Coxiella burnetii Infections in Small Ruminants and Humans in Switzerland.

The recent Q fever epidemic in the Netherlands raised concerns about the potential risk of outbreaks in other European countries. In Switzerland, the prevalence of Q fever in animals and humans has not been studied in recent years. In this study, we describe the current situation with respect to Coxiella (C.) burnetii infections in small ruminants and humans in Switzerland, as a basis for future epidemiological investigations and public health risk assessments. Specific objectives of this cross-sectional study were to (i) estimate the seroprevalence of C. burnetii in sheep and goats, (ii) quantify the amount of bacteria shed during abortion and (iii) analyse temporal trends in human C. burnetii infections. The seroprevalence of C. burnetii in small ruminants was determined by commercial ELISA from a representative sample of 100 sheep flocks and 72 goat herds. Herd-level seroprevalence was 5.0% (95% CI: 1.6-11.3) for sheep and 11.1% (95% CI: 4.9-20.7) for goats. Animal-level seroprevalence was 1.8% (95% CI: 0.8-3.4) for sheep and 3.4% (95% CI: 1.7-6) for goats. The quantification of C. burnetii in 97 ovine and caprine abortion samples by real-time PCR indicated shedding of >104 bacteria/g in 13.4% of all samples tested. To our knowledge, this is the first study reporting C. burnetii quantities in a large number of small ruminant abortion samples. Annual human Q fever serology data were provided by five major Swiss laboratories. Overall, seroprevalence in humans ranged between 1.7% and 3.5% from 2007 to 2011, and no temporal trends were observed. Interestingly, the two laboratories with significantly higher seroprevalences are located in the regions with the largest goat populations as well as, for one laboratory, with the highest livestock density in Switzerland. However, a direct link between animal and human infection data could not be established in this study.

Antimicrobial susceptibility of Brachyspira hyodysenteriae in Switzerland.

INTRODUCTION: Brachyspira (B.) hyodysenteriae is the causative agent of swine dysentery (SD), a severe mucohaemorrhagic diarrheal disease in pigs worldwide. So far, the antimicrobial susceptibility patterns of B. hyodysenteriae in Switzerland have not been investigated. Therefore, a panel of 30 porcine B. hyodysenteriae isolates were tested against 6 antimicrobial agents by using the VetMIC Brachy panel, a broth microdilution test. Tiamulin and valnemulin showed high antimicrobial activity inhibiting all isolates at low concentrations. The susceptibility testing of doxycycline revealed values from ≤0.25 µg/ ml (47%) to 2 µg/ml (10%). The MIC values of lincomycin ranged between ≤0.5 µg/ml (30%) and 32 µg/ml (43%). For tylosin, 57% of the isolates could not be inhibited at the highest concentration of ≥128 µg/ml. The MIC values for tylvalosin were between ≤0.25 µg/ml (10%) and 8 µg/ml (20%). These findings reveal Switzerland's favourable situation compared to other European countries. Above all, tiamulin and valnemulin are still effective antimicrobial agents and can be further used for the treatment of SD.

INTRODUCTION: Brachyspira (B.) hyodysenteriae est l'agent de la dysenterie porcine, une affection diarrhéique muco-hémorragique grave des porcs connue dans le monde entier. Jusqu'à ce jour, la sensibilité aux antibiotiques B. hyodysenteriae n'avait pas été étudiée en Suisse. C'est pour cela qu'on a examiné, au moyen du test de micro dilution VetMIC Brachy panel, un choix de 30 isolats porcins de B. hyodysenteriae quant à leur sensibilité face à 6 substances antimicrobiennes. La Tiamuline et la Valnémuline ont montré une activité antimicrobienne élevée, bloquant tous les isolats à de faibles concentrations. Les tests de sensibilité vis-à-vis de la Doxycilline ont donné des valeurs comprises entre ≤0.25 µg/ml (47%) et 2 µg/ml (10%). Les valeurs de CMI de la Lincomycine variaient entre ≤0.5 µg/ml (30%) et 32 µg/ml (43%). Avec la Tylosine, 57% des isolats n'ont pas pu être bloqués avec la concentration la plus élevée de ≥128 µg/ml. Les valeurs de CMI pour la Tylvalosine se situaient entre ≤0.25 µg/ml (10%) et 8 µg/ml (20%). Ces résultats montrent que la situation suisse est favorable en regard d'autres pays européens. La Tiamuline et la Valnémuline en particulier restent des substances antimicrobiennes efficaces qui peuvent continuer à être utiliser pour lutter contre la dysenterie porcine.

