General response policy
In most cases, the response to an exotic EAD outbreak in Australia will include stamping out through containment and eradication. Features of an EAD response include:
Movement controls, including quarantine
Contains the disease where it currently occurs and prevents spread to other areas. Animals and products are controlled through movement controls but it is also important to ensure that disease is not spread by the movement off property of fomites, equipment, vehicles, waste products, vectors and human movements.
Destruction and disposal of infected and/or exposed animals
Destruction of the infected animals and their in-contact group removes the infected source and prevents further spread. For FMD it quickly stops virus replication and excretion. The destruction of livestock through processing at abattoirs or knackers’ yards is preferred but only possible where the pathogen is not highly infectious outside the animal and the meat can be used. Many EADs have a high risk of spread and require the creation of destruction facilities close to disposal sites. The most common disposal methods used are burial, burning, rendering and composting.
This topic is comprehensively covered in the AUSVETPLAN Operational manuals: Destruction of animals (PDF download), and AUSVETPLAN Operational manual: Disposal procedures (PDF).
Decontamination of infected premises (IPs)
Decontamination is the combination of physical and chemical processes that kills or removes pathogenic microorganisms to non-infective levels. While the specific decontamination strategy will depend on the identified agent’s biological properties, basic principles include isolation of the source, preliminary cleaning before the use of chemical disinfectants, allowing time and the natural elements of heat, dehydration and solar radiation to destroy microorganisms. Decontamination of personnel, equipment, vehicles and sites permits personnel to safely move between properties and reduces the period between slaughter and restocking on contaminated and affected properties.
More information can be found in AUSVETPLAN Operational manuals: Decontamination (PDF download).
Tracing of animals and/or goods that present a transmission risk
Tracing of movements of animals, products and carriers of fomites, such as vehicles, determines how far the disease may have spread and where it may have come from. Trace-forward of animals from infected premises (IPs) determines where the disease could have been moved to and helps prioritise surveillance. Trace-back of animals that have moved onto an IP in the past may reveal where the infection has come from. Information for tracing is gathered at the property level on the time and movement of animals and objects onto and off the property. Specific information collected for each disease are found in the AUSVETPLAN disease manuals. For example, FMD includes susceptible species, vehicles, people, animal products and things such as hay etc. within at least the past 14 days.
Australian government and industry have invested heavily in livestock identification and tracing systems such as the National Livestock Identification System for cattle, sheep and goats. The faster animals are traced, the greater the chances of controlling a disease outbreak and minimising the costly effects on industry and its supporting sectors.
Surveillance of susceptible animals
While tracing of animals and risk items determines the spread of the disease through known infected networks, broader surveillance processes are required to delimit the extent of infection in the rest of the susceptible animal population. Passive surveillance depends on reporting by animal owners and private veterinarians as well as the monitoring of social media networks for discussions that may indicate presence of disease. Active surveillance involves the follow up examination of traces, structured sampling methods based on risk assessment and active visits of all farms in the vicinity of IPs/Dangerous Contact Premises (DCP). The actual surveillance strategy is specific to the disease outbreak and is developed during an outbreak according to the individual disease AUSVETPLAN strategy.
These measures may be supplemented where necessary by one or more of the following options:
Vaccination is used during disease outbreaks to impede the progress of disease in a population by provoking immunity in the hosts, protecting them from the pathogen and inhibiting its ability to multiply. Protective vaccination involves the vaccination of at risk susceptible animals that are not suspected to be infected. Suppressive vaccination involves the vaccination of animals already infected to reduce the pathogen load being shed. Anthrax is an emergency disease well controlled by vaccination, and vaccination is the method of choice in responding to arthropod-borne diseases. The decision to vaccinate can be controversial with diseases such as FMD, largely due to extended trade restrictions. FMD Vaccination FAQs provides further information.
Wild animal or vector control
Wildlife and feral animals may be involved in the spread of some EADs including velogenic Newcastle Disease, highly pathogenic avian influenza (HPAI), Hendra virus, African swine fever (ASF) or Classical swine fever. Arboviruses are insect-borne viruses spread by insect vectors and include EADs such as blue tongue virus. These living vectors contribute to the lifecycle of infectious agent or allow it to multiply. They often do not comply with man-made barriers or imposed movement controls, making control and eradication difficult.
The treatment of infected animals can reduce shedding and the length of the infectious period. While the preferred approach to exotic EAD incursions is depopulation or test and slaughter there are some cases where treatment is justified. In the event of an incursion of the exotic parasite, screw-worm-fly, to Australia, the use of chemical pesticides to treat infestations and to protect animals from strike will be a significant component of the response. The cattle tick (Rhipicephalus microplus) is endemic to Northern Australia but can emerge in parts of the country through the movement of untreated cattle. Treatment of the livestock with a pour-on acaricide together with prophylactic administration of imidocarb for babesiosis is a useful control strategy.
Infected and infection-free zones may be established to contain the outbreak and to protect Australia’s export trade. In some circumstances, containment and/or eradication may be deemed impossible or unfeasible, and allowing the disease to become endemic may be the only option.
A major EAD response is a complex operation requiring rapid mobilisation of resources and coordination of a diverse team of people and other resources, amounting to a whole-of-government response. Private veterinarians engaged by the government to assist on an EAD response must be aware of the relevant response policies and procedures as they may need to communicate consistent information to affected members of the public and communities.
The AUSVETPLAN defines four phases of an EAD response: