P. B. Spradbrow

The major impediment to village poultry production is Newcastle disease. Conventional vaccines are unsuitable for sustained use because of their cost, large dose presentation and thermolability. The Australian Centre for International Agricultural Research (ACIAR) has sponsored projects to develop thermostable vaccines more suited to use in village flocks. Vaccine strain V4 is now available as a commercial vaccine, and strain I2 as seed material that can be used for local production of vaccine. Thermostable vaccines are best delivered by eye drop but they can be given in drinking water or on suitable particles of food. These vaccines, suitably applied, have proved effective in many trials under laboratory conditions and in villages. Extensive use of these vaccines should allow the development of a new science of village poultry production. However wider use of these vaccines will require further training on their production and use, and the adoption of suitable, and probably novel, extension methods.

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Village chickens
The importance of village chickens to the rural and peri-urban poor in developing countries is not contested. Another universal truth is that these flocks are poorly productive, and cost-effective remedies should be available. Many advocate a holistic approach to these problems. The author, with a virological bias, sees the pivotal problem as Newcastle disease. Genetic interventions, alterations to husbandry practices or improvements in nutrition are of no avail unless there are live chickens in the flocks. The author sees the control of Newcastle disease as the key to a new science of village chicken production. Vaccination offers the only prospect for control. Eradication of the virus is not feasible, so vaccination programmes must be continual and sustainable.

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Any of the usual commercial Newcastle disease vaccines will protect village chickens against Newcastle disease, if the vaccines reach the chickens in a potent form. There are special problems. Many commercial vaccines are thermolabile and sometimes extremely thermolabile. Cold chains are impossibly expensive to develop and maintain. Village flocks are small, scattered and multi-aged. The minimal unit container for a commercial vaccine is usually 1000 doses, which is expensive and inconvenient for very small flocks. Commercial vaccines require foreign exchange.

The Australian Centre for International Agricultural Research (ACIAR) has supported projects on the vaccination of village chickens since 1984. The original concept was the production of a thermostable strain of Newcastle disease virus, developed by artificial selection. This seemed to the original applicants a novel approach at the time, although manipulation of the storage medium had already been used to improve the thermostability of liquid poliomyelitis vaccine. In fact, the concept of thermostable variants of conventional viruses had a longer history. The early work in Hungary that resulted in the Bartha vaccine for Aujeszky´s disease used heat selection to yield variants of reduced virulence. Other herpesviruses appear to respond similarly to heat selection. A heat-resistant rinderpest virus vaccine was described in 1992 (Provost and Borredon, 1992). Hofstad and Yoder (1963) had suggested that robust Newcastle disease vaccines might be produced by seeking strains of virus that possessed superior thermostability. Heat-resistant strains of Newcastle disease virus had actually been produced in the 1950s for use as phenotypic markers in genetic experiments (Goldman and Hanson, 1955).

Thermostability is a relative term. It has been unfortunate that thermostable vaccines have sometimes been considered as another basic commodity, like a sack of rice, that needs no special treatment. All vaccines need careful nursing. Thermostable vaccines have some viability away from the cold chain, but transport conditions should still be as cool as possible. When the cold chain ends, thermostable vaccines should be transported in wet cloth, preferably in an open weave basket. Beside the base of a water pot is often a cool storage position in a hut. One sometimes sees criticisms of agencies that have purchased thermostable vaccines and then afforded the vaccine cold storage. Such criticism is misguided.

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The thermostable vaccine that has been most used is a variant of the avirulent Australian V4 strain of Newcastle disease virus, described by Simmons (1967). This virus had an inherent degree of thermostability (Kim and Spradbrow, 1978) and it responded to selection for enhanced heat-resistance (Robyn Schalkoort, 1979, unpublished data). Ideris (1989) has published detailed data on the selection of heat-resistant variants of strain V4. Heat-resistant variants of V4 are now contained in commercial vaccines. The two sources known to the author are:Malaysian Technology Development Corporation Sdn Berhad and Fort Dodge Australia Pty. Ltd.

