SoutheaSt aSian J trop Med public health 610 Vol 45 No. 3 May 2014 Correspondence: Yong Poovorawan, Center of Excellence in Clinical Virology, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok 10330, Thailand. Tel: +66 (0) 2256 4909; Fax: +66 (0) 2256 4929 E-mail: Yong.P@chula.ac.th HUMAN PARAINFLUENZA VIRUS INFECTION IN THAI CHILDREN WITH LOWER RESPIRATORY TRACT INFECTION FROM 2010 TO 2013 Hathaiphan Ruampunpong 1 , Sunchai Payungporn 1 , Rujipat Samransamruajkit 2 , Thitikarn Pratheepamornkul 2 , Apiradee Theamboonlers 3 and Yong Poovorawan 3 1 Department of Biochemistry, 2 Department of Pediatrics, 3 Center of Excellence in Clinical Virology, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Abstract. Human parainfuenza virus (HPIV) is a common cause of upper and lower respiratory illness in infants and young children. In order to classify the HPIV isolates circulating in the central part of Thailand, 650 samples obtained from the lower respiratory tract of patients from two hospital pediatric wards during 2010 to 2013, were analyzed for the presence and types of HPIVs by mul- tiplex semi-nested PCR of hemagglutinin-neuraminidase (HN) gene. The results showed that 4.8% of the samples were positive for HPIV, among which 0.5%, 2.5% and 1.5% were positive for HPIV-1, HPIV-3, and HPIV-4, respectively, and none were positive for HPIV-2. A phylogenetic tree constructed from 31 HPIV HN gene sequences compared to those in GenBank showed greater than 80% identity to other reference strains. Prevalence of HPIV infection and phylogenetic characteristics of the circulating HPIVs may help explain the impact of HPIVs infection in Thai children. Keywords: human parainfuenza virus (HPIV), classifcation, epidemiology, hemagglutinin-neuraminidase gene, Thailand of age in 2000 (O’Brien et al, 2009; Watt et al, 2009). Major viral contributors to childhood RTIs are respiratory syncy- tial virus (RSV), human parainfluenza virus (HPIV), human metapneumovirus (HMPV), and infuenza virus (Murphy, 1988; Forster et al, 2004; Mullins et al, 2004). First discovered in 1959, HPIV is a common virus that causes acute RTI worldwide including rhinitis, otitis, la- ryngotracheobronchitis, bronchitis, and pneumonia (Billaud et al, 2005). Asymp- tomatic infections are also suspected from infections with HPIV (Laurichesse et al, 1999). HPIV is an enveloped single INTRODUCTION Respiratory tract infections (RTIs) affecting the sinus, throat, airway or lung are usually caused by viruses or bacteria. Bacterial pathogens, such as Streptococcus pneumoniae and Haemophilus influenzae type b, are estimated to account for 36% and 16%, respectively, of the global pneu- monia mortality in children under 5 years