Response of sheep to experimental concurrent infection with tick-borne fever (Cytoecetes phagocytophila) and louping-ill virus

The pathogenesis of concurrent Cytoecetes phagocytophila and louping-ill virus infection was studied in two experiments. In the first experiment 18 four- to seven-year-old rams were used. Ten were infected with C phagocytophila and five days later eight of these animals and the remaining eight sheep were infected with louping-ill virus. The two rams infected with C phagocytophila alone developed no clinical signs apart from a transient pyrexia, while only three of the eight rams infected with louping-ill virus alone showed mild clinical signs. In marked contrast, all eight dually infected sheep developed severe clinical signs with pronounced depression and dysentery and three died and five were killed in extremis. They developed higher titres of viraemia and the antibody response was depressed while necrotising lesions affecting a variety of organs were detected at post mortem examination. Rhizomucor pucillus was recovered from these lesions in seven of the eight sheep. A second experiment using 10 sheep, five aged seven months and five aged two to three years, confirmed the findings of the first experiment indicating that the age of the animal had not significantly influenced the initial result. It was concluded that C phagocytophila infection could enhance the pathogenicity of louping-ill virus and that, operating together, the two pathogens facilitated fungal invasion. It is postulated that sudden deaths in sheep recently transferred to tick-infested pastures may be due to this newly described syndrome.     

The effects of Ehrlichia (Cytoecetes) phagocytophila on the clinical chemistry of sheep and goats

Tick-borne fever (TBF) is a rickettsial disease of domestic and wild ruminants in temperate climates where the hard tick Ixodes ricinus is present. The disease is characterized by a high temperature and severe leukopenia. In the present study, the effects of TBF on the activity of serum alkaline phosphatase (ALP), and on the concentrations of plasma zinc, iron, total bilirubin, urea, creatinine and albumin were investigated by inoculating one group of eight sheep and one group of eight goats with the Old Sourhope (OS) strain of Ehrlichia (Cytoecetes) phagocytophila. All goats and sheep experimentally infected with E. phagocytophila reacted with fever, rickettsiaemia and leukopenia. The leukopenia was due to an acute lymphocytopenia and prolonged neutropenia. In both groups of animals. TBF was characterized by significant reductions in the activities of serum ALP and concentrations of plasma zinc, iron and albumin. However, there were significant increases in the concentrations of plasma total bilirubin, urea and creatinine in both species of animals. The reductions in ALP and iron were significantly more pronounced in sheep than in goats.     

Lymphocyte responses to mitogens and rickettsial antigens in sheep experimentally infected with Ehrlichia (Cytoecetes) phagocytophila.

Infection of sheep with Ehrlichia (Cytoecetes) phagocytophila, the causative agent of tick-borne fever (TBF), was characterised by a significant reduction in lymphocyte reactivity to the mitogens phytohaemagglutinin, concanavalin A, pokeweed mitogen and Escherichia coli lipopolysaccharide during the period of rickettsiaemia. The addition of the prostaglandin inhibitor, indomethacin, or the nitric oxide inhibitor, N(G)-monomethyl-L-arginine, had no significant effect on the suppressive effects of E. phagocytophila on lymphocyte reactivity to the mitogens. However, peripheral blood lymphocytes obtained from primed sheep proliferated in the presence of live or heat-inactivated E. phagocytophila. Antigen-specific proliferation was detected in lymphocytes samples obtained 11 to 21 days post-inoculation with E. phagocytophila.     

Efficacy of long-acting oxytetracycline for the prevention of tick-borne fever in calves

Twenty-six calves which had not previously grazed tick-infested pasture were divided into two equal groups. On May 26, 1988 (day 0) they were turned out into a field of rough grazing where cases of redwater fever had occurred the previous spring. Seven, 14, 21 and 28 days after the start of the trial the animals in one group each received an intramuscular injection of 20 mg/kg bodyweight of long-acting oxytetracycline. During the 60 days of the trial the animals received a severe tick-borne fever challenge, in some cases combined with a redwater fever challenge. An unforeseen complicating factor was the presence of animals persistently infected with bovine viral diarrhoea virus, present in almost equal numbers in both groups. At the end of the trial the treated group weighed on average 16 kg more than the control group, a difference which was attributed to the suppression of tick-borne fever by oxytetracycline.     

