Experimental production of tick pyaemia

Lambs aged 2 weeks were inoculated with a tick-borne fever (TBF) stabilate on Day 0 and Staphylococcus aureus-contaminated ticks were applied on Day 5. Tick pyaemia was produced experimentally for the first time using Ixodes ricinus as a mechanical vector of S. aureus. Lambs aged 18 weeks were rechallenged with a homologous strain of TBF, and S. aureus-infected ticks applied 5 days later. No significant changes were noted at post-mortem examination.     

The effect of two different oxytetracycline treatments in experimental Ehrlichia phagocytophila infected lambs

The effect of 2 different oxytetracycline treatments in acute E. phagocytophila infected lambs was investigated. Twenty 5-month-old lambs of the Dala and Rygja breeds were used. Ten lambs were inoculated intravenously with a stabilate of an ovine E. phagocytophila strain. On the third day of fever, 4 lambs were given long-acting oxytetracycline (Terramycin prolongatum vet, Pfizer) (20 mg/kg) intramuscularly and another 4 lambs were given short-acting oxytetracycline (Terramycin vet, Pfizer) (10 mg/kg) intravenously for 5 consecutive days. The lambs were examined for the presence of Ehrlichia infection by blood smear evaluation, polymerase chain reaction (PCR) and antibody titre against E. equi. One month after the last antibiotic treatment, 250 ml citrate blood from each of these lambs were inoculated into each of 10 susceptible lambs, which were observed during the following 6 weeks. The results indicate that oxytetracycline given in the acute stage of the infection may effectively terminate the development of fever, rickettsemia and weight reduction in E. phagocytophila infected lambs. No difference was observed between the 2 treatment groups. However, at least 3 of 8 antibiotic treated lambs (37.5%) were still infected with granulocytic Ehrlichia 3 months after treatment.     

Persistence of Ehrlichia phagocytophila infection in two age groups of lambs

Tick-borne fever (TBF) is caused by the rickettsiae Ehrlichia phagocytophila and is a common disease in sheep in tick (Ixodes ricinus) infested areas in Norway. Earlier investigations have shown that some sheep could remain infected for several months after the primary infection. In this study, the persistence of E. phagocytophila after experimental infection was investigated in 2 age groups of lambs. Six lambs (1-2 weeks old) and 14 lambs (6-8 months old) were inoculated intravenously with an ovine strain of E. phagocytophila and thereafter examined clinically (including daily body temperature recording) and by haematological and serological (E. equi antibodies) methods for the next 4 months. At the end of this period, the lambs were examined for a TBF infection by blood smear investigation and blood inoculation studies. The infection was demonstrated in 19 (95%) of the 20 lambs.     

Lymphocyte reactivity to antigens of Haemonchus contortus in antigen-inoculated and H contortus-naive lambs.

Lambs were inoculated during either fetal or early neonatal life with antigens of Haemonchus contortus (HcAg) third-stage larvae, or ovalbumin (OVA), or were left untreated. By the time lambs were 4 weeks old, blood lymphocytes from all of them responded to HcAg. This was evident in all lambs, regardless of the previous inoculation regimen, although higher response was seen in HcAg-inoculated lambs, compared with naive lambs. Only lambs inoculated with OVA had OVA-specific lymphocyte activity. In HcAg-naive lambs, the maximal HcAg lymphocyte response was observed between the ages of 5 and 25 weeks, with gradual decrease thereafter. In vitro detection of HcAg-reactive lymphocytes was affected by antigen concentration and presence of plasma. Plasma inhibited HcAg-reactive lymphocytes from all lambs at high in vitro antigen concentration and completely abrogated the response in H contortus antigen-naive lambs.     

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.     

Use of counter immunoelectrophoresis in detection of antibodies to tickborne fever

A micromethod using the counter immunoelectrophoresis technique for the detection of antibodies to Cytoecetes phagocytophila, the causative agent of tickborne fever (TBF) is described. Antibodies were first detected nine to 11 days after experimental infection of lambs with TBF and persisted for six to 10 weeks after infection. The test was also applied to approximately 440 field samples of ovine sera collected from tick infested farms in Scotland and the north of England, 16 per cent of which proved positive and showed a marked seasonal variation.     

