Chapter 6: Health

In most family flocks, disease is an important problem. Although farmers are familiar with the signs and symptoms of disease (see Table 6.1), the underlying causes are less well known. Almost every farmer and most extension workers hold Newcastle Disease (ND) responsible for most deaths, and the disease has a local name in all languages.

Table 6.1 Signs of poultry disease observed by farmers in East Kalimantan villages, Indonesia

Source: Ramm et al., 1984

However, not all infectious diseases are due to the Newcastle Disease Virus (NDV). Digestive problems resulting in slow growth and diarrhoea may be the result of rancid feed or too much salt, and may also be symptoms of diseases such as coccidiosis, salmonellosis, or Gumboro Disease (Also called Infectious Bursal Disease [IBD]). ND often has the symptom of greenish faeces, which indicates a loss of appetite.

Poultry have highly developed and sophisticated respiratory systems. Their heart and breathing rate are faster than humans, and their body temperature is 5 °C higher. Their lungs are connected at the lower ends to a complex series of membrane-enclosed air sacs, which in turn are connected to air cavities in their major skeletal bones. These features contribute to their lightness and flying ability. The disadvantage is extreme susceptibility to respiratory infections caused by a wide range of bacteria, viruses and fungi. These infections become more of a problem in domestication, which usually involves some degree of increase in stock density - even if only for overnight accommodation - and thus increases the risk of cross-infection.

Inadequate ventilation of poultry houses results in a build-up of ammonia gas from poultry faeces, which contain urea. This can predispose the poultry to respiratory disorders, such as sneezing, running eyes and mucous discharges from the mouth. Providing good ventilation easily prevents this. More prolonged respiratory disorders are usually caused by diseases such as ND, Infectious Bronchitis (IB), Infectious Laryngotracheitis (ILT), Chronic Respiratory Disease (CRD) and diphtheria.

Coordination disorders such as paralysis, limping, twisted neck and slow movement may be caused by a variety of factors, such as physical injury, nutrient deficiencies and diseases, including ND (twisted necks or torticolis), Marek's Disease (paralysis), synovitis (tendon infections in which feet joints feel warm) and Avian Encephalomyelitis (AE).

COMMON DISEASES

The common diseases and disorders of free-range poultry may be either infectious or non-infectious, and are caused by a wide range of organisms or deficiencies. These are summarised in Table 6.2. Disease control is discussed in a later section of this chapter.

Table 6.2 Causes and examples of poultry diseases

INFECTIOUS DISEASES

Viral diseases

Viral diseases are some of the most important infectious diseases affecting poultry. They are characterised by not being able to be treated, but most can be prevented with vaccines. The more important viral diseases are outlined below.

Newcastle Disease (ND)

This disease (called Ranikhet Disease in Asia) spreads rapidly via airborne droplets spread by the coughing or sneezing of infected birds. The virus can be carried by wild birds, through contaminated eggs, and on clothing. As mortality is often 100 percent in young chickens, ND is probably the most important constraint to family poultry development. Birds of any age can be affected, although young ones are more susceptible. Mortality in older chickens is usually lower, but egg production is usually severely reduced.

The incubation period of three to five days is followed by dullness, coughing, sneezing and gasping. Rapid breathing is accompanied by a gurgling noise in the throat. The respiratory signs usually develop first and are sometimes followed by nervous signs, characterized by twisting of the neck, sometimes combined with dragging of wings and legs. Depending on the environment and the degree of resistance of the birds, not all symptoms may be shown, or they may be in a mild or subclinical form. Some farmers have observed that the twisting of the neck occurs only in birds that survive. Early loss of appetite results in a greenish diarrhoea. The most obvious diagnostic sign of ND is very sudden, very high mortality, often with few symptoms having had time to develop. Diagnosis of ND can be difficult from just the symptoms, as they are so varied, and as many other diseases share the same symptoms. For a discussion on the control of ND, see the “ND Control” section below. The high incidence of ND among family free-range flocks is due to the following factors:

• the prevalence of virulent strains (velogenic, viscerotropic and pneumotropic) in tropical countries;

• continuous contact with other domestic and wild species of birds (such as ducks and pigeons), which can carry the virus without showing the disease (Majiyagbe and Nawathe, 1981); and

• uncontrolled movement of birds between villages.

There is a seasonal pattern to outbreaks of ND (Sharma et al., 1986), influenced by:

• the arrival of migratory birds;

• changes in climatic conditions leading to stress, which predisposes birds to the disease;

• hot, dry and windy periods, which encourage airborne spread of the virus; and

• overuse of the few supply points of water available (during the dry season), which then become heavily contaminated with the virus.

Fowl pox

Fowl pox is still prevalent in many poultry flocks, for the following reasons:

• The fowl pox virus can remain alive in the pox scabs (which have fallen off the birds) for up to ten years, which contaminate the environment.

• Mosquitoes and other blood-sucking insects can transmit the virus.

The disease tends to be seasonal, occurring after mosquito breeding times. It is endemic in Papua New Guinea, where it is significant economically because the only NDV in the country is the non-symptomatic form (Sugrim, 1987). It is also a major disease in many other tropical countries.

