Age at which dairy cattle become Mycobacterium avium subsp. paratuberculosis faecal culture positive.

Age at which cattle become faecal culture positive for Mycobacterium avium subsp. paratuberculosis (Map) can be used as a proxy parameter for age at onset of faecal shedding, which is an important parameter in the control of Map in cattle herds. To investigate the age at becoming faecal culture positive, survival analysis methods were applied. The analyses were carried out on asynchronous interval censored data of faecal culture results of samples collected from 18,979 female Holstein-Frisian cattle in 353 Dutch herds between 1996 and 2002. The data were analysed with a Weibull proportional hazards model. The results indicate that the distribution of age at onset of faecal shedding in Holstein-Frisian dairy cattle in infected herds is associated with the within-herd prevalence. In higher classes of apparent prevalence, cattle started to shed Map at younger age on average. In herds with an apparent prevalence <0.05, 0.05-0.1, 0.1-0.2 and ≥0.2, the proportion (95% CI) of cattle with onset of faecal shedding before 2 years of age was estimated at 1% (0.5%; 2%), 4% (3%; 5%), 8% (5%; 10%) and 20% (11%; 32%), respectively. This study indicates that a considerable proportion of young stock is shedding Map, especially in high prevalence herds. Therefore, infectious young stock should be a major concern in the control of paratuberculosis.

Fasciola hepatica procathepsin L3 protein expressed by a baculovirus recombinant can partly protect rats against fasciolosis.

Fasciola hepatica juveniles express immunodominant cathepsin L proteins, which are mainly found in their immature, procathepsin form. A gene encoding such a procathepsin L (FheCL3) was expressed by a baculovirus recombinant and by Saccharomyces cerevisiae. The glycosylated FheCL3 proteins obtained by both systems were used in a vaccination/challenge experiment in rats. Both antigens evoked similar antibody responses, but only the baculovirus expressed FheCL3 caused a significant protection against the number of liver flukes (52% protection, P=0.01), whereas the S. cerevisiae expressed FheCL3 did not. In a second experiment in rats, deglycosylated versions of both antigens were used, but this did not improve their efficacies.

Comparison of the sensitivity of in vitro and in vivo tests for detection of the presence of a bovine viral diarrhoea virus type 1 strain.

Veterinary vaccines are usually tested for the absence of contaminants. However, the quality control does not always imply that vaccines are not contaminated as, for example, illustrated by the bovine herpes virus 1 (BHV1) vaccine used in The Netherlands in 1999 that contained a small amount of bovine viral diarrhoea virus (BVDV1). Thousands of cows were vaccinated with BHV1 vaccine batches, and the question arose as to whether these small amounts of BVDV1, most likely not detected with in vitro tests, could have infected cattle. More in general, the question was whether the outcome of the in vitro tests, i.e. the in vitro infectivity, was indicative for the infectivity for cattle, i.e. the in vivo infectivity. We therefore carried out in vitro experiments to determine the sensitivity of a BVDV1 isolation assay. In addition, we performed two animal experiments, in which we estimated the lowest dose needed to infect calves with BVDV1. We extrapolated the experimental in vitro and in vivo results from a tissue culture infectious dose (TCID50) to a cattle infectious dose (CID50). We observed a partial response in the calves inoculated with this dose: four out of six calves turned out to be infected. In the tissue culture test, all 20 samples tested negative. The response in vivo, however, was not significantly higher than the in vitro response, which implies that no difference in susceptibility was observed between the animal test and the tissue culture test. Based on the results in our experiments, some cattle may have been infected with BVDV1 after the application of the contaminated BHV1 vaccine during the vaccination campaign. The question remains that how many cattle received contaminated vaccine, and became infected with BVDV1.