The haematology of experimentally-induced B divergens and E phagocytophila infections in splenectomised calves

An examination was made of the haematology of spenectomised calves experimentally infected with Babesia divergens and Ehrlichia phagocytophila, inoculated separately or simultaneously. Animals infected with both pathogens had less marked changes in their haematology than those inoculated with either pathogen separately. This appeared to result from the early elimination of the more pathogenic Babesia as Ehrlichia spread through the granulocytes. The apparent suppression of Babesia by Ehrlichia would appear to merit further investigation.     

Clinical and microbiologic findings in lambs inoculated with Pasteurella haemolytica after infection with ovine adenovirus type 6

Colostrum-deprived lambs (10 to 20 days old) were inoculated with either ovine adenovirus type 6 (OAV-6; n = 6), Pasteurella haemolytica type A1 (n = 6), or OAV-6 followed by P haemolytica 5 days later (n = 10). Another group (n = 3) served as sham-inoculated controls. Lambs inoculated with OAV-6 or P haemolytica developed mild and moderate respiratory tract disease of 6 and 3 days' duration, respectively. Lambs inoculated with virus and bacteria developed clinical signs of respiratory tract disease of greater intensity and duration (9 days) than with either agent alone. Within 3 hours of bacterial inoculation, all lambs that received P haemolytica were anorectic, listless, and febrile, and had hyperpnea and dyspnea. Ovine adenovirus type 6 was isolated from all virus-inoculated lambs. Although P haemolytica was not recovered from all bacteria-inoculated lambs, it was recovered for a longer period in the group that received both agents. Antibody to OAV-6 was detected in virus-inoculated lambs as early as day 6 after inoculation. The control lambs remained clinically normal and neither virus nor bacteria were recovered at necropsy.     

Pathogenicity of Mycoplasma capricolum in sheep after experimental infection

Mycoplasma (M.) capricolum has been frequently isolated from diseased as well as from healthy sheep in Morocco. In order to determine its pathogenicity for sheep, experiments were performed in three trials with the Moroccan isolate 012. The following results were obtained: Ewes inoculated intramammarily developed acute mastitis; the organism was transmitted to lambs suckling these ewes. Only a mild mastitis appeared after a second inoculum, performed 5 weeks after the first. Young lambs, 1 month of age, fed four times with M. capricolum broth culture, died during the septicemic phase, showing a generalized septicemia, polyarthritis and a diffuse interstitial pneumonia. Lambs, 2 and 3 months of age inoculated intrabronchially developed a disease, which appeared to be age and weight dependent. The more susceptible animals died within 1-2 weeks after infection. The older lambs recovered gradually from the disease, which was characterized by pneumonia, conjunctivitis and arthritis. A significant increase of antibodies against M. capricolum developed in the older animals in the complement fixation test.     

Short interval intradermal skin testing in farmed red deer (Cervus elaphus) inoculated with Mycobacterium bovis

Two groups of 26 red deer (Cervus elaphus) were tuberculin skin tested for 41 weeks at three and six week intervals respectively, except at 17 weeks when the internal was two and five weeks. Seventeen weeks after the start of the experiment 36 deer were inoculated intratracheally with Mycobacterium bovis, and the remaining 16 were run in-contact. At six weeks post inoculation, 35 of the 36 inoculated deer reacted to the skin test with a mean skin thickness difference (STD) of 6.3 mm. In inoculated deer further testing led to a suppression of skin sensitivity which was significantly greater in the three-weekly tested group. There was no statistical difference in skin thickness response between 1 and 2 mg/ml bovine purified protein derivative (PPD). Of 454 tests on noninoculated deer (noninfected), 107 produced reactions. These reactions were small and 96% had a STD of less than 2 mm.     

Experimentally induced Fasciola hepatica infection in white-tailed deer. II. Pathological features.

Six white-tailed deer (Odocoileus virginianus) and six sheep were inoculated with metacercariae of Fasciola hepatica. Two animals of each species were given 100, 500 or 2500 metacercariae. One animal in each inocluated group was killed and examined at six weeks postinoculation and the remainder at 15 weeks postinoculation. At six weeks postinoculation the parietal surface of the livers from inoculated deer was covered with gray fibrous plaques and rust colored patches. Fibroplasia with mononuclear cell infiltration characterized Glisson's capsule on the parietal surface. Granulomas were found in the hepatic parenchyma and on the dorsal surface of the lung. Fresh and healing tracks were occasionally found in the liver. In the sheep fibrinous exudate and numerous subcapsular tracks were found on both surfaces of the liver. Inflammatory changes in portal areas and numerous fresh and healing tracks in the hepatic parenchyma were prominent features. At 15 weeks postinoculation inflammatory changes in Glisson's capsule of inoculated deer were less marked than at six weeks but portal fibrosis and hyperplasia of bile duct epithelium were more advanced. A zone of hemorrhage surrounded ducts that contained mature F. hepatica in one deer. The livers from the sheep were rough, pitted and covered with fibrous tags and adhesions to the diaphragm and greater omentum were common. Hemorrhagic tracks were common in the sheep given 500 and 2500 metacercariae. Portal fibrosis and hyperplasia of bile duct epithelium were seen in the sheep (100 metacercariae) that harbored mature F. hepatica.     