Marek's Disease

Infection occurs early in life, and once a bird is infected, it can shed the virus in skin flakes throughout its life, if it survives. Clinical signs occur in young growing birds in the Acute Marek’s Disease (MD) form, characterised by high mortality from visceral tumours. Another peak of mortality occurs in the Classical MD form, characterized by nerve paralysis in the legs and wings of birds aged from 15 weeks to early in the laying period.

Mycoplasmal diseases

Mycoplasmas are not classified as bacteria or viruses, but as Pleuro-pneumonia-cocci-like organisms (PPLO). These are primarily associated with Chronic Respiratory Disease (CRD), a complex syndrome caused by Mycoplasma gallisepticum in partnership with bacteria (often E. coli), fungi and viruses (often Infectious Bronchitis). M. gallisepticum can be transmitted through the egg. Multi-age flocks, nutritional deficiency and water deprivation are important factors in the epidemiology of the disease in rural poultry flocks.

Bacterial diseases

Fowl Cholera (Avian Pasteurellosis)

This is a contagious septicaemia (caused by Pasteurella multocida) that affects all types of fowls. It is often transmitted by wild birds or other domestic birds, and spreads by contamination of the feed or water and by oral or nasal discharges from infected birds. The incubation period is four to nine days, but acute outbreaks can occur within two days of infection. In some cases, birds die within a few hours of showing the first signs, which vary depending on the form of the disease. The respiratory form is characterized by gasping, coughing and sneezing, while in the septicaemic form there is diarrhoea with wet grey, yellow, or green droppings. In the localized form, the signs are lameness and swelling of legs or wing joints. In acute cases, the head and comb change colour to dark red or purple. If the infection is localized in the region of the ears, a twisted neck (torticolis) can sometimes be observed. In chronic cases, the comb is usually pale, with swellings around the eyes and a discharge from the beak or nostril. Fowl Cholera is common everywhere among free-range village flocks, because they are comprised of different species and are in continuous contact with wild birds.

Pullorum (Bacillary White Diarrhoea)

This is an egg-transmitted disease (caused by Salmonella pullorum) that spreads during incubation or just after hatching. White diarrhoea can be seen from three days to several weeks of age. The chicks refuse to eat, keep their heads tucked in and their wings hanging down. They huddle together and make a peeping sound. Mortality in the acute form ranges from 20 to 80 percent, and in the chronic form is around five percent. In the chronic form, the signs are a marked swelling of the hock joints, poor feather development, lack of appetite and depression. Table 6.3 shows the results of a survey in Zaria, Nigeria, conducted by Adesiyun et al. (1984) for Pullorum antibodies, which indicate a past infection with the bacteria.

Table 6.3 Prevalence of Salmonella pullorum antibody in chickens in northern Nigeria

Source: Adesiyun et al., 1984

The free-range stock sampled was indigenous, and the other two groups were exotic. As the age of the birds in the free-range survey was not known, birds not in lay were counted as young.

Fowl Typhoid

Fowl typhoid is caused by Salmonella gallinarum, and commonly affects adult fowls. When it occurs in young birds, the signs are similar to those of S. pullorum. The incubation period is four to five days, and two days later the birds become depressed and anorexic. The colour of the comb and wattles becomes dark red; the droppings become yellow and the birds close their eyes and keep their heads down. Usually the affected chickens die within three to six days. Pullorum and fowl typhoid complex are both prevalent under free-range conditions.

Avian Salmonellosis (Paratyphoid)

Salmonellosis is usually used to describe infection with any organism of the Salmonella group other than S. pullorum or S. gallinarium. In countries with intensive poultry systems, poultry meat and eggs are a major source of infection for humans. The opposite may be true of family poultry, with humans infecting poultry. Ojeniyi (1984) reported that S. hirschfeldii was isolated from cloacal swab samples in fowls and from an adult human male in the same village.

Parasitic diseases

External parasites (ectoparasites)

These are very common in scavenging poultry, and include:

• Lice: these live on the skin of the birds, especially around the cloacae and under the wings. The irritation they cause can lead to reduced production. Lice species commonly found on poultry are Menacanthus straminens, Lipeurus caponis, Monopon gallinae, Goniodes gigas and Chelopistes meleagride.

• Mites: these are troublesome ectoparasites, which hide in the cracks of housing and perches, and come out only at night. They are bloodsuckers and lower egg production. Mites such as Dermanyssus gallinae can also transmit the bacteria Borrelia, which causes fever, depression, cyanosis and anaemia (spirochaetosis).

• Ticks: a heavy infestation can produce severe anaemia and, in extreme cases, death due to blood loss. Argas persicus is particularly dangerous, being the vector of several blood parasites such as the haemoprotozoa and microfilaria. In Malaysia, it was reported (Sani et al., 1987) that out of 201 blood samples taken from village birds, more than 100 contained Leucocytozoon sabrazesi, 30 had microfilaria, and six carried Plasmodium gallinaceum (Avian malaria). Avian malaria infection is much higher among exotics and cross-breeds.

Internal parasites (endoparasites)

The more important internal parasites are:

• Helminths (worms): these are common in scavenging poultry, especially nematodes and cestodes. Ssenyonga (1982) showed that worms were a major cause of lowered egg production of scavenging poultry in Uganda, the most commonly found being Ascaridia galli (Round Worm), Heterakis gallinae (Caecal Worm), Syngamus trachae (Tracheal Worm) and Raillientina spp. (Tape Worm).

