Dog has fever, lethargy, low platelets, tick tests negative. What's next?
Maxi certainly sounds quite sick, but I am glad to hear that she is eating and drinking normally. As I'm sure your vet discussed, tick borne diseases are one of the more common causes of a fever of unknown origin (FUO). However, FUOs can also be caused by other infectious diseases (toxoplasmosis, Bartonella, Brucella, mycoplasma, fungal diseases, etc.) as well as immune-mediated or cancerous causes.
To answer your question, yes, you will need to do some more diagnostics to get to the bottom of this issue. Different causes of the FUO will require different treatments. Maxi's vet will be able to guide you as to their next tier of diagnostic testing based upon their clinical suspicions. I hope that all goes well!
Updated on September 23, 2025