Once V4 became a commercial vaccine, the target for vaccination became commercial chickens. Village use continued in Malaysia where the vaccine was produced. While the vaccine was supplied on food (pellets and later wheat) it was reported that Newcastle disease was largely controlled in Malaysian villages (Anonymous, 1997). Ideris (1998) noted that use of vaccine in villages declined when the commercial producers stopped supplying vaccine on food. The commercial freeze-dried vaccine in 1000 dose ampoules was not convenient for village use, but vaccine use is increasing in villages with the production of 100 dose ampoules. Further large-scale application in villages was restricted to a few countries where foreign agencies purchased the vaccine. There were however many small-scale trials.

The focus turned to local production of thermostable vaccine and the supply of seed material free of commercial ownership. ACIAR sponsored the development of a second thermostable vaccine, strain I2, from an avirulent Australian isolate similar to V4. The selection was made after studying a collection of 42 Australian isolates (Spradbrow et al., 1995). I2, already a thermostable virus, was selected for enhanced thermostability (Bensink and Spradbrow, 1999). The seed material can be made available to laboratories in developing countries that wish to test and possibly produce vaccine locally. Successful laboratory and field trials led to strain I2 being adopted as the vaccine for use in village chickens in Vietnam (Tu et al., 1998).

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Other thermostable variants of Newcastle disease have been produced ì in Hungary from a local isolate, in Vietnam from La Sota and in Indonesia from a virus that is possibly mesogenic. The process is not difficult, but we know very little on the persistence of thermostability on continued passage without further selection.

Thermostable vaccines seem to be a partial answer to the problem of Newcastle disease in village chickens. In this discussion paper the author attempts to review the successful field trials from both formally published and unpublished sources. For unpublished reports I have tried to indicate a contact from whom further information could be sought. I know there will have been other trials that have not come to my attention. I would welcome information on these.

More importantly, there are sometimes reports that cast doubt on the thermostable vaccine approach. For example, Kitalyi (1998) saw the need for more on-farm research into sustainable control of Newcastle disease. Other reports contain no data, nor references to published data. As a practising editor, I recognise how difficult it is to have negative results accepted for publication. However it is urgent that unsuccessful vaccine trials are brought to notice and the reasons for vaccine failures are sought. We were successful in having some unproductive results included in a paper from Thailand (Tantaswasdi et al., 1992). Failures in the preliminary experiments probably resulted from maintaining the experimental chickens on wire. Vaccination was effective when chickens were placed on a solid floor.

I solicit examples of unsuccessful trials with thermostable vaccines and analysis of the reasons for failures.

More detailed considerations of earlier trials are contained in two ACIAR publications. Copland (1987) and Spradbrow (1992) - and in a review ì Spradbrow (1993/94).

ACIAR and the University of Queensland are attempting to consolidate data on village chickens in a website ì http://www.vsap.uq.edu.au/ruralpoultry

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Liquid vaccine
Newcastle disease virus vaccines are less heat-stable in liquid form than in freeze-dried form. However, under village conditions, Newcastle disease vaccines must often be stored and transported in liquid form. Various additives are available to protect virus infectivity during freeze-drying and subsequent storage. Not all of these have been tested as protectants of viral vaccines stored in liquid form.

The Malaysian thermostable variant of V4 survived exposure at 56oC for at least 9 hours; the parent stock was entirely destroyed after exposure for 3 hours (Ideris, 1989). The author also noted that for long-term protection (3 weeks) at 20-25oC, polyvinyl-pyrollidone (PVP) was more effective than skim milk, gelatin, methylcellulose or carboxymethylcellulose. Claxton and Leonard (1987) reported that V4 virus lost less than 1 log10 unit after storage for 1 hour at 50oC and less than 3 log10 units after 6 hours.

