Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2007
Publication Date: 2/23/2007
Citation: Sylte, M.J., Hubby, B., Suarez, D.L. 2007. Influenza neuraminidase antibodies provide partial protection for chickens against high pathogenic avian influenza infection. Vaccine. 25:3763-3772. Interpretive Summary: Avian influenza is a virus infection of both wild and domestic birds, but it is extremely variable in its ability to cause disease. The worst form of the disease is highly pathogenic avian influenza that can cause high mortality in chickens and turkeys. Vaccination has been used to protect poultry from clinical disease. Most vaccines are designed to produce antibodies to the hemagglutinin protein of avian influenza because it is known to be protective. Antibodies to the neuraminidase protein of avian influenza are also known to provide some protection, but little work has been performed to determine how effective vaccines to just the neuraminidase protein can be. This study used three different types of vaccines targeted strictly to the neuraminidase. For the birds that developed high levels of neuraminidase antibody, they were protected from clinical disease, but not infection, from challenge from a virulent virus. This studies show value in having antibodies to the neuraminidase, but in general it does not appear as protective as antibodies to the hemagglutinin protein and to be protective you must have high neuraminidase antibody levels.
Technical Abstract: Protection of chickens against avian influenza (AI) in chickens is mostly attributed to production of antibodies against the viral glycoprotein hemagglutinin, whereas less is known about antibodies produced against the other surface glycoprotein neuraminidase (NA). Therefore, vaccines encoding NA antigen alone (e.g., DNA and alphavirus vectored vaccines) or baculovirus-derived recombinant NA (rN2) were tested for their ability to protect against highly pathogenic AI challenge in chickens. Vaccination with alphavirus expressing the A/Pheasant/Maryland/4457/93 (Ph/MD) N2 gene (95% amino acid homology to challenge virus N2) a minimum of two times produced significant elevation of serum NA-inhibition (NI) activity (P < 0.01) and modest protection against highly pathogenic H5N2 challenge (63% protection). In contrast, vaccination with alphavirus expressing a distant N2 from A/Turkey/Ohio/313053/04 (Tk/OH) (84% homology to challenge virus N2) produced no protection against challenge. Vaccination with Ph/MD rN2 produced higher levels of NI activity than DNA vaccination, which resulted in significant enhancement of survival. Protection was correlated with higher levels of N2 NI activity, but high NI activity failed to affect viral shedding. Consideration for the sequence of the NA gene for vaccine to challenge strain may provide improved immunity if high levels of NI activity are obtained.