Use of recombinant ApxIV in serodiagnosis of Actinobacillus pleuropneumoniae infections, development and prevalidation of the ApxIV ELISA

Actinobacillus pleuropneumoniae is the etiological agent of porcine pleuropneumonia, which causes worldwide severe losses in pig farming. The virulence of the 15 serotypes of A. pleuropneumoniae is mainly determined by the three major RTX toxins ApxI, ApxII and ApxIII, which are secreted by the different serotypes in various combinations. A fourth RTX toxin, ApxIV, is produced by all 15 serotypes only during infection of pigs, but not under in vitro conditions. Pigs infected with A. pleuropneumoniae show specific antibodies directed against ApxIV. In contrast, antibodies against the other three toxins ApxI, ApxII and ApxIII are also found in pigs free of A. pleuropneumoniae. The antibodies to the three latter might result from other, less pathogenic Actinobacillus species such as A. rossii and A. suis. We used a recombinant protein based on the N'-terminal part of ApxIV to serologically detect A. pleuropneumoniae infections in pigs by immunoblot analysis. The analysis of sera of experimentally infected pigs revealed that ApxIV-immunoblots detected A. pleuropneumoniae infections in the second to third week post infection. We developed an indirect ELISA based on the purified recombinant N'-terminal moiety of ApxIV. The analysis of sera from pigs that were experimentally or naturally infected by A. pleuropneumoniae, and of sera of pigs that were free of A. pleuropneumoniae, revealed that the ELISA had a specificity of 100% and a sensitivity of 93.8%. The pre-validation study of the ApxIV-ELISA revealed that the latter was able to detect A. pleuropneumoniae-positive herds, even when clinical and pathological signs of porcine pleuropneumonia were not evident. Pigs vaccinated with a subunit vaccine Porcilis App were serologically negative in the ApxIV-ELISA.

[The occurrence of Toxoplasma gondii and Neospora caninum as regards meat hygiene]

Toxoplasma gondii and Neospora caninum are phenotypically and phylogenetically closely related cyst-forming coccidia, both of which may cause abortion in livestock animals. T. gondii exhibits also zoonotic potential by causing diaplacental infections in the human fetus and harmful infections in immunosuppressed individuals. Humans get infected either by consuming inappropriately prepared cyst-containing meat or by ingesting oocysts originating from cat feces. Therefore, in order to assess infection risk we need to have knowledge on the prevalence of the parasite in consumable meat and thus slaughtered animals. So far, no data indicate any zoonotic potential for N. caninum. Due to its high economic impact in the bovine production in Switzerland, we included this parasite in the present study as well. The prevalence of both parasite species were investigated by PCR in muscle and brain samples of slaughtered bovines, sheep, pigs and horses. Comparatively, a serum sample from each animal was simultaneously tested serologically by a Toxoplasma-P30-ELISA and a Neospora-SA-ELISA. The prevalences determined by the T. gondii-PCR were the followings: adult cows 3%, young bulls 2%, young cows prior to gravidity 6%, calves 1%, sheep 6%, horses and pigs each 0%. For N. caninum, the PCR-prevalence was 2% for adult cows and 0% for all other animal groups. Conversely, the seroprevalences were much higher for both parasite species and all animal groups, with the exception of the fattening pigs. However, as T. gondii was principally detectable in bovine (cows and calves) as well as in sheep meat, the consumption of this meat harbours a potential infection risk for humans. In contrast, the lack of any parasite detectability in fattening pig and horse meat allows to consider this infection source as neglectable when compared to bovine and ovine meat.

The morantel sustained release bolus in the control of gastro-intestinal nematodiasis of cattle in Switzerland (preliminary results)

The efficacy of the morantel sustained release bolus was evaluated in 20 first-season grazing calves and 92 cattle in two separate trials. All animals grazed contaminated pastures and were exposed at the time of spring turnout to a risk of infection from gastrointestinal nematodes. In the first study 45 bolus-treated and 47 nontreated control (second or third season) cattle grazed similar but separate communal pastures, while in the second study nine bolus-treated and 11 nontreated control cattle grazed together on a single pasture. Efficacy determinations were conducted by frequent observations throughout the grazing season on faecal worm egg output, serum pepsinogen levels and liveweight gain. In the older group of animals (Trial 1), small differences were recorded between treated and control animals in faecal worm egg output and levels of serum pepsinogen as monitored throughout the grazing season. A significant mean liveweight advantage of 20.27 kg (P less than 0.001) was observed in the bolus-treated group. However, unrecorded pregnancy could not be excluded with certainty as a factor responsible for weight differences. The use of the morantel sustained release bolus provided an adequate protection against parasitic gastroenteritis in the first season grazing calves (Trial 2) despite the fact that bolus-treated animals were co-mingled with control animals. Both the worm egg counts and serum pepsinogen values were lower in the bolus-treated group. The morantel sustained release bolus was well tolerated in both trials.