INTRODUCTION AND LITERATURE REVIEW
Newcastle Disease (ND) is the most important viral disease of poultry in the world including developing countries (Adene, 1999; Spradbrow, 1997). In Africa and Asia ND is a major constraint against the development of both industrial and village poultry production (Alders et al., 2001). ND has been reported as one of the greatest constraints to the development of rural poultry production in Nigeria (Shamaki et al., 1989; Oladele et al., 2003). ND is a highly contagious and commonly fatal ribonucleic acid virus infection of birds which can cause up 100 percent mortality in susceptible chickens. Many avian species may become infected but dramatic losses are seen most often in domestic fowl and to a lesser extent in turkeys and Pheasants (Rosenbeger, 1981; Vickers and Hanson, 1982; Gordon and Jordan,1982)
ND is caused by avian paramyxovirus type-1(APMV-1) which is classified with other paramyxoviruses in the genus Avulavirus, subfamily paramyxovirinae, family paramyxoviridae, and order mononegavirales. It is an enveloped virus and has a negative sense single strand RNA genome (Lamb et al., 2005). The genome contains six genes 31-MP-P-M-F-HN-L-51 that encode six major proteins: nucleoprotein, phosphoprotein, matrix protein, fusion protein, haemmaglutinnin-neuraminidase, and RNA- dependent RNA polymerase (Chamber et al., 1986; Alexander, 2008). Beard and Hanson (1984) classified Newcastle disease virus strains into highly virulent (Velogenic), intermediate virulent (Mesogenic) or avirulent (Lentogenic) based on their pathogenicity in chickens. Lentogenic strains produce mild or inapparent respiratory infections; the mesogenic strains produce low mortalities, acute respiratory disease and neurological signs in some birds while the velogenic strains which can be either neurotropic velogenic NDV (NVNDV) or viscerotropic velogenic NDV (VVNDV) cause disease with high mortality (Huang et al., 2004; Piacenta et al., 2006). The known surface antigens are the haemagglutinin and neuraminidase (Nagai et al., 1976) and the fusion (F) protein. The first, haemagglutinin-neuraminidase (HN), is important in the attachment and release of the virus from the host cells, in addition to its role in serologic identification (Beard and Hanson, 1984; OIE, 2008). The other, the fusion (F) protein, has a critical role in the pathogenesis of the disease (Beard and Hanson, 1984; OIE, 2008). ND may be employed as an antigen in a wide variety of serological tests, enabling neutralization or ELISA or HI tests to be used for diagnosis (Aiello et al., 2003)
According to FARD (2008), the poultry population of Nigeria is estimated to be 137.6 million, with backyard poultry population constituting 84% (115.8million) and exotic poultry 16% (21.7 million), with a higher percentage of this poultry raised for subsistence production. Ogundipe (1998) reported that close to 75% of Nigerian population live in rural areas where most households keep small number of local and village chickens which scanvage on free range and usually taken care of by women and children. Establishment of the disease status in Nsukka is therefore of great importance to avoid economic losses caused by the disease.
1.1.1 Statement of Problem
ND is rated as one of the greatest constraints to the development of rural poultry production in Nigeria and in most developing countries, causing serious threats (Shamaki et al., 1989; Oladele et al., 2003). In Africa and Asia, ND is a major constraint against the development of both industrial and village poultry production (Alders et al., 2001) Despite the numerous roles of village chickens in the life of the poor rural families such as provision of meat and eggs, food for special festivals, offerings for traditional ceremonies, pest control and petty cash for purchase of medicines and payment of school fees (Alders and Spradbrow, 2001), ND is responsible for high economic losses due to high mortality, morbidity, stress, decreased egg production and hatchability (Alexender, 2003).
1.1.2 Aim of the Research
To determine the prevalence of Newcastle disease virus in local chickens within Nsukka Area and its environs.
1.1.3 Objectives of the Research
- To determine the seroprevalenec of Newcastle disease from four selected Local government Areas in Nsukka, including Udenu, Nsukka Central, Igbo-Eze North, and Igbo-Eze South Local Government Areas.