Prototheca species and Pithomyces chartarum as Causative Agents of Rhinitis and/or Sinusitis in Horses.

Pyogranulomatous rhinitis associated with an algal infection was diagnosed in a 25-year-old gelding and a 23-year-old mare had necrotizing sinusitis with intralesional algae and pigmented fungi. Algae were identified immunohistochemically in both cases as Prototheca spp. In the gelding, further characterization by polymerase chain reaction and sequencing revealed that the organism was Prototheca zopfii genotype 2. Fungi from the mare were identified as Pithomyces chartarum by molecular analysis. Prototheca species are achlorophyllous algae and P. chartarum represents a dematiaceous fungus; they are saprophytes and facultative pathogens. Prototheca spp. and P. chartarum should be considered as rare respiratory pathogens of horses.

MALDI-TOF MS for identification of porcine Brachyspira species.

UNLABELLED: The aim of this study consisted in evaluating MALDI-TOF MS as a tool for the identification of the genus Brachyspira (B.) and its relevant species for the pig industry. First, a database was created with 30 control strains, and superspectra for five different porcine Brachyspira species were calculated. In a second step, 67 field isolates were investigated using MALDI-TOF MS, and results were compared to those obtained using nox gene-based RFLP (reference method) and biochemical tests. Among the 67 field isolates, five different Brachyspira species were detected using nox gene-based RFLP analysis. MALDI-TOF MS analysis correctly assigned all isolates to the genus Brachyspira and identified all isolates from B. hyodysenteriae (29/29), B. pilosicoli (11/11), B. intermedia (4/4) and B. innocens (11/11). In terms of B. murdochii, MALDI-TOF MS assigned one of 12 isolates ambiguously as B. innocens/B. murdochii. The results of this study indicate that MALDI-TOF MS facilitates the diagnosis of swine dysentery and porcine intestinal spirochaetosis. SIGNIFICANCE AND IMPACT OF THE STUDY: Current methods for the discrimination of pathogenic Brachyspira hyodysenteriae and Brachyspira pilosicoli from Brachyspira species with low pathogenic potential have proven to be laborious and time-consuming and are therefore not suitable for routine diagnostics. This study describes the evaluation of MALDI-TOF MS for the identification of different porcine Brachyspira species in routine diagnostic laboratories. The results suggest that MALDI-TOF MS is an effective method for the identification of porcine Brachyspira spp. and accelerates diagnosis of swine dysentery and porcine intestinal spirochaetosis.

Quantitative analysis of fecal flora in goat kids with and without floppy kid syndrome.