Tick-borne fever (Ehrlichia phagocytophila infection) on a dairy farm in Friesland

Disease outbreaks, associated with ixodid ticks, among cows on a dairy farm in Friesland, in the north of the Netherlands, were monitored during the summers of 1996, 1997, and 1998. The most important symptoms were a sudden drop in milk yield, fever, apathy, and problems with locomotion. The diagnosis 'tick-borne fever' was confirmed by finding Ehrlichia phagocytophila inclusion bodies in neutrophils of blood smears from sick animals. Significant economic losses due to the disease were recorded each year. Borrelia burgdorferi, although transmitted by the same tick, did not seem to be involved. Further research on tick-borne fever is of particular relevance in connection with recent E. phagocytophila cases diagnosed in dogs and in a human patient in the Netherlands.     

Prophylactic efficacy of clorsulon against Fasciola hepatica in calves and sheep

A daily oral 5 mg kg-1 dose of clorsulon for 28 days in calves given Fasciola hepatica cysts at 3, 5, and 7 days after initiation of treatment was highly effective in reducing worm burdens (98%) and preventing liver pathology. In similarly infected and treated sheep, clorsulon showed little effect as a prophylactic for delaying the onset of liver pathology. The size of flukes recovered from treated sheep was reduced. Although clorsulon prevented development of fascioliasis in treated calves, the host antibody response was qualitatively similar to that of untreated infected calves, but the magnitude of the response was reduced. Blood clorsulon levels in calves rose to 2.90 micrograms ml-1 within the first week of treatment then fluctuated between 2.65 and 2.90 micrograms ml-1 for the next two weeks. Clorsulon levels in sheep were 0.50-0.60 micrograms ml-1 lower than those in calf blood. The difference in bioavailability of clorsulon between sheep and calves may have contributed to differences in efficacy of the drug.     

Functions of neutrophils in sheep experimentally infected with Ehrlichia phagocytophila

Ehrlichia phagocytophila infection in sheep is characterized by persistent neutropaenia, indicative of decreased phagocytic capacity. This predisposes infected animals to other infections. A whole blood flow cytometrical method was used to document the degree and extent of reduced phagocytic and respiratory burst activity in phagocytes during an experimental infection with E. phagocytophila, and monitored until 56 days post-infection. Six sheep at 5 months of age were inoculated with an intravenous injection of infected blood. Six age-matched sheep were used as controls. A period of reduced respiratory burst lasting up to Day 17 post-infection was recorded. The population of cells showing phagocytic activity without respiratory burst was larger in the infected animals compared to controls up to Day 45 post-infection.     

Teratogenicity of a mutagenised Rift Valley fever virus (MVP 12) in sheep

A 5-fluorouracil mutagenised Rift Valley fever virus strain, which was shown to be attenuated and immunogenic in cattle and sheep, was evaluated for its ability to cause teratogenic effects in pregnant sheep. A group of 50 sheep at various stages of pregnancy was inoculated with the virus and the pregnancies followed to term. There were two abortions and 14% of the lambs produced by vaccinated ewes showed teratogenic effects, the most prevalent being spinal hypoplasia, hydranencephaly, brachygnathia inferior and arthrygryposis. The foetal malformations of the central nervous and musculo-skeletal systems were mostly consistent with those observed in sheep vaccinated with the attenuated Smithburn RVF strain. The teratogenic effects of MVP12 were not seen in previous experiments by other authors as immunisation of sheep took place in the second to third trimester of pregnancy, when the foetal brain tissue has completed most of its cell division.     

