Interaction of Streptococcus equi with the equine nasopharynx

The tonsil of the soft palate and the lingual tonsils were the chief entry points for Streptococcus equi (Se), the cause of equine strangles, in intranasally inoculated horses. Microplicae on the stratified squamous epithelial cells were important in initial attachment. Within a few hours, small numbers of Se were present in the tonsillar crypts, lining reticular epithelium, and the deeper lymphoid tissue. At 20 h, Se was cultured from the draining lymph nodes. Mutants of Se lacking capsule, SeM or streptolysin S did not infect lymph nodes, an indication that resistance to phagocytosis was important in survival in the tonsil. At onset of fever, 2 to 10 days after inoculation, large numbers of Se (extra- and intracellular) were present in the tonsils. In affected lymph nodes, only long chains of extracellular Se were evident.