BACKGROUND: Floppy kid syndrome (FKS) affects goat kids in the first month of life and is associated with high morbidity and mortality rates. The condition is characterized by neurological signs that can be ascribed to increased plasma D-lactate concentrations. The source of D-lactate has not been identified conclusively, but D-lactate-producing bacteria in the large intestine are thought to be involved. OBJECTIVES: To determine the number of colony-forming unit (CFUs) of certain groups of bacteria in the feces of kids with and without FKS. ANIMALS: Nineteen goat kids with clinical signs of FKS, acidemia (pH ≤ 7.2), and plasma D-lactate concentration >7 mM and 15 healthy goat kids without acidemia (pH >7.2) and D-lactate concentration <1 mM. METHODS: In this case-control study, the goat kids were examined clinically and blood was collected to measure D-lactate concentration, blood gases, and acid-base parameters. Fecal samples were collected and the total aerobic bacterial count and CFU counts of coliforms, enterococci, staphylococci, streptococci, lactobacilli, and clostridia were determined using the surface plating method. RESULTS: Goat kids with FKS had a mean plasma D-lactate concentration of 10.9 ± 3.7 mM compared with 0.3 ± 0.9 mM in healthy kids, and significantly greater CFU counts for enterococci, streptococci, staphylococci, and lactobacilli than healthy kids. CONCLUSIONS AND CLINICAL IMPORTANCE: The groups of bacteria present in greater numbers in the feces of goat kids with FKS include several D-lactate-producing species, which makes dysbacteriosis a likely cause of the increased plasma D-lactate concentration in FKS.

Fungal contamination of paraffin wax blocks in a pathology archive.

While searching for paraffin wax blocks for research purposes in our archive we detected numerous larval and some dead adult moths. Some wax blocks were riddled with a white-brown crumbling substance. The entire archive was checked and profoundly-infested blocks were separated from unaffected blocks. Mycological and parasitological investigations were performed. Fungi were identified by culture and polymerase chain reaction, which revealed high sequence homology to six different fungal species. The moths were determined to be Nemapogon personellus. A total of 8,484 wax blocks had to be removed from the archive and destroyed. Pathologists should be alerted to the importance of checking the humidity of the air where archival material is stored.

[Antimicrobial resistance of Staphylococcus aureus and coagulase negative staphylococci isolated from mastitis milk samples from sheep and goats]. / Antibiotikaresistenz von Staphylococcus aureus und Koagulase-negativen Staphylokokken isoliert aus Mastitismilchproben von Schafen und Ziegen.

Staphylococcus aureus and coagulase negative staphylococci (CNS) were isolated from ovine and caprine mastitis milk samples originating from more than 40 Swiss farms. CNS dominated as causal microorganisms of mastitis in small ruminants. By restriction fragment length polymorphism (RFLP) analysis of the groEL gene and sequencing of 16S rDNA, various CNS species were identified, albeit certain of them predominated. For susceptibility testing of mastitis pathogens to selected antibiotics, minimal inhibitory concentrations were determined. Of the 67 S. aureus and 208 CNS strains, 31.3 % and 8.2 % were resistant to penicillin, 29.9 % and 1.0 % to ampicillin, 1.5 % and 10.6 % to erythromycin, and 3.0 % and 7.7 % to tetracycline, respectively. Moreover, 10 CNS strains (4.8 %) were resistant to oxacillin and one CNS strain to sulfamethoxazole/trimethoprim. The results obtained describe for the first time the resistance situation of mastitis pathogens from sheep and goats in Switzerland. However, accompanying and preventing measures are also of importance in mastitis control of small ruminants.

[Benefit of clinical and laboratory parameters for the diagnosis of endometritis in dairy cows]. / Nutzen von klinischen und labordiagnostischen Parametern zur Diagnostik der Endometritis beim Rind.

