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Chapter 6: Managing pig industries for freedom from Nipah virus infection

Actions from the pig industry
Actions from governments
Managing the risk from the wildlife reservoir

There are three broad areas that require attention in managing pig industries for freedom from Nipah virus infection (Daniels 2000; Daniels et al. 2001b):

- actions from the pig industry;
- actions from governments; and
- definition and management of the risk posed by the wildlife reservoir.

Actions from the pig industry

It is recommended that the pig industry in at-risk countries adopts a code of practice to preclude the possibility of an outbreak of such major proportions as was seen in Malaysia. This would involve the implementation of simple good management practices which are advantageous to producers even in the absence of threats such as Nipah virus. Firstly, where animals are intensively farmed there is a need for herd health monitoring, through record keeping and analysis, to identify any change in the health of the herd on each farm. Early recognition of syndromes consistent with the clinical case description (see Chapter 3) followed by laboratory testing (see Chapter 4) will be the most efficient means of containing any potential outbreaks. Full implementation of this approach implies a strong involvement of veterinarians (probably employed as farm consultants) who have skills in epidemiology for the management and analysis of animal health records. Commitment to this style of management is of broader benefit to the farmers, as it enables the control of the whole range of disease and production issues.

Secondly, the principles of farm-gate biosecurity need to be strictly and widely applied. In Malaysia, Nipah virus spread from farm to farm through the trading of pigs (as have many other diseases of pigs previously). Where it is necessary to purchase new breeding stock, the methods for the introduction of these animals to the herd must be clearly defined. This step may include serological testing and/or quarantine.

There is little economic sense in risking the whole farm for the sake of small financial benefit from trading a few pigs, and a realignment of commercial practices is needed to better manage the risks from introductions. As with herd health monitoring, strict on-farm biosecurity allows better control of a range of porcine diseases, to the financial benefit of farmers and the long-term protection of their investment.

Actions from governments

The Nipah virus outbreak in Malaysia resulted in trade and policy responses from governments internationally. In the absence of agreed OIE guidelines, various bilateral restrictions regarding trade in pigs and pork, and other animal movements were developed by Malaysia’s neighbours and trading partners. After the outbreak was controlled, a period of serological surveillance was necessary to demonstration of freedom from Nipah virus (see Chapter 5). The design and management of such programmes require veterinarians who are trained and proficient in epidemiological procedures. Cost effective sampling strategies applicable to local circumstances need to be designed, and acceptance of the suitability of the programme negotiated with the client bodies, be they trading partners, public health authorities or the OIE. A laboratory testing capability has to be established and maintained, and the interpretation of test results has to be undertaken using epidemiological principles and knowledge of test performance. Ideally, a partnership with an international reference laboratory will allow follow up testing on any samples giving results of concern.

The outbreak in Malaysia highlighted a number of areas of veterinary expertise essential for an efficient response capability: epidemiology, laboratories and equipment, and diagnostic testing and quality control.

Epidemiology is the discipline within veterinary science on which the rational scientific management of the health of animal populations is based. Within the context of Nipah virus, epidemiologists are needed in both the private and public sectors to:

- interpret and respond to the information collected in herd health programmes;

- design and manage surveillance programmes;

- conduct outbreak investigations;

- advise on the drafting of legislation for the management of the domestic industry; and

- advise on appropriate restrictions on the movement of animals and animal products.

While many countries have allocated resources to the training of epidemiologists from time to time, these people are frequently transferred or promoted, giving rise to difficulties in maintaining a critical mass of trained people everywhere they are needed. An answer in the medium term is to ensure the study of epidemiology to a high standard in undergraduate degrees, and to provide further training opportunities which address the needs of animal health authorities and the intensive animal industries.

The provision of laboratory services for Nipah virus diagnosis is a complex issue, given that work propagating the virus should be done under the PC4 conditions. Such facilities are expensive to maintain, and it may not be cost effective to have a PC4 lab in each country. Systems of bilateral and regional collaboration should be negotiated.

Diagnostic tests need to be both sensitive and specific (Daniels et al. 2001a), and a new generation of such tests requires ongoing research and development effort. In addition, the application of quality assurance (QA) programmes is of great value in ensuring that tests are performing within predetermined limits of acceptability and minimizing spurious reactions. Regional QA programmes based on collaboration among a number of laboratories have a role in the future for all laboratory testing.

Another area to be addressed is management and regulation of the pig industry. If a code of practice is required of industry, there may need to be a framework of legislation within which to work. Experience in Malaysia has shown that successful management of the pig industry for freedom from Nipah virus requires a partnership approach between government agencies, the industry representatives and the individual farmers. The expectations that each group has of the others can be defined through consultation and communication. Ultimately the government must legislate and the industry must adopt methods of operation that will protect individual farms from infection, and prevent any spreading of new infection.

Managing the risk from the wildlife reservoir

Preliminary research has established that species of bats (genus Pteropus) are a natural host of the virus (Chua et al. 2001; Johara et al. 2001); however the geographic range of the virus in the Malaysian species, and the presence or absence of infection in related species outside Malaysia is unknown. A regional and collaborative approach is needed to map the distribution of the virus in bat populations, the incidence of infection in bats, risk factors for infection in bats, and risk factors for spillover to pigs. The pathogenesis of the virus in bats also remains to be described, particularly the mode of transmission, to enable industry to develop cost effective risk management measures. While spillover from the natural host may be a very rare event, it is worth noting that there have now been three separate outbreaks of Hendra virus disease in horses in Australia, indicating a “jump” from the wildlife reservoir on three separate occasions (Field et al. 2000; Hooper et al. 2000). Thus, wherever there is an intensive pig industry in tropical countries with similar fruit bat fauna to that in Malaysia there is a possibility of a new Nipah virus outbreak. Careful and informed management of the industry by both the private sector and government offers the best protection for public health and industry prosperity.

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