Abstract
Objective: The biennial epidemic pattern of respiratory syncytial virus (RSV) circulation in Croatia has been preserved and could not be related to climatic factors and the predominant RSV subtypes. The possibility that the circulation of different RSV genotypes affect the outbreak cycle in children in Croatia (Zagreb region) over a period of 3 consecutive years was explored in the paper. Methods: The study group consisted of inpatients, aged 0-10 years, who were hospi- talized with acute respiratory tract infections caused by RSV, in Zagreb, over the period from 1 January 2006 to 31 De- cember 2008. The virus was identified in the nasopharyngeal secretion using direct immunofluorescence method. The virus subtype and genotype was determined by real-time PCR and sequence analysis, respectively. Results: RSV infec- tions identified in 731 children. RSV subtype A caused 399 infections, and subtype B 332. Two subtype A genotypes (NA1 and GA5) and three subtype B genotypes (BA7, BA9 and BA10) were found. During persistent RSV biennial cycles namely four succeeding outbreaks, the new genotype from the previous smaller outbreak persevered into the up- coming larger outbreak. Conclusion: Our molecular-epidemiology study of RSV subtypes and genotypes during calen- dar months demonstrates that the biennial RSV cycle cannot be fully explained by the dynamic of the predominant cir- culating genotype of RSV. Other unknown factors account for the biennial cycle of RSV epidemics in Croatia.).
Highlights
The biennial pattern of respiratory syncytial virus (RSV) circulation in Croatia, which is similar to that reported in other Central European countries [1,2,3,4,5,6] has documentedly been preserved for the last 15 years [1,2,7,8]
Since the two-year periodicity of RSV infections in Croatia could not be related to climatic factors [1], we examined whether this epidemiological characteristic of RSV infections in Croatia could be related to a regular exchange of the two viral subtypes [9]
It was established that subtype A isolates were found in 13 groups of the phylogenetic tree, that consisted of two genotypes (NA1 and GA5)
Summary
The biennial pattern of respiratory syncytial virus (RSV) circulation in Croatia, which is similar to that reported in other Central European countries [1,2,3,4,5,6] has documentedly been preserved for the last 15 years [1,2,7,8]. Many earlier studies have attempted to explain the epidemic pattern of RSV activity. Biennial virus cycles were found to be persistent, the predominant RSV subtype in the first two epidemic waves was subtype B, while in the second two subtype A. According to that findings, it may be concluded that neither of the predominant RSV subtypes has an effect on the periodicity of RSV infections in Croatia
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