337 research outputs found
Towards a Human Metapneumovirus Vaccine
Het humaan metapneumovirus (HMPV) behoort tot de familie Paramyxoviridae, subfamilie
Pneumovirinae, genus Metapneumovirus, en is voor het eerst beschreven in 2001. HMPV
is verwant aan het humaan respiratoir syncytieel virus (HRSV), een belangrijke veroorzaker van
luchtweginfecties. Na HRSV is HMPV een van de belangrijkste veroorzakers van bronchiolitis
in jonge kinderen. Bij volwassenen resulteert infectie met HMPV normaliter in relatief milde,
verkoudheid-achtige symptomen. Jonge kinderen, ouderen en individuen met een verzwakte
weerstand vormen de risicogroepen voor infecties met HMPV. In deze belangrijkste risicogroepen
kunnen ernstige infecties aan zowel de bovenste als onderste luchtwegen ontstaan en om die
reden is het ontwikkelen van een vaccin tegen HMPV gewenst. Dergelijke vaccinatie strategieën
moeten vooral gericht zijn op het voorkomen van ernstige infecties in de onderste luchtwegen.
Het voorkomen van verschillende varianten van HMPV zou van invloed kunnen zijn op de
werkzaamheid van een vaccin. Een vaccin dat bescherming biedt tegen infectie met de ene variant
hoeft namelijk niet vanzelfsprekend bescherming te bieden tegen infectie met een andere variant.
Omdat er aanwijzingen waren voor de aanwezigheid van meerdere HMPV varianten, hebben
we in hoofdstuk 2 de genetische en antigene eigenschappen van verschillende HMPV-isolaten
bestudeerd. Hiervoor zijn de sequenties (genetische blauwdruk) bepaald van 84 fusie eiwitten (F)
en 35 aanhechtingseiwitten (G). Dit zijn eiwitten aan de buitenkant van virusdeeltjes waartegen
de afweerreactie van de mens voornamelijk gericht is. Aan de hand van deze sequenties konden
de virus-isolaten worden ingedeeld in twee genetische hoofdgroepen (A en B), die beiden verder
konden worden verdeeld in 2 subgroepen (A1, A2, B1 en B2). Tevens werden tussen deze twee
hoofdgroepen grote antigene (serologische) verschillen aangetoond. Antistoffen gericht tegen
een groep A virus bleken veel beter in staat te zijn om groep A virussen dan groep B virussen
te herkennen. Op basis van deze genetische en antigene verschillen hebben wij twee HMPVserotypen
gedefi nieerd
Epidemiological and genetic investigations of human-to-human transmission of zoonotic influenza viruses.
In September 2013, leptospirosis was diagnosed in two Spanish travellers returning from Thailand. The first case walked in floodwater in the Phi Phi Islands in pouring rain: 20 days later he presented with fever and acute hepatitis. The second presented with fever and renal failure 17 days after visiting the islands. These cases remind clinicians to consider leptospirosis in febrile patients with a history of contact with flood or fresh water while travelling to tropical countries
Transmission routes of respiratory viruses among humans
Respiratory tract infections can be caused by a wide variety of viruses. Airborne transmission via droplets and aerosols enables some of these viruses to spread efficiently among humans, causing outbreaks that are difficult to control. Many outbreaks have been investigated retrospectively to study the possible routes of inter-human virus transmission. The results of these studies are often inconclusive and at the same time data from controlled experiments is sparse. Therefore, fundamental knowledge on transmission routes that could be used to improve intervention strategies is still missing. We here present an overview of the available data from experimental and observational studies on the transmission routes of respiratory viruses between humans, identify knowledge gaps, and discuss how the available knowledge is currently implemented in isolation guidelines in health care settings
Reassortment between Avian H5N1 and Human Influenza Viruses Is Mainly Restricted to the Matrix and Neuraminidase Gene Segments
