Cold-Adapted Strain of Avian Pneumovirus as a Vaccine in One-Day-Old Turkeys and the Effect of Inoculation Routes

Immunization with avian metapneumovirus harboring chicken Fc induces higher immune responses

In this study, we evaluated the immune responses of avian metapneumovirus harboring chicken Fc molecule. Stable Vero cells expressing chicken Fc chimera on its surface (Vero-cFc) were established, and we confirmed that aMPV grown in Vero-cFc incorporated host derived chimera Fc into the aMPV virions. Immunization of chicken with aMPV-cFc induced higher level of antibodies and inflammatory cytokines; (Interferon (IFN)-γ and Interleukin (IL)-1β) compared to those of aMPV. The increased levels of antibodies and inflammatory cytokines in chicken immunized with aMPV-cFc were statistically significantly (p<0.05) to that of aMPV and control. The aMPV-cFc group also generated the highest neutralizing antibody response. After challenges, chickens immunized with aMPV-cFc showed much less pathological signs in nasal turbinates and trachea so that we could confirm aMPV-cFc induced higher protection than that of aMPV. The greater ability of aMPV harboring chicken Fc to that of aMPV presented it as a possible vaccine candidate.

Comparison of avian cell substrates for propagating subtype C avian metapneumovirus

Avian metapneumovirus (AMPV) is a respiratory viral pathogen that causes turkey rhinotracheitis (TRT) or swollen head syndrome (SHS) in chickens. AMPV was first isolated in South Africa during the early 1970s and has subsequently spread worldwide during the 1980s to include Europe, Asia, and South America. In 1996, a genetically distinct AMPV subgroup C was isolated in the US following an outbreak of TRT. Vero cells are currently the best available substrate for AMPV propagation but are of non-avian origin. A number of different avian cell substrates have been compared to determine which is the most suitable for the propagation of AMPV to sufficiently high titers. Of the cell substrates tested, primary turkey turbinate and kidney and chicken kidney cells produced titers equal to or greater than Vero cells. Turkey turbinate and kidney epithelial cells that were life-span extended by the ectopic expression of human telomerase catalytic subunit (HTERT) initially displayed AMPV titers comparable to Vero cell controls, but declined in virus production with increased passage in culture. Interestingly, plaques emanating from Vero propagated virus were relatively small and dispersed, when analyzed by immunofluorescent assays (IFA), while both turkey turbinate and kidney cell propagated AMPV produced larger plaques. Even with these differences, there were no changes in the predicted amino acid sequences of the nucleocapsid (N) and phosphoprotein (P) genes of AMPV propagated in either turkey turbinate or Vero host cells. However, the fusion (F) gene showed 11 amino acid differences (98.7% identity) between the two host cell types. These results suggest that AMPV propagated in homologous avian cellular substrates may produce more infectious virus with possibly more effective fusion activity, compared to Vero cell propagation.

Human metapneumovirus as a major cause of human respiratory tract disease

BACKGROUND

Human metapneumovirus (hMPV) is a newly identified paramyxovirus that appears to be one of the most significant and common viral infections in humans. The virus, first isolated in 2001, is a clear cause of lower respiratory tract disease in both the very young and the frail elderly. The virus causes acute wheezing in children or, less commonly, croup or pneumonia.

METHODS/RESULTS

Molecular epidemiology studies have shown that field strains exhibit sufficient sequence diversity to designate 2 subgroups of circulating viruses. Small animal and nonhuman primate models of infection have been described, which will allow studies of pathogenesis and immunity. Recombinant viruses have already been generated by several groups using reverse genetics, which facilitates the study of the biology of the virus and the generation of live attenuated vaccine candidates.

CONCLUSIONS

Ongoing research promises to elucidate the molecular basis for pathogenesis and immunity of human metapneumovirus infections and to pave the way for rapid vaccine development.