By Lisa Schnirring
Over the past few days, South Korea reported three more highly pathogenic H5N6 avian influenza outbreaks, including the first of the season on a layer chicken farm and the first in Gyeonggi province, which surrounds the country's capital city, Seoul.
In research developments, two different groups that conducted lab experiments to gauge the threat of H5N6 to mammals and poultry found that the virus doesn't easily spread by the airborne route among ferrets, though it can infect ducks, chickens, and mice, and can cause severe disease in mice, which may signal a threat to other mammals.
H5N6 strikes chickens near Seoul
South Korea's agriculture ministry reported the three new H5N6 outbreaks in reports today and Jan 3 to the World Organization for Animal Health (OIE). One began on Jan 1 at a broiler duck farm in South Jeolla province, which led to the culling of 8,300 susceptible ducks.
Of the two other outbreaks detailed in a separate report, one began Jan 2 at a layer farm in Gyeonggi province and another started on Jan 4 at a parent duck farm in South Jeolla province. Between the two locations, the virus killed 66 of 218,700 susceptible birds, with the remaining ones destroyed to curb the spread of the disease.
It's not clear if the strain detected in the three latest outbreaks is the new reassortant recently identified for the first time in South Korea, which was then reported from a handful of other countries.
H5N8 in Saudi Arabia
Elsewhere, Saudi Arabia has reported 19 more highly pathogenic H5N8 outbreaks over the past few days, according to an agriculture ministry statement translated and posted by Avian Flu Diary, an infectious disease news blog.
Most occurred in different parts of Riyadh province in central Saudi Arabia, but one was reported from Jeddah, located in in the far west of the country.
Saudi Arabia reported its first H5N8 outbreak toward the end of December in Riyadh, and since then, the virus has quickly spread to poultry in other parts of the country.
H5N6 transmission in lab animals
The highly pathogenic H5N6 strain that has triggered outbreaks in some Asian countries and a limited number of human infections in China doesn't appear to pose an airborne threat, based on newly reported lab studies on ferrets, an international research team led by Erasmus University in the Netherlands reported in the Jan 3 edition of mSphere.
They found the virus has only one of three genetic markers that have been shown to allow H5N1 to spread by the airborne route, which the team said might explain the lack of airborne transmission in their experiments with ferrets.
When the animals were inoculated with the virus intranasally, H5N6 replicated at high titers in respiratory tracts where ferrets excreted the virus for about 6 days. Intratracheal inoculation resulted in severe pneumonia.
They concluded that H5N6 causes more severe disease in ferrets than other H5 viruses of the same clade (2.3.4.4), but so far the risk from airborne spread is currently low and for now isn't a direct public health threat. However, they noted that the increasing diversity of the H5 viruses requires regular risk assessments.
Meanwhile, another research team from China investigated highly pathogenic H5N6 isolated from three healthy wild birds in southern China in 2014 and 2015, focusing on the threat to birds and mammals. They reported their findings yesterday in the Journal of Infection. Birds that yielded the strains included a magpie robin, a common moorhen, and a sandgrouse.
After testing the pathogenicity of the viruses in ducks, chickens, and mice, they found that ducks can asymptomatically carry and shed the virus, and H5N6 can efficiently infect, transmit among, and kill chickens. Also, the viruses were highly pathogenic in mice.
The findings they saw in ducks suggest that, given overlapping habitats, they could play a key role in circulating the virus between poultry and wild birds and that wild birds could spread the virus to poultry along their flyways, presenting a threat to the poultry industry.
A H5N6 virus isolated in 2015 was more deadly to the animals than the other two that were collected in 2014, raising the possibility that H5N6 viruses could be becoming more lethal. "Therefore, it is necessary to vigilantly monitor H5N6 HPAIVs (highly pathogenic avian influenza viruses) in wild birds and poultry," they wrote.