Which finding helps differentiate bacterial infection from parasitic infestation in this case?

• A. Cytology showing cocci and neutrophils
• B. Absence of eroded patches
• C. No licking behavior
• D. Positive serology for mites

Answer: (A)

The important concept is using cytology to tell apart bacterial infection from parasitic infestation by looking at what is present under the microscope and how the tissue responds. Seeing cocci bacteria with neutrophils on cytology is a classic sign of an acute bacterial infection because neutrophils rush in to fight bacteria, and cocci represent a common bacterial shape. In contrast, parasitic infestations typically evoke a different inflammatory pattern—often eosinophils—and you’d expect to see parasites or parasite-associated structures if you sampled the lesion. Serology for mites would indicate exposure to mites but not necessarily an active bacterial infection, and absence of eroded patches or licking behavior are nonspecific clues. So the cytology showing cocci and neutrophils best differentiates bacterial infection from parasitic infestation.