Abstract
Low pathogenicity avian influenza virus (LPAIV) and lentogenic Newcastle disease virus (lNDV) are commonly reported causes of respiratory disease in poultry worldwide with similar clinical and pathobiological presentation. Co-infections do occur but are not easily detected, and the impact of co-infections on pathobiology is unknown. In this study chickens and turkeys were infected with a lNDV vaccine strain (LaSota) and a H7N2 LPAIV (A/turkey/VA/SEP-67/2002) simultaneously or sequentially three days apart. No clinical signs were observed in chickens co-infected with the lNDV and LPAIV or in chickens infected with the viruses individually. However, the pattern of virus shed was different with co-infected chickens, which excreted lower titers of lNDV and LPAIV at 2 and 3 days post inoculation (dpi) and higher titers at subsequent time points. All turkeys inoculated with the LPAIV, whether or not they were exposed to lNDV, presented mild clinical signs. Co-infection effects were more pronounced in turkeys than in chickens with reduction in the number of birds shedding virus and in virus titers, especially when LPAIV was followed by lNDV. In conclusion, co-infection of chickens or turkeys with lNDV and LPAIV affected the replication dynamics of these viruses but did not affect clinical signs. The effect on virus replication was different depending on the species and on the time of infection. These results suggest that infection with a heterologous virus may result in temporary competition for cell receptors or competent cells for replication, most likely interferon-mediated, which decreases with time.
Highlights
Low pathogenicity avian influenza virus (LPAIV) and lentogenic Newcastle disease virus are two of the most economically important viruses affecting poultry worldwide
No differences in the severity of the clinical signs were observed between the groups inoculated with both LPAIV and lentogenic Newcastle disease virus (lNDV) and the group inoculated only with LPAIV
In our co-infection studies, all chickens and turkeys became infected with lNDV and LPAIV, and a significant reduction in virus replication was observed when birds were co-infected versus single virus infected
Summary
Low pathogenicity avian influenza virus (LPAIV) and lentogenic Newcastle disease virus (lNDV) are two of the most economically important viruses affecting poultry worldwide. They originate from their natural reservoirs, wild birds, with cross species transmission to domestic poultry producing subclinical infections and occasionally upper respiratory disease. NDV’s vary in the type and severity of the disease they produce, and different pathotypes, based on virulence in chicken and the sequences surrounding the protease cleavage site of the fusion (F) protein, have been described in poultry: viscerotropic velogenic, neurotropic velogenic, mesogenic, lentogenic or respiratory, and asymptomatic [2]. Pathogenic avian influenza (HPAI) and Newcastle disease (ND), caused upon the infection of poultry with virulent (velogenic and mesogenic) strains of NDV, are diseases notifiable to the World Organization for Animal Health [3]
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