Sunday, February 25, 2018

Frontiers: Two Studies On The Epidemiology of Avian Influenza Viruses


Although the debate over the role of wild and migratory birds in the spreading of both LPAI and HPAI viruses - at least across moderate to long distances - appears to be settled (see Revisiting The Migratory Bird Debate), often when we see outbreaks among tightly clustered poultry farms, other vectors appear to be in play.

MAY 2015 North American Epizootic

In the spring of 2015 we saw a number of clusters of North American farms impacted with H5N8 and/or H5N2, while surrounding areas appeared to have been `skipped over'. Furthermore, while HPAI was detected in a small number of wild birds, they were widely scattered, and wouldn't have directly accounted for the hundreds of farms affected. 
The lateral transfer of the virus from one farm to another via the movement of poultry products, vehicles, or personnel is often cited, but epidemiological investigations have often failed to find a link (see APHIS Releases Updated HPAI Epidemiology Report).
One idea, increasingly being considered, is the possibility that the virus is being dispersed – at least across short distances - `on the wind’.   It's a topic we looked at in some depth less than a month ago in `It's Raining Viruses'.

Going back even further, in December of 2012  (see Barnstorming Avian Flu Viruses?) we looked at a study in the Journal of Infectious Diseases called Genetic data provide evidence for wind-mediated transmission of highly pathogenic avian influenza that found patterns that suggested farm-to-farm spread of the 2003 H7N7 in the Netherlands due to the prevailing wind.
Another study of the same outbreak, Modelling the Wind-Borne Spread of Highly Pathogenic Avian Influenza Virus between Farms (PloS One 2012), found that wind borne transmission could have accounted for up to 24% of the transmission over distances up to 25 km. 
While the amount of virus a single wild bird might shed is fairly limited, when you have hundreds of thousands of infected chickens - all confined in a small area, producing copious amounts of waste products, and shedding feathers - it isn't difficult to envision a plume of infectious material being exhausted into the air by their ventilation system.
Given the right environmental conditions (temperature, humidity, UV light, wind speed & direction), farm-to-farm spread via airborne particles begins to make sense.  Particularly when you see some of the tight clustering of outbreaks in recent epizootics. 
All of which brings us to the first of two open-access studies today that have recently been published in Frontiers Epidemiology of Avian Influenza Viruses. This one looks at airborne detection of HPAI viruses during the 2016-17 H5N8 epizootic in France, which saw more than 400 farms affected.  

Airborne Detection of H5N8 Highly Pathogenic Avian Influenza Virus Genome in Poultry Farms, France

Axelle Scoizec1*, Eric Niqueux2, Rodolphe Thomas1, Patrick Daniel3, Audrey Schmitz2 and Sophie Le Bouquin
In southwestern France, during the winter of 2016–2017, the rapid spread of highly pathogenic avian influenza H5N8 outbreaks despite the implementation of routine control measures, raised the question about the potential role of airborne transmission in viral spread. 

As a first step to investigate the plausibility of that transmission, air samples were collected inside, outside and downwind from infected duck and chicken facilities. H5 avian influenza virus RNA was detected in all samples collected inside poultry houses, at external exhaust fans and at 5 m distance from poultry houses. For three of the five flocks studied, in the sample collected at 50–110 m distance, viral genomic RNA was detected. 

The measured viral air concentrations ranged between 4.3 and 6.4 log10 RNA copies per m3, and their geometric mean decreased from external exhaust fans to the downwind measurement point. These findings are in accordance with the possibility of airborne transmission and question the procedures for outbreak depopulation. 


Our results also question the management of infected flocks. The confinement inside housing does not seem to be effective enough to prevent viral diffusion into the environment surrounding infected premises and the culling process requiring the loading of the animals into containers located outside the poultry house seems to generate an important emission of potentially infectious dust and/or aerosols into the environment. It would be essential to reduce this diffusion by rapidly implementing the depopulation using a method that reduces the air viral emission. To achieve this goal, new case management methods must require less human resource in terms of time and volume because human resources availability is the main cause of increasing time between the confirmation date and the depopulation. 

