Tissue tropism of Toxoplasma gondii in turkeys (Meleagris gallopavo) after parenteral infection.

Turkeys are known to be natural hosts for the zoonotic protozoan parasite Toxoplasma gondii. The objective of the present study was to gain further knowledge of possible predilection sites of T. gondii infection in this species after parenteral application of tachyzoites. A total of 38 turkeys were infected with different doses of T. gondii tachyzoites. Birds were killed either 6 to 8 or 10 to 12 weeks after the experimental infection. Fourteen different tissues per bird were investigated by a nested polymerase chain reaction (PCR) for the presence of the parasites' DNA. T. gondii DNA was found in any type of tissue analysed; in 86.1 % of all infected birds, at least one sample was tested positive. Over all intravenously infected birds, 15.4 % of all analysed samples contained T. gondii DNA. Most frequently affected tissues were liver (43.3 % positive samples), breast muscle (26.7 % positive samples) and heart (20.0 % positive samples), while the brain was less frequently positive (6.7 %). The number of positive tissues varied from zero to seven tissues per animal with at least one T. gondii-positive edible tissue sample in 80 % of all intravenously infected birds. Still, the results did not indicate defined target tissues or a cyst distribution pattern. Nonetheless, edible organs were most frequently parasitised. The number of positive findings did not differ between the early and the late examination time points. Therefore, a persistence of the tissue stages until the end of the study (12 weeks after infection) is concluded.

Detection of methicillin-resistant Staphylococcus pseudintermedius with commercially available selective media.

AIMS: Commercially available selective media for methicillin-resistant Staphylococcus aureus (MRSA) were tested for the detection and isolation of methicillin-resistant Staphylococcus pseudintermedius (MRSP). METHODS AND RESULTS: Five different screening agars [mannitol salt agar with oxacillin and BD BBL™ Chromagar™ MRSA (BD Diagnostics); chromID™ MRSA agar (bioMérieux); Oxacillin resistance screening agar base (ORSAB); and Brilliance MRSA agar (Oxoid)] were analysed for the detection of MRSP. Bacteria that may be isolated together with MRSP and may grow on the screening agars were included in the study to determine possible interference with the growth of MRSP. MRSP grew well on all selective media except on BD BBL™ Chromagar™ MRSA (BD Diagnostics) and chromID™ MRSA agar (bioMérieux), on which a low to moderate growth rate was noted. CONCLUSIONS: ORSAB (Oxoid) and Brilliance MRSA agar (Oxoid) are most suitable for the detection and isolation of MRSP from clinical material. SIGNIFICANCE AND IMPACT OF THE STUDY: The importance of MRSP in veterinary medicine is increasing. Diagnostic systems are needed to detect MRSP carrier as soon as possible. This study provides information about selected MRSA screening agars for the detection of MRSP to the clinical microbiologists.

Growth inhibiting activity of lipophilic extracts from Dipsacus sylvestris Huds. roots against Borrelia burgdorferi s. s. in vitro.

Fresh first year roots from Dipsacus sylvestris HUDS. were extracted with 70% ethanol, ethyl acetate as well as dichloromethane. Extracts were solubilized in water (lipophilic extracts with addition of polysorbate 80) and tested for their activity against Borrelia burgdorferi sensu stricto in vitro during an eight-day period using amoxicillin as standard. The hydroethanolic extract showed no growth inhibition whereas significant growth inhibiting activity could be shown in the two less polar fractions for the first time. Strongest inhibition was found in the ethyl acetate extract. The effect of polysorbate 80 on bacterial growth was examined and found to be negligible. As the nature of bioactive constituents has not been clarified yet, a micellar electrokinetic capillary chromatography fingerprint analysis for a methanolic extract was applied including loganin, chlorogenic acid, cantleyoside and caffeic acid as marker substances.

Growth inhibiting activity of volatile oil from Cistus creticus L. against Borrelia burgdorferi s.s. in vitro.

