If heartwater entered the United States, the most likely scenario would be:

• A. Asymptomatic infections in most breeds of cattle
• B. Chronic, lingering illness in sheep and goats, with acute cases in cattle
• C. High mortality in all susceptible ruminants, with a high incidence of peracute or acute disease
• D. Chronic, lingering illness in most cattle, with acute cases in sheep and goats

Answer: (C)

Heartwater is a highly virulent tick-borne disease that causes rapid and severe illness in susceptible ruminants. In populations with no prior exposure or immunity, outbreaks progress quickly and are often fatal, with animals showing acute or even peracute signs rather than long, lingering illness. The pathogen is transmitted by ticks that can spread the infection across cattle, sheep, and goats, so when it enters a naïve United States herd, you’d expect high mortality across all susceptible species and a predominance of quick, severe, acute disease. Chronic or asymptomatic infections are not the typical pattern in a naïve population, which is why the scenario described—high mortality in all susceptible ruminants with acute or peracute disease—is the best fit.