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Drug resistance in gastrointestinal nematodes is a severe problem for sheep farmers. With the recent introduction of monepantel (Zolvix®) and of derquantel plus abamectin (Startect®) in New Zealand, two new anthelmintic classes will be available to control gastrointestinal nematodes. While monepantel covers a broad spectrum of nematodes, the efficacy of derquantel is mid-spectrum and limited to a smaller number of species and stages. The combination of derquantel and abamectin allows to enlarge the spectrum and to cover most parasitic nematodes in sheep. However, the question remained open, if the efficacy of the new anthelmintics can be maintained in the presence of severe anthelmintic resistance. The present study investigated the efficacy against adult stages of a multi-resistant Haemonchus contortus isolate. While monepantel resulted in 100 % elimination, derquantel in combination with abamectin resulted in efficacies <95 % (faecal egg counts and worm counts).

Drug resistance has become a global phenomenon in gastrointestinal nematodes of sheep, particularly resistance to macrocyclic lactones. New anthelmintics are urgently needed for both the control of infections with multi-resistant nematodes in areas where classical anthelmintics are no longer effective, and the prevention of the spread of resistance in areas where the problem is not as severe. Recently, two new active ingredients became commercially available for the treatment of nematode infections in sheep, monepantel (Zolvix®) and derquantel, the latter used only in a formulated combination with the macrocyclic lactone, abamectin (Startect®). In order to assess the potential of the new actives for the control and prevention of spread of anthelmintic resistance, two characterized multi-resistant field isolates from Australia were used in a GLP (good laboratory practice) conducted efficacy study in sheep. Eight infected sheep in each group were treated orally according to the product labels with 2.5 mg/kg body weight monepantel, 0.2 mg/kg abamectin, or with the combination of 2.0 mg/kg derquantel and 0.2 mg/kg abamectin. The results demonstrate that monepantel was fully effective against multi-resistant species, Trichostrongylus colubriformis and Haemonchus contortus (99.9%). In contrast, the combination of derquantel and abamectin was effective against T. colubriformis (99.9%), but was not effective against larval stages of the barber's pole worm H. contortus (18.3%).

Monepantel is the first compound from the amino-acetonitrile derivative class of anthelmintics to be developed for the control of gastrointestinal nematodes of sheep. An analysis of pooled data from a series of controlled studies is reported providing a single point of efficacy (+/- 95% confidence interval) for each gastrointestinal nematode tested at the fourth larval and/or adult stages. For most nematode species, the pooled efficacy was greater than 99%, and for the remaining few species, efficacy was greater than 90%. These data are well supported by field studies conducted across five countries, where the pooled efficacy (on the basis of fecal worm egg count reduction) was in most cases, greater than 99% (depending on the calculation used). Monepantel is highly effective when administered to sheep at 2.5 mg/kg, and its introduction as a new anthelmintic for sheep is timely, given the problems with anthelmintic resistance that the world's sheep farmers are now experiencing.

This analysis investigated the influence of breed and gender on the pharmacokinetics of monepantel, and influence of breed, age, and gender on its efficacy against gastrointestinal nematodes of sheep. In a comparison of pharmacokinetic profiles from two studies, Merino lambs had significantly greater maximum concentrations of monepantel and monepantel sulfone, and faster times to reach these concentrations than Dorset cross lambs. Males had a statistically greater area under the curve (0-504 h) than females for monepantel sulfone. The biological relevance of these relatively small differences is unclear because efficacy was not evaluated in these studies. For efficacy, a breed effect existed for some nematodes when sheep were treated at a sub-optimum dose (1.25 mg/kg). There were no gender effects between sheep infected with adult parasites and treated at 1.25 mg/kg but there were differences between females and males treated at this dose when infected with fourth-stage larvae of Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus colubriformis, and Cooperia curticei. There were no breed or gender differences for sheep treated at the recommended dose (2.5 mg/kg). There was a potential trend for declining efficacy with increasing animal age for fourth-stage Trichostrongylus axei. This analysis demonstrated that, similarly to what is observed with other anthelmintics, the pharmacokinetics and efficacy of monepantel can vary with factors like breed, age, and gender. Identifying these covariates is important for understanding inter-individual variability in drug response. While further investigation is warranted, correctly treating sheep at the recommended dose of 2.5 mg/kg appears to mitigate any associated risk.

