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.     

Resistance to tick-borne fever in young lambs.

Lambs were inoculated with Ehrlichia phagocytophila infected blood at the age of either two or six weeks. The temperature response and degree of parasitaemia were both most pronounced in the lambs inoculated at six weeks old. The half-life of antibodies to E phagocytophila was estimated to be 17.5 days. Lambs inoculated with tick-borne fever (TBF) had lower liveweights in the autumn than TBF-free controls.     

Effects of the dose of Ehrlichia phagocytophila on the severity of experimental infections in lambs

Twenty-one lambs were used to investigate whether their response to an infection with Ehrlichia phagocytophila was dose-dependent Four groups of four lambs were infected intravenously with a dilution in physiological saline of E phagocytophila-infected sheep blood containing either 1.3 x 10(5) infected cells, or approximately 43 infected cells, 4.3 infected cells, or 1.3 infected cells (mean values) and four lambs were left uninfected. The incubation period was significantly shorter in the lambs infected with the highest dose of E phagocytophila. However, the clinical and haematological changes observed, and the weekly weight gains of the lambs were independent of the dose of E phagocytophila. As little as one Ephagocytophila infected cell may be enough to transmit the infection.     

Chemotherapy and pharmacokinetics of some antimicrobial agents in healthy dwarf goats and those infected with Ehrlichia phagocytophila (tick-borne fever)

The therapeutic efficacy and pharmacokinetics of oxytetracycline (10 mg kg-1), ampicillin (20 mg kg-1) and a combination (TSS) of trimethoprim (20 mg kg-1), sulphadimidine (50 mg kg-1) and sulphamethylphenazole (50 mg kg-1) were investigated in normal dwarf goats and in those infected with Ehrlichia phagocytophila. Goats given oxytetracycline or TSS intravenously showed improvement, whereas ampicillin was ineffective. The infected goats had significantly prolonged elimination half-life values for sulphadimidine and oxytetracycline. The disposition kinetics of ampicillin and sulphamethylphenazole showed no marked differences between the healthy and infected animals. The tick-borne fever model used in the present study can be of value in testing the therapeutic efficacy and pharmacokinetics of chemotherapeutic agents in rickettsial infections.     

Experimental and clinical trials of long acting oxytetracycline in the treatment of canine ehrlichiosis

Four splenectomized dogs were experimentally infected with Ehrlichia canis and treated at the point of illness with long acting (LA) Oxytetracycline at different dosages. Terramycin LA, when given at a dose of 20 mg/kg body weight (deep intramuscularly) twice, at a four-day interval, was found to have effectively controlled the disease and has replaced the usual 7-14 successive days' treatment regimen when other groups of tetracycline drugs are used. Predef 2X at the rate of 2 mg given intramuscularly concurrently eliminated the local inflammatory reaction caused by the injection of Terramycin LA. Twenty-four out of the 26 naturally infected dogs which were treated in a similar way were completely cured; one died before it could receive the full treatment, and another received a second medication five weeks after the first treatment, showing recurrent epistaxis; blood samples taken from this dog were negative for E. canis.     

Progression and control of leptospirosis in a sow herd

After a short review about etiology, epidemiology, clinical symptoms, diagnosis and therapy of leptospirosis the course and therapy of an acute leptospirosis outbreak in a breeding herd with nearly 240 sows is described. The microscopic agglutination test (MAT) served for diagnosis and was most reliable for estimation the actually stage of infection when used twice with an interval of several weeks. As causative agent serovar L. pomona was identified, whereby cross-reactions were seen to serovars L. grippotyphosa, L. bratislava and L. copenhageni. Therapy of all animals with Terramycin/LA (Pfizer) at three times with intervals of five days and doses of 20 mg oxytetracycline/kg b.w. distinctly reduced the incidence of abortion and stillborn or mummified pigs. Local irritations, relative to the intramuscular administration of oxytetracycline, mostly were low-graded and temporary. For the next months acute infections could not be registered. Probably due to infections from leptospires-reservoirs, maintained by numerous existing mice and puddles on the pasture-ground, leptospirosis occurred again six months later. Only another antibiotic therapy of the whole herd and simultaneous eradication of rodents as well as closing the pasture led to a long-termed control of leptospirosis in this herd.     