Strain I2 had similar thermostability to V4 in tests conducted by Uruakpa (1997). In a favourable diluent (with lactose, sodium glutamate and bovine serum albumin) I2 lost only 0.3 log10 units on storage for one month at 22oC.

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Freeze-dried vaccine
The thermostability of heat-resistant V4 vaccine, obtained by selection in a liquid medium, is also evident in the freeze-dried vaccine. The commercial vaccine was stable in freeze-dried form for 3 months at 18-22oC, and lost only about 1 log10 on storage for a further 3 months (Heath et al., 1991).

Freeze-dried I2 vaccine lost about 1 log10 of infectivity when stored for 6 days at 26-32oC (Tu et al., 1998). However in the same study vaccine reconstituted after storage for 24 days at 30-35oC still produced substantial protection in vaccinated chickens. It should be possible to reach village chickens in any part of Vietnam with this vaccine, without refrigerated transport.

Dr. Ian Wilkie confirmed that I2 vaccine was reaching remote hill areas of Vietnam. The vaccine was apparently viable. In April 1999 he visited villages where some chickens had been vaccinated and tagged. The vaccinated chickens were surviving while unvaccinated chickens in neighbouring flocks were dying, apparently of Newcastle disease (Wilkie, 1999).

Vaccine on food

Oral vaccination of chickens with thermostable vaccines requires that the virus attaches to the food, and survives to be released on ingestion by the chicken. Not all foodstuffs are virus friendly. Problems are probably associated with substances that inactivate viruses and with binding to food lectins. The role of heat inactivation of Newcastle disease virus on food can be estimated only with the most innocuous of food carriers. Cooked white rice is possibly the best for this purpose (Samuel et al., 1993).

In Malaysia commercial food pellets were coated with thermostable V4 and stored at 20-25oC. The food vaccine was stable for at least 1 month (Ideris, 1989). Further evidence of this stability was obtained when commercial pellets coated with thermostable vaccine were sent from Malaysia to The Gambia. The vaccine was 8 days in transit, and then was kept at close to room temperature for another 14 days during transport to villages. About half the chickens receiving the oral vaccine produced antibodies suggestive of protection, while there was no antibody response in control villages (Jagne et al., 1991).

In Malaysia oral vaccine was prepared in bulk with wheat grains as the carrier. Wheat in 100kg quantities was placed in a special food mixer and sprayed with liquid V4 vaccine. After air drying the vaccine-coated wheat was packaged in 100g amounts, suitable for delivery to 20 chickens. In experiments conducted by Dr. Jah Hussein (Hussein, 1991) vaccine stored for 6 or 7 weeks at room temperature still gave substantial protection. There was no advantage in storing the vaccine at 4oC. The residue from the production of maize porridge has been used as a carrier for V4 vaccine in Nigeria. This vaccine remained viable for over 3 months on storage at 20oC (Olabode, 1998).

The results obtained by vaccinating chickens are not always in accord with those obtained when virus is soaked from the food and titrated. It may be that chickens are better than saline solutions in removing virus, or that chickens will respond to inactivated virus given orally. Rehmani and Spradbrow (1995) presented evidence indicating that this can happen.

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Measuring efficacy
There are several methods in common use to measure the efficacy of vaccines. They vary in sophistication and they vary in cost effectiveness.

Circulating antibody
Chickens successfully vaccinated with Newcastle disease vaccines produce antibodies that are present in the plasma and that will react specifically with Newcastle disease virus. Various laboratory tests are available to detect and to quantify these antibodies.

