End-season daily weight gains as rationale for targeted selective treatment against gastrointestinal nematodes in highly exposed first-grazing season cattle.

A two-year study was carried out to assess the feasibility of a targeted selective treatment to control gastrointestinal nematodes (GIN) in 24 groups of first grazing season (FGS) cattle. A two-step procedure aiming at defining exposure risk at group level and at identifying the most infected individuals within groups through measurement of the average daily weight gain (ADWG) at housing was used. The first step was to define retrospectively, by grazing management practices (GMP) indicators, two levels of groups' exposure to GIN determined by anti O. ostertagi antibody ODR level (cut-off 0.7). For the low level of exposure, no relationship between parasitological parameters and heifer growth was seen, whereas for the high level ADWG was negatively correlated with increasing Ostertagia ODR values. The best classification was obtained with an expert system modelling the number of Ostertagia L3 generations on plots. GMP input for the expert system included standard data (turnout/housing data and supplementary feeding amount) combined with paddock rotation planning and monthly temperatures. The threshold of 3 successive generations of L3 or more on plots allowed identifying the groups according to low or high infection exposure level, except two groups that were misidentified as being highly exposed. In the second step, individual ADWG was found to be negatively associated with Ostertagia ODR in heifers from groups classified as highly exposed (≥3 generations of L3). In these groups, sensitivity and specificity of ADWG thresholds were calculated for several individual Ostertagia ODR thresholds. The best compromise between sensitivity (i.e., correctly treating the heifers that need to be treated) and specificity (i.e., not treating animals that should not be treated) was equivalent respectively to 76% and 56% (AUC≈0.7) and was reached using an end-season ADWG threshold of 683g/day to detect animals exhibiting an Ostertagia ODR cut-off at 0.93. Other ADWG thresholds were proposed taking into account the farmers' or the veterinarians' objectives: either maximizing the production through both an increase of the ADWG threshold and the sensitivity or keeping a significant nematode population in refugia with a corresponding limitation of anthelmintic treatments through a decrease of ADWG threshold and an increase of the specificity. Finally, a targeted selective treatment for FGS cattle based on GMP and flexible ADWG thresholds seems feasible at housing without laboratory analysis, accepting that some resilient animals with high Ostertagia ODR will not be treated due to their ability to perform under parasitic challenge.

Unexpected Decrease in Milk Production after Fenbendazole Treatment of Dairy Cows during Early Grazing Season.

Gastrointestinal nematodes (GIN) infection can impair milk production (MP) in dairy cows. To investigate whether MP would be optimized by spring targeted-selective anthelmintic treatment in grazing cows, we assessed (1) the effect on MP of an anthelmintic treatment applied 1.5 to 2 months after turn-out, and (2) herd and individual indicators associated with the post-treatment MP response. A randomized controlled clinical trial was conducted in 13 dairy farms (578 cows) in western France in spring 2012. In each herd, lactating cows of the treatment group received fenbendazole orally, control cows remained untreated. Daily cow MP was recorded from 2 weeks before until 15 weeks after treatment. Individual serum pepsinogen and anti-Ostertagia antibody levels (expressed as ODR), faecal egg count and bulk tank milk (BTM) Ostertagia ODR were measured at treatment time. Anthelmintic treatment applied during the previous housing period was recorded for each cow. In each herd, information regarding heifers' grazing and anthelmintic treatment history was collected to assess the Time of Effective Contact (TEC, in months) with GIN infective larvae before the first calving. The effect of treatment on weekly MP averages and its relationships with herd and individual indicators were studied using linear mixed models with two nested random effects (cow within herd). Unexpectedly, spring treatment had a significant detrimental effect on MP (-0.92 kg/cow/day on average). This negative MP response was particularly marked in high producing cows, in cows not treated during the previous housing period or with high pepsinogen levels, and in cows from herds with a high TEC or a high BTM ODR. This post-treatment decrease in MP may be associated with immuno-inflammatory mechanisms. Until further studies can assess whether this unexpected result can be generalized, non-persistent treatment of immunized adult dairy cows against GIN should not be recommended in early grazing season.

Antibody prevalence and molecular identification of Babesia spp. In roe deer in France.