Tick-Borne Fever in Lambs of Different Ages

Four groups of lambs aged 1 week, 4 weeks, 1/2 year and 1 year old respectively were inoculated with Ehrlichia phagocytophila infected blood. Clinical signs, temperature reactions, haematological changes and parasitaemia were more moderate in lambs inoculated with E. phagocytophila at the age of 1 week than those recorded in the older animals. The clinical response to tick-borne fever (TBF) appears to be more severe with increasing age of the lambs. The lymphocyte reactivity to mitogens was reduced in the TBF infected lambs, and was most pronounced in lambs in the 3 older age groups.     

Experimental and clinical trials of long acting oxytetracycline in the treatment of canine ehrlichiosis

Summary

Four splenectomized dogs were experimentally infected with Ehrlichia canis and treated at the point of illness with long acting (LA) Oxytetracycline at different dosages. Terramycin LA, when given at a dose of 20mg/kg body weight (deep intramuscularly) twice, at a four‐day interval, was found to have effectively controlled the disease and has replaced the usual 7–14 successive days’ treatment regimen when other groups of tetracycline drugs arc used.

Predej^® 2X* at the rate of 2 mg given intramuscularly concurrently eliminated the local inflammatory reaction caused by the injection of Terramycin LA.

Twenty‐four out of the 26 naturally infected dogs which were treated in a similar way were completely cured; one died before it could receive the full treatment, and another received a second medication five weeks after the first treatment, showing recurrent epistaxis; blood samples taken from this dog were negative for E. canis.     

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.     

Comparison of three oxytetracycline regimes for the treatment of persistent Anaplasma marginale infections in beef cattle

Anaplasmosis, caused by the tick-borne rickettsia, Anaplasma marginale, is an economically important disease of cattle in the United States and worldwide. Cattle that recover from acute infection become carriers in which low or microscopically undetectable A. marginale rickettsemia persists. Tetracycline antimicrobials are currently the only drug used in the US for treatment of acute anaplasmosis. There are currently no drugs specifically licensed for elimination of persistent infections. This study tested the efficacy of three oxytetracycline treatment regimens to clear A. marginale from cattle that were persistently infected. Forty Angus x Simmental steers, aged 6-12 months were experimentally infected with A. marginale. After the steers recovered from acute infection, seroconverted, and were confirmed infected using nested PCR followed by DNA hybridization, the carrier status of each animal was ascertained by sub-inoculation of blood into a separate, splenectomized Holstein calf. The steers were then blocked by bodyweight and randomly assigned as follows to four treatment groups: Treatment A, 300 mg/ml solution of oxytetracycline (Tetradure LA-300, Merial Canada Inc.) administered at 30 mg/kg, by intramuscular (i.m.) injection on day 0; Treatment B, the same 300 mg/ml solution of oxytetracycline administered at 30 mg/kg, i.m. on day 0 and again on day 5; Treatment C, a 200 mg/ml solution of oxytetracycline (Liquamycin LA-200, Pfizer Animal Health) administered at 22 mg/kg, intravenously (i.v.), q 24 h for 5 days (a treatment dose that corresponds with current Office International des Epizooties (OIE) recommendations for treatment prior to export). The fourth group consisted of untreated infected control cattle. All steers were still nested PCR and cELISA positive at 60 days after treatment. Infection was confirmed by subinoculation of blood into a splenectomized Holstein calf. These results demonstrated that the treatment regimens tested failed to clear A. marginale infections in carrier cattle.     

Antibodies reactive with Ehrlichia canis, Ehrlichia phagocytophila genogroup antigens and the spotted fever group rickettsial antigens, in free-ranging jackals (Canis aureus syriacus) from Israel.

A seroepidemiological survey was conducted to investigate the prevalence of antibodies reactive with the Ehrlichia canis and Ehrlichia phagocytophila genogroup antigens, and the spotted fever group (SFG) rickettsiae antigens in jackals in Israel (Canis aureus syriacus), to assess the possible role of the jackal in the epidemiology of these diseases. Fifty-three serum samples from jackals were assayed by the indirect immunofluorescence antibody test. Antibodies to E. canis were detected in 35.8% serum samples while 26.4% of the samples tested were positive to Ehrlichia chaffeensis. Twenty-six percent of the jackals tested were seropositive to E. phagocytophila, of which 5.7% were seropositive to E. phagocytophila alone without any seroreactivity to either E. canis or E. chaffeensis. Fifty-five percent of the jackals were seropositive to the SFG-rickettsiae antigens. The results suggest a high exposure rate of jackals in Israel to E. canis. Positive reactivity to E. chaffeensis was considered to be due to antigenic cross-reactions with E. canis. The study demonstrated for the first time the presence of E. phagocytophila antibodies in free-range jackals. The high incidence of antibodies to the SFG-rickettsiae and their relatively high antibody titers was suggestive of either recent or persistent infection. The possibility that jackals may play a role in the transmission of E. canis, E. phagocytophila and the SFG-rickettsiae for human and canine infections is discussed.     