Borreliosis patients from self-help groups reported considerable pain relief after ingestion of Cistus creticus leaf preparations. C. creticus leaf extracts of different polarities such as aqueous, ethyl acetate, hexane extracts as well as the volatile oil fraction obtained by steam distillation were tested for their antibacterial activity against Borrelia burgdorferi sensu stricto (Bbss) in vitro using the antibiotic amoxicilline as standard and polysorbate 80 as solubilizer for lipophilic extracts. Comparison of the four plant preparations shows that the volatile oil exerts the strongest growth inhibitory effect. Even concentrations of 0.02% (w/v) volatile oil in cultivation media reduced the total number of bacteria to 2% in comparison to a growth control after an eight-day cultivation period. While the aqueous extract did not reduce bacterial growth, incubation with hexane and ethyl acetate extracts clearly inhibited microbial growth. The main volatile components of the three active extracts tested were analyzed by GC-MS. The number of different labdane-type diterpenes as well as the total relative amount of diterpenes in the samples tested was highest in the essential oil of C. creticus. Identification of ten different volatile labdane-type diterpenes was assigned to the essential oil of C. creticus. Among these, manoyl oxide, 13-epi-manoyl oxide, 3-acetoxy-manoyl oxide and the monoterpene carvacrol were determined to be major constituents, accompanied by minor amounts of 3-hydroxy-manoyl oxide, all of which are known to exert antimicrobial activity.

Acceleration of the identification of sepsis-inducing bacteria in cultures of dog and cat blood.

OBJECTIVES: To evaluate matrix-assisted laser desorption ionisation time of flight mass spectrometry (MALDI-TOF MS) combined with the Sepsityper kit (Bruker Daltoniks GmbH, Bremen) for the direct detection of bacterial species from inoculated blood cultures from dogs and cats. MATERIALS AND METHODS: Canine and feline blood samples were inoculated with typical sepsis-causing bacteria such as Staphylococcus intermedius, Staphylococcus aureus, Streptococcus canis, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa at two distinct concentrations (each in triplicate), resulting in 72 blood culture bottles incubated at 37°C. Samples were comparatively analysed with MALDI-TOF MS after preparation with the Sepsityper kit and also by standard bacteriology (culturing and biochemical characterisation). RESULTS: Bacterial species identified from agar plates and by MALDI-TOF MS from blood culture bottles were identical for all samples. The MALDI Biotyper software (Bruker Daltoniks) correctly identified all bacterial strains from inoculated canine and feline blood with analysis indicating very good precision. CLINICAL SIGNIFICANCE: MALDI-TOF MS analysis combined with the Sepsityper kit is a reliable tool for a quick detection of veterinary-relevant bacterial species directly from blood culture bottles. This approach could reduce the time for identification of critical species to only 24 hours.

Morphology of Naturally-Occurring Tuberculosis in Cattle Caused by Mycobacterium caprae.

This study describes the pathomorphological alterations of bovine tuberculosis through gross and histopathological examinations, assessment of the distribution of lesions and the demonstration of mycobacteria. Samples from lungs, liver, small intestine, their regional lymph nodes and retropharyngeal lymph nodes were collected from 84 cattle with tuberculosis from the Allgäu, Germany. Organs were evaluated grossly, histopathologically and by transmission electron microscopy. Mycobacteria and mycobacterial antigens were demonstrated using acid-fast staining and immunohistochemistry (IHC). Bacteriological tests revealed Mycobacterium caprae in all animals. Gross alterations were classified into five patterns (I to V) with an additional pattern of acute exudative pulmonary inflammation (pattern VI). Histological lesions were classified into four types (1-4) with additional lesions occurring in lungs only. Acid-fast staining revealed a low number of bacteria in all tissues, while IHC showed comparatively more mycobacterial antigens within the lesions and also at their periphery. The alimentary tract (68%) was the main portal of entry followed by an aerosol infection (19%). It was assumed that the observed lesions reflect a continuous primary period of infection; there were no lesions typical of a secondary (post-primary) period, as reported in man and also described in the older literature on bovine tuberculosis. The broad spectrum of changes described formerly was not observed in the present cases and the route of infection and nature of acid fast staining showed differences when compared with previous studies of naturally-occurring bovine tuberculosis.