The goal of this work was to answer the question of whether or not there are significant differences between cows with abnormal vaginal discharge and cows with the diagnosis of puerperal or chronic endometritis, using blood and urine parameters. In addition, cows with and without vaginal discharge were examined for significant bacteriological differences in uterine mucous samples. The question of false positive and false negatives from the diagnosis of endometritis was also investigated. A total of 35 matched-pairs (+/-vaginal discharge) from 27 stables was examined 21 to 63 days post partum. The examination consisted of a rectal and vaginal exam, urine and blood samples as well as vaginal swab from the corpus uteri using a Folmer-Nielsen-Catheter. Based on the history vaginal discharge occurred more frequently in dystocia and retentio secundinarium. Cows with a history of distocia and retentio secundinarium showed significantly more vaginal discharge. Gammaglutamyltransferase (GGT; p=0.01) and cholesterine (p=0.04) were different in cows with endometritis. The bacteriology results showed a statistically significant difference (p<0.01) only for Escherichia coli and Arcanobacterium pyogenes. The Folmer-Nielsen smears/endometritis showed a significant difference between the two groups (p<0.01). In a multivariate analysis with final step-back procedure regarding endometritis Gammaglutamyltransferase (GGT) and Betahydroxybutteracid (BHB) were significant different (p=0.02). The hypothesis vaginal discharge alike endometritis showed that 34 % of the clinical suspicious cases were recorded as false negatives. In the non-suspicious cases 20 % were diagnosed as false negative.

Comparison of a rapid immunoassay for antibodies to the C6 antigen with conventional tests for antibodies to Borrelia burgdorferi in dogs in Europe.

A commercial immunoassay for antibodies to the C6 antigen of Borrelia burgdorferi was evaluated against an IgG in-house ELISA in combination with a Western blot assay to examine 104 samples of serum from 53 healthy Bernese mountain dogs, which were suspected to have a breed predisposition to Lyme borreliosis, and 55 samples from 30 healthy large-breed longhair dogs. The two test methods correlated in 125 (79 per cent) of the samples with an agreement of kappa=0.571 (P<0.001). In comparison with the in-house ELISA in combination with a Western blot, the sensitivity and specificity of the C6 test were 81 per cent and 77 per cent respectively. The agreement between the tests was better with the samples from the Bernese mountain dogs (k=0.681) than with the samples from the control dogs (k=0.347).

Infection with Mycobacterium avium subspecies avium in a 10 year old Freiberger mare.

In this case report a 10 year old Freiberger mare with a Mycobacterium avium subsp. avium infection is presented. This infection leads to a tuberculosis like disease with granulomatous alterations particularly of the intestines and lungs and is only sporadically reported in horses of Central Europe. Diarrhoea, mastitis and neck stiffness as well as dyspnoea and chronic cough are more specific symptoms of the infection, while weight loss, weakness and lethargy are nonspecific signs. As these clinical signs can occur in many other diseases, the diagnosis of mycobacterial infection is difficult and consists of rectum or distal colon biopsies and staining for acid-fast bacilli and bacteriological culture of granulomatous lesions. Classification of M. avium subsp. avium was achieved by PCR-RFLP. Even though an infection with Mycobacterium avium subsp. avium is rare, it belongs to the differential diagnosis of granulomatous diseases.

[The dilemma with Lyme borreliosis in the dog with particular consideration of "Lyme nephritis"]. / Das Dilemma der Lyme Borreliose beim Hund unter besonderer Berücksichtigung der "Lyme Nephritis"

Lyme borreliosis is the most commonly reported tick-transmitted infectious disease in the northern hemisphere in humans. Certain diseases are associated with Lyme borreliosis in the dog as well, but only intermittent lameness with articular swelling, lymphadenomegaly, fever, and anorexia were experimentally documented. Lyme borreliosis is considered an over diagnosed disease. The term "Lyme nephritis" was introduced for dogs with characteristic renal lesions and typical clinical signs, in which antibodies against Borrelia burgdorferi were found. Different studies have been aimed at showing a relation between renal disease and B. burgdorferi infection; however, this was not possible until now. Reasons for the uncertainty of the effects of B. burgdorferi in the dog are the high prevalence of circulating antibodies, the unspecific clinical picture and the inaccuracy of serologic tests.

A DNA microarray facilitates the diagnosis of Bacillus anthracis in environmental samples.