In a region-wide serologic study carried out in 2004 on free-ranging hunted roe deer in various landscapes, we found that 58% of the animals (237 out of 406) were antibody positive for Babesia divergens antigen. Serologic and infection status was also analyzed for 327 roe deer live-trapped in two fenced forest areas over 5 yr (2004-08). For two consecutive years during this period, 92 and 94% of the deer in these closed populations were antibody-positive for B. divergens. Babesia spp. were isolated in autologous red blood cell culture for 131 of the trapped animals (40%). Molecular typing was done on 76 isolates with polymerase chain reaction (PCR)-restriction fragment length polymorphism methods targeted at the 18S ribosomal subunit gene (18 isolates) and the Bd37 gene coding for a merozoïte surface antigen implicated in a protective response (60 isolates). Results indicated continuous cocirculation of B. capreoli and B. venatorum in both forests and possible coinfection of animals with both species. No infection with B. divergens was detected. Fifteen isolates were confirmed to be B. capreoli by sequencing part of the 18S rRNA gene. Using PCR detection of the Bd37 gene, all nine isolates of B. venatorum in this study were negative, whereas the 15 confirmed and 50 putative B. capreoli isolates showed very variable restriction profiles, distinct from those known for Bd37 in B. divergens. Two isolates showed conflicting results, suggestive of mixed infection.

Determination of erythrocyte susceptibility of Chinese sheep (Tan mutton breed) and French sheep (Vendéen breed) to Babesia sp. BQ1 (Lintan) by in vitro culture.

The Babesia species "BQ1 (Lintan)" is infective to sheep and goats. The species was isolated from Haemaphysalis qinghaiensis collected in the Gannan Tibet Autonomous Region, China in April 2000. In this study, an in vitro culture system was developed for the propagation of Babesia sp. BQ1 (Lintan). Continuous cultivation and 5.0% parasitemia was obtained in vitro in RPMI 1640 medium with sheep red blood cells (RBC) (7.5%) supplemented with Fetal Bovine Serum (FBS) (20%), Amphotericin B (0.5 microg/ml) and Gentamicin (50 microg/ml) in an incubator at 37 degrees C and 6% CO(2) in 24-well and 6-well plates. Parasitemia could attain 10% in 75 cm(2) flasks with the same culture medium but with 2.5% RBC. A clonal line of Babesia sp. BQ1 (Lintan) was screened using the limiting dilution method and designated G7. Growth of Babesia sp. BQ1 (Lintan) in vitro was measured by microtitre-based spectrophotometric method and from parasitemia counts. The generation time was between 20.57 h (based the A(405) of the culture supernatant) and 26.41 h (based on parasitemia). Three French sheep were successfully infected with the culture and the infectivity of the clonal line G7 was determined. Finally, this in vitro culture system was used to compare the susceptibility (capacity to sustain Babesia sp. growth in vitro) of RBC from French sheep (Vendéen breed) and Chinese sheep (Tan mutton breed) for Babesia sp. BQ1 (Lintan) and B. divergens. The lower susceptibility to B. divergens and Babesia sp. BQ1 (Lintan) of RBC from French sheep, compared to Chinese sheep, is discussed.

Redescription of Babesia capreoli (Enigk and Friedhoff, 1962) from roe deer (Capreolus capreolus): isolation, cultivation, host specificity, molecular characterisation and differentiation from Babesia divergens.

The recent use of the sole molecular identification of Babesia infecting European cervids has led to confusion between the closely related Babesia divergens and Babesia capreoli, and to their grouping together as "B. divergens-like". In order to clarify this taxonomic confusion, Babesia from roe deer, cattle and human blood were isolated, cultured and their biological as well as molecular characteristics compared. On this basis, we conclude that: (i) the parasites isolated from roe deer blood are B. capreoli; (ii) there are no intraspecific variations in the 18S rDNA within B. capreoli and B. divergens spp.; (iii) these two species are closely related as demonstrated by their morphology, serological cross-reactions and 99.83% identity in their 18S rDNA; (iv) these two species are distinct as demonstrated by their different abilities to grow in vitro in cattle, human and sheep erythrocytes, by their infectivity for gerbils, and by a conserved three bases difference at positions 631, 663 and 1637 of their 18S rDNA; (v) B. capreoli does not pose a threat to either humans or livestock. An integrated description is given of the host range, geographical distribution, biological and molecular characterisation of B. capreoli, and reference materials have been deposited at the Museum d'Histoire Naturelle de Paris.

Experimental in vitro transmission of Babesia sp. (EU1) by Ixodes ricinus.

Babesia sp. (EU1), first characterized in 2003, has been implicated in human cases of babesiosis in Italy, Austria and Germany. It has been identified in roe deer and in its suspected tick vector, Ixodes ricinus, in several European countries. The aim of the present study was to validate the competence of I. ricinus as a vector of Babesia sp. (EU1) via experimental infections. For this purpose, a parasite strain isolated from roe deer was cloned in sheep erythrocytes. After experimental infections, parasite DNA was successfully amplified by PCR in both eggs and larvae originating from infected I. ricinus females and in the salivary glands of females exposed to Babesia sp. (EU1) as nymphs. We also demonstrate that infected females were able to transmit parasite DNA during a new blood meal. Together with previous epidemiological studies, these results validate I. ricinus as a competent vector for Babesia sp. (EU1).