The avian influenza virus H5N1 takes its name from two kinds of spikes adorning the viral surface, hemagglutinin (HA) and neuraminidase (NA). Influenza viruses of Type A or Type B use hemagglutinin to attach to cell surface receptors, allowing viral infection of the cell. Neuraminidase later acts to remove these receptors from infected cells, allowing newly synthesized viruses particles to escape and infect other cells.
(There are 17 different types of hemagglutinin, from H1 to H17 and nine different types of neuraminidase, from N1 to N9 among influenza A viruses. Each virus has one type of H (such as H5) and one type of N (such as N1).)
Through the analysis of 226 HA and 92 NA sequences, Scotch and his colleagues used a phylogeographic approach to trace the preponderance and transmission routes of H5N1 in Egypt. Phylogeography is a particularly fruitful approach for animal-to-human (or zoonotic) RNA viruses, due to short genomic sequences and rapid rates of evolution.
The group's findings revealed a geographic spread of the 220.127.116.11 viral form of H5N1 across Egypt's four primary areas: Cairo, Nile Delta, Canal and Upper Egypt. Statistical analysis suggests the northern governorate of Ash Sharqiyah as the point of origin for the spread of H5N1, however, the mathematical association is too weak to claim certainty. Analysis also implied that the strongest transmission routes for H5N1 were from Ash Sharqiyah to Al Gharbiyah and Al Fayyum to Al Qalyubiyah.
Most of the identified routes of transmission appeared in the densely populated Delta region of Egypt. The Al Qalybiyah governate in particular appears to be a popular area for viral transition, though dispersion to and from this region remains uncertain, requiring further research. The study also noted considerable viral diversity over a limited time frame-perhaps an evasive response to a country-wide poultry vaccination program.
"This has significant public health implications for the rest of the world," Scotch says. "It is important to focus on variant clades in order to better understand how this virus has evolved and which governorates are propograting its spread."
The authors are further developing the ZooPhy software's graphical interface. The tool requires no specialized knowledge of phylogeography or bioinformatics, making it convenient for field use by public health officials. By zeroing in on trade routes, migration patterns and highways of viral transmission, health authorities can conserve limited resources, applying them where they can be most effective.
Source: Arizona State University