Subclinical mastitis in dairy cattle and buffaloes among small holders in Egypt: Prevalence and evidence of virulence of Escherichia coli causative agent.

This study aimed first to estimate the prevalence of subclinical mastitis (SCM) among dairy cows and buffaloes of smallholders who sell milk directly to consumers through bulk tanks of milk distributors. The second aim is to estimate the prevalence of Escherichia coli in milk of SCM cases and identify its virulence genes and to emphasize the public health risk form drinking this milk. A total of 227 and 174 dairy cows and buffaloes, respectively from Kafrelsheikh Governorate, Egypt were examined with California Mastitis Test (CMT) to estimate the prevalence of SCM. Samples were also screened for E. coli using classical bacteriological and molecular methods. The prevalence of CMT-positive cows and buffaloes samples examined was 47.4% (49.9% and 44.3% for cows and buffaloes, respectively). Cows were found to be at a higher risk of getting high CMT score than buffaloes. E. coli was detected bacteriologically in 16.4% and in 27.2% of the CMT-positive cows and buffalo samples, respectively. A total of 83.1% and 75.6% of isolates were confirmed as E. coli using PCR technique. A multiplex PCR assay was used to identify five virulence genes in the E. coli isolates; the eae gene for enteropathogenic E. coli, stx for Shiga toxin-producing E. coli, elt and est for enterotoxigenic E. coli, and the hlyA of the enterohemolysin gene for enterohemorrhagic E. coli. Only one E. coli strain identified carried two virulence genes (eae and est). The high prevalence of SCM among dairy cows and buffaloes in the study area indicated that there is high risk to consumers who consume milk of these animals. Also, control of SCM is a prerequisite among smallholders in Egypt in order to minimize its deleterious effects such as microbial antibiotic resistance and public health hazards. To our knowledge, this is the first study that highlights the ecology of virulence by E. coli causing SCM in Kafrelsheikh governorate, Egypt. This study offers the basis for further phenotypic and molecular characterization of E. coli found in raw milk in order to guarantee safe consumption of raw milk and milk products.

Investigation of intra-herd spread of Mycobacterium caprae in cattle by generation and use of a whole-genome sequence.

Single nucleotide polymorphisms (SNPs) calculated from whole genome sequencing (WGS) are ideally suited to study evolutionary relationships of pathogens and their epidemiology. Mycobacterium caprae infections have been documented frequently in cattle and red deer along the Bavarian and Austrian Alps during the last decade. However, little is still known about the transmission within cattle holdings and possible alterations of the genomes of M. caprae during such events. The aim of this study was to study the molecular epidemiology of bovine tuberculosis (bTB) in selected herds based on isolate-specific genome-wide SNPs and to perform a phylogenetic network analysis. In total, 61 M. caprae isolates were collected originating from eight cattle farms over a period of twelve years between 2004 and 2015. Analysis of their sequence data revealed that the M. caprae isolates of an affected farm differ at all in a few SNPs. In contrast, many more SNPs were found when comparing the M. caprae genomes originating from different herds. The results demonstrated that the spread of bTB in the affected farms occurred by direct transmission between the members of each herd rather than between herds and a M. caprae introduction in farms after contact events e. g. on summer pastures can readily be traced by WGS analysis. Furthermore, we assembled a nearly complete whole genome sequence of M. caprae derived from several cattle isolates originating from bTB cases in the Bavarian Alpine region.

The Region of Difference Four is a Robust Genetic Marker for Subtyping Mycobacterium caprae Isolates and is Linked to Spatial Distribution of Three Subtypes.

