Passive immunization does not provide protection against experimental infection with Mycoplasma haemofelis

Sugiarto, Sarah; Spiri, Andrea M.; Riond, Barbara; Novacco, Marilisa; Oestmann, Angelina; de Miranda, Luisa H. Monteiro; Meli, Marina L.; Boretti, Felicitas S.; Hofmann-Lehmann, Regina; Willi, Barbara

Interestingly, one cat in group B (JHW3) stayed PCRnegative and seronegative during the 100-day follow-up period, but it developed bacteremia and seroconverted 154 days after Mhf inoculation. Although low-level bacteremia, below the detection limit of the PCR assay, cannot be completely excluded in this cat, we would expect a productive infection to result in seroconversion [20, 50] . Because all cats in this study were kept under strictly controlled hygienic conditions, vector-borne transmission between the cats can be excluded. However, all cats of group B were housed together and four out of five cats in group B tested Mhf PCR-positive at the time that bacteremia and seroconversion occurred in cat JHW3. Therefore, direct transmission between the cats, i.e., by aggressive interactions, seems most likely, although no obvious clinical signs of aggressive interactions were observed in the cats in this study at any time during the experiment. A direct transmission of Mhf through saliva seems unlikely because only low hemoplasma loads can be detected in saliva of Mhf-infected cats [22] and transmission by oral or subcutaneous inoculation of saliva has not been successful for another feline hemoplasma species, CMt [19] .