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TRACHEAL WASHES FOR THE DIAGNOSIS OF BRSV

The impact a tracheal wash may have on the diagnosis of bovine respiratory syncytialvirus (BRSV) infection often is not fully realized.  The proce­dure is easy to perform, but seldom are tracheal wash samples received at the diag­nostic laboratories.  In one study, positive BRSV fluorescence was demonstrated on cells recovered from tracheal lavages of 20 of 42 calves, while BRSV could be isolated in only 6 nasal swabs from the same 42 animals (ActaVet Hung 1987;35:475-7).  In another study, 21 of 32 lavages were positive by FA, and 17 of those 21 were also cell culture positive.  After experimental inoculation of calves with BRSV, FA tests were positive


for 12-18 days.  Virus isola­tion attempts from nasal swabs collected from these experimen­tally infected animals were consistently negative (Am J Vet Res 1986;47:143-7).  A similar study in young children infect­ed with a human respiratory syncytial virus (RSV) had com­parable results:  49 tracheal washes, but only 27 nasal swabs from 121 children were positive for RSV virus on culture. Fifty-two washes, but only 12 swabs were FA positive (DiagnMicrobiolInfDis 1987; 8:101-5).

The virus is very labile and inactivates quickly.  Calves mount a rapid immune response. Antibodies tend to neutralize the virus as the disease progresses, and the likelihood of isolating BRSV decreases rapidly.  To perform a tracheal wash on a bovine, pass a ster­ile gastric tube through the nasal cavity into the lungs. Infuse 50-60 ml of sterile me­dia that contains antibiotics, such as viral transport media or Hank's salt solution, and immediately withdraw the wash solution.  In general 15-30 ml can be recovered.  Submit the tracheal wash sample on ice to the laboratory for FA testing and virus isolation.

This procedure is not just a bovine technique.  Tracheal washes and lung lavages have applications for all domestic animals (use smaller volumes in smaller animals) and the diag­nosis of other viral diseases.

Charles A. Baldwin Reprinted with permission of author Charles A. Baldwin, Veterinary Diagnostic and Investigational Laboratory, Tifton, GA

 

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