biosecurity HPAI

THE FUNDAMENTAL PRINCIPLES OF BIOSECURITY
Biosecurity has many definitions.
The somewhat broad definition FAO used in its position paper for the Inter-Ministerial
Conference on Avian and Pandemic Influenza, held in New Delhi in December 2007, was:
Biosecurity refers to those measures that should be taken to minimize the risk of incursion
of HPAI into individual production units (bioexclusion) and the risk of outward transmission
(biocontainment) and onward transmission through the production and marketing chain.
This definition can theoretically include many activities, including vaccination. For the
purposes of this paper, a slightly narrower definition is taken:
Biosecurity is the implementation of measures that reduce the risk of the introduction
and spread of disease agents; it requires the adoption of a set of attitudes
and behaviours by people to reduce risk in all activities involving domestic, captive
exotic and wild birds and their products.
Although there is often an emphasis on structures, equipment and materials such as
disinfectants, biosecurity is put in place and carried out by people, often acting in concert.
To be effective, it must part of daily routine, and both hard to avoid and easy to comply
with. Even the most sophisticated biosecurity measures can be breached by human error.
The key is to persuade people of the need for and advantages of adopting biosecurity and
to develop with them sets of practices and behaviours that are seen by them as possible,
practical and sustainable.
Crucially, any biosecurity measure that is recommended must take into account
the socio-economic realities of those who will be expected to implement it.
It is usually not feasible to achieve perfect biosecurity that prevents all spread. The aim
should be for a level of biosecurity that contributes to reducing spread to below a certain
threshold. It is an established principle that if on average an infected site infects less than
one uninfected site, disease control will be achieved. In these circumstances, the disease
will eventually die out. The number of uninfected premises that an infected premise infects
is often described as the reproductive rate, ‘R’; for a disease to be eradicated, ‘R’ does not
have to be zero, but reliably less than 1.
In terms of an epidemic, spread matters as much as the initial infection and
biosecurity is one of the key pillars in slowing spread.
There are several ways of defining different elements of biosecurity. One system divides
it into three goals: isolation, sanitation and traffic control. Under this system, biosecurity
is achieved through three elements: conceptual, structural and operational. Although this is technically correct, it is often too complex and apparently theoretical for practical use in
the field.
A simpler way to describe biosecurity is that it consists of the following steps:
1) Segregation
2) Cleaning
3) Disinfection
Segregation is the first step. It does not refer to keeping species separately, but to
keeping potentially infected animals and materials away from uninfected animals. Segregation
should be expected to have the greatest impact on achieving good levels of biosecurity.
If the virus does not enter a poultry holding, no infection can take place. No animals or
materials should enter or leave a poultry holding unless they have to.
Segregation involves the creation of barriers and the control of what passes through
them. The barriers should be physical and/or temporal where possible, and procedural
where not. However, such barriers will only be effective when controlled to exclude potentially
contaminated items. This includes such measures as enforcing the changing of footwear
and clothing for all people crossing the barrier, and restricting the entry of vehicles.
It is instructive that even, and perhaps particularly, in large-scale highly integrated
production systems, where biosecurity is more critical because of the potential impact of
disease in such an intensive high input/high output/low margin system, segregation is the
basis of most biosecurity measures, from the farm gate to individual poultry sheds. This is
the first and most important line of defence.
The second and next most effective step in biosecurity is cleaning. Most virus contamination
on physical objects is contained in faecal material or in respiratory secretions that
adhere to the surface. Cleaning will therefore remove most of the contaminating virus.
Any materials that must pass through the segregation barrier (in either direction) should be
thoroughly cleaned. This means that there should be no visible dirt on the surface of materials.
Soap, water and a brush are adequate for small objects, but a high pressure washer
is needed for large vehicles such as lorries or tractors (high pressure = 110-130 bar). The
difficulty of properly cleaning large complex items such as lorries emphasizes the need for
segregation as the first and best line of defence.
The third and final step is disinfection. This is often incorrectly done and so can be
regarded as the least effective step. Under ideal controlled conditions, there are many
disinfectants that destroy avian influenza viruses but under field conditions they are often
much less effective. Disinfectants will not necessarily penetrate into dirt in sufficiently high
concentrations to be effective and many disinfectants are inactivated by organic materials
such as wood or faecal material. Disinfectants are often not available in village conditions
so any programme that emphasizes their use will be hampered from the start. Disinfection
is important when performed consistently and correctly, but should be regarded as a final
“polishing” step in biosecurity, used after effective cleaning.
In most cases, the emphasis in biosecurity for poultry flocks should be on keeping
the virus out of uninfected farms and villages (i.e. bioexclusion). Once an outbreak has
occurred and has been detected, then post-infection biocontainment becomes the most
important activity. However, because containment is difficult, prevention is the most efficient
form of control.