Background: Abortion is a major source of economic losses in cattle breeding. Abortion occurs due to a wide range of causes, but infections are the most frequently diagnosed. However, establishing an aetiological diagnosis remains challenging due to the large variety of bacteria, protozoa, viruses, and fungi that have been associated with abortion in cattle. Economic restraints limit the range of diagnostic methods available for routine diagnostics, and decomposition of the conceptus or lack of proper fetal and/or maternal samples further restrict the diagnostic success. In this study, we report recent diagnostic findings from bovine abortions in Denmark, a country that has a large dairy sector and is free from most infectious agents causing epizootic abortion in cattle. The aims of the study were: (i) to identify infectious causes of bovine abortion in Denmark, (ii) to categorise the diagnostic findings based on the level of diagnostic certainty, and (iii) to assess the diagnostic rate. Due to economic restraints, only a limited panel of routine diagnostic methods were available. Placentas and/or fetuses from mid-to late-term abortions and stillbirths (n = 162) were submitted to the Danish National Veterinary Institute between January 2015 and June 2017. The aborted materials were examined macroscopically, histologically, and by bacterial culture. Maternal blood samples were tested for bovine viral diarrhoea virus (BVDV) antibodies. Results: The likely aetiology of the abortion was diagnosed in 52 cases, resulting in a diagnostic rate of 33%. The most common cause was protozoal infection (19%) followed by infection with Trueperella pyogenes (3%), Staphylococcus aureus (2%), and non-haemolytic Escherichia coli (2%). Lesions in fetuses with a protozoal infection were consistent with neosporosis. In many cases (38%), inflammatory changes were found in the placenta and/or fetal organs but no specific aetiology was identified. Neither infection with Brucella spp. nor maternal BVDV antibodies were detected. The majority of submitting herds (92%) were each represented by fewer than three abortion cases over the study period. Conclusions: Protozoal infection, most likely neosporosis, was the most commonly diagnosed cause of abortion and the only one associated with potential epizootic abortion events. Despite using a reduced number of diagnostic methods in comparison to other abortion studies, the diagnostic rate of this study was within the range reported in an earlier Danish study, as well as in recent international studies. The low number of submitted cases per herd and the sparse anamnestic information provided at submission hampered conclusions on the potential epizootic character of the abortion events in question.

"Candidatus Mycoplasma turicensis" infects felids. The pathogenesis of "Candidatus M. turicensis" chronic infection is poorly understood. The goals of the present study were to (1) induce reactivation of the infection in chronic carrier cats by attempted immunosuppression, (2) identify potential tissue sequestration using real-time TaqMan® PCR and (3) monitor the humoral immune response by DnaK enzyme-linked immunosorbent assay (ELISA). Ten specified pathogen-free cats that had ostensibly recovered from experimental "Candidatus M. turicensis" infection were used: five cats (group 1) received high dose methylprednisolone (attempted immunosuppression), while five cats served as untreated controls (group 2). Besides weekly blood samples, tissue samples were collected from bone marrow, kidney, liver and salivary glands at selected time points. The cats in group 1 had significantly lower lymphocyte counts and higher blood glucose levels after methylprednisolone administration than the controls. After methylprednisolone administration one blood and three tissue samples from cats in group 1 tested PCR-positive; before the administration, only one sample was positive. All other samples tested PCR-negative. All cats stayed seropositive; the antibody levels of the cats in group 1 showed a significant transient decrease after methylprednisolone administration. This is the first study to report the presence of "Candidatus M. turicensis" in tissues of chronically infected cats and the persistence of anti-feline hemoplasma antibodies in the absence of detectable bacteremia. Methylprednisolone administration did not lead to a significant reactivation of the infection. Our results enhance the knowledge of "Candidatus M. turicensis" infection pathogenesis and are clinically relevant to the prognosis of hemoplasma-infected cats.

In felids, three hemotropic mycoplasma species (hemoplasmas) have been described: Mycoplasma haemofelis, "Candidatus Mycoplasma haemominutum," and "Candidatus Mycoplasma turicensis." In particular, M. haemofelis may cause severe, potentially life-threatening hemolytic anemia. No routine serological assays for feline hemoplasma infections are available. Thus, the goal of our project was to identify and characterize an M. haemofelis antigen (DnaK) that subsequently could be applied as a recombinant antigen in a serological assay. The gene sequence of this protein was determined using consensus primers and blood samples from two naturally M. haemofelis-infected Swiss pet cats, an experimentally M. haemofelis-infected specific-pathogen-free cat, and a naturally M. haemofelis-infected Iberian lynx (Lynx pardinus). The M. haemofelis DnaK gene sequence showed the highest identity to an analogous protein of a porcine hemoplasma (72%). M. haemofelis DnaK was expressed recombinantly in an Escherichia coli DnaK knockout strain and purified using Ni affinity, sizeexclusion, and anion-exchange chromatography. It then was biochemically and functionally characterized and showed characteristics typical for DnaKs (secondary structure profile, thermal denaturation, ATPase activity, and DnaK complementation). Moreover, its immunogenicity was assessed using serum samples from experimentally hemoplasma-infected cats. In Western blotting or enzyme-linked immunosorbent assays, it was recognized by sera from cats infected with M. haemofelis, "Ca. Mycoplasma haemominutum," and "Ca. Mycoplasma turicensis," respectively, but not from uninfected cats. This is the first description of a full-length purified recombinant feline hemoplasma antigen that can readily be applied in future pathogenesis studies and may have potential for application in a diagnostic serological test.

Haemotropic mycoplasmas (or haemoplasmas) are the causative agents of infectious anaemia in many mammalian species. They were previously known as Haemobartonella and Eperythrozoon species. The development of sensitive, specific PCR assays has expanded our knowledge of these agents and PCR is the method of choice to diagnose and differentiate haemoplasma infections. In felids, Mycoplasma haemofelis, 'Candidatus Mycoplasma haemominutum' and 'Candidatus Mycoplasma turicensis' have been described. They vary strongly in their pathogenic potential and co-factors may influence the disease severity. In dogs, Mycoplasma haemocanis and 'Candidatus Mycoplasma haematoparvum' are known; clinical signs are mainly found in immunocompromised dogs. Transmission of haemoplasmas may occur via infected blood (aggressive interaction, transfusion) or blood-sucking arthropods. Infections can be treated with Doxycycline, although it is disputable whether the infection is completely eliminated. Feline haemoplasmas must be expected in cats all over Europe, while canine haemoplasmas are mainly encountered in dogs in Mediterranean countries but should also be considered in Swiss dogs with a travel history.