T. Leclipteux

Fetal infection with Neospora caninum in dairy and beef cattle in Belgium

Neospora caninum is a protozoan parasite, which causes fetal and neonatal mortality in livestock and companion animals. In 224 abortions in Belgian cattle, different diagnostic methods were used to demonstrate infection, and the presence of N. caninum. An indirect fluorescent antibody test (IFAT) was used to analyze fetal and maternal sera and immunohistochemistry (IHC) was performed when lesions consistent with neosporosis were observed in the brain, heart or liver. Twenty dairy cattle sera out of 70 (29%) and 13 beef cattle sera out of 93 (14%) were positive by IFAT. A positive titer to N. caninum was found in seven and three fetuses born to beef and dairy cows, respectively. Lesions consistent with N. caninum infection were observed in 17 fetuses. Of nine positive beef fetuses, five were confirmed by IHC while, all but one dairy fetus were confirmed using the same technique. Age had no influence on the serological status of the mother (P = 0.486) whereas husbandry system had a borderline influence (P = 0.082). However, a strong association (P = 0.004) between the level of antibodies in the dam and the occurrence of lesions in the fetus was observed and lesions were more prominent in dairy than in beef fetuses. Additionally, the distribution of intra-cerebral lesions was more extensive in dairy than in beef fetuses (P < 0.0001). Age and serological status of the fetus were found to influence the occurrence of lesions in beef fetuses (both P < 0.001) but no such significant relationships could be demonstrated in dairy fetuses. The study indicated that N. caninum must be considered as an important cause of bovine abortion in Belgium.

USE OF EXCRETORY/SECRETORY ANTIGENS IN A COMPETITION TEST TO FOLLOW THE KINETICS OF INFECTION BY FASCIOLA HEPATICA IN CATTLE

Eight 16-18-month-old Charolais heifers were experimentally infected with Fasciola hepatica. An antigen competition assay was used to follow the kinetics of the infection and was compared to antibody tires and serum liver enzymes. The antigen competition assay was able to detect the presence of infection as soon as 6 days after the start of the experimental infection which is considerably sooner than other methods. Consequently, this assay would be useful in diagnosing fasciolosis early in the prepatent period. The animals were slaughtered at the end of the experiment, the livers recovered and post-mortem fluke burdens determined. However, only serum liver enzyme levels gave any indication of the intensity of infection in the different animals.

In vitro tests for evaluation of the hatchability of the eggs of Psoroptes mites following exposure to acaricidal compounds.

Abstract.  Three in vitro assays for the evaluation of the hatchability of the eggs of the mite Psoroptes ovis (Hering) (Acari: Psoroptidae) are described. Preliminary trials showed that hatching occurs at very high rates when eggs are incubated under conditions of high humidity, on a liquid medium and in agarose dishes. These three protocols were compared, taking into account the ease of preparation, follow‐up and accuracy of counting. The best protocol was found to be the use of agarose dishes. It was accurate, easy to carry out and reproducible for further evaluation of existing or potentially new compounds against both adults and eggs of Psoroptes spp. The acaricidal properties of phoxim and amitraz were then evaluated against eggs and adults using the three protocols. Results showed that for both drugs, in vitro adulticidal activity was complete, whereas the in vitro ovicidal activity was only partial. Nevertheless, efficacy of amitraz against both adults and eggs was shown to be higher than that of phoxim.

Ultrastructural morphology of the male and female genital tracts of Psoroptes spp. (Acari: Astigmata: Psoroptidae).

The structure of the male and female genital systems of the astigmatid mite Psoroptesovis (Hering) is described. The male genital system is composed of a paired testis, fused at its proximal part, two vasa deferentia, an ejaculatory duct, into which a single accessory gland opens, and a copulatory organ. The testis is characterized by a peripheric syncytial cell surrounding spermatogonia, spermatocytes, spermatids and spermatozoa which are distributed regularly in the gonad according to the sequence of spermatogenesis. The female genital system consists of a copulatory pore (the bursa copulatrix), a seminal receptacle, paired ovaries and oviducts, a glandular uterus and an ovipositor which leads to the oviporus. Ovaries are composed of somatic cells, germ cells and a central cell, with a multilobular nucleus, connected to oocytes by a stalk. Similarities with other astigmatic mites belonging to Psoroptidia and Acaridia are also discussed.

Field Efficacy of Injectable Doramectin against Chorioptes Bovis in Naturally Infected Cattle

A single subcutaneous injection of doramectin at a dose rate of 200 μg/kg bodyweight was effective in controlling an infection of Chorioptes bovis mites in naturally infected cattle. From 14 days after treatment, the geometric mean number of live mites was significantly lower (P<0.001) in the doramectin-treated cattle than in the control group at each sampling until day 35. The percentage efficacy (treated versus controls) of doramectin against C bovis at day 35 was 99.9 per cent and the percentage reduction (day 35 versus day 0) in the treated animals was 99.3 per cent. At day 35, all seven controls were still positive for C bovis whereas five of the eight doramectin-treated animals were free of live mites.