Final answer:
A cat's blood sample may test negative multiple times for Haemobartonella due to the intermittent circulation of the parasites in the blood, which causes fluctuating levels that might fall below detectable thresholds during some tests.
Step-by-step explanation:
The reason why a cat's blood sample might test negative three times before finding evidence of Haemobartonella infection is option c) The infection is intermittent, and the parasites may not be circulating in the blood at all times. Haemobartonella, now more commonly referred to as Mycoplasma haemofelis, is a bacterial parasite that cyclically appears in the bloodstream of infected cats. The level of bacteria can fluctuate, sometimes falling below detectable levels on blood smears, which explains why multiple tests can yield different results. In addition, the effectiveness of the detection can depend on the timing of the test in relation to the fluctuating levels of the parasite in the bloodstream.