Usefulness of Bronchoalveolar Lavage for Diagnosis of Acute and Persistent Respiratory Syncytial Virus Lung Infections in Guinea Pigs Azzeddine Dakhama, PhD, Nancy G. Chan, BSC, Homa Y. Ahmad, BSC, Andrew M. Bramley, PhD, Timothy Z. Vitalis, PhD, and Richard G. Hegele, MD, PhD* Summary. To investigate whether bronchoalveolar lavage (BAL) fluid specimens can be used to diagnose acute and persistent respiratory syncytial virus (RSV) lung infections in guinea pigs, we tested BAL fluid and lung tissue specimens for evidence of viral infection, and compared BAL cytology between infected and uninfected animals. RSV-inoculated guinea pigs were studied during acute bronchiolitis (days 3 and 7 postinoculation), convalescence (Day 14 postinocula- tion), and persistent infection (Days 28 and 60 postinoculation), and were compared to the sham-infected control animals. BAL and lung tissue specimens were cultured for virus and tested by immunocytochemistry for viral protein. A reverse transcription-polymerase chain re- action (RT-PCR) method was used to test for viral nucleic acid. Total and differential BAL cell counts were compared between RSV-inoculated and control animals on each study day. In BAL specimens, replicating RSV was isolated by culture in one out of four of the animals on Day 3 postinoculation; immunocytochemistry for RSV antigens was positive in all virus- exposed animals from Days 3–14 postinoculation, and viral nucleic acid was detected by RT- PCR in one-fourth of the animals on Day 3 postinoculation. In contrast, replicating virus, viral antigens, and viral nucleic acid were documented in lung tissues obtained from the same RSV-infected animals on all study days. BAL specimens of RSV-inoculated animals contained more eosinophils on all study days (two-tailed P value < 0.01) compared to the controls. The results of this animal study demonstrate that BAL fluid is not useful for diagnosis of persistent RSV infection. However, BAL fluid may be helpful for the documentation of acute RSV lung infection when immunocytochemistry may provide a more accurate test for virus detection than RT-PCR or viral culture. Pediatr Pulmonol. 1998; 26:396–404. © 1998 Wiley-Liss, Inc. Key words: respiratory syncytial virus; bronchoalveolar lavage; animal model; polymerase chain reaction; histology. INTRODUCTION Respiratory syncytial virus (RSV) is the most common cause of acute bronchiolitis in infants and young chil- dren 1 and is implicated in the pathogenesis of postbron- chiolitis wheezing and asthma. 2–4 To study the role of RSV in the pathogenesis of the sequelae of acute bron- chiolitis, we developed an animal model of acute RSV bronchiolitis in juvenile guinea pigs. 5 In this model, RSV-inoculated animals develop acute bronchiolitis characterized by intrapulmonary viral replication that is maximal at 3 days postinoculation. Bronchiolar inflam- mation, characterized by increased airway epithelial ne- crosis, mononuclear cell and granulocyte (eosinophil and neutrophil) infiltrates, are maximal at Days 6–7 postin- oculation. RSV-infected guinea pigs develop increases in airway reactivity that parallel airway inflammation. 6 Fol- lowing the resolution of acute bronchiolitis, we demon- strated that RSV protein and genome can persist for two months in the lungs after experimental inoculation of guinea pigs. 7,8 Other investigators have reported that guinea pigs develop chronic increases in airway reactiv- ity and persistence of viral antigen for 6 weeks post-RSV inoculation. 9 It is unknown whether RSV causes persis- tent infection of the human lung after an episode of acute bronchiolitis. University of British Columbia Pulmonary Research Laboratory, St. Paul’s Hospital, Vancouver, BC Canada V6Z 1Y6. Grant sponsor: the Medical Research Council of Canada; Grant num- ber: MT-13766; Grant sponsors: the Respiratory Health Network of Centres of Excellence, and the British Columbia Lung Association. Current address for Azzeddine Dakhama: Research Department, Laval Hospital, St-Foy, Quebec, Canada G1V 4G5. *Correspondence to: Richard G. Hegele, MD, PhD, University of Brit- ish Columbia, Pulmonary Research Laboratory, St. Paul’s Hospital, 1081 Burrard Street, Vancouver, B.C., Canada V6Z 1Y6. E-mail: rhegele@prl.pulmonary.ubc.ca Received 23 April 1998; accepted 19 August 1998. Pediatric Pulmonology 26:396–404 (1998) © 1998 Wiley-Liss, Inc.