• Protozoa: the most pathogenic are the coccidiosis disease species of Eimeria tenella and E. necatrix. Coccidiosis is a common parasitic infection in scavenging poultry. It affects mostly young birds, and the most important signs are emaciation, thirst, listlessness, ruffled plumage, bloodstained faeces and birds huddling together. Surveys in Southeast Asia and East Africa showed that 73 and 47 percent of birds, respectively, had positive faecal samples of Eimeria spp. (Eissa, 1987). The presence of the coccidia organism in faecal samples indicates an infection, but not necessarily at clinical disease levels. Like antibody presence in blood samples, it may indicate a degree of immunity. This should not be “treated”, as doing so eliminates the immunity.

Fungal diseases

Mycotoxicosis

The fungus Aspergillus flavus commonly grows on stored feed ingredients where moisture content is over eleven percent, especially cereal grains (such as maize [corn]) and oilcake meal (such as groundnut [peanut] meal). The aflatoxin called mycotoxin is the specific toxin produced by A. flavus. The toxin itself may remain after all sign of the fungus mould is gone. Ducks are more vulnerable to the toxin (with a lethal dose in the feed of one part per million [ppm] of aflatoxin) than chicken, which can tolerate up to four ppm. In acute forms of the disease, mortality can be as high as 50 percent. Common adverse effects include immunosuppression, reduced growth in young stock and reduced egg production in hens (Smith, 1990).

Aspergillosis

This disease is also called airsaculitis. The fungus Aspergillus fumigatus causes the disease by growing as a fungus in the lungs and interconnected air sacs. The fungus grows on damp litter or feed, and the bird breathes in the spores, which grow into easily visible lesions as green and yellow nodules, which can completely fill the lungs.

NON-INFECTIOUS DISEASES

Deficiencies

Poultry health is also affected by nutritional and environmental factors, such as insufficient feed or feed deficiencies. A high mortality rate among chicks during the first days or weeks after hatching may be caused by insufficient feed and water. A high mortality in adult birds may be due to nutritional problems, such as salt deficiency.

Energy and protein deficiencies and imbalances can arise when the feed contains insufficient quantities of these nutrients, resulting in poor growth in young stock and a drop in egg production and egg weight in laying hens. Mineral and vitamin deficiencies may result in poor growth, low production or death. Vitamin D deficiency causes rickets (bone deformities) in young chicks and, if combined with a calcium deficiency, in chickens of all ages. A lack of manganese results in deformities of the feet of older chickens.

Toxicities

An excess of certain nutrients, especially minerals, can cause abnormalities. An excess of common salt (NaCl), for example, results in deformed eggshells as well as increased water consumption, and if drinking water is restricted (as is often the case with free-ranging birds), signs of toxicity may develop. Free access to feed of high carbohydrate and low fat, combined with lack of exercise, high temperatures and stress, can cause Fatty Liver Syndrome, which can result in high mortality.

Ingestion of toxic plant parts (such as leaves, seeds and sap) is a common hazard for free-range birds. Some toxins are produced by micro-organisms, such as those liberated by the bacteria Clostridium botulinum and C. perfringens, both found in the soil. C. perfringens causes necrotic enteritis, caused when the bacteria multiplies in the favourable conditions of the digestive tract and liberates a potent toxin that results in high mortality. Occasionally affected birds show anorexia, depression and diarrhoea, but most die without showing any clinical signs. C. botulinum causes botulism disease, which is acute food poisoning. This is more common in ducks, which show the nervous symptoms of neck bent down and feathers falling out easily when lightly pulled. Botulism results from the bird eating rotting vegetable scraps, which contain the toxins produced by the C. botulinum. Household vegetable scraps which are not regularly removed are a potential hazard for botulism.

EPIDEMIOLOGY

Management system effects

Although nearly all the important poultry diseases are found under all types of management, the pattern of disease in free-range birds is different from that seen in intensive poultry production. Free-range flocks usually comprise different species of all ages, and are constantly exposed to the weather, environment and seasonal outbreaks of disease, as well as to germs and parasites found in the soil and in wild birds and animals.

In a 15-year study of the incidence of poultry diseases in northern Nigeria, Sa'idu et al. (1994) found viral infections (such as ND in chickens and pox in turkeys) to be the most common cause of disease, although concurrent viral infection with parasites constituted about half the cases studied (see Table 6.3). They concluded that viruses and parasites caused the most important diseases in indigenous chickens and that they were seasonal in their onset.

Table 6.4 Diseases affecting local chickens and turkeys in Zaria, northern Nigeria

Source: Sa'idu et al., 1994

Another study (Adene and Ayandokun, 1992), which looked at the changing pattern of diseases in southern Nigeria over the period from 1949 to 1955, found that mortality in the free-ranging flocks at the University of Ibadan was due mostly to the following:

• Helminthiasis, due to Raillietina, Heterakis, Ascaridia, Capillaria, Tetrameres and Syngamus spp.;

• Pediculosis, due to Menopon, Gonoeodes, Goniocotes and Lipeuris spp.; and tropical poultry mites (Ornithonyssus bursa) in chickens, and Numidilipueria tropicalis in guinea fowls.

These parasitic infections were greater causes of mortality than Newcastle Disease at that time.