- To determine age-specific prevalence of HI antibody titre in local chickens.
- To determine whether it is necessary to vaccinate the local chickens against Newcastle disease.
1.2 Literature Review
Poultry are birds domesticated by man and include chickens, turkeys, ducks, geese, quails, ostriches, guinea fowl and certain other birds. They are kept by households as a source of protein (eggs and meat) and income to meet everyday family needs (Law and Payne, 1996). The economic significance of poultry varies significantly from country to country. In developing countries and sub-Saharan Africa, there is an increasing demand for livestock product for the ever growing and more affluent population (Delgado, 2003; Gulati et al., 2005). Chicken is the livestock most commonly owned by women and families in the developing world, and increasing their productivity will contribute significantly toward increasing their food security and livelihood of the rural families (Alders and Spradbrow, 2001a).
In an address at the World Food Day Ceremony in Rome, 2007, the Director General of the United Nations’ Food and Agricultural Organization (FAO), Jacques Diouf said “our planet produces enough food to feed its entire population. Yet, tonight, 854 million women, men and children will be going to sleep on an empty stomach”. This statement of Jacques Diouf is true especially for sub-Saharan Africa, which has the highest prevalence of under nourishment, with one in three people deprived of access to sufficient food (FAO, 2006). Poultry production is generally acknowledged as the most efficient and cost-effective way of increasing the availability of high protein food (FAO, 1987) Eggs have long been presented as the standard reference food that is perfectly balanced, containing most essential amino acids, minerals and vitamins. Approximately 11.5% of daily protein requirement and 5% of daily energy requirement is provided by one egg (Branckaert et al., 2000). Poultry production as a socio-economic activity has been turned to a commercial entity from the mere subsistence form of agriculture (FAO, 2005). With the increasing population pressure challenging developing economies and the need to provide food security and meet the global Millennium Development Goals (MDGs), the need for every country to build up their poultry production capacity cannot be overemphasized. Unfortunately, the growth of the livestock industries or enterprises in developing countries has been severely constrained by animal diseases (Perry and Sones, 2007). Poultry production systems, especially in developing countries, are faced with a myriad of challenges, key amongst which is disease. De Haan and Bekure (1991) reported an estimated annual loss of about US $2 billion in direct losses (mortality) and another US $2 billion in indirect losses (slow growth, lower productivity, increase morbidity and lower fertility, etc) in sub-Saharan Africa due to livestock diseases. The effect of these diseases is most severe in the developing economies where modern vaccines and medicaments, modern technologies for quick diagnosis and sound management practices are in short supply. Many of these developing economies are stacked with outdated service delivery systems that are incompatible with and do not meet the needs or requirement of their poor clients and are compounded by inadequate funding (Perry and Sones, 2007). In view of this, disease entities especially viral diseases have continued to pose a threat to the poultry industry despite efforts made at controlling them. Some of the viral diseases of poultry among others include Infectious Bursal disease (Gumboro), Egg Drop Syndrome (EDS), Highly Pathogenic Avian Influenza (HPAI), Infectious Laryngotracheitis (ILT), Mareks disease and Newcastle disease (ND).
