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

At day 0, RBC OF was significantly lower in cats in group A when compared to cats in group B (p MWU = 0.0127), but mean RBC OF of both groups remained within the reference interval (group A and B, 50% hemolysis in NaCl 0.54 and 0.56% w/v, respectively; reference interval, 50% hemolysis in NaCl 0.50-0.57% w/v, Figure 4C ). Thereafter, at days 21 and 100 pi, RBC OF was significantly higher in cats in group A compared to cats in group B (p MWU < 0.05; Figure 4C ). When cat JHW3 was excluded from the analyses, there was no longer a significant difference between the groups on day 100 pi. Remarkably, compared with baseline values, RBC OF was still increased in several cats in groups A and B at day 100 pi (Figures 4A and B ) ; therefore, one further measurement was obtained at day 179 pi. RBC OF significantly changed during the course of infection only in cats in group A (p F = 0.0004, Figure 4A ). The RBC OF reached maximal values at day 21 pi in eight out of ten animals in group A (range, 50% hemolysis in NaCl 0.63-0.79% w/v) and at day 100 pi in cat JHZ1 (50% hemolysis in NaCl 0.62% w/v) and at day 179 pi in cat JHW1 (50% hemolysis in NaCl 0.66% w/v; Figure 4A ). Cat JHW3 in group B, which turned Mhf PCR-positive only after the end of the experiment (day 154 pi), showed a pronounced increase in relative RBC OF at the time of Mhf bacteremia (50% hemolysis in NaCl 0.75% w/v, day 179 pi; reference interval, 50% hemolysis in NaCl 0.50-0.57% w/v; Figure 4B ). All cats in both groups tested negative in the direct Coombs test at all time points (data not shown).