Avian Influenza Distribution after H5N1
Saturday, 9 April 2016
By: Tri Satya Putri Naipospos (Center for Indonesian Veterinary Analytical Studies)
Lately we see Avian Influenza (AI) is still causing outbreaks in several areas. We fail to realize that for the last two years new types of AI subtypes have emerged.
There are 18 different types of H and 11 different types of N. Any combination [between H and N] could happen, and there are different strains within each virus subtype, such as H5N2, H5N3, H5N6, H5N8, H7N2, H7N3, H7N6, H7N8, H7N9, H9N2, and H10N8. Among the subtypes, only outbreaks caused by H5N2 and H7N9 became headlights in international news.
Experts are still concerned that these viruses could be easily transmitted to humans and start a pandemic. Adaptation of AI viruses is possible because the genes continue to change, either through mutation or exchanging genes with other influenza viruses.
Genetic change can modify the biological characteristics of viruses, possibly increasing its pathogenicity to poultry or increase its transmission rate to humans. This is how H5N2, H5N6, and H5N8 viruses came to exist, which originated from gene transfer with zoonotic H5N1 viruses.
After H5N1 was first detected in 2003 in China, this virus seemed to almost disappear in 2004. Once it reemerged, the spread of the virus was uncontrollable, spreading to all of Asia by the end of 2004, East Europe in 2005, and moved to Middle East, Africa and rampaged through almost all of Europe in 2006.
In fact, the H5N1 virus has spread to poultry in 55 countries. Outbreaks in a number of countries, including Indonesia, on a low scale is still happening until now. By March 2016, there are 846 cases of human infection, with half being fatal. In Indonesia alone there was 199 human cases, but with higher mortality (84 percent).
A total of 309 AI outbreaks in poultry was reported to the World Animal Health Organization (OIE) in 2015, 147 percent higher than 2014. By summer 2014, AI outbreaks have died out in East Asia. But, in September 2014, besides H5N1, outbreaks of H5N2, H5N3, H5N6, and H5N8 in poultry was detected in China. H5N6 outbreaks were also reported in Laos, Vietnam and Hongkong.
Outbreaks caused by highly pathogenic H5N8 occurred in January to April 2014 in South Korea and Japan. After 5 months of no incidence, the H5N8 virus was once again detected in September in South Korea and November in Japan. Outbreaks of H5N2, H5N3, and H5N8 was reported in Taiwan in early 2015. H5N8, which started in South Korea and Japan, was assumed to have moved to Europe in the end of 2014 through migratory birds. Since then a number of outbreaks were reported in several European countries from H5N8 and H5N2 virus subtypes which has exchanged genes.
The first H5N8 outbreak in commercial poultry was detected in Germany in November 2014, followed by the Netherlands, England, and Italy. Because of these outbreaks, Indonesia closed the import of chicken parent and grandparent stock from Germany, the Netherlands, and England.
The H5N8 virus was first isolated in the United States from wild birds, then backyard chickens in December 2015. The virus was isolated again from commercial turkey operations in January 2015. The worst H5N2 outbreak occurred in commercial poultry operations all over the United States in March 2015. This outbreak caused over 50 million birds in 20 states to be culled. Consequently, over 40 countries (including Indonesia) stopped poultry import from the US.
Similarly, outbreaks caused by H7 subtype AI viruses emerged in the last 2 years. H7N3 was reported in Mexico and H7N7 reported in England. In early 2016, H7N8 was reported in the US.
A number of AI viruses, besides H5N1, which could infect humans include H7N3, H7N7, H7N9, H9N2, and H10N3. Several infections were so severe, it caused mortality, however others were mild or even without symptom.
The most recent product of virus gene exchange that emerged in China in 2013 was the H7N9 virus. By March 2016, 791 human cases were reported and 38 percent resulted in mortality. The pathogenicity of H7N9 in poultry is low and without symptom, making it difficult to detect in poultry.
Sporadic human infections with H5N6, H9N2, and H10N8 viruses have also been reported. The first case of human H5N6 infection was reported from China in May 2014, with 3 infected patients and 2 deaths.
The H9N2 virus also needs to be closely observed because it donated genes for the H5N1 and H7N9 virus. Egypt also reported H9N2 cases in human.
The H10N8 virus was first reported in November 2013 in China, causing 3 human infections and 2 deaths. Research indicates that live bird markets were the source of the infection.
AI viruses spread through feces and nasal discharge from wild birds. Most birds do not exhibit clinical signs of infection. These healthy birds fly according to their flyways.
There are roughly 9 different bird flyways in the world. Besides separated flyways in North America, other flyways mostly overlap in the North Pole. Through this mechanism, wild birds from Asia could spread the virus to other wild birds, which then spread the virus to other countries.
Although the direction of global AI virus dynamics is still unknown, but the world must stay vigilant. WHO reminds us of the diversity and global distribution of AI viruses circulating in domestic poultry and wild birds, which was never been done before.
There are signs that influenza viruses, particularly from poultry, exchange genetic materials and birth new types of virus. Therefore, experts must use modern surveillance and genetic analysis tools continuously.