Avian influenza virus monitoring in wintering waterbirds in Iran, 2003-2007

Abstract

Background: Virological, molecular and serological studies were carried out to determine the status of infections with avian influenza viruses (AIV) in different species of wild waterbirds in Iran during 2003-2007. Samples were collected from 1146 birds representing 45 different species with the majority of samples originating from ducks, coots and shorebirds. Samples originated from 6 different provinces representative for the 15 most important wintering sites of migratory waterbirds in Iran.

Results: Overall, AIV were detected in approximately 3.4% of the samples. However, prevalence was higher (up to 8.3%) at selected locations and for certain species. No highly pathogenic avian influenza, including H5N1 was detected. A total of 35 AIVs were detected from cloacal or oropharyngeal swab samples. These positive samples originated mainly from Mallards and Common Teals.Of 711 serum samples tested for AIV antibodies, 345 (48.5%) were positive by using a nucleoprotein-specific competitive ELISA (NP-C-ELISA). Ducks including Mallard, Common Teal, Common Pochard, Northern Shoveler and Eurasian Wigeon revealed the highest antibody prevalence ranging from 44 to 75%.

Conclusion: Results of these investigations provide important information about the prevalence of LPAIV in wild birds in Iran, especially wetlands around the Caspian Sea which represent an important wintering site for migratory water birds. Mallard and Common Teal exhibited the highest number of positives in virological and serological investigations: 43% and 26% virological positive cases and 24% and 46% serological positive reactions, respectively. These two species may play an important role in the ecology and perpetuation of influenza viruses in this region. In addition, it could be shown that both oropharyngeal and cloacal swab samples contribute to the detection of positive birds, and neither should be neglected.

Figure 1

The geographical distribution of sampling sites in Iran (blue spots; capital letters in the spots indicate the province: A: West Azerbaijan, F: Fars, G: Gilan, K: Khuzestan, M: Mazandaran, T: Tehran).

Figure 2

Prevalence (%) of AIV in total sampled birds and in Anatidae in different months of sampling in Iran.

Figure 3

Frequency of different hemagglutinin and neuraminidase subtypes identified in wild bird samples during 2003-2007.

Figure 4

Phylogenetic tree for the full length hemagglutinin gene of H9N2 influenza viruses. The tree constructed by Neighbour-joining method. Sequences obtained in this study were labelled by red (2003 virus) and green dots (2007 viruses). The other sequences were selected from GenBank. The numbers represent bootstrap values which were determined using 1000 replications.