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Effect of serial pig passages on the adaptation of an avian H9N2 influenza virus to swine

View Article: PubMed Central - PubMed

ABSTRACT

H9N2 avian influenza viruses are endemic in poultry in Asia and the Middle East. These viruses sporadically cause dead-end infections in pigs and humans raising concerns about their potential to adapt to mammals or reassort with human or swine influenza viruses. We performed ten serial passages with an avian H9N2 virus (A/quail/Hong Kong/G1/1997) in influenza naïve pigs to assess the potential of this virus to adapt to swine. Virus replication in the entire respiratory tract and nasal virus excretion were examined after each passage and we deep sequenced viral genomic RNA of the parental and passage four H9N2 virus isolated from the nasal mucosa and lung. The parental H9N2 virus caused a productive infection in pigs with a predominant tropism for the nasal mucosa, whereas only 50% lung samples were virus-positive. In contrast, inoculation of pigs with passage four virus resulted in viral replication in the entire respiratory tract. Subsequent passages were associated with reduced virus replication in the lungs and infectious virus was no longer detectable in the upper and lower respiratory tract of inoculated pigs at passage ten. The broader tissue tropism after four passages was associated with an amino acid residue substitution at position 225, within the receptor-binding site of the hemagglutinin. We also compared the parental H9N2, passage four H9N2 and the 2009 pandemic H1N1 (pH1N1) virus in a direct contact transmission experiment. Whereas only one out of six contact pigs showed nasal virus excretion of the wild-type H9N2 for more than four days, all six contact animals shed the passage four H9N2 virus. Nevertheless, the amount of excreted virus was significantly lower when compared to that of the pH1N1, which readily transmitted and replicated in all six contact animals. Our data demonstrate that serial passaging of H9N2 virus in pigs enhances its replication and transmissibility. However, full adaptation of an avian H9N2 virus to pigs likely requires an extensive set of mutations.

No MeSH data available.


Related in: MedlinePlus

Nasal virus excretion and direct contact transmission of A/Qa/HK/P0, A/Qa/HK/P4 and A/Cal/04/09 influenza viruses in pigs.Three pigs were intranassally inoculated with 6.5 log10 TCID50 of the indicated virus per pig and individually housed in different isolators. Forty-eight hours later, two direct contact animals were co-housed with the inoculated pigs. Each graphic is identified with a two digits number: the first one corresponds to the isolator number and the second to the virus tested. Therefore, each column represents a different virus and each row represents a different isolator. The detection limit (dotted line) of the test was 1.7 log10 TCID50/100 mg of secrete.
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pone.0175267.g002: Nasal virus excretion and direct contact transmission of A/Qa/HK/P0, A/Qa/HK/P4 and A/Cal/04/09 influenza viruses in pigs.Three pigs were intranassally inoculated with 6.5 log10 TCID50 of the indicated virus per pig and individually housed in different isolators. Forty-eight hours later, two direct contact animals were co-housed with the inoculated pigs. Each graphic is identified with a two digits number: the first one corresponds to the isolator number and the second to the virus tested. Therefore, each column represents a different virus and each row represents a different isolator. The detection limit (dotted line) of the test was 1.7 log10 TCID50/100 mg of secrete.

Mentions: Fig 2 shows the nasal virus shedding of the inoculated and the co-housed direct contact animals. All piglets remained clinically healthy, based on clinical observation scores. All inoculated animals excreted virus between days one and eight post-inoculation. Comparison of the AUC revealed lower virus excretion for A/Qa/HK/P0 (18.4) and A/Qa/HK/P4 (19.1) than for A/Cal/04/09 (26.6), although these differences were not statistically significant (p<0.05). Of all nine inoculated animals five reached a maximum virus titer of ≥ 6.5 log10 TCID50/100 mg of secrete. All inoculated animals developed antibodies against the homologous virus (Table 2). Higher antibody titers were observed in A/Cal/04/09 inoculated pigs than in H9N2 infected animals.