Highly pathogenic avian influenza H5N1 viruses have devastated the poultry industry in many countries of the eastern hemisphere. Occasionally H5N1 viruses cross the species barrier and infect humans, sometimes with a severe clinical outcome. When this happens, there is a chance of reassortment between H5N1 and human influenza viruses. To assess the potential of H5N1 viruses to reassort with contemporary human influenza viruses (H1N1, H3N2 and pandemic H1N1), we used an in vitro selection method to generate reassortant viruses, that contained the H5 hemagglutinin gene, and that have a replication advantage in vitro. We found that the neuraminidase and matrix gene segments of human influenza viruses were preferentially selected by H5 viruses. However, these H5 reassortant viruses did not show a marked increase in replication in MDCK cells and human bronchial epithelial cells. In ferrets, inoculation with a mixture of H5N1-pandemic H1N1 reassortant viruses resulted in outgrowth of reassortant H5 viruses that had incorporated the neuraminidase and matrix gene segment of pandemic 2009 H1N1. This virus was not transmitted via aerosols or respiratory droplets to naïve recipient ferrets. Altogether, these data emphasize the potential of avian H5N1 viruses to reassort with contemporary human influenza viruses. The neuraminidase and matrix gene segments of human influenza viruses showed the highest genetic compatibility with HPAI H5N1 virus
Detection of influenza a viruses from different species by PCR amplification of conserved sequences in the matrix gene
The recently raised awareness of the threat of a new influenza pandemic has stimulated interest in the detection of influenza A viruses in human as well as animal secretions. Virus isolation alone is unsatisfactory for this purpose because of its inherent limited sensitivity and the lack of host cells that are universally permissive to all influenza A viruses. Previously described PCR methods are more sensitive but are targeted predominantly at virus strains currently circulating in humans, since the sequences of the primer sets display considerable numbers of mismatches to the sequences of animal influenza A viruses. Therefore, a new set of primers, based on highly conserved regions of the matrix gene, was designed for single-tube reverse transcription-PCR for the detection of influenza A viruses from multiple species. This PCR proved to be fully reactive with a panel of 25 genetically diverse virus isolates that were obtained from birds, humans, pigs, horses, and seals and that included all known subtypes of influenza A virus. It was not reactive with the 11 other RNA viruses tested. Comparative tests with throat swab samples from humans and fecal and cloacal swab samples from birds confirmed that the new PCR is faster and up to 100-fold more sensitive than classical virus isolation procedures.</p
Detection of influenza a viruses from different species by PCR amplification of conserved sequences in the matrix gene
The recently raised awareness of the threat of a new influenza pandemic has stimulated interest in the detection of influenza A viruses in human as well as animal secretions. Virus isolation alone is unsatisfactory for this purpose because of its inherent limited sensitivity and the lack of host cells that are universally permissive to all influenza A viruses. Previously described PCR methods are more sensitive but are targeted predominantly at virus strains currently circulating in humans, since the sequences of the primer sets display considerable numbers of mismatches to the sequences of animal influenza A viruses. Therefore, a new set of primers, based on highly conserved regions of the matrix gene, was designed for single-tube reverse transcription-PCR for the detection of influenza A viruses from multiple species. This PCR proved to be fully reactive with a panel of 25 genetically diverse virus isolates that were obtained from birds, humans, pigs, horses, and seals and that included all known subtypes of influenza A virus. It was not reactive with the 11 other RNA viruses tested. Comparative tests with throat swab samples from humans and fecal and cloacal swab samples from birds confirmed that the new PCR is faster and up to 100-fold more sensitive than classical virus isolation procedures.</p
The Molecular Basis for Antigenic Drift of Human A/H2N2 Influenza Viruses.