Another survey of backyard chicken flocks in Zimbabwe (Kelly et al., 1994) tested 450 blood samples from 52 flocks, and found Infectious Bronchitis (IB) in 85 percent and Newcastle Disease (ND) in only 27 percent of the samples (see Table 6.4). A possible explanation for the lower frequency of ND is that the mortality is usually much higher from ND than for IB, so fewer birds survive to be counted.

Similarly, in Zambia, a survey based on 2000 blood samples (Alders et al., 1994) found that the mean seroprevalence of Newcastle Disease was 37 percent, which varied between 29 percent in the northern province and 51 percent in the Copper-belt province. A summary of the relative importance of poultry diseases gathered from other sources is tabulated in Table 6.5.

Table 6.5 Disease status in backyard chicken flocks in Zimbabwe as shown by blood testing

Source: Kelly et al., 1994

Table 6.6 Relative importance of family poultry diseases

Poultry species effects

In tropical countries, Newcastle Disease is considered to be the most important disease of village flocks because of its high mortality, which is above 70 percent in most African countries. However, not all poultry species are equally susceptible. Guinea fowl, although sometimes affected, appear to have better resistance to ND even when kept with chickens. They are however more susceptible to Trichomonas, to which chickens appear to be immune. Ducks are not thought to be susceptible to ND (although they are significant carriers of the disease), or to most other common diseases of chicken, but they succumb easily to diseases specific to ducks, such as:

• Duck Virus Enteritis (Duck Plague): this is an acute and highly contagious disease of ducks, with a mortality rate of up to 100 percent.

• Duck Virus Hepatitis and Mycotoxicosis: these pose a great danger for ducklings. Mycotoxicosis is mostly contracted from ingesting aflatoxin from mouldy compound feeds; a dose of 0.75 ppm can kill a duckling.

• Duck Cholera (Pasteurella multocida infection): this is a widespread disease of ducklings in village flocks, and chickens can also be infected.

• Pasteurellosis (Pasteurella anapestifer): this is an important disease of ducklings, while Escherichia coli infection (Colibacillosis) is a septicaemic disease of growing ducks. Chickens can also be infected with E. coli.

The above diseases are largely responsible for the huge losses of ducklings that are a feature of free-range duck production.

Although salmonellosis is not a major disease in ducks, duck eggs are a significant source of salmonellosis in humans. This may explain the taboo against touching duck eggs prevalent in many cultures, particularly in Africa. Duck eggs should not be stored in contact with vegetables that will be eaten raw, such as carrots, lettuce and cabbage.

Season and age effects

Disease patterns vary according to the season. Newcastle Disease is more serious during the dry season. In Thailand, Pasteurellosis, Coryza and streptococcal infections also occur more frequently in the dry season, and Fowl Cholera, Colibacillosis and Pseudomoniasis in the rainy season (Thitisak, 1992). In northern Nigeria, where Sa'idu et al. (1994) studied 522 cases involving 8 800 chickens, ND accounted for 30 percent of all cases. Of these, 38 percent occurred immediately before the dry season of October to December, and only 10 percent during the rainy season of July to September. As for Fowl Pox, more outbreaks occurred in the rainy season and were highest in the month of July, and about 60 percent of the outbreaks affected young chicks. In Thailand, Thitisak et al. (1989) noted that a catastrophic mortality had occurred in March in both 1987 and 1988, this being the late dry season when early storms cause sudden drops in temperature which chill the birds. They also found that chickens under two months of age (normally a rapid growth-rate phase), and those over six months of age (in the process of becoming sexually mature) were more susceptible to infectious diseases (see Table 6.6).

Table 6.7 Cause-specific mortality rates per 100 birds at risk

Source: Thitisak et al., 1989, and Janviriyasopak et al., 1989.
Data from surveys in 1987 of 2231 and 3239 birds

Need for epidemiological studies

Epidemiological studies of village poultry are essential for the development of appropriate village-based poultry health programmes. These have been attempted in many countries, but the work undertaken in Thailand (Janviriyasopa et al., 1989) will be used as an example.

The North-Eastern Regional Veterinary Research and Diagnostic Centre, Tha Pra, Khon Kaen, Thailand, with assistance from the German Agency for Technical Cooperation (GTZ) and the Department of Veterinary Clinical Sciences of Massey University, New Zealand, embarked on a long term-study (“Health and Productivity of Native Chickens”). This was part of a programme of epidemiological investigations of factors affecting livestock productivity in the region. The objective of the study was to decide on the priority of the problems for which control programmes could be developed within the regional Basic Poultry Health Service.

In selected villages, about 15 families with flocks of 15 to 20 birds were recruited. In most of the villages, vaccinations against ND, Fowl Pox and Fowl Cholera were carried out in order to encourage interest. Two villages were paid to represent a totally unvaccinated control population. Birds were wing-tagged and grouped by age:

• under two months;

• two to six months;

• six to twelve months;

• one to two years;

• two to three years; and

• over three years of age.