Prophylactic use of antibiotics in surgery

"Sound and careful surgery is the sine qua non of wound management; antimicrobials are adjunctive." The key to successful use of prophylactic antibiotics in surgery is careful selection of cases and medication. There are no final rule or formulas that will always give optimal results. Listed below are some guidelines that may assis the clinician in determining the need and form of antimicrobial use. 1. The operation must carry a significant risk of bacterial contamination. Refined-clean and clean procedures should not be given prophylactic antibiotics. 2. Bacterial cultures should be taken when possible, and the medication used for prophylaxis should be effective against the organisms expected to be encountered. 3. Narrow spectrum antibiotics should be used to conserve the body's normal flora. Broad spectrum antibiotics needed to combat resistant infections should not be used for prophylaxis. 4. The antibiotic should be present in the wound in effective concentrations at the time of the incision and be maintained only as long as the risk of new bacterial contamination exists.     

The use of fine-particle phenothiazine against Trichostrongylus colubriformis in sheep with observations on its use against other species of worms

Extract

There has been an increasing amount of evidence in recent years that small-particle phenothiazine is more efficient than the usual commercial grades, particularly against Trichostrongylus spp., which are often inadequately controlled by the latter.     

Use of long-acting oxytetracycline against pasteurellosis in lambs

The efficacy of long-acting oxytetracycline in the control of pneumonic pasteurellosis in lambs was tested on seven Scottish farms. After laboratory confirmation of pasteurella-related deaths in lambs, half the lambs in each flock were given long-acting oxytetracycline (20 mg/kg intramuscularly) and half were left untreated. On three farms a single treatment was given and on four farms two doses were administered four days apart. Eighteen of the 878 control lambs died as a result of confirmed Pasteurella haemolytica pneumonia compared with one of the 878 treated lambs. In addition nine of the control lambs were diagnosed clinically to have pasteurellosis which responded to treatment with oxytetracycline. None of the treated lambs were seen to be ill during the trial.     

Chemoprophylaxis of Anaplasma ovis infection in sheep with a long-acting oxytetracycline

The chemoprophylactic efficacy of long-acting oxytetracycline was determined in 13 susceptible ewes infected with Anaplasma ovis. The drug was administered intramuscularly at a dose rate of 20 mg kg-1 body weight during the prepatent period. When the ewes were exposed to an equivalent homologous challenge on Day 45 post-infection, each showed a mild or inapparent reaction. The host reactions, i.e., body temperature, parasitaemia, packed-cell volume (PCV), haemoglobin, humoral and cell mediated immunity (CMI) were also studied. The results indicate that the use of oxytetracycline during the incubation period would minimise clinical signs of an Anaplasma infection; this may be due to an increasing CMI response.     

Efficacy of a long-acting formulation of ivermectin against Psoroptes ovis (Hering, 1838) on cattle

A study was conducted in cattle experimentally infested with Psoroptes ovis to compare the prophylactic control against P. ovis provided by a long-acting injectable formulation of ivermectin to that of a commercially available injectable formulation of doramectin. Thirty Holstein steers were used. Animals were allocated by restricted randomization based on Day 0 body weight, forming six replicates of five animals each. Within each replicate, one animal was randomly allocated to one of the following treatment groups, with ivermectin and doramectin administered subcutaneously where indicated: (1) untreated controls; (2) ivermectin long-acting injectable (LAI) 630 mcg/kg, 56 days before challenge; (3) ivermectin LAI 630 mcg/kg, 42 days before challenge; (4) ivermectin LAI 630 mcg/kg, 35 days before challenge; or (5) doramectin 200 mcg/kg, 35 days before challenge. Animals were housed in individual pens 1 week prior to treatment. All animals were experimentally infested with P. ovis mites in the area between the shoulders, on the same day. Live mites were counted in scrapings from mange lesions at 2 sites on each animal 14, 21 and 28 days after challenge. Live mites were found in 33, 67 and 83% of the untreated controls on each respective evaluation. No P. ovis mites were found in steers treated with ivermectin LAI. Those animals showed lower (P < 0.05) mite counts than untreated controls on evaluations conducted 21 and 28 days after challenge. These results indicate that the ivermectin long-acting injectable formulation prevents induced infestations by P. ovis for at least 56 days after treatment. Doramectin injectable formulation, used at 200 mcg/kg, did not have a prophylactic effect 35 days after treatment.