M. Eysker

Dogs shed Neospora caninum oocysts after ingestion of naturally infected bovine placenta but not after ingestion of colostrum spiked with Neospora caninum tachyzoites

An experiment was carried out to determine whether bovine colostrum or placenta could be a source of infection of Neospora caninum for dogs. For this purpose, two dogs were fed bovine colostrum to which culture-derived N. caninum tachyzoites were added and two other dogs were fed placental cotyledonary tissue from N. caninum seropositive cows. One dog served as a negative control during the start of the experiment but this control dog was fed cotyledonary tissue later on. None of the dogs did produce serum antibodies to N. caninum. All three dogs that were fed cotyledonary tissue did shed N. caninum oocysts, but no oocyst shedding was seen in the two dogs that were fed colostrum with N. caninum tachyzoites. Oocyst excretion did not resume in two dogs after repeated feeding of N. caninum infected placenta. The identity of the oocysts was confirmed by a bioassay in gerbils. It is concluded that ingestion of bovine placenta by dogs is an effective mode of transmission of N. caninum from cattle to dogs.

Value of present diagnostic methods for gastrointestinal nematode infections in ruminants.

In this paper the different options for the diagnosis of gastrointestinal nematode infections are discussed. Diagnostic tests have a role in confirming the clinical diagnosis of parasitic gastroenteritis, but are more important for herd health monitoring of nematode infections, in particular for cattle. Therefore, emphasis is placed on discussing the available diagnostic parameters on their usefulness for that purpose. For clinical diagnosis the clinical signs, combined with the history of the animals is usually sufficient and a laboratory confirmation is not required. Faecal egg counts are, with two exceptions, not suitable for confirmation of the clinical diagnosis, because correlation between faecal egg counts and infection levels is usually low. These exceptions are the diagnosis of haemonchosis in small ruminants and the detection of anthelmintic resistance. This also limits the value of DNA-based tests of faecal material; even quantitative tests of nematode species specific DNA will have little value for diagnosis and monitoring. Pasture larval counts and worm counts are useful parameters for basic epidemiological studies on nematode infections. However, they are too laborious to be used for either routine diagnosis or monitoring. Blood parameters, such as gastrin and pepsinogen and serology are valuable tools for diagnosis. Pepsinogen and ELISAs based on recombinant proteins show most promise as parameters for herd health monitoring. However, extensive epidemiological studies are still needed before these parameters can be implemented in routine herd health monitoring schemes for parasitic gastroenteritis.

Natural transmission routes of Neospora caninum between farm dogs and cattle

Twelve dairy herds with evidence of post-natal infection with Neospora caninum were compared with 21 control herds with no evidence of post-natal infection. On the former farms, dogs consumed placenta or licked uterine discharge in 75 and 67% of the farms, respectively, while on control farms these activities occurred in 38 and 24% of the farms, respectively. On all control farms and all but three post-natally infected farms the dogs were fed colostrum or milk. Defecation of dogs on the feeding alley was observed in 92% of the post-natally infected farms and in 24% of the control farms. The same trend was observed for defecation of dogs in grass silage, in 75% of the post-natally infected farms and in 19% of the control farms; and in corn silage, in 50% of the post-natally infected farms and in 10% of the control farms. Consumption of placenta, material of aborted foetuses or uterine discharge in combination with defecation on the feeding alley, storage of grass or corn silage was observed in 19% of the control farms and in 75% of the post-natally infected farms. This study supports the hypothesis that farm dogs may become infected by foetal fluids or placental material of infected cattle, and may subsequently cause a post-natal infection of cattle in the herd by shedding oocysts.

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.

Effect of naturally occurring nematode infections in the first and second grazing season on the growth performance of second-year cattle.

Antibody titres against Ostertagia spp., Cooperia spp. and Dictyocaulus viviparus as well as pepsinogen values, reflecting exposure to nematode infection, differed significantly among herds of second-year cattle on 87 farms. Faecal examinations revealed that gastrointestinal nematode infections were present in all herds. Similar results were found in yearling-herds on the same farms a year earlier. Liveweight of yearlings per herd deviated from -64.7 kg to +94.4 kg from an age-adjusted population mean after the second grazing season. This mean herd weight deviation was significantly related negatively to antibody titre against Ostertagia spp. (linear regression, P less than 0.05; segmented curvilinear regression, P less than 0.01) and to antibody titre against Cooperia spp. (segmented curvilinear regression, P less than 0.05), both measured in the second grazing season. Antibody titre against Ostertagia spp. measured in the first grazing season, when yearlings were calves, was significantly correlated positively to age-adjusted body weights at the end of the second grazing season. The results suggested that immunity built up during the first year had a positive effect on growth performance in the second year, but that on average the acquired immunity was insufficient to prevent reduced weight gains in the second grazing season.