During each visit, the number of eggs and chickens were weighed, counted and scored, and blood was collected from the wing vein for determination of ND titre and for Pullorum, CRD, IB and Gumboro (IBD) tests. Each tagged bird was subjected to health, feather and ectoparasite scoring. Sick and dead birds were collected for pathological examinations at the laboratory, in order to identify the cause of death or illness, and refrigerators were provided in some villages to store dead birds for later examination. Dead or diseased birds were exchanged for healthy birds in order to examine as many as possible, but as the villagers would sometimes eat dead or dying birds, most of those exchanged tended to be the immature birds which owners were less willing to eat. By calculating age-specific mortality rates and then determining cause-specific rates within each age-group, the contribution of each disease to the mortality within an age-group was determined. A questionnaire was used to gather additional information.

The objectives of the survey were to establish:

• a productivity index;

• population dynamics;

• the importance of common diseases, their incidence and prevalence;

• the average life span of birds;

• patterns of disease outbreaks; and

• the relationship between disease and production levels.

The parameters used for the survey were:

• egg production;

• egg hatching rate;

• number of deaths in each age group;

• weight gain of growers;

• number of birds killed for eating;

• number of birds sold; and

• unexpected losses.

Some of the results of the survey are seen in Table 6.6 above. Poor management of eggs, hatching and young chicks, as well as malnutrition, particularly in the dry season, were found to be important predisposing factors to infectious diseases and parasitic infestation (Thitisak et al., 1989).

DISEASE CONTROL IN FAMILY FLOCKS

Non-medical disease control

The most economical and effective means of preventing non-viral diseases is improved management and nutrition, of which the most important aspects are hygiene, housing, flock structure, and young chick care and feeding.

Hygiene

The following simple hygiene measures, which help in disease prevention, were recommended by the FAO/UNDP Small Stock Development Project in North Kivu, Zaire (FAO/Anonymous, 1989):

• Droppings, feathers and dead birds are sources of pathogens and should be removed from overnight housing and the free-range compound, and then properly disposed of. This will also reduce the incidence of external parasites.

• New arrivals to the flock should be isolated. Birds bought or received as gifts should be quarantined in a basket or cage for at least 15 days; if they remain healthy, they can then join the flock.

• All new arrivals should be treated for ectoparasites and endoparasites as well as vaccinated on arrival if possible.

• Sick birds should be isolated or slaughtered promptly, and dead birds buried.

• The litter in the poultry house should be turned frequently and changed if wet.

• Overnight security baskets should be put in the sun to dry properly or suspended near a fire during the rainy season.

• Feeders and drinkers should be cleaned frequently.

• Broken pots used as drinkers should be heated over a fire before refilling.

• The poultry house or basket should be regularly disinfected every two months.

Housing

Simple improvements and maintenance can be carried out when the poultry house is not in use. Important factors in good housing are:

• Ventilation: if poultry baskets are used for overnight housing, they should not be covered with cloths or sacks. Huts, coops and baskets should not be placed near dunghills or pit latrines.

• Proper spacing: overcrowding should be avoided, and numbers of poultry should be restricted to the space available. Weaned chicks and growers should be kept in separate overnight housing. Laying and brooding nests should be left undisturbed.

• Separate species: it is better to keep only one species of poultry but if this is not possible, the species should be housed separately overnight to avoid the spread of disease.

Flock structure

Of all the common free-range poultry species, chickens are the most susceptible to disease. Ducks, geese and guinea fowl are often symptom-less carriers of chicken diseases, or have mild forms of them. This represents a common source of infection in chickens, while the opposite is rare. Therefore in mixed flocks special attention should be paid to the health of chickens. Separation into different species and age groups may not be possible, but simple devices such as creep cage-baskets may be used as a temporary measure for procedures such as vaccination of chicks or special feeding.

Feeding

The importance of nutrition in flock health is well known. There is a need for further research into alternative feeds for rural poultry, which avoid the use of grain for human consumption (see Chapter 3).

Medical disease control

Simple medical control measures appropriate for free-range village flocks include:

• Vaccination against Newcastle Disease, Fowl Pox and Fowl Cholera.

• Deworming for internal parasites in a mixed flock, with a polyvalent poultry dewormer such as Piperazine (added to drinking water). With guinea fowl, a dewormer against Trichomonas should be used.

• Treatment for external parasites. Insects and other external parasites build up quickly in poultry huts, coops and baskets. There are effective traditional methods against ectoparasites. All the surfaces of the basket, coop or hut can be sprayed with a suitable insecticide, using the same type of hand-pump used for spraying mosquitoes. This procedure should only be carried out when the house is empty in the morning, and the birds should not be allowed back inside until evening. External parasites living on poultry can best be treated by adding powdered mothballs (naphthalene) and ash to the dust bath area. Ash dust is more abrasive than ordinary soil dust, and thus removes the waxy coating of the insect exoskeleton when the bird takes a dust bath. If enough of the waxy coating is removed, the insect will dehydrate and die.

Newcastle Disease control

There are three general approaches to the control of ND:

• Hygiene: this is always important, especially in the control of ND in semi-intensive systems where birds are confined within a fenced yard or house. Hygiene includes measures such as cleaning, disinfection, limiting access to wild birds, and personal hygiene of the farm staff.

• Slaughter of infected flocks: this is a drastic measure, which has been successfully employed in isolated regions or islands that are essentially free of the disease.

• Vaccination in combination with appropriate hygiene measures: this remains the most effective way of controlling ND.