Efficacy of ivermectin against Cooperia curticei infection in sheep

Lambs were inoculated with a single dose of Cooperia curticei. Subcutaneous administration of ivermectin at a dosage of 200 micrograms/kg of body weight resulted in 61.1% and 90.4% anthelmintic efficacy, when measured at 7 and 14 days after treatment, respectively. In the treatment groups, parasites that remained were located more distally in the small intestine than those in the lambs in the control groups.     

Detection of granulocytic Ehrlichia species DNA by PCR in persistently infected dogs

Three female beagle dogs inoculated with granulocytic Ehrlichia species were monitored for four to six months to determine whether there was evidence that the organisms persisted. The dogs were inoculated intravenously with blood containing an Ehrlichia species closely related to Ehrlichia equi and Ehrlichia phagocytophila, and identical to the human granulocytic ehrlichiosis agent with respect to its 16S rRNA gene sequence. The clinical signs were evaluated, and blood samples were collected for haematology, serum biochemistry and serology. Ehrlichial inclusions in the blood were monitored by microscopy, and ehrlichial DNA was detected by the polymerase chain reaction (PCR). Two of the dogs were injected with prednisolone on days 54 to 56 and days 152 to 154 after infection, and the other was injected with prednisolone on days 95 to 97 after infection. The dogs were euthanased and examined postmortem. Ehrlichial inclusions were demonstrated in the neutrophils and seroconversion occurred shortly after inoculation. Two of the dogs developed acute disease with rectal temperatures above 39.0 degrees C, after which no further clinical signs were observed. The administration of corticosteroids seemed to facilitate the detection of ehrlichial inclusions. Ehrlichial DNA was detected intermittently by PCR in blood samples from two of the dogs throughout the study. Persistent infection was demonstrated up to five-and-a-half months after inoculation.     

Experimentally induced Faciola hepatica infection in white-tailed deer. I. Clinicopathological and parasitological features.

Six white-tailed deer (Odocoileus virginianus) and six sheep were inoculated with metacercariae of Fasciola hepatica. Two animals of each species were given 100, 500 or 2500 metacercariae. Clinicopathological features of these infections were determined by analyses of blood samples collected each week from inoculated deer and sheep as well as from two noninoculated animals of each species. One animal in each inoculated group was killed and examined at six weeks postinoculation and the remainder at 15 weeks postinoculation. Compared with the values obtained from noninoculated controls, eosinophilia, hyperproteinemia and hyperglobulinemia occured in inoculated deer. There were no other significant changes in hematological values or in serum aspartate aminotransferase levels. Marked leukocytosis and eosinophilia, with hyperproteinemia, hyperglobulinemia, hypoalbuminemia, elevated serum aspartate aminotransferase levels and mild macrocytic normochromic anemia characterized the infection in lambs. Although approximately 29% of the inoculum was recovered from the hepatic parenchyma of the sheep, F. hepatica was found in only one of six inoculated deer. A patent infection was established in this deer and constitutes the second report of mature F. hepatica in this host.     

Effects of the timing of the administration of Mycoplasma hyopneumoniae bacterin on the development of lesions associated with porcine circovirus type 2

To determine whether there is an effect of the timing of vaccination on porcine circovirus type 2 (PCV-2) replication and PCV-2-associated lesions, 78 pigs were randomly assigned to eight groups: group 1 (10 pigs) was vaccinated with a commercial Mycoplasma hyopneumoniae vaccine at two and four weeks of age, group 2 (nine pigs) was vaccinated at four and six weeks of age, group 3 (10 pigs) at six and eight weeks of age and group 4 (10 pigs) at eight and 10 weeks of age; group 5 (nine pigs) was vaccinated once with a double dose at four weeks of age, and group 6 (10 pigs) was vaccinated once with a double dose at eight weeks of age. Groups 7 and 8, both of 10 pigs, were not vaccinated. At eight weeks of age, the pigs in groups 1 to 7 were inoculated with PCV-2. Fourteen days after they had been inoculated, the pigs in groups 1, 4 and 5 had significantly (P<0.05) more copies of the PCV-2 genome in their serum than the unvaccinated pigs. Microscopically, 14 of the 68 inoculated pigs had normal lymphoid tissues, 40 had mild PCV-2-associated lymphoid lesions and 14 had moderate lesions. The mean overall lymphoid lesions (lymphoid depletion, granulomatous inflammation, and quantity of PCV-2 antigen in spleen, tonsil, and five lymph nodes) were significantly (P<0.05) more severe in groups 4 and 5 than in groups 2, 3, 7 and 8.     