AIMS: In order to improve the diagnosis of Bacillus anthracis in environmental samples, we established a DNA microarray based on the ArrayTube technology of Clondiag. METHODS AND RESULTS: Total DNA of a bacterial colony is randomly biotinylated and hybridized to the array. The probes on the array target the virulence genes, the genomic marker gene rpoB, as well as the selective 16S rDNA sequence regions of B. anthracis, of the Bacillus cereus group and of Bacillus subtilis. Eight B. anthracis reference strains were tested and correctly identified. Among the analysed environmental Bacillus isolates, no virulent B. anthracis strain was detected. CONCLUSIONS: This array clearly differentiates B. anthracis from members of the B. cereus group and other Bacillus species in environmental samples by chromosomal (rpoB) and plasmid markers. Additionally, recognition of B. cereus strains harbouring the toxin genes or atypical B. anthracis strains that have lost the virulence plasmids is feasible. SIGNIFICANCE AND IMPACT OF THE STUDY: The array is applicable to the complex diagnostics for B. anthracis detection in environmental samples. Because of low costs, high security and easy handling, the microarray is applicable to routine diagnostics.

Mycoplasma suis invades porcine erythrocytes.

Mycoplasma suis belongs to the hemotrophic mycoplasma group and causes infectious anemia in pigs. According to the present state of knowledge, this organism adheres to the surface of erythrocytes but does not invade them. We found a novel M. suis isolate that caused severe anemia in pigs with a fatal disease course. Interestingly, only marginal numbers of the bacteria were visible on and between the erythrocytes in acridine orange-stained blood smears for acutely diseased pigs, whereas very high loads of M. suis were detected in the same blood samples by quantitative PCR. These findings indicated that M. suis is capable of invading erythrocytes. By use of fluorescent labeling of M. suis and examination by confocal laser scanning microscopy, as well as scanning and transmission electron microscopy, we proved that the localization of M. suis was intracellular. This organism invades erythrocytes in an endocytosis-like process and is initially surrounded by two membranes, and it was also found floating freely in the cytoplasm. In conclusion, we were able to prove for the first time that a member of the hemotrophic mycoplasma group is able to invade the erythrocytes of its host. Such colonization should protect the bacterial cells from the host's immune response and hamper antibiotic treatment. In addition, an intracellular life cycle may explain the chronic nature of hemotrophic mycoplasma infections and should serve as the foundation for novel strategies in hemotrophic mycoplasma research (e.g., treatment or prophylaxis).

OmpA and antigenic diversity of bovine Chlamydophila pecorum strains.

Infections with the intracellular bacterium Chlamydophila (C.) pecorum are highly prevalent worldwide in cattle. These infections cause significant diseases such as polyarthritis, pneumonia, enteritis, genital infections and fertility disorders, and occasionally sporadic bovine encephalomyelitis. Subclinical respiratory infections of calves with C. pecorum have been associated with airway obstruction, pulmonary inflammation, and reduced weight gains. This investigation examined four chlamydial strains with biological properties of C. pecorum isolated from feces of clinically normal cattle, from calves with pneumonia, and from bulls with posthitis. The objective was to characterize the evolutionary relationships of these bovine chlamydial isolates to other chlamydiae by genetic analysis of the ompA gene, and by the immunological cross-reactivities in Western immunoblot analysis. PCR typing of the ompA gene identified these isolates as C. pecorum. The OmpA-deduced amino acid dissimilarities between these four strains spanned 10-20%. In phylogenetic analysis, the four isolates clustered with C. pecorum ruminant, porcine, and koala strains of different geographic origins rather than with each other. All four isolates showed different patterns of Western immunoblot reactivity with antiserum against bovine C. pecorum strain LW63, and, interestingly, no cross-reactivity of the OmpA proteins with the anti-LW613 OmpA antibodies. These data underscore the polyphyletic population structure of C. pecorum and suggest that the spectrum of C. pecorum OmpA proteins in a host species can occupy the entire evolutionary bandwidth within C. pecorum. The variant immunoblot reactivities support the notion of considerable genomic plasticity of C. pecorum.