Furthermore, the methods must include a depopulation process minimizing the air viral diffusion to the surrounding environment. Methods such as emergency mass culling of poultry using a foam blanket over birds and in-house carcasses and litter composting could contribute to improve the control of influenza outbreaks (25, 26).

In conclusion, our results sustain the hypothesis of a potential airborne transmission contribution to the spread of the H5N8 HPAIV. However, more investigations would be required to support this hypothesis so as to provide evidence of virus viability in fine particles emitted from poultry outbreaks and epidemiological evidence.

(Continue . . . )

Another potential for spreading HPAI - to other farms, and back into the environment (where it can be picked up by wild or migratory birds, and spread onward) -  is the disposal of infected garbage and other waste material from poultry farms.

This is an area of vulnerability that - until recently - hasn't received much attention.  First some excerpts from the study, then I'll return with a bit  more.

Garbage Management: An Important Risk Factor for HPAI-Virus Infection in Commercial Poultry Flocks

Emily Walz1*, Eric Linskens1, iJamie Umber1, Marie Rene Culhane2,David Halvorson1, Francesca Contadini3 and Carol Cardona1

Garbage management represents a potential pathway of HPAI-virus infection for commercial poultry operations as multiple poultry premises may share a common trash collection service provider, trash collection site (e.g., shared dumpster for multiple premises) or disposal site (e.g., landfill). The types of potentially infectious or contaminated material disposed of in the garbage has not been previously described but is suspected to vary by poultry industry sector. 

A survey of representatives from the broiler, turkey, and layer sectors in the United States revealed that many potentially contaminated or infectious items are routinely disposed of in the trash on commercial poultry premises. On-farm garbage management practices, along with trash hauling and disposal practices are thus key components that must be considered to evaluate the risk of commercial poultry becoming infected with HPAI virus.


This exploratory survey identified items in garbage that may contain infectious HPAI virus, some of which may carry high titers of infectious virus. Given that there is potential for HPAI virus to be associated with trash contents and garbage management practices, and taking into account the ease with which virus could be introduced into the poultry house, the potential for a commercial poultry flock becoming infected with HPAI virus due to garbage management during an outbreak should be considered.
Further research is needed to determine prevalence of garbage management practices in different production systems and across geographic regions in the United States and producers should develop appropriate mitigation measures in the event of a HPAI outbreak in commercial poultry.

(Continue . . . )

As the above study points out, garbage trucks - which often go from one farm to the next - may not only spread viruses along their route, the waste material they deposit in landfills may also contribute to the environmental spread of HPAI. 
In recent years we've seen efforts to quickly bury infected carcasses (either on site, or in landfills) in North America, Europe, Japan and South Korea. After the lessons from North America's Epizootic, the USDA's APHIS issued updated  Landfill Disposal Guidance—Recommended Waste Acceptance Practices for Landfills.
But in other places around the globe, we've seen thousands of dead birds dumped into rivers, ponds, and open ditches.  Most go unreported, but a few (of many) examples include:
All of this can make a real difference as avian influenza viruses can - under the right  environmental circumstances - survive for days or even weeks in water, soil, or in biological materials (see EID Journal: Persistence Of H5N1 In Soil).

A study reported in the August 2010 issue of Applied and Environmental Microbiology  determined that the H5N1 virus may persist on the dropped feathers from infected ducks for weeks or even months.
The bottom line is improper or sub-optimal disposal of infected bird carcasses and waste materials from poultry farms may not only be infecting nearby farms, it may also help reseed the migratory and wild bird population with new and improved HPAI viruses. 
While the risk of spread of avian viruses via airborne routes, or by improper carcass or waste disposal, remains uncertain -  the circumstantial evidence continues to mount. And given the stakes involved, the sooner we have firm answers and implement the right solutions, the better.