The economic threshold for thick infestations on Zambian cattle was analyzed considering both direct production losses and mortality from transmitted diseases. Probability theory applied to mortality risks was used to derive the functional form for disease damage. With only noninfectious ticks, the economic threshold based on liveweight gain losses was three ticks per calf. The threshold recommended dipping calves whenever any disease-infectious ticks were present. Similar threshold results held for cows when considering milk production and disease mortality losses. If disease control benefits are omitted, as in some past work, thresholds will be overstated and dipping recommendations understated when infectious ticks are present.