Sex differences in Seoul virus infection are not related to adult sex steroid concentrations in Norway rats

Field studies of hantavirus infection in rodents report that a higher perce ntage of infected individuals are males than females. To determine whether males were more susceptible to hantavirus infection than females, adult mal e and female Long Evans rats (Rattus norvegicus) were inoculated with doses of Seoul virus ranging from 10(-4) to 10(6) PFU. The 50% infective doses ( ID50) were not significantly different for male and female rats (10(0.05) a nd 10(0.8) PFU, respectively). To determine whether sex differences in resp onse to infection were related to circulating sex steroid hormones, sex ste roid concentrations were manipulated and antibody responses and virus shedd ing were assessed following inoculation with the ID50. Regardless of hormon e treatment, males had higher anti-Seoul virus immunoglobulin G (IgG) and I gG2a (i.e., Th1) responses than females and IgG1 (i.e., Th2) responses simi lar to those of females. Males also shed virus in saliva and feces longer t han females. Manipulation of sex steroids in adulthood did not alter immune responses or virus shedding, suggesting that sex steroids may organize adu lt responses to hantavirus earlier during ontogeny.