Doxycycline clearance of experimentally induced chronic Ehrlichia canis infection in dogs

BACKGROUND: Ineffective clearance of Ehrlichia canis after doxycycline administration has been reported despite the fact that the recommended treatment for canine ehrlichiosis is doxycycline. The effectiveness of doxycycline in clearing E canis infection from the blood and tissues of dogs requires additional evaluation. HYPOTHESIS: Doxycycline (5 mg/kg PO q12h), administered for 4 weeks, will eliminate E canis infection from the blood and tissues of experimentally infected dogs. ANIMALS: Fifteen Walker hound-mixed breed dogs were inoculated subcutaneously with E canis-infected canine histiocytic cells 4 months before doxycycline treatment. METHODS: Four dogs were treated with doxycycline (5 mg/kg PO q12h for 3 weeks), 5 dogs were treated with doxycycline at the same dosage for 4 weeks, and 5 control dogs were not treated. Dexamethasone (0.4 mg/kg i.v.) was given after treatment to precipitate recrudescence of any remaining E canis organisms. Platelet counts, anti-E canis immunofluorescent antibodies, and polymerase chain reaction (PCR) detection of E canis deoxyribonucleic acid (DNA) in blood and tissues were evaluated. RESULTS: E canis DNA was not detected in the blood and tissues of doxycycline-treated dogs after treatment. Platelet counts were within reference intervals, and E canis antibodies decreased. Spontaneous clearance of E canis infection occurred in 2 of 5 control dogs. Three control dogs had E canis DNA detected in blood and tissues, platelet counts remained low or within the reference interval, and E canis antibodies remained high. CONCLUSIONS AND CLINICAL IMPORTANCE: As administered in this study, doxycycline cleared E canis from the blood and tissues of experimentally infected dogs.     

Immunisation against East Coast fever by the infection and treatment method: evaluation of the use of ice baths for field delivery and appraisal of an acid formulation of long-acting tetracycline

Immunisation by the infection and treatment method using the Katete strain is currently the most efficient prophylactic technique to control East Coast fever (ECF) in the endemic areas of the Eastern Province of Zambia. The maintenance of the cold chain in liquid nitrogen up to the time of inoculation and the cost of the reference long-acting oxytetracycline (Terramycin LA, Pfizer) are the main drawbacks of the method. The work presented in this paper aims at reducing the cost of immunisation against ECF by using an ice bath for the field delivery and a cheaper long-acting oxytetracycline formulation as chemotherapeutic agent. In experimental conditions, the results from 40 calves immunised after various periods of storage on ice ranging from 4 to 32 h indicate that deferred immunisation performed with a stabilate kept on ice for up to 6h after thawing has an efficiency of 90%. Moreover, sporozoites kept on ice were still surviving 32 h after thawing. In a field trial, 91 calves were inoculated with a stabilate kept for 3.5-5.5 h after thawing and dilution whereas 86 calves were immunised using the standard method. Clinical and parasitological reactions to immunisation were monitored as well as the seroconversion. In the field trial, the deferred immunisation was more efficient than the standard method. The acid formulation of oxytetracycline that was tested was found as suitable as the reference alkaline formulation for the chemotherapeutic control of the Katete strain in ECF immunisation. One indoor trial was carried out on 10 animals and a field trial involved 93 calves.     

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.     

Listeriosis in Sheep: Tick-Borne Fever used as a Model to Study Predisposing Factors

Three groups of 6 months old lambs, each group consisting of 5 animals, were infected experimentally with Ehrlichia phagocytophila (Ep), Listeria monocytogenes (Lm) and Ep/Lm, respectively. All the animals had a period with fever and reduced appetite after infection, and these symptoms were most pronounced in the group with the combined infection (Ep/Lm). One animal in group Lm developed listeric meninigo-encephalitis.Lm was isolated from blood samples from both groups infected with Lm during the first week after infection, and from faecal samples during the first 2 weeks. Lm was also isolated from organs from several animals in these 2 groups at post-mortem examination.Group Ep/Lm developed the highest reciprocal geometrical mean titres and the stromgest delayed hypersensitivity reaction against Lm.After infection, a fall in serum iron and albumin was recorded, and the groups infected with Ep had a substantial fall in neutrophils.The myeloid : erythroid ratio in the bone marrow tended to decrease in Group Ep/Lm after infection.An increase in leucocyte counts and total protein content was found in the cerebrospinal fluid in the 2 groups infected with Lm, The experiment indicates that the blood changes induced by tick-borne fever viz, neutropenia and probably also impaired function of the neutrophils, may predispose for listeric septicaemia, but probably not for listeric meningo-encephalitis.     

