Avian influenza in shorebirds: experimental infection of ruddy turnstones (Arenaria interpres) with avian influenza virus

Abstract

Background: Low pathogenic avian influenza viruses (LPAIV) have been reported in shorebirds, especially at Delaware Bay, USA, during spring migration. However, data on patterns of virus excretion, minimal infectious doses, and clinical outcome are lacking. The ruddy turnstone (Arenaria interpres) is the shorebird species with the highest prevalence of influenza virus at Delaware Bay.

Objectives: The primary objective of this study was to experimentally assess the patterns of influenza virus excretion, minimal infectious doses, and clinical outcome in ruddy turnstones.

Methods: We experimentally challenged ruddy turnstones using a common LPAIV shorebird isolate, an LPAIV waterfowl isolate, or a highly pathogenic H5N1 avian influenza virus. Cloacal and oral swabs and sera were analyzed from each bird.

Results: Most ruddy turnstones had pre-existing antibodies to avian influenza virus, and many were infected at the time of capture. The infectious doses for each challenge virus were similar (10(3·6) -10(4·16) EID(50)), regardless of exposure history. All infected birds excreted similar amounts of virus and showed no clinical signs of disease or mortality. Influenza A-specific antibodies remained detectable for at least 2 months after inoculation.

Conclusions: These results provide a reference for interpretation of surveillance data, modeling, and predicting the risks of avian influenza transmission and movement in these important hosts.

Figure 1

Oral excretion of avian influenza virus RNA from experimentally inoculated ruddy turnstones. Cycle threshold (C _t) values determined by H5 or H7 hemagglutinin‐specific RT‐PCR analyses for 8 or 9 days post‐inoculation (DPI). Each panel represents the mean C _t values of infected birds inoculated with (A) low pathogenic avian influenza virus A/shorebird/DE/42/2006 (H7N3), (B) A/northernpintail/California/44242‐758/2006 (H5N2), or (C) highly pathogenic avian influenza virus A/whooperswan/Mongolia/244/2005 (H5N1). Error bars represent the standard deviation at each time point. The titers of virus are expressed as log₁₀ EID₅₀/100 μl.

Figure 2

Stability of serum antibodies in ruddy turnstones after inoculation with low pathogenic avian influenza virus A/shorebird/DE/42/2006 (H7N3). Birds were maintained for the number of days post‐inoculation (DPI) indicated, and sample/negative control (S/N) ratios were determined in four birds by using IDEXX MultiSpecies ELISA. S/N ratios <0.50 are considered seropositive.