Piroplasmid protozoa Theileria equi and Babesia caballi and zoonotic rickettsial bacterium Anaplasma phagocytophilum are important agents of equine vector-borne diseases (EVBD). This study aimed at investigating the prevalence of infections with or exposure to these pathogens in horses from the north of Portugal. Blood was randomly collected from 162 horses, living in 72 different stables, to prepare Giemsa-stained slide smears. Additionally, plasma samples were tested for antibodies to T. equi and B. caballi by two competitive enzyme-linked immunosorbent assays and to A. phagocytophilum by an indirect fluorescence antibody test. Five horses were positive to T. equi by microscopy (3.1 %), three to B. caballi (1.9 %), and none to A. phagocytophilum with no horse simultaneously positive for the two piroplasms. Clinically suspect animals had a significantly higher positivity to T. equi by microscopy in comparison with the nonsuspect ones (21.4 vs. 1.4 %). Twenty-nine horses were seropositive to T. equi (17.9 %), 18 to B. caballi (11.1 %), and 21 to A. phagocytophilum (13.0 %). Combined serology and microscopy positive results to T. equi and B. caballi were 19.1 and 11.7 %, respectively, with 33.3 % of the horses found positive to at least one agent. Forty horses were positive to single agents and 14 to more than one agent. An outdoor or mixed outdoor/indoor type of housing was found to be a risk factor for the combined positivity to T. equi. Infections with T. equi, B. caballi, and A. phagocytophilum are endemic in the north of Portugal. In addition to the treatment of positive horses, preventive measures should be put in practice to reduce exposure to and infection with agents of EVBD.

The infection of mice with the wild-type (WT) strain of Y. pseudotuberculosis did not induce polyclonal activation of B lymphocytes. Suppression in the production of certain isotypes of Ig was observed, provoked mainly by YopH, YopJ and YpkA. The WT strain induced a progressive increase in the serum-specific IgG, which peaked after 4 weeks after infection, IgM being produced only after 1 week. Autoantibodies against phosphorylcholine, myelin, thyroglobulin and cardiolipin could be detected in the serum of mice infected with the WT strain. The infection of mice provoked suppression in the production of immunoglobulins by splenic B cells and that YopH, YopJ and YpkA must be involved here.