A lack of association between the serological status of daughters and mothers also indicated horizontal transmission of the infection. Low avidity indices in the seroconverted animals confirmed a recent infection in this herd. However, there was no increased abortion rate in connection with the seroconversion, which indicates that mass seroconversions in dairy herds may remain unnoticed. There was circumstantial evidence that the farm dog played a role in the transmission of the infection to the cattle. However, also evidence was found for an unexplained ongoing horizontal transmission after the initial point source exposure.

Natural postnatal Neospora caninum infection in cattle can persist and lead to endogenous transplacental infection.

A serological follow-up study of 3.5 years duration was done of a dairy herd that had experienced a mass seroconversion to Neospora caninum following a point source exposure shortly before the 17th of January 2000. A total of 913 blood samples of 244 animals at seven sampling dates were used to investigate the seroprevalence dynamics in the herd. Most postnatally infected cattle remained seropositive during the period of investigation but 11 animals became seronegative after 6-27 months indicating transient infection. Six animals seroconverted later than the main group of 45 animals and 5 animals became seronegative after at least two seropositive records possibly due to a low infection dose or difference in the haplotypes of the infected animals. In total 58% (14/24) of the offspring of postnatally infected dams was seropositive. Nine of 16 (56%) daughters originating from inseminations after the postnatal infection of their dams were seropositive indicating endogenous transplacental infection.

Polioencephalo- myelitis in a calf due to infection with Schmallenberg virus

SINCE December 2011, an epizootic of congenital malformations, designated as arthrogryposis-hydranencephaly syndrome, has occurred in ruminants, mainly sheep and cattle, in several countries in western Europe (Van den Brom and others 2012). The disease has been associated with a new Orthobunyavirus, named Schmallenberg virus (Hoffman and others 2012). After Schmallenberg virus was detected by RT-qPCR in brain tissue from malformed lambs on December 15, 2011, the Dutch …

Prevalence of Coxiella burnetii infections in aborted fetuses and stillborn calves

Coxiella burnetii infections are mostly subclinical in cattle, but can occasionally be associated with abortion. In the present study, 100 aborted fetuses or stillborn calves that were submitted for postmortem examination between September 2007 and March 2008 were examined for infection with C burnetii. Samples of both pooled fetal tissues and placental cotyledon were tested using a real-time PCR assay. In addition, the sections of placental cotyledon were examined using immunohistochemistry (IHC). The IHC of four placentas was positive. The PCR results of the IHC-positive placentas were high positive (HP); the PCR results of the organs of these four fetuses and calves varied from low positive (LP) to HP. The four IHC-positive fetuses had a gestation length of seven to nine months. All four placentas had histological signs of inflammation, but only one of four placentas had gross pathological signs of inflammation possibly due to a concomitant infection with Bacillus licheniformis. Five other IHC-negative placentas had (high) positive PCR results; the PCR results of the organs of these fetuses were LP or negative. The present study indicates that C burnetii infections are detected in a limited percentage of aborted fetuses and stillborn calves by IHC. To assess the importance of placentas with PCR-positive and IHC-negative test results, more research is needed.