Differential haematological effects of tick-borne fever in sheep and goats

Tick-borne fever (TBF) is a rickettsial disease of domestic and wild ruminants in temperate climates. It is characterized by high fever and severe leukopenia. In the present study, the possible difference in the severity of disease in sheep and goats was investigated by inoculating one group of eight goats and one group of eight sheep with the Old Sourhope (OS) strain of Ehrlichia (Cytoecetes) phagocytophila. All sheep and goats experimentally infected with E. phagocytophila reacted with fever and rickettsiaemia, but there were significant differences between goats and sheep in the severity of clinical disease, the duration and magnitude of fever, the magnitude of rickettsiaemia and the patterns of reduction in the number of total leucocytes. Sheep reacted with fever significantly earlier than goats and the febrile period lasted for a significantly longer period. In contrast, the magnitude of rickettsiaemia was significantly higher in goats than in sheep. Infection with TBF was characterized by a transient increase in the number of neutrophils, which was quickly followed by an acute reduction in the number of lymphocytes and a prolonged reduction in the number of neutrophils in both sheep and goats. In both groups of animals, infection with TBF was also characterized by significant reductions in the total number of red blood cells (RBCs), thrombocytes and packed cell volume (PCV) and the concentration of haemoglobin (Hb). However, the mean corpuscular volume (MCV) and mean corpuscular Hb (MCH) were significantly increased in sheep only.     

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.     

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.     

Some aspects of tick-borne diseases of British sheep

The significance of tick-borne fever (TBF) and other tick-borne diseases of British sheep are reviewed. Experimental and field studies were carried out to clarify the role of TBF as a pathogen per se and as a predisposing factor in other diseases. Experimental TBF infection caused anorexia and depression in two- to three-week-old lambs, which under the stress of a hill environment could alone be a cause of mortality. Nine out of 10 lambs experimentally inoculated with Staphylococcus aureus during the febrile phase of a TBF reaction developed pyaemic lesions compared with four out of 20 lambs inoculated with S aureus alone. Specific pathogen-free lambs inoculated with an aerosol of Pasteurella haemolytica serotype A1 during a TBF reaction showed more severe clinical signs and had more extensive pathological changes at necropsy than control lambs given P haemolytica alone. Dual infection with TBF and louping-ill virus showed that not only were dually infected sheep more susceptible to louping-ill but almost all of them succumbed to a haemorrhagic syndrome involving a systemic mycotic infection with Rhizomucor pucillus. None of eight sheep given louping-ill virus alone developed this syndrome. Field studies indicated that morbidity and mortality in lambs in south-west Scotland could be markedly reduced by dipping and long acting antibiotic prophylaxis. Lamb groups in which both of these were carried out incurred losses of only 0.6 per cent compared with 10.3 per cent in control groups. In addition antibiotic-treated lamb groups demonstrated significantly better weight gains than untreated groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Studies on Oral Transmission of Potomac Horse Fever

Eight normal ponies placed in direct contact with ponies experimentally infected with Ehrlichia risticii for 30 to 90 days did not develop signs of Potomac horse fever. They also did not seroconvert, and they remained susceptible to IV infection. One of 8 ponies that were force fed fresh feces from infected ponies while in direct contact with ponies experimentally infected with E. risticii developed Potomac horse fever and seroconverted. The other 7 remained asymptomatic, did not seroconvert, and were susceptible to IV infection. Six of 9 ponies inoculated with E. risticii via nasogastric intubation and oral drench developed Potomac horse fever and serocon verted. The other 3 remained asymptomatic and did not seroconvert. One of these latter ponies and 2 normal ponies that were inoculated via oral drench only developed Potomac horse fever and seroconverted. The high fever, maximum clinical score for decreased feed intake, depressed mental attitude, decreased borborygmal sounds, severity of diarrhea, and the length of illness of the orally infected ponies was not significantly different from those of IV infected control ponies, although the signs occurred significantly later ( P < .05).