Should the Worst Epidemic Yet of Avian Flu Revive Concerns About Urban Homestead Poultry Farming in the US? | Outbreak News Today Outbreak News Today
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I understand the enthusiasm for backyard chicken farming.  It is guided by the spirit of providing eggs and meat for the family table, at lower costs, from humanely treated animals that are spared the application of antibiotics.  The narrative goes that these animals are less susceptible to diseases compared to animals at commercial poultry farms (from where the rest of us slobs obtain our poultry products).  Oftentimes, the reality has turned out less well than advertised.

Public domain image/Ben Rudiak-Gould

Public domain image/Ben Rudiak-Gould

Feed, bedding and sheltering materials don’t come cheaply.  Costs mount from unforeseen vet services (medications for sick animals) and losses from predators.  The dark side is that hens that lived in a cushy coop or a ‘free range environment’ in somebody’s back yard often find themselves looking for a home after their ‘prime lay’ years.  This usually means off-loading to commercial farms or municipal animal shelters where they are euthanized; on the flip side, birds usually have to be obtained from commercial farms because roosters are banned from backyard farms in many jurisdictions.  So, let’s admit the dividing line between commercial and backyard animals is a little blurry.

The spread of infectious agents does not always go in one direction, with large, commercial farms spreading disease to small farms. In 2002, it was the other way around.  The only outbreak in the US since 1971 of an extremely contagious and lethal virus for birds, exotic Newcastle disease, originated in backyard chicken farms (in California, Nevada, Arizona and Texas) and ultimately spread to commercial farms. The owners of the small farms were raising birds for fighting; the conditions on these farms were likely far less hygienic than those of responsibly operated backyard farms. Apparently, some of the fighting birds had been smuggled from Mexico where the disease is endemic.  But, that is the point.  Not every amateur farmer or pet owner acts responsibly.  Just ask Florida Fish and Wildlife Conservation officials why boa constrictors and pythons have overrun the Everglades.

Have you noticed the price of a dozen eggs at your local grocery store recently?  Over 35 million egg-laying chickens have died or been culled at farms across 15 states since March of this year because of highly pathogenic avian influenza (HPAI) strains of influenza A–the ‘family’ of viruses that can infect humans.  Fortunately the strains infecting these chickens (mostly H5/N2 and H5/N8) cannot. The concern is that some other flu bug subtypes (including H3N2) that circulate among humans each year, were essentially once avian bugs that mutated. Just two years ago in China, an exclusively avian influenza, H7N9, made the jump to infect humans.  It has so far been incapable of spreading from human-to-human, but it has been deadly for about a third of those who caught it from poultry exposure.

The HPAI strains causing the current epidemic apparently were carried on the wings of wild water fowl; low pathogenic components from North American birds combined with especially virulent components from Asian birds. These novel, mixed-origin viruses were dispersed along major migratory flyways of the Northern hemisphere. But, the perpetuation of this outbreak into the Midwest has been more complicated than that. The USDA’s Animal and Plant Health Inspection Service (APHIS) believes contact with infected wild birds has been compounded by insufficient ‘biosecurity’ efforts at farms and even transmission through the air; carriage of viral particles by winds cannot be completely ruled out.

HPAI strains are so contagious that whenever one or more domesticated birds at a farm are found to be infected, all birds are at risk of death and are routinely destroyed to break the chain of transmission–somewhat like felling trees and setting small fires to stop the spread of a great forest fire.  The chief ‘biosecurity’ precautions a chicken farm must take is to isolate its healthy flocks from potential infection:

  • enclosing flocks to prevent contact with wild birds and their infectious excreta
  • limiting access of workers and outsiders from their farms
  • avoidance of sharing equipment between farms
  • hosing down service trucks with disinfectants
  • shoe sterilization procedures
  • sequestering affected farmers from feed stores

A number of responsible turkey farmers in the Midwest who made exemplary efforts to protect their flocks could not prevent HPAI from finding their birds.  Sadly, small backyard flocks have not escaped infection, either.  Vaccination should have provided good protection, but currently available vaccines have not been effective against these novel strains.  Ironically, the process of vaccination itself could pose a risk of transmission of latent virus to unaffected farms from careless vaccinators and their equipment.  Many small-plot chicken farmers find it unpalatable to kill their old hens or meat stock themselves; mobile slaughtering service trucks provide another of many channels of potential transmission between small farms.

Of the largest 25 US cities by population, all but four permit backyard chicken farming.  Most cities have zoning requirements for size and placement of chicken plots within household properties.  Some cities require farming permits, limit the number of birds, or prohibit roosters; a few allow chickens only for eggs or as pets.  Not much regulation beyond that.  It surprises me that virtually none of the cities require licensing or certified tracking of chickens.  Licensing of cats and dogs is standard procedure in most cities.  Why should it be any different for pet chickens?  In the event of an outbreak, contact-tracing is essential to control infection.

I am not against backyard chicken farms.  But, maintaining animals– that serve as reservoirs and mixing vessels for influenza viruses—in close proximity to dense human populations provides the potential for reassortment of viral components into chimeras with pandemic potential.  More regulation should be well received by passionate urban chicken farmers and should discourage irresponsible ones.  Otherwise, our conviction that we are more enlightened than those who banned animal farming in cities one hundred years ago could expose us to consequences they did not consider unthinkable.

Steven Smith, M.Sc. is an Infectious diseases epidemiologist


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