Immunization against ovine haemonchosis with three low molecular weight somatic antigens of adult Haemonchus contortus

Individual bands (15) from electroblotted soluble extracts of adult Haemonchus contortus were excised and three peptides of molecular weight ca. 56 (F4), 39 (F8) and 18.5 kDa (F14) used to vaccinate 4-4.5-months-old lambs against the nematode. Immunizing doses from each peptide were administered in 1 ml Freund complete adjuvant (first 50 microg injection) and 1 ml Freund incomplete adjuvant (second and third 50 microg injections) to six lambs. Two weeks after last immunization, animals were challenged with 300 L-3/kg live weight (LW). Lambs were slaughtered 34 days after challenge. Immunization induced a strong antibody response estimated by enzyme-linked immunosorbent assay, whereas no peripheral lymphoproliferative response was observed. Lambs in the F8-vaccinated group showed on average delayed pre-patent period, lower faecal egg counts and reduction of abomasal worm burdens, although the differences were not statistically significant.     

Studies on transmission of maedi virus to lambs

Lambs born to 5 ewes in 3 successive years were studied for presence of maedi virus and its antibodies. In the middle of the first-year pregnancies the ewes and the only ram of the colony were inoculated with maedi virus. No antibodies or viraemia could be detected in the lambs at birth. After sucking colostrum, antibodies appeared in the lambs of the ewes which themselves were seropositive, and reached their peak in a few days. Maternal antibodies disappeared within 12 weeks in all the lambs. Neutralizing antibodies were demonstrated in the colostrum and their content declined rapidly after lambing. Virus was isolated from the milk of 2 ewes in the third year of the studyIn the first year the spread of maedi virus was demonstrated to only 1 of the lambs, but in the other 2 years maedi virus was detected in tissues of half of the lambs sacrificed at 3–12 weeks of age. It was concluded that lambs born to chronically infected ewes are readily infected, indicating excretion of virus by ewes. The study yielded no information on the specific routes of transmission, except for the finding of the virus in milk of 2 ewes in the third year of the study. No evidence was obtained of transplacental transmission of maedi.     

Dual infection of lambs with Trichostrongylus colubriformis and chlamydiae

Lambs in one group were inoculated with chlamydiae and Trichostrongylus colubriformis larvae simultaneously; lambs in a second group were inoculated with chlamydiae after a T. colubriformis infection was established. Results were compared to those from groups inoculated with T. colubriformis only and chlamydiae only. There were no significant differences in fecundity associated with chlamydial inoculation. Packed cell volumes (PCVs) were depressed in groups inoculated with chlamydiae, and chlamydial antibody formation appeared to be inhibited when chlamydiae was superimposed on a T. colubriformis infection. Relatively few T. colubriformis adults were recovered in lambs inoculated with chlamydiae and T. colubriformis simultaneously.     

Immunization of sheep against Theileria hirci infection with schizonts propagated in tissue culture

Two experiments were carried out. In the first, three groups of lambs were inoculated subcutaneously with 3 X 10(6) schizonts of different passages (3, 30 and 63) of Theileria hirci propagated in tissue culture. Severe reactions were observed in lambs inoculated with organisms derived from the 3rd passage. In the second experiment, four groups were inoculated with 5 X 10(5), 3 X 10(6), 1 X 10(7) and 5 X 10(8) schizonts of the 63rd passage. No clinical reactions or parasites were detected in lambs inoculated with 5 X 10(5) schizonts. Mild reactions were observed in lambs inoculated with 3 X 10(6), 1 X 10(7), and 5 X 10(7) schizonts. Lambs inoculated with 3 X 10(6) schizonts were resistant to challenge with a virulent strain. The indirect fluorescent antibody (IFA) test was used to determine the antibody titre.