Newcastle Disease vaccines and vaccination campaigns

For viral diseases, vaccination is the only form of prevention. A proper vaccination campaign can rapidly and significantly minimize losses due to disease. In Indonesia, after an ND vaccination campaign, mortality in village flocks dropped from 50 to 8 percent and the population of chickens increased from 900 to 3 500, representing a 250 percent increase (Moerad, 1987). ND vaccines are available in either “live” or “dead” forms:

• Live vaccines are fragile and have very precise rules for use, requiring a cold chain up to the point of application to the bird. Their effectiveness is reduced if there are residual antibodies in the chickens. This is especially important with maternal antibodies, which are retained by the newborn chick and protect it for up to ten days. Even a low level of maternal antibody reduces the effectiveness of gaining immunity from the vaccine. Group vaccination can be administered in very clean drinking water in very clean drinkers, or by aerosol (in enclosed buildings). The conventional live vaccine, Hitchner B1, cannot be given in drinking water to village flocks, but can be given using the eye-drop method, which has the advantage that each bird receives its dose individually. This has been successfully carried out in Morocco, where it led to a considerable reduction in mortality (Bell et al., 1990a). The eye-drop method should be used only if there are veterinary personnel available for training vaccinators.

• Killed vaccines give good immunity but require priming with a live vaccine for best results, unless a natural infection has already served this purpose. They have been used successfully in Burkina Faso (Verger, 1986, and Ouandaogo, 1990). Killed vaccines have two disadvantages: they must be administered individually by intramuscular injection, which requires some veterinary training, and - as with live vaccines given by eye-drops - the birds must be caught, a cumbersome task which cannot be avoided with the techniques presently available. Killed vaccines have the advantage that they do not require as rigid a cold chain as do live vaccines, and, because they have a consequently longer shelf life, they can be used in more remote locations. They appear to be most effective in birds that have already acquired some degree of immunity from natural NDV exposure or an initial live vaccine inoculation. Another advantage of killed vaccine is that the virus-killing chemical used in its preparation also acts against all other possible vaccine pollutants, such as unwanted viruses, bacteria and other micro-organisms. Killed vaccines are usually cheaper than live vaccines because the product is more durable, but this is only viable for large flocks. Evidence from Burkina Faso and Niger indicates that because each vial contains at least 100 individual doses, there was a high degree of wastage, as the villagers only managed to vaccinate a few dozen birds a day at best. Much of the advantage gained in efficient manufacturing, packaging and dispatching can be lost at this final stage if the contents of the vial are not fully utilized.

Constraints to rural flock vaccination

The low success rate of ND vaccination is almost entirely due to inactivation of the vaccine because of the absence of an efficient cold chain. This in turn is aggravated by the scattered distribution of village flocks, bad road conditions and lack of transport. In Indonesia, the period between the vaccine leaving a central laboratory and vaccination in the village can be several days.

Vaccination programmes should be carried out at appropriate times. There are seasonal patterns to outbreaks of ND and Fowl Pox, the diseases for which vaccination campaigns are usually carried out. The farming programme should be taken into consideration. In Thailand, for example, ND vaccinations are carried out in the dry season when the farmers are not involved with rice cultivation (Danvivatanaporn, 1987).

It has frequently been said that lack of motivation is a major cause of the low vaccination rates in rural areas. To overcome this problem, a pilot project in Thailand organized a training course in primary schools for children of 12 years of age. They were introduced to the concept of the advantages of vaccination against ND and taught to recognise the simple clinical signs of the disease. Another training course for livestock volunteers was given to five selected young village leaders. Upon return to their village, they gave their services and advice on ND control to the village, free of charge. It was hoped that the increased knowledge and commitment would result in better motivation of the villagers to develop their own vaccination programmes.

In Bangladesh, the subdistrict livestock officer organizes special training in vaccination and livestock husbandry, in consultation with the local subdistrict committee chairman and members, who then select the farmers and volunteers for vaccinator training. The course is divided into two phases: theoretical and practical. On completion, the vaccinators are supplied (at cost) with vacuum flasks and other necessary equipment, to vaccinate their own and other villagers’ flocks, for a fee. They then return the empty vials and receive fresh vaccine. The Department of Livestock Services runs the livestock disease control programme for small farmers as part of its poultry development programme, usually with the assistance of local non-government organization (NGO) groups (Bangladesh Department of Livestock Services, personal communication 2000).

The ND V4 vaccine

This is a new vaccine, which has the following advantages:

• It is a heat-tolerant vaccine selected from non-virulent forms of NDV naturally occurring in Australasia. In an experiment conducted in Malawi, young chicks which received the vaccine after it had been exposed to ambient temperature for six weeks developed high antibody titres and resisted challenge with a velogenic, viscerotropic ND virus strain (Sagild and Spalatin, 1982).

• After about half of the birds of a household flock are caught and vaccinated, and if all the birds are then confined together overnight, the vaccine will spread naturally from vaccinated to unvaccinated birds. The antibody response of these “naturally” vaccinated is comparable with that of the vaccinated birds (Young, 1991).

• Unlike conventional vaccines, which cannot be given if the birds are under stress, the ND V4 is so mild that it can be given to birds under stress.

• The vaccine can be administered by mixing with feed, although the eye-drop method of inoculation is much more effective.

