 | PROTECTION AGAINST IMPORTANT DISEASES INCLUDING NEWCASTLE DISEASE |
| P.B.Spradbrow | |
| Department of Veterinary Pathology, The University of Queensland, Brisbane, Australia |
Newcastle disease is the most important infectious disease affecting village poultry, often destroying the entire chicken population of villages. Control by vaccination is now possible with the use of thermostable vaccines that are given on food if necessary. The Australian Centre of International Agricultural Research (ACIAR) has funded numerous trials of these vaccines in Asia and Africa. Delivery of vaccine to villages is now a major problem, as commercial vaccines are not available in the small quantities required by single families or single villages. Local small scale production of thermostable vaccine for distribution in liquid form may provide a solution. ACIAR has sponsered the development of a new thermostable vaccine in Australia, Strain I2, that is freely available to laboratories in developing countries. Once Newcastle disease can be controlled, vaccines to protect village chickens against other killing diseases, including fowl cholera, will be required.
INTRODUCTION
Village chickens that survive mainly by scavenging are an important resource for rural people in most developing countries. Chickens and eggs become available for consumption, sale or barter and for various social or traditional uses. The productivity of village chickens is low but the inputs are minimal. Housing is simple, or often no special housing is provided. Small amounts of grain may be used to supplement household scraps as an additional source of food in some areas. In the poorest countries the chickens depend entirely on the scavenging resource base of their environment. In many countries women and children tend the poultry and receive any benefits that result.
Village chickens have, until recently, received little scientific attention. In most areas they receive scant attention from their owners, who favour a system of opportunistic harvesting of such birds that survive. Two major areas of attrition are apparent. The first is Newcastle disease. The velogenic forms of Newcastle disease virus that are present in Asia and Africa frequently destroy entire village flocks. Because of these losses, regarded as inevitable by the owners, improving the husbandry of the village flock is deemed wasteful. Consequently a secondary cycle of major losses occurs during the brooding perod, attributed to starvation, predation and exposure. The losses during brooding could be reduced by improved husbandry, which will not eventuate until Newcastle disease can be controlled. Until recently it has been very difficult to vaccinate village chickens against Newcastle disease.
Constraints On Vaccination of Village Flocks
Vaccination of commercial chickens against Newcastle disease is a relatively successful undertaking. Village chickens, by contrast, have proved very difficult to vaccinate. Conventional Newcastle disease vaccines are relatively heat-labile, and it is difficult to retain viability during transport to remote areas and storage in undeveloped villages. Conventional vaccination requires physical control over the chickens, and near feral village flocks prove very difficult to catch. Conventional vaccines are sold in large dose vials, usually 1000 doses, which are unsuitable for small family flocks. Village flocks are small, scattered and multi aged, placing them beyond the reach of technical vaccination teams. Any method of vaccination that is proposed must be suitable for application by the owner of the chickens.
Thermostable, Oral Newcastle Disease Vaccines
The Australian Centre for International Agricultural Research (ACIAR) has sponsered projects on vaccination of village chickens against Newcastle disease for more than a decade. The initial studies were undertaken in Australia and Malaysia and then extended to other countries in Asia and to parts of Africa. Further studies in Africa have been supported by various non-government organisations and by FAO.
The basis of these vaccines for village flocks are thermostable strains of Newcastle disease virus that infect when given orally and that spread between chickens that are in contact. The viruses that have been used most frequently are variants of the avirulent Australian V4 strain of New castle disease virus. This strain was already relatively heat resistant and it responds readily to selection for enhanced heat resistance. Strain V4 was the parent of several experimental and commercial vaccines. Other strains of Newcastle diesease virus have also responded to selection for enhanced thermostability. In initial studies it was shown that vaccination with V4 virus induced reasonable levels of antibody and protected against challenge with a velogenic Malaysian challenge strain. Protection was demonstrated in laboratory trials, in pilot village studies and in large control areas. Similar protection was demonstrated against velogenic challenge strains from other Asian and African countries. These vaccines overcome the problems of transport, storage and lack of access to the chickens. The first vaccine procedures used V4 virus applied to the surface of a suitable food-for example, commercial pellets, unhusked rice, cooked white rice or wheat. Some foods, such as raw white rice, proved unsuitable vehicles for the vaccine.