Alpine Mycobacterium caprae isolates found in cattle and red deer display at least three genetic variations in the region of difference four (RD4) that can be used for further differentiation of the isolates into the subtypes 'Allgäu', 'Karwendel' and 'Lechtal'. Each genomic subtype is thereby characterized by a specific nucleotide deletion pattern in the 12.7-kb RD4 region. Even though M. caprae infections are frequently documented in cattle and red deer, little is known about the transmission routes. Hence, robust markers for M. caprae subtyping are needed to gain insight into the molecular epidemiology. For this reason, a rapid and robust multiplex PCR was developed for the simultaneous detection of three M. caprae RD4 subtypes and was used to subtype a total number of 241 M. caprae isolates from animals (145 cattle, 95 red deer and one fox) from Bavaria and Austria. All three subtypes occur spatially distributed and are found in cattle and in red deer suggesting transmission between the two species. As subtypes are genetically stable in both species it is hypothesized that the described genetic variations developed within the host due to 'within-host replication'. The results of this study recommend the genomic RD4 region as a reliable diagnostic marker for M. caprae subtype differentiation.

Prevalence of antibodies against Borrelia burgdorferi, Anaplasma phagocytophilum, and Leptospira interrogans serovars in Bernese Mountain Dogs.

OBJECTIVE: Bernese Mountain Dogs (BMD) have a higher prevalence of Borrelia burgdorferi sensu lato (Bbsl) antibodies than other breeds, but it is not known whether this is the case for other pathogens. Therefore, the aim of the study was to determine the frequency and level of specific antibodies against members of the Bbsl group, Anaplasma phagocytophilum (Ap), and Leptospira (L.) interrogans serovars in BMD and compare the results with those found in dogs of other breeds. MATERIALS AND METHODS: A total of 171 healthy BMD and 57 healthy control dogs of other breeds were included in the study. Controls were large dogs (> 30 kg) with long, dark hair coats. A two-tiered testing method consisting of computerized kinetic enzyme-linked immunosorbent assay (KELA) and Western blotting was used for detection of antibodies against Bbsl, an immunofluorescence assay (IFA) was used for detection of antibodies against Ap, and microscopic agglutination test (MAT) for antibodies to 18 different serovars of L. interrogans. RESULTS: The prevalence of anti-Bbsl antibodies was significantly higher in BMD (43.3%) than in controls (17.5%) (p < 0.001). Antibodies to Bbsl attributable to vaccination were excluded from the calculation of prevalence. Antibodies to Ap were found in 50.3% of BMD, whereas only 24.6% of the controls dogs were tested positive for Ap (p < 0.001). Antibody titers of the 18 different serovars of L. interrogans antibodies did not differ significantly between BMD and control dogs except for L. copenhageni antibody titers which were higher in BMD. Significantly higher antibody titers to L. canicola (p = 0.003), L. copenhageni (p = 0.005), L. grippothyphosa (p = 0.029) and L. vanderhoedoni (p = 0.035) were seen in BMD compared to control dogs. CONCLUSION AND CLINICAL RELEVANCE: BMD had a higher prevalence of anti-Bbsl, anti-L. copenhageni and anti-Ap antibodies than control dogs. Significantly higher antibody titers against L. canicola (p = 0.003), L. copenhageni (p = 0.005), L. grippothyphosa (p = 0.029) and L. vanderhoedoni (p = 0.035) were seen in BMD compared with control dogs, but the reason for this and potential clinical implications are not known.

Trans-Atlantic exchanges have shaped the population structure of the Lyme disease agent Borrelia burgdorferi sensu stricto.