The test used most commonly is the haemagglutination inhibition test. Surface glycoproteins on the envelope of Newcastle disease virus have the ability to attach to receptors on chicken red blood cells. When suspensions of red blood cells and virus particles are mixed, the red blood cells are agglutinated. Virus previously exposed to specific antibody loses its ability to haemagglutinate. Various versions of haemagglutination tests have been described. One commonly used with Newcastle disease virus is the micro-test described by Allan and Gough (1974a,b). This test is useful because the authors found that a specific titre (1 in 8 or 1 in 23) or higher gave a good indication of protection against potentially lethal challenge with virulent virus. This observation has been confirmed in subsequent field trials. Now it is not always necessary to undertake challenge experiments to obtain an indication of successful vaccination. In many village trials the moderate antibody titres induced by vaccination can be distinguished from the higher titres that result from challenge with virulent field virus. This is useful in monitoring vaccine trials.

The haemagglutination inhibition test is very useful in village studies. The requirements are simple ì chickens to donate blood, anticoagulants, simple buffers and plastic microtitre trays. The test procedure is sustainable in the absence of outside funding.

Haemagglutination inhibition antibody is only one indication that a series of immune phenomena has been initiated in an infected or vaccinated chicken. The antibody that is measured is not the total immune response. However with maternal transfer of immunity, only antibody from the hen is available to the immune chick. Rehmani and Firdous (1995) showed that the levels of passively acquired antibody needed to indicate protection are higher than the levels that indicate active protection.

The most common of the other tests for antibodies against Newcastle disease virus uses ELISA technology. This test is widely used to monitor the response to vaccination of commercial chickens. ELISAs do require some expensive equipment, but they are very sensitive and require small amounts of reagents. Sufficient quantities of antibody can be obtained from whole blood dried on paper discs or from feather pulp. For use with village chickens a standard ELISA will be required and it will need to be assessed for any correlation with protection.

The virus neutralization test is regarded as the gold standard for viral serology. This test depends on the reduction in infectivity that results when infectious virus particles and specific antibody are mixed. Embryonated eggs or cell cultures are required to quantitate infectivity. Haemagglutination inhibition antibodies and neutralizing antibodies correlate well, for example as shown by Rehmani and Firdous (1995).

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Other indicators of active immunity
The production of circulating antibody is not the only immune response available to the chicken. The other responses are more difficult to measure and there are no routine assays. Cell-mediated immunity has been demonstrated in chickens vaccinated with V4 vaccine (Jayawardane and Spradbrow, 1995a). The test used was leukocyte migration inhibition. Antibody responses did not correlate with cell-mediated immunity. Oral vaccination of chickens with V4 vaccine was also shown to induce the production of IgA antibody and an associated mucosal immunity (Jayawardane and Spradbrow, 1995b). The authors suggested that mucosal immunity might explain the resistance to challenge virus sometimes demonstrated in orally vaccinated chickens that had produced little or no circulating antibody.

Artificial challenge
The crucial test, and one not available when human vaccines are tested, is artificial challenge. Quality assurance protocols for avian vaccines usually include a challenge procedure in which vaccinated and unvaccinated hosts receive a defined dose of virulent challenge organism by injection. This process has usually been avoided in trials with thermostable vaccine. Challenge has nearly always been by contact. This mimics natural challenge. If the challenge virus is injected one component of the vaccinal immunity, mucosal immunity, has been bypassed. Certainly the dose of challenge virus cannot be defined in terms of 50% lethal doses (LD50). However if all control birds succumb, the challenge must be at least one 100% lethal dose (LD100).

Protection trials with thermostable vaccines conducted before 1998 have been reviewed (Spradbrow, 1993/94). There have been several subsequent projects with thermostable Newcastle disease vaccines in which protection has been demonstrated by contact challenge. These include trials in Ghana (Amakye-Anim et al., 1998), Tanzania (Foster et al., 1996, 1999), Ethiopia (Nasser et al., 1998), Vietnam (Tu et al., 1998), Zambia (Alders et al., 1994) and Philippines (Fontanilla et al., 1994).