Judgement of hygienic quality of roughage in horse stables in Switzerland.

In 46 horse farms all over Switzerland, the hygienic quality of the roughage (including silages) was investigated. Therefore, a macroscopic examination as well as the microbial counts (bacteria, yeasts and moulds) was carried out. Further, the contents of lipopolysaccharides (LPS) and the contamination with deoxynivalenol (DON) were determined. In all roughages, the dry matter (DM) content was measured and in silages additionally the pH was measured. Predominantly, the straw showed a lower hygienic quality than hay and silages. The LPS contents were significantly higher in straw than those in hay samples. The macroscopic examination and the microbial counts showed a tendency in the same direction. Eight straw samples and one hay sample with DON contamination were found. The silages showed a DM content with a median of 65.8%. The pH of those silages was between 4.3 and 5.9. Despite the high values of DM and pH, the silages showed mainly a high hygienic quality. In total, the hygienic standard of straw was worse than that of hay. This should be taken into account also in straw used as bedding as much as the hygienic quality of hay.

Quantification of Enterobacteriaceae in faeces of captive black rhinoceros (Diceros bicornis) in relation to dietary tannin supplementation.

Free-ranging browsing herbivores ingest a range of secondary plant compounds, such as tannins, with their natural diet. As many of these substances have been shown to have antibacterial properties, it could be speculated that a lack of such compounds in captive zoo diets could favour the growth of potentially pathogenic intestinal bacteria. The effect of a supplementation of a conventional diet (N, consisting mainly of grass hay and/or lucerne hay and pelleted compound feeds) fed to eight captive black rhinoceroses (Diceros bicornis) from three zoological institutions with either tannic acid (T), a source of hydrolysable tannins, or quebracho (Q), a source of condensed tannins, was investigated. The number of faecal colony forming units (CFU) of Enterobactericeae was determined by colony count of dilution series from fresh faeces applied to MacConkey agar plates. Tannins were added to the diets at approximately 5-15 g/kg dry matter, depending on the varying intake of roughage and compound feeds by the animals. There was no difference in the number of CFU between diets N (95.0 x 10(5) +/- 225.3 x 10(5)/g fresh faeces) and T (164.3 x 10(5) +/- 225.1 x 10(5)/g fresh faeces); in contrast, diet Q led to a significant reduction in CFU (4.3 x 10(5) +/- 6.5 x 10(5)/g fresh faeces) compared with the other diets. These findings suggest that condensed tannins could have the potential to reduce the number of potentially pathogenic intestinal bacteria, and that the deliberate inclusion of tannin sources in the diets of captive wild animals should be further investigated. The fact that tannic acid, shown to have antibacterial effects in various in vitro studies, did not have an effect in this study, emphasizes that the relevance of tannin supplementation for intestinal health must be verified in vivo.

Canine borreliosis: a laboratory diagnostic trial.

The aim of this study was to investigate samples from dogs suggestive of active canine borreliosis (group A) by culture and PCR and the detection of antibodies against Borrelia burgdorferi sensu lato in order to confirm a presumptive clinical diagnosis of canine borreliosis by laboratory results. Criteria for such a diagnosis were: history of tick exposure, lameness, neurological signs, nephropathy, lethargy, anorexia, and fever. A total of 302 samples comprising EDTA blood, urine, synovial fluid, cerebrospinal fluid, and tissue (skin, synovial membrane, kidney) from 98 dogs (26 with arthritis, 46 with neurological signs, 21 with nephropathy, 5 with non-specific symptoms) were collected and examined. Moreover, 55 healthy dogs (group B) and 236 dogs with symptoms or injuries unlikely to be associated with borreliosis (group C) were included in this study. Blood serum samples collected from all individuals (n=389) were analysed by ELISA. Twenty-one (21%) out of 98 dogs from group A, 4 (7%) out of 55 from group B and 15 (6%) out of 236 dogs from group C were positive for antibodies against B. burgdorferi sensu lato. The seroprevalences between groups A, B and C differed significantly. None of the corresponding samples investigated by PCR and culture were positive for spirochetal DNA or viable spirochetes. Borrelia afzelii was grown from one EDTA-blood sample but the corresponding blood serum sample remained antibody-negative. Consequently, the etiologic role of B. afzelii in this case is unclear. In approximately 40% of the presumptive canine borreliosis cases, other lesions have been found to be responsible for clinical signs. This study affirms that a definitive diagnosis of canine borreliosis cannot be made by clinical symptoms and serology based on a single consultation. Moreover, this study clearly revealed that the diagnostic sensitivity is enhanced by a thorough consideration and exclusion of other diseases.