The origin and population structure of Borrelia burgdorferi sensu stricto (s.s.), the agent of Lyme disease, remain obscure. This tick-transmitted bacterial species occurs in both North America and Europe. We sequenced 17 European isolates (representing the most frequently found sequence types in Europe) and compared these with 17 North American strains. We show that trans-Atlantic exchanges have occurred in the evolutionary history of this species and that a European origin of B. burgdorferi s.s. is marginally more likely than a USA origin. The data further suggest that some European human patients may have acquired their infection in North America. We found three distinct genetically differentiated groups: i) the outgroup species Borrelia bissettii, ii) two divergent strains from Europe, and iii) a group composed of strains from both the USA and Europe. Phylogenetic analysis indicated that different genotypes were likely to have been introduced several times into the same area. Our results demonstrate that irrespective of whether B. burgdorferi s.s. originated in Europe or the USA, later trans-Atlantic exchange(s) have occurred and have shaped the population structure of this genospecies. This study clearly shows the utility of next generation sequencing to obtain a better understanding of the phylogeography of this bacterial species.

Histopathological studies of experimental lyme disease in the dog.

Experimental borrelia infection was induced in 62 specific--pathogen-free beagle dogs by exposure to Ixodes scapularis ticks harbouring the spirochaete Borrelia burgdorferi. Clinical signs of Lyme disease occurred in 39/62 dogs, the remaining 23 being subclinically infected. Clinical signs consisted of one to six episodes of transitory lameness with joint swelling and pain, most commonly affecting the elbow or shoulder joints. The polymerase chain reaction and culture demonstrated that the dogs remained infected for up to 581 days. At necropsy, gross findings consisted of lymphadenopathy in the area of tick attachment. Microscopical changes consisted of effusive fibrinosuppurative inflammation or nonsuppurative inflammation, or both, affecting synovial membranes, joint capsules and associated tendon sheaths. Plasma cells dominated areas of chronic inflammation, with CD3(+) T cells being present in lesser numbers. Microscopical signs of arthritis were polyarticular and more widespread than indicated by clinical signs, and most of the subclinically affected animals also had synovitis. In areas of tick attachment to the skin, hyperkeratosis and a mixture of suppurative and nonsuppurative dermatitis were encountered. Lymphadenopathy in superficial lymph nodes resulted from follicular and parafollicular hyperplasia. In 14/62 dogs, lymphoplasmacytic periarteritis and perineuritis were noted, resembling lesions found in human Lyme disease and syphilis, in which an underlying microangiopathy has been proposed.

Antibiotic susceptibility of bacterial isolates from 502 dogs with respiratory signs.

The aim of this study was to investigate the prevalence of bacterial species isolated from bronchoalveolar lavage fluid (BALF) samples taken from dogs with respiratory signs and to determine their antibiotic susceptibility. Clinical cases were included in the study if they showed signs of respiratory disease and data relating to bacterial culture and susceptibility of BALF samples were available. The medical records of 493 privately owned dogs that were presented between January 1989 and December 2011 were evaluated retrospectively. In 35 per cent of samples, no bacteria were cultured. Bacteria isolated from culture-positive samples included Streptococcus species (31 per cent of positive cultures), Enterobacteriaceae (30 per cent, including Escherichia coli (15 per cent)), Staphylococcus species (19 per cent), Pasteurella species (16 per cent) and Pseudomonas species (14 per cent). Bordetella bronchiseptica as a primary respiratory pathogen was isolated in 8 per cent of cases. Enrofloxacin showed the best susceptibility pattern; 86 per cent of all isolates and 87 per cent of Gram-negative bacteria were susceptible to this antibiotic. Amoxicillin/clavulanic acid yielded the best susceptibility pattern in Gram-positive bacteria (92 per cent). Therefore, these antibiotics can be recommended for empirical or first-line treatment in dogs with bacterial lower respiratory tract infections.

[The intradermal tuberculin test: literature, directive and implementation in practice]. / Der Tuberkulin-Hauttest: Literatur, Richtlinie und Umsetzung in der Praxis.

