A seroepidemiological survey of adenovirus activity (types 1--3) at two Finnish calf rearing farms.

Three series of seroepidemiological studies by microneutralization test on activity by serotypes 1, 2 and 3 of bovine adenovirus were carried out at two calf rearing farms. One farm (A) was operated as a closed, and the other (B) as an open herd. At farm A two serial studies were made, covering periods of six and nine months and including groups of 44 and 41 even-aged bull calves, respectively; at farm Β at each bleeding calves of different selected age groups were included, 36 in all.Maternal antibodies against all three types were common. With few exceptions they had disappeared at the age of five months. At farm B, unexpectedly, in view of the open herd nature, no signs of active infection were revealed during the period of study. At farm A infection by type 3 was judged to be present during both studies, though demonstrably affecting a lesser part of the study population only; infections by types 1 and 2 definitely occurred only during the second study, and then extensively. The titers of type 1 and 2 antibodies were, on the average, higher (with highest titers 1/243 and 1/729, respectively) than those of type 3 (highest titer 1/27). The spread of infection within the groups was relatively slow. A possible causative participation of type 2 virus in a smaller epidemic of mild respiratory and enteric disease at farm A was suggested but not verified by the results. Maternal antibodies did not seem to give effective protection against infection.