Avian Influenza Monitoring: Swab Pool Size and Viral Transport Media Matter

The traditional method for avian influenza virus surveillance involves pooling 5 ostrich tracheal swabs in a 50% v/v phosphate-buffered saline (PBS): glycerol transport medium without antibiotics, followed by RT-qPCR testing. However, this approach has limitations, including poor virus isolation rates and suboptimal detection sensitivity. This study aimed to address these issues by adjusting the swab pool size and altering the composition of the viral transport medium.

Does Increasing Swab Pool Size Affect RT-qPCR Detection?

Researchers spiked pools of 10 and 5 ostrich tracheal swabs with either H5N8 highly pathogenic avian influenza virus or H7N1 low pathogenic avian influenza virus, and then performed RT-qPCR testing. The results showed that increasing the swab pool size from 5 to 10 did not adversely affect the sensitivity of the RT-qPCR assay; in fact, it even appeared to improve sensitivity at certain virus concentrations, with statistically significant differences observed in some cases.

Can Modifying the Transport Medium Enhance Virus Isolation?

To improve virus isolation rates, the researchers compared a protein-rich viral transport medium (VTM) containing antimicrobials to the standard PBS: glycerol medium. The use of protein-rich VTM resulted in a higher proportion of positive H5N8 highly pathogenic avian influenza virus isolations (10/18 vs. 7/18), with fewer passages required. For H7N1 low pathogenic avian influenza virus, the protein-rich VTM also yielded higher virus titers.

Implications for Ostrich Monitoring Procedures

Increasing the swab pool size and optimizing the transport medium composition hold significant implications for avian influenza virus monitoring in ostriches. Larger swab pools can improve monitoring efficiency and reduce costs, while an improved transport medium may enhance the success rates of crucial virus isolation and identification efforts. These improvements could facilitate timely detection and control of potential avian influenza outbreaks in ostrich flocks, thereby helping to maintain South Africa's international export status for ostrich products.

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References

Effects of swab pool size and transport medium on the detection and isolation of avian influenza viruses in ostriches