OBJECTIVE: Because of an increase in the number of cases of bovine tuberculosis in southern Germany (Allgäu region, mainly in the administrative district Swabia) during recent years, blanket tuberculosis testing was resumed in this region. The aim of this study was to review the veterinarians' current knowledge regarding the technique of the intradermal tuberculin test. As a consequence, a guide with precise instructions for the execution and interpretation of intradermal tuberculin testing in cattle based on the current legislation should be created. MATERIAL AND METHODS: Using a questionnaire, farm-animal practitioners' knowledge and experiences of intradermal tuberculin testing were surveyed, collected and evaluated. Legislative texts on tuberculosis (particularly testing of tuberculosis) were evaluated in their current and previous versions, and compared with the experiences reported by the veterinarians. RESULTS: A total of 137 veterinarians participated and 130 returned questionnaires could be evaluated. Forty-four of the 130 participants were involved in tuberculosis testing when the survey was performed. Of these 44 questionnaires, 42 were incorporated in the final evaluation. The majority of the veterinarians perform the intradermal tuberculosis test as laid down in the Commission Regulation (EC) no. 1226/2002 of 8 July 2002 amending Annex B to Council Directive 64/432/EEC. However, many practitioners do not comply with the requirements of the Commission Regulation (EC) no. 1226/2002 when evaluating the results of the intradermal tuberculosis test. Veterinarians showing the least accordance with required standards only test single animals or work in areas other than Swabia. CONCLUSIONS: In areas severely affected by tuberculosis, the technique of intradermal tuberculosis testing is performed almost as demanded by the Commission Regulation (EC) no. 1226/2002. However, a more uniform and careful approach should be sought when monitoring the results. The guide designed in the context of this study can help to improve the performance of the intradermal tuberculosis test. The information from the literature review also shows that there is currently no standardized method of intradermal tuberculosis testing.

Prospective study of bacteraemia in acute haemorrhagic diarrhoea syndrome in dogs.

In dogs with idiopathic acute haemorrhagic diarrhoea syndrome (AHDS), a serious loss of intestinal mucosal barrier integrity occurs. However, the incidence of bacterial translocation in dogs with idiopathic AHDS is not known. Thus, the objectives of this prospective study were to identify the incidence of bacteraemia, to evaluate the frequency of septic events and the influence of bacteraemia on various clinical and laboratory parameters, duration of hospitalisation and survival of dogs with idiopathic AHDS. The study included 87 dogs with idiopathic AHDS. Twenty-one healthy dogs served as control group. To evaluate clinical significance of bacterial translocation, blood culture results were compared between patients and controls. Clinical and laboratory parameters were compared between patients with positive and negative blood cultures. There was no significant difference in either incidence of bacteraemia between patients with idiopathic AHDS (11 per cent) and controls (14 per cent) or in severity of clinical signs, laboratory parameters, duration of hospitalisation or mortality between blood culture-positive and culture-negative dogs with idiopathic AHDS. The results of this study suggest that the incidence of bacteraemia in dogs with idiopathic AHDS is low and not different from that of healthy control dogs. Bacteraemia does not influence the clinical course or survival and thus antibiotic treatment is not indicated to prevent sepsis.

Identification of two transcripts of canine, feline, and porcine interleukin-1 alpha.

Reverse transcription-polymerase chain reaction (RT-PCR) with interleukin-1alpha (IL-1alpha)-specific primers using total RNA from lipopolysaccharide (LPS)-stimulated lung macrophages resulted in the amplification of two distinct cDNA fragments. Cloning and sequencing of the canine and feline fragments revealed that, except for the absence of a specific 174 nucleotide sequence, the short and the long transcripts were identical. The in-frame 174 nucleotide deletion corresponds to exon 5 of the human and murine IL-1alpha gene, which encodes the cleavage site for calpain, a protein necessary for the processing of the IL-1alpha precursor into mature IL-1alpha. The two transcripts were found in the dog, cat and pig; analysis by RT-PCR, Southern and Northern blot hybridization showed no expression of the shorter IL-1alpha mRNA in equine or bovine macrophages. Expression of the two canine IL-1alpha transcripts was also detected in synovial membranes and was coordinately up-regulated in response to Borrelia burgdorferi infection under both in-vitro and in-vivo conditions.

