Sampling for low-pathogenic avian influenza A virus in wild Mallard ducks: Oropharyngeal versus cloacal swabbing

[Sally Furniss]

Sampling for low-pathogenic avian influenza A virus in wild Mallard ducks: Oropharyngeal versus cloacal swabbing




<!-- articleText --> Patrik Ellström¹^,^,^c^,, Neus Latorre-Margalef¹^,^c, Petra Griekspoor^c, Jonas Waldenström^c, Jenny Olofsson^c, John Wahlgren^d and Björn Olsen^a^,^b

<!-- authorsNoEnt --> ^aSection for Zoonotic Ecology and Epidemiology, School of Pure and Applied Natural Sciences, Kalmar University, SE-391 82 Kalmar, Sweden ^bSection of Infectious Diseases, Department of Medical Sciences, Uppsala University Hospital, SE-751 85 Uppsala, Sweden ^cSection for Zoonotic Ecology and Epidemiology, School of Pure and Applied Natural Sciences, Kalmar University, SE-391 82 Kalmar, Sweden ^dCentre for Microbiological Preparedness (KCB), Swedish Institute for Infectious Disease Control (SMI), SE-171 82 Solna, Sweden
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Received 5 June 2008.
<!-- graphText, refText -->Available online 27 June 2008.
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Since the emergence in SE Asia in 1997 of the H5N1 highly pathogenic avian influenza (HPAI) virus many countries have started virus surveillance schemes.

Although targeted primarily at detecting HPAI H5N1, these schemes have also been issued to achieve a greater understanding on the general circulation of low-pathogenic avian influenza (LPAI); in particular viruses of hemagglutinin (HA) subtypes H5 and H7, for their potential to mutate into HPAI viruses in poultry.

The traditional way of sampling wild birds have been through cloacal swabbing.

The rational for this method stems from the 1970s when it was noted that cloacal samples gave higher isolation rates compared to tracheal samples, in dabbling ducks (Anas spp.).

However, the methodology for influenza virus detection changed dramatically with the appearance of PCR-based assays.

The current standard for detection in bird samples is RNA extraction and real time RT-PCR (RRT-PCR) targeted at the virus??? matrix gene.

Compared to direct egg culture, this method has increased sensitivity, is less time-consuming and allows the screening of greater sample sizes in surveillance studies. Wild waterfowl (Anseriformes) constitute the main reservoir for LPAI viruses. HPAI viruses are normally found only in poultry, but during the expansion of HPAI H5N1 several reports of dead wild birds came from affected countries.

Experimental infections with HPAI H5N1 showed that dabbling ducks (Anas), particularly Mallards, had little or no symptoms of disease and yet could shed large number of viruses, factors that make them potential vectors for the spread of H5N1 HPAI.

Generally noted in such studies is the fact that virus recovery and titers are much higher from the upper respiratory tract compared to the cloaca.

As a consequence, it has been suggested that oropharyngeal sampling should be used routinely in the surveillance of HPAI H5N1 in Mallards.

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