Histopathological Observations on Lungs of Balb/C Mice Experimentally Infected With Human Metapneumovirus and Human Respiratory Syncytial Virus

Abstract

Background 
 Human respiratory syncytial virus (HRSV) and human metapneumovirus (HMPV) are responsible for a high percentage of pediatric medical admissions and considered major causes of morbidity and mortality among children in developing countries.
 Objective
 To investigate histopathological findings in lungs of BALB/c mice exposed to intranasal inoculation with human respiratory syncytial virus and human metapneumovirus.
 Materials and Methods
 Thirty six BALB/c mice were divided into 4 groups (9 mice/group) as follows, Group 1 mice inoculated by viral transport medium (VTM) treated with nasopharyngeal swabs (NPS) obtained from children positive for HRSV; group 2 mice inoculated by VTM treated with NPS obtained from children positive for the HMPV;
 group 3 mice inoculated by sterile VTM and group 4 mice were free of inoculation. The mice were sacrificed using inhalation anesthesia and their lungs were excised and undergone histopathological processes to prepare tissue sections for microscopic examination.
 Results
 Frequency rates of NPS positive for HMPV and HRSV were relatively high but they coincide with the reported incidences of HMPV and HRSV infections among children worldwide. An intense inflammatory response was observed in HRSV-inoculated mice represented mainly by infiltration of mononuclear inflammatory cells in the perivascular and peribronchiolar areas associated with alveolar distortion and bronchiolar epithelial sloughing and also associated with syncytium formation within the epithelial tissue in two mice. On the other hand, HMPV-inoculated mice showed a less intense mononuclear inflammatory response in the perivascular and peribronchiolar areas associated with bronchiolar epithelial sloughing, slight deposition of edematous fluid within the interalveolar septa and distortion of alveolar tissue.
 Conclusion
 The direct fluorescent assay (DFA) showed high frequency rates of HRSV and HMPV infection among children admitted to the Pediatric Teaching Hospital in Al Sulaimaniyah city and the histopathological examination of the lungs of mice exposed to intranasal inoculation with HRSV revealed an intense mononuclear inflammatory response, alveolar tissue distortion, bronchiolar epithelial sloughing and syncytium formation compared to less intense mononuclear inflammatory response in lungs of HMPV-inoculated mice.