Protection against disease is not protection against infection. Clinically normal chickens vaccinated with V4 vaccine and showing no clinical signs on exposure to virulent virus will excrete the virulent virus. This has been isolated from cloacal swabs and tracheal swabs for at least 14 days after challenge by Dr. Zubaida Mahmood (Mahmood, 1991). More importantly, these birds could infect susceptible in-contact chickens. Chickens with low pre-challenge antibody titres were more likely to excrete virulent virus and transmitted virulent virus more readily by contact than did chickens with high levels of vaccine-induced antibody.

As might be expected, when chickens are vaccinated under laboratory conditions, higher levels of protection are observed than under field conditions. With the thermostable vaccines, protection rates of 90 to 100% are often recorded. The technique of buy-back challenge is often used to measure field efficacy. Chickens that have been vaccinated under village conditions are purchased and subject to laboratory challenge. Selection cannot be truly random, but the purchasor should have no knowledge of any serological data that is available. The owner decides which chickens are for sale and the birds should be roughly matched for size to minimise aggression when they are housed together.

For example in Malaysia, chickens vaccinated under laboratory conditions with food-based vaccine showed better than 90% protection (Aini et al., 1990a). Under simulated village conditions (Aini et al., 1992) and under real village conditions with vaccine delivered by farmers (Aini et al., 1990b), protection rates were about 60%.

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Field challenge
It is surprisingly difficult to quantify field challenge. Constant monitoring is required to determine causes of death if disease-specific mortality is to be determined. A few such studies are available. Ronohardjo et al. (1988) were able to attribute losses in vaccinated and control flocks to Newcastle disease. In Tanzania Foster et al. (1999) had access to most of the chickens that died in vaccinated and control villages. About 70% of the deaths were attributed to Newcastle disease. Johnston et al. (1992) used intense serological monitoring to determine when village flocks were exposed to virulent Newcastle disease virus. He attributed the excess deaths over background levels during these periods to Newcastle disease. Effective field protection varied from 50% for adults to 78% for growers.

Census data
The collection of population data is a relatively simple way of indicating a probable response to vaccination. Where laboratory facilities are lacking, it is the only way. Consequently this approach is often used by NGOs, and the results are rarely published. There are many anecdotal accounts of vaccination being followed by an increase in the chicken population ì from Timor, Myanmar, Laos, Bangladesh and Ghana. From Indonesia (Ronohardjo et al., 1988), Sri Lanka (Jayawardane and Bandara, 1992) and Tanzania (Salum et al., 1997) come similar observations with comparisons with unvaccinated control villages.

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Eye drop
The most effective way to administer thermostable Newcastle disease vaccines is by eye drop ì providing the chickens can be caught. Unless the chickens are provided with some form of night housing this task becomes horrendous. There will usually be an antibody response to a single application of vaccine, and the vaccinator can be relatively certain that each chicken has received vaccine. Vaccine can then be applied by trained village vaccinators, or by the owners of the chickens. However, training is essential. When eye drop vaccination of commercial chickens can result in instances where only 40-50% of the birds receive properly applied vaccine (Anonymous, 1998), the need for proper vaccination technique is essential.

Plastic dropper bottles are relatively cheap. In parts of Vietnam thermostable vaccine is supplied in such bottles. In some countries the supply of dropper bottles is scarce. Tanzanian villages wishing to vaccinate chickens by this route apply the vaccine to the eye on the tip of a chicken feather. They use a similar technique for introducing medication to the eyes of their children.

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Nose drop and mouth drop
The chicken eye is a small and mobile target for a novice vaccinator. It is simpler to apply a drop of vaccine to a nostril and to see it inhaled. This technique may be less effective than eye drop application because the lymphoid tissue of the Harderian gland is not exposed to the vaccine.

Application of thermostable vaccine by mouth drop has also proved effective in Indonesia (Darminto and Daniels, 1992) and Malawi (Sagild and Spalatin, 1982). Dr. Urasri Tantaswasdi has suggested that vaccine could be diluted and placed in the mouth in larger volumes (1.0 ml) to reduce errors by unskilled vaccinators.

