Epidemiologic characteristics and seasonal distribution of human metapneumovirus infections in five epidemic seasons in Stockholm, Sweden, 2002-2006.

The presence of human metapneumovirus (hMPV) was analyzed retrospectively by reverse transcriptase-polymerase chain reaction (RT-PCR) in five epidemic seasons, in Stockholm, 2002-2006. The occurrence of hMPV was compared with five common respiratory viruses; respiratory syncytial virus, influenza A virus, influenza B virus, parainfluenza virus and adenovirus. With a detection rate of 2.9% (n = 143/4,989) in nasopharyngeal samples over the whole period, hMPV was the fourth most common respiratory virus after RSV, influenza A and parainfluenza virus. hMPV genotype A dominated over genotype B, out of 91 genotyped virus samples 87 belonged to genotype A and four belonged to genotype B. Approximately 50.3% (n = 72/143) of the hMPV positive patients were <3 years, 49.7% (71/143) were > or =3 years and 38,5% (n = 55/143) were <1 year. The relative frequencies of hMPV infections in the three age groups were 2.8% (72/2,579), 2.9% (71/2,410) and 2.6% (55/2,122), respectively. This age distribution differed from RSV, influenza A, B and parainfluenza virus. hMPV epidemics peaked in March, not coincident with RSV or parainfluenza virus. In successive epidemic seasons, large outbreaks of hMPV alternated with small outbreaks in a regular, biannual pattern. Large hMPV virus epidemics were anticyclical to large RSV epidemics. It is concluded that the epidemiology of hMPV differs markedly from other common respiratory viruses.

Genotyping of respiratory syncytial virus (RSV) group A in Stockholm, Sweden, using PCR and two-dimensional melting curve analysis.

Genotyping of respiratory syncytial (RS) virus group A, by means of a novel method based on PCR, FRET (fluorescence resonance energy transmission) detection and two-dimensional melting curve analysis, was carried out on 80 RS virus samples of group A collected in Stockholm from 1976 to 2005. The Tm values were assessed for three different genotypes (GA2, GA5 and GA7) circulating in Sweden. Two pairs of probes were used and results of subsequent data analysis were plotted in a two-dimensional system. The results obtained were compared to genotyping using conventional nucleotide sequencing and phylogenetic tree analysis. It was found that the new assay was able to correctly identify genotype in about 89% of the isolates; it identified the remaining 11% as untypeable and as candidates for conventional nucleotide sequencing. The new method constitutes a complement to nucleotide sequencing and could be useful in studies of large numbers of samples in epidemiological studies.

Characterization of mumps virus strains with varying neurovirulence.

Mumps virus strains isolated during an epidemic in Lithuania in 1998 - 2000 were studied. Viruses of the neurovirulent C1 and non-neurovirulent C2 small hydrophobic (SH) genotype variant were sequenced for the haemagglutinin-neuraminidase (HN) and fusion (F) protein genes. Amino acid differences between C1 and C2 strains were found for both proteins. Two amino acid differences were of potential importance for the non-neurovirulent phenotype of the C2 virus. Four of 5 C2 strains exhibited the amino acid arginine instead of lysine at position 335 of the HN protein, and the amino acid phenylalanine was found instead of serine at amino acid position 195 of the F protein. Amino acid differences at these positions have previously been reported to associate with a change in neurovirulence and fusion activity. In addition, the HN gene of the neurovirulent Kilham strain of genotype A was sequenced. The deduced amino acid sequence showed different amino acids compared to both genotypes A and C on some positions. Notably, amino acid differences located in previously identified neutralizing epitopes were found at positions 266, 354 and 356 of the HN protein compared to other genotype A strains. The amino acid differences between Kilham virus strain and other genotype A strains and the similarity of the Kilham HN protein (7 positions) to neurovirulent genotype C strains on some amino acid positions may indicate a possible role for this protein in mumps virus neurovirulence.

Molecular epidemiology of respiratory syncytial virus (RSV) of group A in Stockholm, Sweden, between 1965 and 2003.

The epidemiology of respiratory syncytial virus (RSV) group A was followed by nucleotide sequencing of the variable parts of the glycoprotein (G) gene. The amino acid sequences of an aminoterminal (A-terminal, amino acids 90-132) and carboxyterminal (C-terminal, amino acids 262-298) portion of the G protein in 47 virus strains, collected in Stockholm, between 1965 and 2004, were determined. In phylogenetic analysis jointly with previously described genotypes (GA1 to GA7 and SAA1), 33 virus strains (isolated between 1991 and 2004) belonged to genotype GA5, seven to GA2, three to genotype GA1 (isolated before 1991), one to genotype GA4 (isolated in 1982) and three to genotype GA7 (isolated in 1993 and 2001). Genotype GA5 was predominant in four epidemics, between 2000/2001 and 2003/2004. Little or no variation with time of the C-terminal amino acid sequence of the G protein was found when the virus strains were compared within their own genotype. Identical and nearly identical nucleotide sequences were found between strains isolated more than 10 (GA5) and 25 (GA2) years apart. The A-terminal part of they G protein of genotype GA2 was highly conserved. In contrast, the A-terminal part of the G protein of genotype GA5 exhibited a pronounced variation in its amino acid sequence over time.