I. Aini

Diseases are one of the important factors associated with the limited expansion of the number of village or indigenous chickens in the rural areas. Some efforts have been carried out in many countries in South-east Asia to reduce the losses due to diseases but due to unconfined type of management, disease control is very difficult. Thus, diseases remain a great threat to these chickens.

Rural family chickens or village chickens or indigenous chickens are always associated with free-range, backyard or at most semi-intensive system of management. The types of feed used for this group of chickens and their feeding systems are also very typical to their group and different from those used for commercial breeds in intensive commercial farms. These chickens are however a very important component in the life of villagers or those living in the rural areas.

Village chickens form an integral part of village life, and have an important social value and in some countries. They are considered as an important source of income, besides providing a cheap source of protein to the village/rural people. However, diseases are among the important constraints in the expansion of this industry. In most areas, control of diseases is either lacking, very minimal or unheard of.

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Village chickens are known to be susceptible to most diseases which affect commercial chickens. Intercurrent disease is very important. Survival rates of chicks without disease outbreak ranges from 60-70 percent. The survival rate in the rainy season is generally lower because of high humidity, strong wind, and fluctuating temperatures. These conditions also make the chicks more susceptible to infectious diseases, especially respiratory diseases, thus reducing the survival rates.

Losses resulting from infectious diseases and parasitism in the region are known to be substantial. Unfortunately, statistics on incidence, morbidity, mortalities and causes are inadequate. The outbreaks that we hear about represent only a small proportion of the total, since most of the deaths and disease outbreaks in village chickens go unreported. Whatever data reported in each country is usually as a result of one time survey or limited studies. Due to free-ranging and unconfined type of management, disease control is very difficult and expensive, thus is rarely practised by the villagers (Aini, 1990).

The reports from all countries in South-east Asia point to the main killer and the most destructive disease, which causes the highest economic losses in village chickens being Newcastle disease (Anon, 1984; Ronohardjo et al., 1985; Anon, 1986; Atienza, 1987; Hussein, 1987; U Than Tint, 1987; Supramaniam, 1988). Poultry farmers share the common view that unless Newcastle disease is effectively controlled, all efforts to increase production of village chickens will be wasted. The other common diseases reported in village chickens are: infectious bronchitis, fowl pox, fowl cholera, infectious coryza, Marek's disease, lymphoid leukosis, pullorum, chronic respiratory disease, infectious bursal disease, aspergillosis and coccidiosis. Other health problems include those caused by endoparasites, ectoparasites, haemoprotozoa and to a lesser extent, microfilaria (Aini, 1990).

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ND has been labelled as the most important viral disease of poultry in the world and is particularly serious in the South-east Asian countries. This is due to the presence of velogenic strain of the virus in the region. The effect is devastating in village chickens where vaccination is rarely practised, often destroying the entire chicken population. Appropriate vaccination programme, suitable vaccine strains, interval between vaccination and efficient route of vaccination should be established to ensure the success of village chicken production.

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The incidence of mild IB in village chickens have been reported to be high in Malaysia and Indonesia (Sani et al. 1987; Ronohardjo, 1984). However, most of these reports were based on the survey record, rather than the actual report of disease outbreaks. Basically, vaccination for IB is not a usual practise in village chickens, with the exception of village chickens raised semi-intensively for commercial production. In semi-intensive commercial village chicken production, a combined ND-IB vaccine is usually given, intranasally, during the first week of life followed by another dose three weeks later.

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Marek's disease has also been reported in village chickens but vaccination against MD is not practised, under traditional system of farming. For the semi-intensive commercial group, vaccination against MD is given subcutaneously, at day-old.

Routine vaccination against FP is practised in semi-intensive commercial group but rarely so or none at all in traditional village chicken system. FP can cause serious problem in village chickens leading to secondary bacteria infection.

The incidence of fowl cholera is reported to be on the increase (Raymond, 1998). It is the most common bacterial disease encountered in village chickens. The disease can result in very high mortality, sometimes up to 80%, especially during rainy season. Routine vaccination against P. multocida is commonly practised in semi-intensive village chicken.

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Chronic respiratory disease is another common disease encountered in village chickens, especially during rainy season (Janviriyasopak et al., 1992). The situation becomes worse if another intercurrent infection sets in. Tylosin is commonly used for treatment, in the semi-intensive system. Treatment for chickens under scavenging system is usually unheard of. The economic importance of this disease is associated with reduction in egg production and growth depression.

From serological surveys carried out in several countries, IBD has been shown to be present in village chickens. IBD outbreaks under the traditional system of village chickens, have been reported in China (Fa, 1993) and Indonesia (Parede, 1992).

Salmonella pullorum infection in village chickens is of considerable concern to the commercial poultry industry. In many countries, pullorum is either eradicated or remain at a very low level. The presence of S. pullorum in village chickens may act as potential carriers for the spread of disease in commercial birds. Data on the economic losses in village chickens, due to S. pullorum is however not available. Usually S. pullorum infection in village chickens passed on untreated. Either the chickens survive the infection and become carriers or they die at an early age. Good sanitary measures is virtually impossible under traditional scavenging system. A high prevalence is reported in Thailand (Janviriyasopak et al. 1992), but low prevalence in Malaysia (Sani et al. 1987), and Indonesia (Istiana et al., 1990). The treatment is normally through the application of antibiotics or sulphonamides.

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Coccidiosis is usually not a major in village chickens under field conditions. This is probably due to the free-range habit of village chickens in which access to big land area is easily available. However, if these chickens are confined, coccidiosis is one of the diseases which need to be controlled (Sani et al., 1987).

Ectoparasite and endoparasite infestation is very common in village chickens (Sani et al., 1987; Salfina et al., 1990). Their scavenging habits and constant contact with contaminated environment make them an easy prey to parasitic infestations.

The ectoparasites are known to cause damage to feathers, irritation and skin lesions, resulting in either reduced performance of adult chickens or directly harmful to young chicks. Amin-Babjee et al. (1998a) reported that among the ectoparasites as infesting village chickens in Malaysia are: Haemaphysalis wellingtoni, Megninia cubitalis, Menacanthus stramineus, Neoschongastia gallinarum, Menopon gallinae, Liperus caponis, Cuclotogaster heterographus, Goniodes gigas, G. dissimilis and Goniocotes gallinae. The tick, H. wellingtoni and the trombiculid, N. gallinarum, were also commonly observed in high numbers and caused skin lesions. The prevalence and degree of ectoparasites infestation were closely related to the age of the birds, with higher infestation in older birds. The high prevalence of ectoparasites observed in this study was thought due to the free-range system, which exposed the birds to more species of ectoparasites, compared to those kept under the intensive system. The free-range system provides a more sustainable environment for the parasites.

The most common cestodes reported by Amin-Babjee et al. (1998b) were Raillietina echinobothrida, Hymenolepis carioca and R. tetragona. The trematod Tanaisia zarudnyi was reported in the kidney of 12-week old village chickens. The intermediate hosts of cestodes, such as, flies, ants, beetles, earthworms and slugs are known to be common in a free-range environment.

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In order to ensure that villagers can get access to cheap source of protein, disease prevention must be an integral part of rural family chicken production. Efforts should be made to educate farmers regarding the importance of disease control and prevention. Assistance must be given by the relevant authorities to improve the distribution of vaccines and antibiotics, so that rural family chickens are also protected against the most common diseases.

The author would like to thank Ms Normadiah Sukaimi for typing the manuscript.

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