I am unclear if antibody tests can be conclusive in a tick or even if it is possible to test. If so, what are the limitations once the ticks have been collected. Limits such as temporal limits, storage in ethanol, and shelf life.
Usually RT PCR kit cost for pathogens will be more expensive but it will give you best approach for detection of pathogens DNA without isolation of pathogen pure culture.
For detection by serum you need to perform isolation of pure culture of pathogen. As you know ticks are the vectors of several very harmful infections, isolation of cultures from ticks better to perform in Biosafety level 3 labs.
We work with tick's borne diseases. We do RT PCR for the detection of pathogenic organisms. The ticks are processed alive (not stored in ethanol) and then the DNA extraction is done for the subsequent amplification. It is expensive, but if you have RT PCR equipment, it is convenient because to carry out the antibody test you need to cultivate the pathogens and then obtain the antibodies. It depends on the equipment you have in your laboratory and your experience in culture and RT PCR.