Influenza A/H2N2 viruses caused a pandemic in 1957 and continued to circulate in humans until 1968. The antigenic evolution of A/H2N2 viruses over time and the amino acid substitutions responsible for this antigenic evolution are not known. Here, the antigenic diversity of a representative set of human A/H2N2 viruses isolated between 1957 and 1968 was characterized. The antigenic change of influenza A/H2N2 viruses during the 12 years that this virus circulated was modest. Two amino acid substitutions, T128D and N139K, located in the head domain of the H2 hemagglutinin (HA) molecule, were identified as important determinants of antigenic change during A/H2N2 virus evolution. The rate of A/H2N2 virus antigenic evolution during the 12-year period after introduction in humans was half that of A/H3N2 viruses, despite similar rates of genetic change.IMPORTANCE While influenza A viruses of subtype H2N2 were at the origin of the Asian influenza pandemic, little is known about the antigenic changes that occurred during the twelve years of circulation in humans, the role of preexisting immunity, and the evolutionary rates of the virus. In this study, the antigenic map derived from hemagglutination inhibition (HI) titers of cell-cultured virus isolates and ferret postinfection sera displayed a directional evolution of viruses away from earlier isolates. Furthermore, individual mutations in close proximity to the receptor-binding site of the HA molecule determined the antigenic reactivity, confirming that individual amino acid substitutions in A/H2N2 viruses can confer major antigenic changes. This study adds to our understanding of virus evolution with respect to antigenic variability, rates of virus evolution, and potential escape mutants of A/H2N2
Avian influenza A virus pandemic preparedness and vaccine development
Influenza A viruses can infect a wide range of hosts, creating opportunities for zoonotic transmission, i.e., transmission from animals to humans, and placing the human population at constant risk of potential pandemics. In the last hundred years, four influenza A virus pandemics have had a devastating effect, especially the 1918 influenza pandemic that took the lives of at least 40 million people. There is a constant risk that currently circulating avian influenza A viruses (e.g., H5N1, H7N9) will cause a new pandemic. Vaccines are the cornerstone in preparing for and combating potential pandemics. Despite exceptional advances in the design and development of (pre-)pandemic vaccines, there are still serious challenges to overcome, mainly caused by intrinsic characteristics of influenza A viruses: Rapid evolution and a broad host range combined with maintenance in animal reservoirs, making it near impossible to predict the nature and source of the next pandemic virus. Here, recent advances in the development of vaccination strategies to prepare against a pandemic virus coming from the avian reservoir will be discussed. Furthermore, remaining challenges will be addressed, setting the agenda for future research in the development of new vaccination strategies against potentially pandemic influenza A viruses
Antigenic and genetic variability of human metapneumoviruses
Human metapneumovirus (HMPV) is a member of the subfamily Pneumovirinae within the family Paramyxo- viridae. Other members of this subfamily, respiratory syncytial virus and avian pneumovirus, can be divided into subgroups on the basis of genetic or antigenic differences or both. For HMPV, the existence of different genetic lineages has been described on the basis of variation in a limited set of available sequences. We address the antigenic relationship between genetic lineages in virus neutralization assays. In addition, we analyzed the genetic diversity of HMPV by phylogenetic analysis of sequences obtained for part of the fusion protein (n = 84) and the complete attachment protein open reading frames (n = 35). On the basis of sequence diversity between attachment protein genes and the differences in virus neutralization titers, two HMPV serotypes were defined. Each serotype could be divided into two genetic lineages, but these did not reflect major antigenic differences
Influenza A viruses are transmitted via the air from the nasal respiratory epithelium of ferrets
Human influenza A viruses are known to be transmitted via the air from person to person. It is unknown from which anatomical site of the respiratory tract influenza A virus transmission occurs. Here, pairs of genetically tagged and untagged influenza A/H1N1, A/H3N2 and A/H5N1 viruses that are transmissible via the air are used to co-infect donor ferrets via the intranasal and intratracheal routes to cause an upper and lower respiratory tract infection, respectively. In all transmission cases, we observe that the viruses in the recipient ferrets are of the same genotype as the viruses inoculated intranasally, demonstrating that they are expelled from the upper respiratory tract of ferrets rather than from trachea or the lower airways. Moreover, influenza A viruses that are transmissible via the air preferentially infect ferret and human nasal respiratory epithelium. These results indicate that virus replication in the upper respiratory tract, the nasal respiratory epithelium in particular, of donors is a driver for transmission of influenza A viruses via the air
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