Potomac horse fever

noun

Po·​to·​mac horse fever pə-ˈtō-mək-  -mik- 

: an often fatal disease of horses that is marked by fever, loss of appetite, diarrhea, and laminitis, that is caused by a bacterium of the genus Ehrlichia (E. risticii), and that was discovered in the region of the Potomac River in Maryland but is much more widespread

called also Potomac fever