Chlamydia shedding by four species of wild birds

Four wild bird species--great-tailed grackle (Cassidix mexicanus), common grackle (Quiscalus quiscula), brown-headed cowbird (Molothrus ater), and mourning dove (Zenaidura macroura)--were either inoculated intratracheally with Chlamydia psittaci or exposed indirectly as uninoculated cagemates. Shedding of chlamydiae was monitored by inoculating mice with suspensions of material eluted from cloacal swabs collected from all birds, usually at 3-day intervals. Sporadic shedding of chlamydiae was demonstrated in three species (great-tailed grackle, brown-headed cowbird, and mourning dove) that were inoculated, and also in uninoculated grackles of both species exposed to inoculated great-tailed grackles. All inoculated birds except one mourning dove developed antibody detectable by complement-fixation (CF). Of the exposed birds, only grackles had antibody. However, two great-tailed grackles which did shed chlamydiae did not develop CF antibody. The modified direct CF (MDCF) method was slightly more sensitive than the direct CF method. The agar-gel precipitin method was not entirely reliable for antibody detection, for it did not correlate with CF serology and shedding of chlamydiae. It is concluded that: 1) grackles are potential reservoir hosts that could be important in the transmission cycle of C. psittaci in nature; and 2) epidemiologic studies of chlamydiosis in wild birds should include both serologic testing (preferably by the MDCF method) and attempts to isolate chlamydiae from cloacal swabs.