Effect of serial pig passages on the adaptation of an avian H9N2 influenza virus to swine
Nasal virus excretion and direct contact transmission of A/Qa/HK/P0, A/Qa/HK/P4 and A/Cal/04/09 influenza viruses in pigs.Three pigs were intranassally inoculated with 6.5 log10 TCID50 of the indicated virus per pig and individually housed in different isolators. Forty-eight hours later, two direct contact animals were co-housed with the inoculated pigs. Each graphic is identified with a two digits number: the first one corresponds to the isolator number and the second to the virus tested. Therefore, each column represents a different virus and each row represents a different isolator. The detection limit (dotted line) of the test was 1.7 log10 TCID50/100 mg of secrete.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383288&req=5

pone.0175267.g002: Nasal virus excretion and direct contact transmission of A/Qa/HK/P0, A/Qa/HK/P4 and A/Cal/04/09 influenza viruses in pigs.Three pigs were intranassally inoculated with 6.5 log10 TCID50 of the indicated virus per pig and individually housed in different isolators. Forty-eight hours later, two direct contact animals were co-housed with the inoculated pigs. Each graphic is identified with a two digits number: the first one corresponds to the isolator number and the second to the virus tested. Therefore, each column represents a different virus and each row represents a different isolator. The detection limit (dotted line) of the test was 1.7 log10 TCID50/100 mg of secrete.
Mentions: Fig 2 shows the nasal virus shedding of the inoculated and the co-housed direct contact animals. All piglets remained clinically healthy, based on clinical observation scores. All inoculated animals excreted virus between days one and eight post-inoculation. Comparison of the AUC revealed lower virus excretion for A/Qa/HK/P0 (18.4) and A/Qa/HK/P4 (19.1) than for A/Cal/04/09 (26.6), although these differences were not statistically significant (p<0.05). Of all nine inoculated animals five reached a maximum virus titer of ≥ 6.5 log10 TCID50/100 mg of secrete. All inoculated animals developed antibodies against the homologous virus (Table 2). Higher antibody titers were observed in A/Cal/04/09 inoculated pigs than in H9N2 infected animals.

View Article: PubMed Central - PubMed

ABSTRACT

H9N2 avian influenza viruses are endemic in poultry in Asia and the Middle East. These viruses sporadically cause dead-end infections in pigs and humans raising concerns about their potential to adapt to mammals or reassort with human or swine influenza viruses. We performed ten serial passages with an avian H9N2 virus (A/quail/Hong Kong/G1/1997) in influenza na&iuml;ve pigs to assess the potential of this virus to adapt to swine. Virus replication in the entire respiratory tract and nasal virus excretion were examined after each passage and we deep sequenced viral genomic RNA of the parental and passage four H9N2 virus isolated from the nasal mucosa and lung. The parental H9N2 virus caused a productive infection in pigs with a predominant tropism for the nasal mucosa, whereas only 50% lung samples were virus-positive. In contrast, inoculation of pigs with passage four virus resulted in viral replication in the entire respiratory tract. Subsequent passages were associated with reduced virus replication in the lungs and infectious virus was no longer detectable in the upper and lower respiratory tract of inoculated pigs at passage ten. The broader tissue tropism after four passages was associated with an amino acid residue substitution at position 225, within the receptor-binding site of the hemagglutinin. We also compared the parental H9N2, passage four H9N2 and the 2009 pandemic H1N1 (pH1N1) virus in a direct contact transmission experiment. Whereas only one out of six contact pigs showed nasal virus excretion of the wild-type H9N2 for more than four days, all six contact animals shed the passage four H9N2 virus. Nevertheless, the amount of excreted virus was significantly lower when compared to that of the pH1N1, which readily transmitted and replicated in all six contact animals. Our data demonstrate that serial passaging of H9N2 virus in pigs enhances its replication and transmissibility. However, full adaptation of an avian H9N2 virus to pigs likely requires an extensive set of mutations.

No MeSH data available.


Related in: MedlinePlus