Alders et al. (1994) reported a laboratory vaccine trial with the heat tolerant V4 and the Hitchner B1, in which vaccination with the Heat Resistant (HR) V4 gave slightly higher HI (Haemaglutination Inhibition) titres than vaccination with the Hitchner vaccine. The live HRV4 vaccine was used successfully in the control of ND in village chicken flocks in Malawi (Saglid and Haresnape, 1987). In these field trials, vaccinated birds showed a good immune response when the vaccine was administered through very clean drinking water in very clean drinkers. However, this method can only be used in the dry season, because of the difficulty of confining the birds in completely dry conditions during the rainy season.

A Heat Resistant derivative of the V4 vaccine added to feed was used successfully in Southeast Asia (Copland, 1987). It did not require individual doses, and it spread between birds to some extent. The choice of feed to be used as the vaccine carrier was crucial. Commercial feed as a vaccine carrier has two disadvantages: firstly, its composition varies, and certain components can prove toxic to the vaccine virus; and secondly, prepared feeds are expensive, and one of the essential factors in a smallholder poultry vaccination scheme must be low cost.

In Malaysia, the vaccine is sprayed onto wheat while it is being mixed in a simple, locally manufactured auger-driven mixer. Up to 10 000 doses of vaccine can be mixed at a time. The feed-virus mixture is then put into small plastic bags, each containing 200 g (enough for 20 birds). Even after 45 days storage at ambient temperatures, the bagged vaccine provides up to 90 percent protection.

In other Asian countries where wheat is not readily available, rice has been used. Both rice and wheat have a water-soluble viral inhibitor in the grain coat; thus washed grain maintains a higher virus titre than unwashed grain. Washing is carried out by soaking the grain for 24 hours and then mixing the vaccine with the wet grain. At the village level, the required amount of washed grain (10 g per bird) is measured into a plastic bag and the vaccine added. After mixing thoroughly, the feed-vaccine mixture is fed directly to chickens. It is important to provide creep-feeding for the chicks and growers, otherwise the older birds get all the vaccine.

The V4 strain is being tested in several African countries (Ethiopia, the Gambia, the United Republic of Tanzania, Zimbabwe and Nigeria). The first field test of HRV4 (Heat Resistant V4) was conducted in the Gambia (Jagne et al., 1991). In July 1993, FAO and the governments of the Gambia and Ethiopia signed a Technical Cooperation Programme project agreement, "Assistance to Rural Women in protecting their chicken flocks from Newcastle disease” (TCP/RAF/2376T). The objectives were to introduce and evaluate, under African rural conditions, the HRV4 oral vaccine, which had proved effective in Southeast Asia, and to involve rural women in the implementation of the project. In both countries, repeated oral vaccination (up to four times at regular intervals) did not generally produce the high immunity found in Southeast Asia. However, parallel groups inoculated by eye-drop did achieve high levels of immunity.

In 1995, confined laboratory trials of ND HRV4 feed-based vaccines were carried out in Ethiopia. Oral vaccination, administered in barley, wheat and crushed maize feeds, was compared with eye-drop vaccination and with an unvaccinated control. Eight days after the birds were challenged by the ND virus, the survival rates were: 80 percent of the eye-drop vaccination group; 20 percent of the oral vaccination groups; and none of the control group. Of the three feeds used in the oral vaccination trials, barley proved to be the most efficient vaccine carrier in terms of providing disease resistance, followed by maize and lastly wheat.

Zimbabwe was free of ND from 1986 until 1994, when suddenly infection was introduced from South Africa. Because of unrestricted poultry transport, it spread rapidly across most of the country. During 1994/95, ten million rural chickens nationwide were vaccinated at a project cost of US$1.50 per bird. In early 1996, a FAO-assisted Technical Cooperation Programme was initiated to establish a community-based programme for the prevention of ND epidemics in rural chickens. The approach combined the immediate administration of the V4 vaccine using the conventional eye-drop vaccination method with community-based trials using the feed-mixed oral method under Zimbabwe conditions. Thus it was hoped to avert other epidemics and generate data for planning regular feed-based vaccination of rural chickens as part of the veterinary extension service.

Although V4 has shown promising results in overcoming the major constraints associated with ND vaccination, there are still problems with its use in scavenging systems at the village level, where feeding is irregular and poultry are hatched, bought and sold throughout the year. In all countries, laboratory trials to assess various feeds as carriers and to familiarize technicians with the vaccine and virulent challenge systems should be conducted before field trials. Production data should be collected before, during and after vaccination. This is essential to evaluate the efficiency of vaccination.

Traditional poultry disease control in Africa

Traditional treatment and control of disease is important, as most developing countries cannot afford to import or subsidize veterinary drugs and vaccines for smallholder farms. There is also increasing concern about the effect of synthetic drugs on animals and the environment. Ojeniyi (1985) found a correlation between the use of antibiotics and drug resistance among E. coli strains isolated from intensively managed poultry at the University of Ibadan, Nigeria. All 1248 E. coli strains from the University poultry farm, and 2196 strains from a commercial poultry farm in Ibadan, were resistant to tetracycline, streptomycin and sulphonamide. In contrast, all 2284 strains isolated from free-range town and village poultry were sensitive to these drugs.

Most of the information presented below on traditional medicine used for poultry has been collected informally (Bizimana, 1994), and has not been scientifically tested. The main reason for its inclusion here is to encourage formal research.