Oral vaccination is not as efficient as vaccination by other routes such as the conjunctival sac or nasal cavity. Two doses of oral vaccine are usually required to give protection, but protection is then registered in both vaccinated and in contact chickens. It is envisaged that, once oral vaccination has proved its efficacy to the satisfaction of the villagers, they will be prepared to improve husbandry and more efficient methods of vaccination will become feasible.
Production of Newcastle Disease Vaccine in Regional Laboratories
It has now been amply demonstrated that robust Newcastle disease vaccines of the V4 type, delivered orally if necessary, can reduce the prevalence of Newcastle disease in village chickens. The logistical problems of large dose ampules and of the delivery of single ampules to villages remains. These problems may not be overcome until transport infrastructures are greatly improved. Until that time, it may be possible to produce Newcastle disease vaccine on a cottage industry scale in regional laboratories. The equipment that is required is an egg incubator, a candling lamp and a refrigerator. There is no requirement for freeze drying if the vaccine is to be used within a few weeks of production. Wet vaccine can be produced by mixing infected allantoic fluid with a suitable protective diluent such as 1% gelatin.
ACIAR has funded the production of a new seed vaccine containing an avirulent, thermostable Australian strain of Newcastle disease virus similar to V4. This seed material is available to laboratories in developing countries who wish to explore the possibility of vaccine production. This virus, designated I2, has proved to be antigenic and to spread between chickens by contact. Successful protection trials have been conducted in several Asian countries. The most extensive of these were in Vietnam where both laboratory and pilot village studies were concluded.
In December 1995 ACIAR helped conduct a workshop at the Poultry Reference Laboratory, University of Pretoria, Onderstepoort, Republic of South Africa. Delegates from 14 African countries attended. Those following the laboratory stream of the workshop were instructed in the techniques required for producing Newcastle disease vaccine on a small scale in embryonated eggs, and for testing such vaccines. Vaccines produced in local eggs would need to be tested for safety, but they would not introduce to the vaccinated poultry any micro-organisms that were not already circulating in the population.
OTHER IMPORTANT DISEASES
As Newcastle disease is controlled, a whole new science of village chickens will need to be researched. At first, only the other killing diseases will seem to be important to the villagers. Fowl cholera (a pasteurellosis) will be the next pestilence to require control. ACIAR has a project in progress already that seeks to produce suitable vaccines for use in chickens and in ducks. Only when the disease that kill chickens acutely and in large numbers can be prevented will the infectious disease affecting production require attention. It may well be that, by this time, populations of village chickens will be kept under conditions of improved husbandry. In some countries they will be replaced by small scale commercial operations and conventional vaccines will suffice. Infectious bursal disease and fowlpox, now only an occasional nuisance, will become important. Chickens are not the only species of village poultry. In some areas of some countries, ducks are the predominant bird, while guinea fowl feature in some parts of Africa. In ducks the viral disease duck plague is as important as Newcastle disease is in chickens. A further ACIAR project is attempting to improve vaccines against duck plague.
CONCLUSIONS
The key to improving the overall productivity of village poultry in developing countries has been the control of Newcastle disease. Conventional vaccines were unsuitable for use in villages. Vaccines with the specific properties of thermostability and oral infectively have ovecome this problem. It will now be possible to exploit the productive potential of the village chicken more efficiently, and other infectious diseases will become more important. At first the major killing diseases such as fowl cholera will be encountered, as these will require special vaccines tailored for village conditions. As village poultry come to resemble commercial poultry more closely, infectious diseases that affect production will come to prominence. These will probably be encountered with conventional vaccines.
REFERENCES
COPLAND, J.W. (Ed) (1987) Newcastle Disease in Poultry. A New Food Pellet Vaccine. Monograph No.5 Australian Centre for International Agricultural Research, Canberra, Australia.
SPRADBROW, P.B. (Ed) (1992) Newcastle Disease in Village Chickens Control with Thermostable Oral Vaccines, Proceedings No. 39. Australian Centre for International Agricultural Research, Canberra, Australia.
SPRADBORW, P.B. (1993/94) Newcastle disease in village chickens. Poultry Science Reviews 5; 57–96
