Dexamethasone inhibits virus production and the secretory IgA response in oesophageal-pharyngeal fluid in cattle persistently infected with foot-and-mouth disease virus.

Cattle persistently infected with foot-and-mouth disease virus were treated with dexamethasone to suppress the immune system in an attempt to influence the level of virus recovery from oesophageal pharyngeal (probang) samples. Twelve carrier cattle were assigned to one of three groups: control; 0.1 mg/kg dexamethasone; and 0.5 mg/kg dexamethasone. Groups 2 and 3 were injected intramuscularly three times weekly for 3 weeks with dexamethasone between days 33 and 56 post-infection with foot-and-mouth disease virus (FMDV). Cattle in both groups developed a leucocytosis, neutrophilia and lymphopenia. The secretory IgA response to FMDV infection was inhibited following, but not during, dexamethasone treatment between days 70 and 98 post-infection (P < 0.05). FMDV recovery from probang samples was reduced between days 40 and 64 post-infection (P < 0.05) during treatment with either 0.1 or 0.5 mg/kg dexamethasone. Following cessation of dosing with dexamethasone virus recovery returned to control levels. These observations suggest dexamethasone inhibits shedding of FMDV in a reversible manner which may be related to its immunosuppressive, anti-inflammatory or physiological actions.