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Drinking water
Drinking water is not an option for vaccination in all areas. In the wet tropics chickens find their own sources of water. Where surface water is unavailable or where chickens are confined, application of thermostable vaccines in drinking water is possible.

Vaccination through the drinking water usually gives good results, sometimes similar to those obtained with eye drop vaccine. Examples of this approach can be found in Tu et al. (1998), Foster et al. (1999) and Tantaswasdi et al. (1992).

It might be incorrect to regard drinking water as a form of oral vaccination. The vaccination virus may infect through nasal or pharyngeal mucosal surfaces, rather than through various parts of the digestive tract. The quality of the drinking water and the type of container will influence the results.

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Food carriers
The initial studies with thermostable Newcastle disease vaccines concentrated on oral delivery. This was because the village chickens in Malaysia at that time were seldom provided with housing. A food-based vaccine was the only feasible approach. It was realised that food vaccines would not be as effective as, for example, eye drop vaccine. The expectation was that once villagers found that Newcastle disease could be controlled, husbandry practices would improve. The improvements would include housing and chickens could then be caught for more effective vaccination.

The author is convinced that eye drop application is the most effective way to deliver thermostable vaccines. However, the final decision on vaccination methods will depend on the national veterinary authorities and on the villagers who should always be consulted.

Most of the investigations of food carriers for thermostable Newcastle disease vaccine have been undertaken in Asia and Australia. There have been fewer studies on the foodstuffs, and especially the grains, that are available in Africa.

In Ethiopia, parboiled barley was shown to be a suitable carrier for I2 vaccine. Untreated barley, and parboiled or untreated sorghum were not effective (Nasser et al., 1998). In laboratory trials in Ghana, wheat bran was an effective carrier for V4 vaccine, while millet, maize meal, corn chaff and mill waste were not (Amakye-Anim et al., 1998). Vaccine supplied on boiled sorghum to village chickens in central Tanzania gave only low levels of protection, although this substrate had proved successful in earlier laboratory trials (Foster et al., 1996). In further trials with V4 vaccine in southern Tanzania, dried cassava granules were found to be an adequate food carrier (Salum et al., 1997).

In Asia suitable food carriers have been paddy (unhusked) rice, cooked white rice and cooked parboiled rice. Uncooked white rice is not a suitable food carrier. A detailed review is available (Spradbrow 1993/94). Sufficient food vaccine must be supplied so that each chicken in a feeding group has a chance of receiving vaccine. For most grains this is 7-10 g per chicken. For cooked white rice some 20 g is required for each chicken.

An innovation that deserves further investigation is the production of pellets that each contains a single bird dose of thermostable vaccine. Rehmani et al. (1995) described experimental lactose-based pellets that were effective. They suggested that such pellets could be suitably diluted in other chicken foodstuffs. If vaccine was produced in a central location, it would be easier to carry pellet vaccine (one pellet per dose) than grain vaccine (10 g per dose).

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Sprays and aerosols
Conventional Newcastle disease vaccines have sometimes been applied to confined village chickens as sprays. This technique has not been tested with thermostable vaccines in villages. However, under experimental conditions V4 vaccine has been effective as an aerosol (Schalkoort and Spradbrow, 1980).

Lateral spread
The thermostable variants of Newcastle disease virus, strains V4 and I2, spread readily between groups of chickens confined on solid floors. Spread is uncertain, or does not occur, when chickens are maintained on wire. This indicates the importance of oral/faecal spread with these viruses. Similar spread from vaccinated chickens to village chickens has been demonstrated under village conditions (Tu et al., 1998). Probably the conditions of night housing or of congregation around food and watering points will influence the efficacy of spread.

