A total of 788 cloacal and pharyngeal swabs were taken from 399 free-l
iving, clinically healthy tits. Ten nestlings were examined by cloacal
swabs only. Additionally, six dead tits were necropsied and various o
rgans were collected for testing. All swabs and organ samples were tes
ted for Chlamydia. Chlamydia sp. was detected by immunofluorescence wi
th FITC-conjugated monoclonal antibodies after 90 h incubation on Buff
alo-Green-Monkey (BGM) cell cultures at 37 degrees C. Fifty-four per c
ent of 399 tits examined were Chlamydia positive. Chlamydia was detect
ed in 154 of 399 pharyngeal swabs (39%) and in 144 of 389 cloacal swab
s (37%). Blue tits (Parus caeruleus) were most frequently Chlamydia po
sitive (70%), followed by great tits (Parus major) with 53% and marsh
tits (Parus palustris) with 38%. No significant relationship was estab
lished between Chlamydia detection and time of the year, age, sex or s
ize of birds at the time of sampling. Tits examined two or three times
were intermittent shedders. Four of the 10 tit nestlings (Parus major
) examined were already Chlamydia positive at the age of 10 days. Chla
mydia was detected in four of six necropsied tits. The necropsies show
ed that all of the positive tits were cachectic. The livers of three o
f the four positive tits were pathologically changed and splenomegaly
was observed in two of the four. No CEF (chick embryo fibroblast)-path
ogenic viruses and no bacteria were found in these animals. This indic
ates that chlamydiosis was the only cause of death. Two of the Chlamyd
ia sp. isolates from the dead tits produced cytopathic effects (cpe) i
n BGM cell cultures. These cytopathic isolates may be more virulent th
an the isolates from healthy tits, which did not cause visible alterat
ions in BGM cell cultures. The results of this study and the frequent
shedding of Chlamydia in healthy tits prove that most tits intermitten
tly shed Chlamydia sp. as latent carriers, but that lethal Chlamydia i
nfections can also occur in tits.