The possibility of horizontal transmission of T. gondii was examined in squ
irrel monkeys. After three monkeys were inoculated perorally with 1.1-2.1 x
10(3) cysts of the T. gondii ME49, the animals were divided into two cages
and maintained with one normal monkey for each cage as a cagemate. Two out
of the three T gondii-inoculated monkeys died, and the remaining one monke
y was sacrificed in a moribund state one week after infection because of ac
ute toxoplasmosis. Many T. gondii tachyzoites were recovered from broncho-a
lveolar lavages and were also found histopathologically in the lung, liver,
spleen, kidney and lymph nodes and impression smears of tissues from the t
hree T. gondii-inoculated monkeys by Giemsa staining. Anti-T. gondii antibo
dy was examined by immunoblot assay in these animals, and the antibody to T
, gondii major surface membrane protein (p30) could be detected after the s
tart of experiment. Furthermore, a specific band of T. gondii NTPase gene w
as observed by PCR in the liver and lung of infected and cagemate monkeys,
and the sequence of the second PCR products obtained from the cagemates, wh
ich were clinically normal but gave a positive result in immunoblotting ass
ay, was exactly the same as the sequence of the NTPase gene of T. gondii ME
49. These findings suggested that transmission of T, gondii from the infect
ed monkeys to cagemates occurred easily, and since many T. gondii tachyzoit
es were recovered from the bronchoalveolar lavages of the three T gondii-in
oculated monkeys, we suggest that aerosol infection plays an important role
for the enzootic toxoplasmosis in colonies of squirrel monkeys.