Viral diseases

• Newcastle Disease: in Nigeria, either Lageneria vulgaris or the bark of Parkia filicoidea are given to the flock in drinking water (Nwude and Ibrahim, 1980). In Zimbabwe, the leaves of Cassia didymobotrya or the latex of Euphorbia matabelensis are given in drinking water (Chavunduka, 1976). In the United Republic of Tanzania, in the regions of Arusha and Kilimanjaro, the stem of Euphorbia candelabrum Kotschy var. candelabrum or the fruit of Capsicum annuum together with the leaves of Iboza multiflora are given (Minja, 1989).

• Fowl pox: in Zimbabwe, the leaves of Aloe excelsa are soaked and the extracted fluid is added to drinking water (Chavunduka, 1976). A poultry disease named “Yoko yoko” by the Fulani of Mauritania, Mali and Senegal, is a serious epidemic, affecting hens of all ages. The exact cause of the disease is unknown, but Ba (1982) suggested that it might be a type of Fowl Pox. The signs and symptoms, as described by the Fulani, are dejection, breathing difficulties with the emission of the sound 'yok yok' and sneezing. Obstruction of the nostrils by yellowish crusts makes the birds breathe through their beaks, which are also encrusted. Lack of appetite and purulent conjunctivitis have also been noted. Eventually, the birds suffocate and die. The mortality rate can be as high as 100 percent in growing chickens, but some adults survive. The birds are systematically slaughtered and the hen house burnt to prevent spread. The symptoms, as described above, are indicative of the “wet” form of Fowl Pox, where eventually the bird suffocates from a cheesy growth in the trachea. The pox lesions are sometimes less obvious in this type of Fowl Pox disease, but they can be found on close examination.

• Colds: in Nigeria, Hibiscus subdariffia is pounded, mixed with drinking water and given to birds with ruffled feathers (Nwude and Ibrahim, 1980).

Protozoan diseases

Coccidiosis: in Nigeria, Lageneria vulgaris is dipped in the flocks’ drinking water (Nwude and Ibrahim, 1980).

Bacterial diseases

Fowl Cholera: in Nigeria, the fruit of Adansonia digitata is broken and soaked in the birds' drinking water. The fruit of Capsicum annuum is mixed with soot from the ceilings of thatched buildings (Hausa: Kunkunniya) and given in drinking water (Nwude and Ibrahim, 1980).

Metabolic and infectious diseases

• Abdominal disorders: in Nigeria, the young leaves of Boswellia dalzelii are chopped and soaked in water, and the extracted fluid is given as a diarrhoea treatment (Nwude and Ibrahim, 1980). In South Africa (Natal Province), Leonotis leonurus Ait.f. is given to treat both yellow and green diarrhoea (Watt and Breyer-Brandwijk, 1962). In Southern Africa, farmers use a cold infusion of the leaves of Aloe saponaria Haw. to treat enteritis and indigestion in poultry (Watt and Breyer-Brandwijk, 1962). In West Africa, the chopped leaves of Pergularia extensa are fed to turkeys suffering from diarrhoea (Dalziel, 1937). In Zimbabwe, the bulb of Adenium multiflora is soaked in water for 12 hours, after which the sick animals are drenched to treat for bloody and watery diarrhoea. For the same purpose, the latex of Aloe chabandii or Euphorbia matabelensis is given in drinking water (Chavunduka, 1976).

• Blood in the excreta: in Zimbabwe, the bark of Cussonia arborea is soaked in water, and the sick birds are drenched with the fluid (Chavunduka, 1976).

Poor growth and low production

In Nigeria, the fruit of Cucumis pustulatus is mixed with bran and placed in drinking water to help growth, prevent disease and increase egg production. The fruit of Cyperus articulatus is also placed in drinking water (Nwude and Ibrahim, 1980). In West Africa, the fruit of Cucumis prophetarum or C. pustulatus is placed in drinking water to help growth, prevent disease, discourage predatory hawks and increase egg production (Dalziel, 1937).

Ectoparasites

• Various ectoparasites and parasitic diseases: in Nigeria, the dried leaves and twigs of Guiera senegalensis Lam. are burned in poultry houses to reduce ectoparasites (Nwude and Ibrahim, 1980). In Bulawayo, Zimbabwe, Thamnosma africana Engl. is placed in chicken pens to repel fleas and ants (Watt and Breyer-Brandwijk, 1962).

• Lice: in Nigeria, the leaves of Bandeiraea simplicifolia are placed in hen houses to kill lice (Dalziel, 1937; Nwude and lbrahim, 1980). Ash from the burnt leaves of Nicotiana rustica, N. tabacum or Carica papaya is rubbed into feathers to protect against infestation (Nwude and Ibrahim, 1980). In Senegal, the leaves of Calotropis procera Ait.f. are used to kill lice on poultry (Dalziel, 1937; Watt and Breyer-Brandwijk, 1962).

Endoparasites

Worms: in Nigeria, the fruits of Cucumis prophetarum and Solanum nodiflorum are used by the Hausa people to treat poultry for worms (Nwude and Ibrahim, 1980).

Others

Lameness in ducks: in Nigeria, the Hausa people pulverize the leaves of Momordica balsamina and mix them with feed to treat ducks for lameness (Nwude and Ibrahim, 1980).