An observational study of Eimeria species in housed cattle on Dutch dairy farms.

The prevalence of oocysts of Eimeria species in calves (n = 334), yearlings (n = 254) and cows (n = 1314) was determined on 38 Dutch dairy farms. Twelve species of Eimeria were identified in faecal specimens by sucrose-flotation. The prevalences of Eimeria spp. differed markedly in the different age classes on individual farms as well as between farms. The overall prevalence of Eimeria oocysts in faecal specimens was 46% for calves, 43% for yearlings and 16% for cows. The number of oocysts excreted was generally low in cows and yearlings, whereas high numbers of oocysts per gram of faeces (OPG) were exclusively observed in calves. No cases of clinical coccidiosis were observed in this survey. Linear regression analysis showed that there is significant reduction in the OPG levels (P < 0.05) in calves infected with Eimeria, aged between 7 and 38 weeks. Finally, the data are discussed in relation to management practices and the acquisition of immunity.

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.

The effect of ivermectin treatment against inhibited early third stage, late third stage and fourth stage larvae and adult stages of the cyathostomes in Shetland ponies and spontaneous expulsion of these helminths

A controlled and critical test on the efficacy of ivermectin against larval and adult stages of the cyathostomes was carried out in six yearling castrated male Shetland ponies. The ponies grazed together as one group from 3 May to 4 October 1990, after which they were housed. Three ponies were treated with ivermectin on 29 October while the others served as controls. The shedding of helminths in the faeces was followed in all ponies until necropsy on 14 November. Comparison of worm counts of both groups before and after necropsy showed no evidence for an effect of ivermectin against inhibited early third stage larvae (EL3) and mucosal late third stage (LL3) and fourth stage larvae (L4). However, a high, but not 100%, efficacy was observed against adults and lumenal L4. A remarkable observation was the high incidence of spontaneous expulsion of L4 and adult populations of some species in two of the untreated ponies.

Seasonally inhibited development of cyathostomine nematodes in Shetland ponies in The Netherlands.

Two groups of three yearling Shetland ponies were used in 1988 to study the epidemiological significance of inhibited development of the Cyathostomine nematodes. In Group 1, acquisition of infections was prevented throughout the grazing season whereas in Group 2 strongylid infections were acquired from the beginning of July until the end of September. Worm counts showed that the Cyathostomine nematode populations of Group 1 ponies mainly consisted of adult worms and those of Group 2 ponies of inhibited early third stage larvae (L3). These results indicate that a large proportion of Cyathostomine larvae which establish between the beginning of July and the end of September inhibit their development. The results also suggest that the pool of inhibited larvae which has overwintered in young ponies will be depleted in autumn.

Control of strongylosis in horses by alternate grazing of horses and sheep and some other aspects of the epidemiology of strongylidae infections

Alternate grazing of horses and sheep as a control measure for gastrointestinal helminthiasis was studied in three grazing experiments in 1981, 1982 and 1983. Each year a group of three mare yearling Shetland ponies, which were kept on a small pasture from spring to autumn, were compared with a similar group which grazed a similar or the same pasture until July and were subsequently removed to a similar pasture which had been grazed by sheep from April to July. In addition both groups were treated with an anthelmintic when the latter group was removed to the sheep pasture. Pasture larval counts and worm counts and, in 1982 and 1983, faecal egg counts, clinical condition, total protein, albumin and beta-globulin levels demonstrated that the groups removed to sheep pasture acquired considerably lower burdens of nematodes of the subfamilies Cyathostominae and Strongylinae, but considerably higher burdens of Trichostrongylus axei than the groups which were not moved. These T. axei infections resulted in higher serum pepsinogen levels in the former groups compared to the latter in 1981 and 1982. At necropsy an important part of the T. axei burdens and, in 1982 and 1983, the Cyathostominae burdens consisted of inhibited early third stage larvae. A total of 20 species of the subfamily Cyathostominae and 7 species of the Strongylinae were found. Generally the composition of species was in agreement with other observations in western Europe, the most common species being: Cylicostephanus longibursatus, Cylicostephanus minutus, Cylicostephanus calicatus, Cylicostephanus goldi, Cylicostephanus poculatus, Cyathostomum labratum, Cyathostomum coronatum, Cyathostomum catinatum, Cylicocyclus leptostomus, Cylicocyclus nassatus, Cylicocyclus insigne, Strongylus edentatus and Strongylus vulgaris.