1.2.2 History of Newcastle Disease
The first description of a disease outbreak in poultry that resembled and was later named Newcastle disease (ND) occurred in 1926 in Java, Indonesia (Kraneveld, 1926) and Newcastle-upon-Tyne, England (Doyle, 1927). However, there were reports of outbreaks of a similar disease in Central Europe that predates the Java and Newcastle reports (Macpherson, 1956; Halasz, 1912). Macpherson (1956) was of the view that the death of all chickens in the Western Isles of Scotland in 1896 was due to ND. Doyle (1935) named the disease “Newcastle disease” after the outbreak in Newcastle-upon-Tyne in Great Britain. This was to avoid giving a scientific name that may be confused with other disease entities. The name or nomenclature “avian paramyxovirus serotype -1” (APMV-1) as suggested by Tumova et al (1979) is frequently used in place or together with the name ND in an effort to conform with the rules of naming individual isolates as recommended by the World Health Organization (WHO 1980). Citing Ochi and Hashimoto, Levine (1964) was of the view that ND might have been present in Korea as early as 1924. ND outbreaks also occurred in Ranikhet, India in 1927 (Edwards, 1928). In the United States, a disease of poultry characterized by mild respiratory and neurological signs was reported and termed pneumoencephalitis (Beach, 1942) but was later discovered to be ND. Since then numerous Newcastle disease viruses (NDV) that produce mild or no disease in chickens have been isolated and reported around the world (Hitchner and Johnson, 1948; ASplin, 1952; Simmons, 1967; McFerran and Nelson, 1971). It is however possible that several outbreaks of ND may have occurred earlier and gone unrecognized in other places possibly due to the lack of expertise to recognize the new disease (Alexander, 1988b). Alexander et al. (2004), looking at the pattern of outbreaks all over the world, was of the suggestion that several panzootics of ND in poultry might have occurred since 1926. According to them, the first panzootic which started in the far East spread very slowly across the globe and poultry in the USA. The second panzootic which started at the end of 1960s was able to spread to all corners of the earth within the span of 4 years (Hanson, 1972). The reason for the fast spread of the second panzootic was attributed to the development of the poultry industry, the commercialization of feed production and the enhanced trade in captive birds due to improved air transportation – all of which lead to greater contact between individual farms and birds of different regions of the world. Imported cage birds were known to be responsible for the introduction of panzootic virus into California poultry (Hanson, 1972; Francis, 1973). Outbreak of ND in 1970 to 1972 in USA were linked to the importation of exotic birds (Walker et al., 1973).
The third panzootic started in late 1970s going by antigenic and genetic evidence (Alexander et al., 1997; Lomniczi et al., 1998; Herczeg et al., 2001). Its spread was masked by the global use of vaccines since the mid-1970s. The fourth panzootic occurred in the 1980s in racing and show pigeons (Columba livia) and not in poultry, but the latter was said to be responsible for the spread of the virus into these categories of birds (Alexander et al., 2004).
In Nigeria, the first tentative diagnosis of the diseases was in April 1951 in two outbreaks in some poultry farms in Eastern Nigeria (Kirby, 1951; Hill et al, 1953; Hill 1954), and was confirmed by Laboratory tests in Vom (Anon, 1952-53, 1953-54). Presently, ND in the most dreaded devastating fatal poultry disease of importance in Nigeria (Uzoukwu, 1967; Fatunbi and Adene, 1979).
1.2.3 Aetiology – The Newcastle Disease Virus (NDV)
Fig. 1: The Newcastle disease virus (source: poultry.com and www.isracast.com)
The etiological agent of Newcastle disease, Newcastle disease virus is of the order Monanegavirales, of the family paramyxoviridae and Avulavirus genus (Lamb et al., 2000; Mayo, 2002a; 2002b). The diagram of the virus is shown in fig. 1. Also referred to as avian paramyxovirus-1 (APMV-I), the current taxonomy has nine APMV serotypes (APMV-I to APMV-9) as contained in Alexander (1988c), with APMV-1 known to infect numerous avian species (Lamb et al., 2000). Most of these serotypes appear to be present in natural reservoirs of specific feral avian species although other host species are also susceptible (Lewis, 2005). APMV-2 and APMV-3 virus are the only serotype apart from APMV-1 that have made significant disease and economic impact on poultry production (Alexander, 1993; Lewis, 2005) although APMV-6 and APMV-7 are also known to cause disease in poultry (Alexander, 2003). APMV-1 cross-reacts with other serotypes especially APMV-3 (Alexander, 1993). Because of the severity of the disease produced/induced even in a given host such as chickens by the different isolates and strains of NDV, Beard and Hanson (1984) summarized and divided NDV into forms or pathotypes based on the clinical signs of the disease produced in infected chickens (table 1).