The anti-microbial activity of electrolysed oxidizing water against microorganisms relevant in veterinary medicine.

Standards of the German Association of Veterinary Medicine (DVG) for the evaluation of chemical disinfectants were used to assess the anti-microbial efficacy of electrolysed oxidizing water (EOW). Enterococcus faecium, Mycobacterium avium subspecies avium, Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans were exposed to anode EOW (pH, 3.0+/-0.1; oxidation-reduction potential (ORP), +1100+/-50 mV; free chlorine, 400+/-20 mg/l Cl2) and combined EOW (7:3 anode:cathode, v/v; pH, 8.3+/-0.1; ORP, 930-950 mV; free chlorine, 271+/-20 mg/l Cl2). In water of standardized hardness (WSH), all bacterial strains were completely inactivated by a 30 min exposure to maximum 10.0% anode EOW (approximately 40.0 mg/l Cl2) or 50.0% combined EOW (approximately 135.5 mg/l Cl2). The sensitivity ranking order for anode EOW to the bacterial test strains was P. mirabilis>S. aureus>M. avium ssp. avium>E. faecium>P. aeruginosa. P. mirabilis and S. aureus decreased to undetectable levels after 5 min of exposure to 7.5% anode EOW (approximately 30.0 mg/l Cl2). Candida albicans was completely inactivated by a 5-min exposure to 5.0% anode EOW. Both, anode and combined EOW exhibited no anti-microbial activities in standardized nutrient broth or after addition of 20.0% bovine serum to the WSH. Further research is necessary to evaluate the efficacy of EOW as a disinfectant under operating conditions in animal production facilities.

Mycoplasma suis antigens recognized during humoral immune response in experimentally infected pigs.

Today, serodiagnostic tests for Mycoplasma suis infections in pigs have low accuracies. The development of novel serodiagnostic strategies requires a detailed analysis of the humoral immune response elicited by M. suis and, in particular, the identification of antigenic proteins of the agent. For this study, indirect enzyme-linked immunosorbent assay (ELISA) and immunoblot analyses were performed using pre- and sequential postinoculation sera from M. suis-infected and mock-infected control pigs. M. suis purified from porcine blood served as the antigen. Eight M. suis-specific antigens (p33, p40, p45, p57, p61, p70, p73, and p83) were identified as targets of the immunoglobulin G (IgG) antibody response during experimental infection, with p40, p45, and p70 being the preferentially recognized M. suis antigens. Besides the M. suis-specific antigens, porcine immunoglobulins were identified in blood-derived M. suis preparations. By immunoglobulin depletion, the specificity of the M. suis antigen for use in indirect ELISA was significantly improved. M. suis-specific Western blot and ELISA reactions were observed in all infected pigs by 14 days postinfection at the latest and until week 14, the end of the experiments. During acute clinical attacks of eperythrozoonosis, a derailment of the antibody response, determined by decreases in both the M. suis net ELISA values and the numbers of M. suis-specific immunoblot bands, was accompanied by peaking levels of autoreactive IgG antibodies. In conclusion, the M. suis-specific antigens found to stimulate specific IgG antibodies are potentially useful for the development of novel serodiagnostic tests.