Control

Measures implemented to control avian influenza infection are based on achieving early disease control to reduce virus transmission with the final goal of eradication using the following methods based on controlled marketing, slaughter of infected poultry, move- ment controls, vaccination, compartmentalisation, and compensation (Halvorson 2002, Capua & Marangon 2006). Control strategies for HPAI H5N1 influenza are described by Anonymous (2005a).

Controlled marketing

Controlled marketing of infected flocks is applied as a means to reduce bird density in an area in order to limit disease transmission while at the same time ensuring that producers have a means for disposing of affected birds. This approach has been practiced for turkey flocks that have recovered from LPAI infections in the USA (Halvorson 2002). There is no reported use of controlled marketing of HPAI infected flocks.

Slaughter

Slaughter and disposal is the preferred method by which NAI infected birds are elimi- nated. Various terms have been applied including stamping out, depopulation, culling and

2.8 Control and prevention 35

pre-emptive slaughter. Culling refers to the process of humanely killing animals, while stamping out refers to the slaughter of infected and in-contact birds.

Movement controls

The idea behind movement control is to reduce the probability that disease will be trans- ferred from one area to another via the act of movement of poultry, equipment used with poultry, or poultry product. The success of this method of disease control is dependent on early identification of the index flock as well as the ability to trace all movements off in- fected farms. Movement controls are generally implemented on suspicion of the presence of both HPAI and LPAI virus infections in order to reduce spread of disease from infected to susceptible farms.

Vaccination

Vaccination reduces the susceptibility of the population in order to limit or prevent disease spread (Marangon et al. 2008). Experimental and field experience show that vaccination can increase resistance to field challenge, reduce shedding of virus and reduce rates of disease transmission (van der Goot et al. 2005). Emergency vaccination can be used as an alternative to culling, the success of which is dependent on bird density, biosecurity, virus strain, and the availability of vaccine and personnel to administer it. Prophylactic vacci- nation is an appropriate means for augmenting biosecurity during high risk situations. Most countries in which outbreaks of avian influenza have occurred have been hesitant to use vaccination as a means for control for a number of reasons. The first reason is related to the difficulty associated with disease freedom declarations and re-establishment of trade. The second is related to the fact that the currently available vaccines, although able to protect birds from infection, may not stop virus replication and shedding causing the phenomenon of silent spread. The third reason is associated with the difficulty dif- ferentiating vaccinated birds from naturally infected birds thereby interfering with sero- logical surveillance. Differentiating vaccinated animals from naturally affected animals (DIVA) strategies (Marangon et al. 2008) have been proposed as an alternative to facilitate vaccination, but problems remain with its implementation. A number of DIVA methods are available and serological or virological testing of unvaccinated birds (sentinel birds) placed within vaccinated flocks is the most widely method used (see Berg et al. 2008 for a review of other methods). Use of sentinel birds requires birds to be marked in order to

Table 2.5: Use of vaccination to control LPAI and HPAI outbreaks due to H5 and H7 subtype viruses. Adapted from Marangon et al. (2008).

Country Year Virus Vaccine type Species

Mexico 1995 – 2001 HPAI H5N1 Inactivated H5N2 Broilers, layers, breeders Mexico 1998 – 2001 HPAI H5N1 Recombinant fowlpox H5 Broilers, breeders Utah USA 1995 LPAI H7N3 Inactivated H7N3 Turkeys Connecticut USA 2003 LPAI H7N2 Inactivated H7N3 H7N2 Layers Egypt 2006 HPAI H5N1 Inactivated H5N2 Backyard poultry Italy 2003 – 2006 LPAI H7N3 Inactivated H7N1 H5/H7 H5N9 Turkeys, layers, cockerels

LPAI H5N2

Pakistan 1995 LPAI H7N3 Inactivated H7N3 Breeders Pakistan 2006 – 2007 HPAI H5N1 Inactivated H5N2 Breeders Hong Kong 2002 - 2003 HPAI H5N1 Inactivated H5N2 Broilers China 2003 - 2006 HPAI H5N1 Inactivated H5N2, H5N1 Ducks, chickens Vietnam 2005 - 2006 HPAI H5N1 Inactivated H5N2, H5N1 Ducks, geese, chickens Afghanistan 2007 HPAI H5N1 - Broilers, layers, breeders Russia 2006 – 2007 HPAI H5N1 Inactivated H7N1 Backyard poultry Siberia 2006 HPAI H5N1 Inactivated H7N1 Broilers, layers, breeders Ivory coast 2006 - 2007 HPAI H5N1 Inactivated H5N9 Backyard, commercial poultry

be easily recognised. In addition, vaccinated birds produce low levels of antibodies to cir- culating field strains, requiring diagnostic tests of high sensitivity in order to avoid false negative results. On the positive side, a DIVA strategy may allow countries to resume or continue trading as they are able to provide sufficient evidence of the absence of disease in vaccinated flocks. Italy used a H7N3 heterologous vaccine against outbreaks caused by LPAI H7N1 virus strain in 2001 and was able to differentiate infected animals from those that were vaccinated and were therefore able to continue trading poultry products (Capua, Terregino, Mutinelli, Terregino & Rodriguez 2003). A DIVA strategy was cited as an acceptable alternative to mass culling of birds as occurred in Chile in 2002, The Netherlands in 2003 and Canada in 2004 (Capua & Alexander 2004). Table 2.5 provides details of outbreaks of LPAI and HPAI where vaccination has been used as part of control efforts.

Compartmentalisation

Zoning and compartmentalisation are two processes to facilitate implementation of con- trol measures and maintain trade (Zepeda & Salman 2007). Zoning is the process of declaring defined geographical areas as infected, to facilitate the implementation of con- trol measures (Anonymous 2007c). Compartmentalisation is a procedure implemented to

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define and manage poultry populations under a common biosecurity management system in order to facilitate international trade. Within the compartment are subpopulations of animals with similar health status that are subjected to a common intensity of surveil- lance, control and biosecurity measures. Compartments could refer to live bird marketing systems or integrated domestic poultry companies as described by Myers et al. (2003). Given the tendency of the avian influenza virus to persist in the environment in combina- tion with movement of wild birds, it is not likely that zoning as a single control measure would be acceptable to trading partners.

Compensation

Compensation refers to the process of reimbursing poultry producers for losses incurred during a NAI outbreak (Anonymous 2006a). It has been used as an incentive to encour- age early reporting of disease by owners and as a way of encouraging owners to comply

with culling programmes (Anonymous 2006a). Compensation has been used in a num-

ber of infectious disease outbreaks including FMD and CSF. The expected benefits from compensation include a reduction in the time between incursion and implementation of control measures, which in turn reduces the likelihood of virus mutation. Potential nega- tives are that this may encourage producers to neglect basic biosecurity measures aimed at preventing disease entry and other factors related to the design and implementation of the compensation scheme. A successful compensation programme to enhance avian influenza control must have the following features: (1) a clear definition of who will be compensated and who will be responsible for funding the compensation programme, (2) the types of losses to be compensated, (3) a clear understanding by all parties (particulary producers) of what is required in terms of reporting, (4) an organised structure for pay- ments, and (5) availability of funds. Avian influenza compensation schemes have been

implemented in The Netherlands, Canada, Vietnam and Thailand (Anonymous 2006a).