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Local production of vaccine
Thermostable vaccines can protect village chickens against Newcastle disease. Most of the scientific studies that were needed have been done. Why are these vaccines not being widely used? The residual problems are in part commercially based. These are commercial vaccines. They come in large dose formats, inappropriate for small village flocks, and they must be paid for in foreign currencies.

An attractive answer to this problem would seem to be local production of thermostable vaccine. Many countries now make avian vaccines for commercial chickens in their central laboratories. They do not usually use specific-pathogen-free (SPF) eggs. Could simple vaccines for village chickens also be made in these same central laboratories, or even in district laboratories. My group, supported by ACIAR, believes this is possible.

What are the requirements? A seed vaccine. We have produced thermostable strain I2 and seed material is available without cost to countries that wish to test, and possibly produce, the vaccine. We ask only that seed lot procedures be followed and that there is a policy of cost recovery, but not of exploitation of the village poultry producer. We believe that if eggs are obtained locally for vaccine production, no new infectious agents will be introduced into the area. The vaccines are produced from allantoic fluid, not from embryonic tissues. They are not injected into chickens.

We advocate the production of vaccine in a liquid form (wet vaccine) consisting of allantoic fluid in a suitable diluent. This avoids the expense of freeze-drying and the purchase of refined ampoules and labels. Wet vaccines can be distributed in volumes appropriate for flock size.

The other requirement is appropriate training. We have conducted dual workshops in African and Asian countries for ACIAR, GRM International and World Bank and FAO. Another is planned for AusAid. One workshop is designed for administrators and extension workers. It considers such topics as village chickens, Newcastle disease, thermostable vaccines, gender aspects of poultry production and extension activities.The second workshop is for laboratory workers who are given practical training in the skills of egg inoculation, harvesting allantoic fluid, bleeding chickens, preparation of serum and red blood cells and serology. These are the skills required for the production and testing of simple thermostable vaccines. Dr. Robyn Alders and the author usually present the administration/extension workshop and Ms. Sally Grimes the laboratory workshops. The latest versions of the workshop manuals ì Alders, R. and Spradbrow, P.: Newcastle Disease in Village Chickens. A Field Manual. and Spradbrow, P., Bensink, Z. and Grimes, S.: Laboratory Manual. Small Scale Production and Testing of Newcastle Disease Vaccine. ì are available on our rural chicken website:
http://www.vsap.uq.edu.au/ruralpoultry.

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Extension
The production of thermostable Newcastle disease vaccines and their testing under laboratory conditions were relatively easy tasks. Pilot village trials were more difficult. Delivering the vaccine to villages over whole regions on a regular basis will be extremely difficult. An infrastructure for the delivery of vaccine will have to be developed. Either farmers or village vaccinators will have to be trained to administer the vaccine. Systems for cost recovery must be developed. However the major task will be with the extension workers who must explain the concept of vaccinating chickens and have the concept accepted. The extension workers have the task of working with the very poorest people ì people who are often illiterate, sometimes innumerate, and whose spoken language may have no word for vaccine or no written form.

Participatory rural appraisals, especially those involving women´s groups, will often focus on village chickens and the problem of Newcastle disease. Village chicken projects will sometimes not proceed when the problems with Newcastle disease are realised, or are abandoned because of outbreaks of Newcastle disease. These projects are more likely to succeed if vaccination becomes part of the planning. The establishment of vaccination programs will depend on effective extension.

Some non-conventional extension approaches are being investigated by Dr. Robyn Alders. As well as simple pictorial flipcharts and radio broadcasts, she has commissioned a vaccination song to spread the vaccine message. Dr. Alders has also promoted a play dealing with the vaccination of village chickens. This was written and is performed by a troupe of professional actors who first attended meetings in villages.

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A new science of village chicken production
With the control of Newcastle disease in village chickens, all aspects of village chicken production become available for scientific investigation. If village chicken production can be optimised, there will be major benefits in terms of poverty alleviation and human nutrition. No animal industry in the developing world has greater potential for improvement than the production of village chickens.

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