Neospora caninum ranges among the major causes of infectious abortion in cattle worldwide. The present study was designed to improve the serodiagnostic tools by complementing a conventional ELISA with a highly sensitive and species-specific N. caninum immunoblot. To evaluate this test combination, sera from several groups of cows were tested. The first group, consisting of experimentally infected calves, showed that immunoblot antibody reactivities were detectable 1 to 3 days earlier than those found in ELISA. The first immunodominant bands that appeared were a 29-kDa (NcSAG1) and a 36-kDa (NcSRS2) antigen. Other groups, based upon naturally infected cattle, were used to compare the diagnostic sensitivity of ELISA and immunoblotting. Overall, N. caninum immunoblotting exhibited a higher sensitivity (98%) than ELISA (87%). Conversely, immunoblotting also confirm in two other cases, true transient negativation in some animals. In general, banding patterns and band staining intensity correlated to the semiquantitative ELISA findings. On the other hand, the banding pattern could not be used to discriminate between sera from animals with a recent abortion and those of cows with latent N. caninum infection. We also addressed putative cross-reactions due to infection with Toxoplasma gondii. Sera from animals with a serologically proven T. gondii infection were either clearly negative by Neospora immunoblotting or they yielded a specific immunoblot antibody profile indicating a double infection with N. caninum. Sera from animals with positive findings in both Toxoplasma and Neospora ELISA thus provided dichotomic results in the immunoblot by allowing to confirm or to rule out the specificity of the antibody reaction in Neospora ELISA. Altogether, our findings demonstrate that N. caninum immunoblotting is a very sensitive and specific complementary tool to improve the serology for N. caninum infections in cattle.

Neospora caninum is widely recognized as one of the most important infectious organisms causing abortion and stillbirth in cattle. This parasite causes severe economical losses worldwide. Infection is mostly passed vertically from mother to calf during pregnancy. Under certain circumstances, an infection can lead to abortion, but in most cases it results in a chronically infected calf, which itself will represent the next endogenously infectious generation. So far, no reliable therapeutic or metaphylactic tool has been developed. One possibility to control the problem may consist of treating newborn calves that became vertically infected by a persistently infected mother. This may allow parasite-free offspring. The aim of the present study was to address the questions: (1) can serology be used to assess efficiency of treatment in toltrazuril-medicated animals? and (2) is a strategic prevention measure possible by means of producing N. caninum-free calves from positive cows? Calves from Neospora-seropositive cows and heifers were randomly split into two different medication groups: 36 calves were medicated with toltrazuril and 36 calves obtained a placebo. Medication (20 mg toltrazuril per kg bw) was administered three times, every second day, within the 7 days post natum. Three months after medication, there was no difference in antibody reactivity between the two groups. At later time points (4-6 months), however, significant differences were found, as explained by a strong humoral immunity after chemotherapeutical affection of parasites, while the placebo-treated animals only responded weakly to the persistent infection. In summary, we concluded that (1) serology was not an entirely appropriate tool to answer our initial question and (2) toltrazuril has the potential to eliminate N. caninum in newborn calves. As a consequence, we plan to follow up toltrazuril-medicated calves clinically and serologically over a longer period and investigate if they give birth to Neospora-free calves.

The present study was designed to exploratively determine (a) how many healthy calves, born from seropositive mothers, were also precolostrally seropositive; (b) how many precolostrally negative calves became postcolostrally positive; and (c) in these calves, how the IgG1/IgG2 situation developed pre- and postcolostrally. All calves were born from mothers that were determined to be seropositive in a conventional Neospora caninum-ELISA and by immunoblotting. When the diagnostic performance of the conventional ELISA was compared with that of immunoblotting and an IgG1/IgG2-ELISA in the calves, the latter two exhibited a higher sensitivity: From a total of 15 precolostral calf sera, 7 were positive in the conventional ELISA (diagnostic sensitivity 47%) compared to 15 that were positive by immunoblotting (diagnostic sensitivity 100%) and 12 that were positive by the IgG1/IgG2-ELISA (diagnostic sensitivity 80%). With regard to IgG1/IgG2 findings in the dams, IgG2 appeared as the dominant subclass in the humoral immune response of adult cattle, while in calves, IgG1 appeared as the main prenatally/precolostrally reactive antibody isotype. Provided that precolostral seropositivity reflects postnatal persistent infection with N. caninum, we then postulate that, basically, all of our study calves born form N. caninum-seropositive mothers were prenatally infected with the parasite, and may, thus, all become members of the next transmitting generation.

Toxoplasma gondii is a protozoan parasite with a worldwide distribution. In both sheep and humans, if the parasite is encountered during pregnancy, fetal infection and abortion can occur. Therefore, Toxoplasma infection in sheep has a major economic impact upon sheep farming. Clinically, there is a need to distinguish recent (acute) infections from longstanding (chronic) infections. However, current serological techniques, such as detection of anti-T. gondii IgG, cannot discriminate between acute and chronic infections. Increasing immunoglobulin avidity is a good determining factor of how recent an infection is. In this study, we describe the application and validation of a T. gondii IgG avidity ELISA, based on the use of an affinity-purified, native T. gondii P30 antigen. The assay was used to examine sera from eight sheep experimentally infected with T. gondii and found that all seroconverted within 21 days post-infection (p.i.), beginning with avidities that were initially low but that increased over time, with all sheep reaching high IgG avidity within 10 weeks p.i. In addition, sera from clinically healthy but T. gondii-seropositive lambs and ewes and seropositive ewes with a history of abortion were also subjected to a preliminary serological investigation. High IgG avidities were found in 80% of the seropositive lambs, in 90% of the clinically healthy ewes and in 97% of the ewes with abortion problems. These findings indicate that the animals had most likely contacted the parasite a longer time ago.