Last spring the United States endured the largest, and most expensive, outbreak of highly pathogenic avian influenza in its history, which resulted in the loss of 48 million birds, and economic losses of billions of dollars. Although it has now been 90 days since the last outbreak, HPAI is expected to return this fall, and the USDA, APHIS, and other agencies have spent the summer working on how they can deal with it.
Yesterday we looked at the release of the APHIS Fall 2015 HPAI Preparedness & Response Plan, a 22-page overview of extensive plans and documentation that have been reviewed or prepared over the summer. Among the many details included, one in particular immediately sparked national headlines:
Reuters UK - 10 hours ago
CHICAGO U.S. agriculture officials seeking to control deadly bird flu have approved a method of killing infected poultry that entails sealing barns shut, turning up the heat and shutting off ventilation systems, an option that has been condemned by ...
San Jose Mercury News - 11 hours ago
DES MOINES, Iowa (AP) — A new federal bird flu control policy says ventilation systems must be shut off as a means of suffocating entire poultry barns if other methods of euthanasia cannot be completed within 24 hours. It was among several new ...
Last July, in Debating The Humane Methods Of Depopulating Infected Chickens, we looked at this disturbing – yet potentially necessary – option for quickly depopulating hundreds of thousands (even millions) of poultry who are infected with one of these highly infectious HPAI viruses.
Technically, it is called VSD - or Ventilator Shutdown - and it involves shutting down the exhaust ventilators and turning up the heat in affected chicken barns, making inside temperatures quickly rise. This heat stresses and suffocates the birds, and is viewed by many animal rights advocates as an unnecessarily slow and cruel culling method.
Yesterday’s announcement brought a sharp response (see USDA Condones, While HSUS Condemns, Inhumane Mass Baking of Live Chickens Exposed to Avian Flu) from the Humane Society of the United States (HSUS) and it seems destined to become a cause célèbre in social media.
As I share the same revulsion that others have expressed over these methods, it would be easy enough to add my voice to the growing chorus of condemnation, and demand a `better, more human way’ of depopulating infected birds.
The problem is, VSD may very well be the best of a bad lot of options.
To understand why, we need to look at the USDA documents on depopulation, the CDC’s concerns over human exposure to HPAI H5, several studies on airborne spread of the virus, and some of the delays and bottlenecks reported during last spring’s outbreaks.
When a chicken barn – which may contain 100,000 birds or more – becomes infected with HPAI, it spreads very quickly, and virus particles are shed in huge quantities as long at the birds are alive. Were these facilities fully contained, then cullers could take their time depopulating the birds.
But they aren’t. These barns have huge exhaust systems designed to maintain air quality and proper temperatures, and they can emit tens of thousands of cubic feet of potentially virus laden air every hour.
Over the summer APHIS released a 38-page partial epidemiology report on the spread of HPAI H5 across the United States (see APHIS: Partial Epidemiology Report On HPAI H5 In The US). While they were unable to pinpoint specific factors that fully explained this AI spread, they acknowledged the possibility that prevailing winds may have carried contaminated dust particles from farm to farm.
Environmental factors may also play a part in transmitting HPAI. APHIS found that genetic material from the HPAI virus could be detected in air samples taken inside and outside infected poultry houses, supporting the idea that the virus can be transmitted through air. Further reinforcing this concept is preliminary analysis of wind data that shows a relationship between sustained high winds (25 mph or greater for 2 days or longer) and an increase in the number of infected farms 5 to 7 days later.
Over the summer we saw Senate Hearing testimony that there were cases where depopulation didn’t begin for more than a week after discovery, and on larger farms the actual depopulation took as long as two weeks to complete. All of which provides plenty of time and opportunities for the virus to spread - via barn exhaust or the movement of people and equipment in and out of these barns.
There are also human health hazards to consider in this culling process.
Workers must `suit up’ in full protective gear before entering chicken houses and can only work inside for a short time due to the heat, thus limiting the number of birds that can be culled in a single day. While human infection with these North American subtypes of HPAI H5 have not been reported, earlier this summer in CDC HAN:HPAI H5 Exposure, Human Health Investigations & Response, the CDC warned:
While these recently-identified HPAI H5 viruses are not known to have caused disease in humans, their appearance in North American birds may increase the likelihood of human infection in the United States.
The simple equation is, the more man-hours of exposure to the virus, the more chances the virus has to jump to a human host. Even if it produced only a mild infection, it would seriously complicate the nation’s response to the avian flu threat, and worst-case, it could produce a significant public health threat.
All reasons why this fall, the USDA has announced an aggressive APHIS DEPOPULATION GOAL.
Due to the risk of virus amplification in infected poultry, poultry that meet the HPAI presumptive positive case definition will be depopulated as soon as possible, with the depopulation goal of 24-hours or less. Poultry on Contact Premises, or those meeting the suspect case definition, may also be depopulated as soon as possible.
Their document goes on to stress:
In almost all cases, water based foam, carbon dioxide, or alternative methods will be the depopulation methods available to rapidly “stamp-out” the HPAI virus in poultry. Each premises will be evaluated individually, considering epidemiological information, housing and environmental conditions, currently available resources and personnel, and other relevant factors.
Unfortunately, the experience last spring was that farms with more than 100,000 birds often took more than a day to completely cull. With some poultry farms sporting 3 million birds or more, it might take a week or longer completely stamp out all of the birds on a large farm using standard methods.
Which explains why – as unpalatable as it is - the USDA is keeping the VSD option on the table, stating:
However, if standard methods cannot achieve the 24-hour goal, the APHIS National Incident Coordinator will approve—on a case-by-case basis—the use of ventilation shutdown for depopulation. This method is considered by some to be less humane than other methods, but it can spare the lives of potentially thousands of other birds by halting the infection as soon as it is detected. Ventilation shutdown requires no specialized equipment or personnel. It would be implemented only upon recommendation by Federal and State officials and the producer, with concurrence by the National Incident Coordinator that all other options have been considered and that no other method will achieve the 24-hour depopulation goal.
I have to believe that no Federal agency would purposely unleash the kind of public derision this policy will evoke unless they truly felt there was no other viable option. And that speaks volumes as to just how concerned they really are over the return of bird flu this fall and winter.
Which is why – while I’m far from happy about it – unless and until someone comes up with a practical alternative, I’m grudgingly forcing myself to accept that VSD may sometimes be the least `bad’ option available.