Up-regulation of inducible nitric oxide synthase mRNA in dogs experimentally infected with Borrelia burgdorferi.

The up-regulation of the inducible nitric oxide synthase (iNOS) mRNA was determined by RT-PCR in 25 tissues each from 22 specific pathogen-free (SPF) dogs experimentally infected with Borrelia burgdorferi by tick exposure and from five uninfected control dogs. Using primers specific for a homologous region of the human and canine iNOS sequence, and canine macrophage mRNA, we isolated and partially sequenced canine iNOS. A sequence of 1775 bases was obtained and primers specific for canine iNOS mRNA constructed to investigate the expression of iNOS in dog tissues in response to infection with B. burgdorferi. In 12 out of 22 dogs infected with B. burgdorferi, acute lameness occurred within 55-82 days after infection whereas the other 10 dogs showed no or only mild clinical signs despite persistent infection up to Day 175. The numbers of iNOS mRNA-positive tissues in dogs with acute lameness were significantly higher than in dogs without lameness, while uninfected dogs showed only negligible iNOS expression. Dogs with acute lameness also had higher numbers of borrelia-positive tissues as well as higher scores in histopathological evaluations than infected dogs without lameness. Our results show that the expression of iNOS mRNA is related to the number of B. burgdorferi-positive tissues and the severity of inflammation as assessed by histopathology. These results implicate an up-regulation of the iNOS mRNA as part of the host's immune response to borrelia infection and a possible role for NO in the pathogenesis of canine Lyme arthritis.

Clinical manifestations, pathogenesis, and effect of antibiotic treatment on Lyme borreliosis in dogs.

BACKGROUND: Borrelia burgdorferi, the causative agent of Lyme disease, infects humans and animals. In humans, the disease primarily affects the skin, large joints, and the nervous system days to months after infection. Data generated with appropriate animal model help to understand the fundamental mechanisms of the disease. OBJECTIVE: 1) More clearly define the clinical manifestation and pathogenetic mechanisms of Lyme disease in dogs; 2) evaluate the effect of antibiotics in dogs infected with B. burgdorferi; 3) describe the effects of corticosteroids on dogs persistently infected with B. burgdorferi. DESIGN: Specific-pathogen-free beagles were infected with B. burgdorferi using ticks collected in an endemic Lyme disease area. Clinical signs were recorded daily. Antibody titers were measured by ELISA at two-week intervals. B. burgdorferi organisms were detected in tissues by culture and PCR. Synovial fluids were evaluated microscopically and with a chemotaxis cell migration assay. Histological sections were examined for pathological lesions. Specific cytokine up-regulation in tissues was detected by RT-PCR. INTERVENTIONS: In three separate experiments, B. burgdorferi-infected dogs received antibiotic treatment (amoxicillin; azithromycin; ceftriaxone; doxycycline) for 30 consecutive days. Two subclinical persistently infected dogs received oral prednisone for 14 consecutive days starting at day 420 post-infection. RESULTS: Dogs developed acute arthritis in the joints closest to the tick bites after a median incubation period of 68 days. Synovial membranes of lame and non-lame dogs produced the chemokine IL-8 in response to B. burgdorferi. Antibiotic treatment prevented or resolved episodes of acute arthritis, but failed to eliminate the bacterium from infected dogs. Corticosteroid treatment reactivated Lyme disease in persistently infected dogs, which had not received antibiotics previously. CONCLUSIONS: B. burgdorferi disseminates through tissue by migration following tick inoculation, produces episodes of acute arthritis, and establishes persistent infection. The spirochete survives antibiotic treatment and disease can be reactivated in immunosuppressed animals.