You find a large, colorful, orange and black tick on a cow. What disease(s) might it be carrying?

• A. African swine fever
• B. Heartwater
• C. Equine babesiosis
• D. East Coast fever

Answer: (B)

The key idea is linking the tick species to the disease it transmits in cattle. The large, colorful orange-and-black tick described matches the tropical bont tick, Amblyomma variegatum, a well-known vector of Ehrlichia ruminantium. This pathogen causes heartwater in cattle and other ruminants, so finding that tick on a cow makes heartwater the most likely disease the tick could be carrying.

African swine fever is a pig disease transmitted by soft ticks, not cows, so it doesn’t fit. East Coast fever is caused by Theileria parva and spread by the brown ear tick (a different vector with a distinct distribution), not the orange-and-black tropical bont tick. Equine babesiosis affects horses, not cattle. So the association between the observed tick and the cow makes heartwater the best answer.