POULTRY MARKETS CONTACT NETWORKS IN ETHIOPIA

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Introduction

Poultry keeping is a common practice in rural households in Ethiopia. The total chicken population in Ethiopia has been recently estimated at 49 million (CSA, 2011). The vast majority of these birds, over 97%, are indigenous chickens kept in an extensive, scavenging system, also known as the backyard or village system, where birds scavenge around the house during the daytime. Three poultry production systems are recognized in Ethiopia, namely the scavenging backyard or village, small-scale commercial and commercial production systems (GRM, 2007; Tadelle Dessie, personal communication) that roughly correspond to sector 4, sector 3 and sector 2, respectively, according to the FAO classification (Demeke, 2007; Alemu et al., 2008). In addition, there are several multiplication and rearing centres, which serve as a genetic improvement programme, in the regional states in Ethiopia. Large scale and small-scale commercial poultry production is concentrated in the vicinity of Debre Zeit, near the main market in the capital Addis Ababa, while the local indigenous flocks in the village production system are found all over the country (Figure 1.1). The small-scale commercial system of production is a newly emerging one in urban and peri-urban areas as a household income source, using exotic birds and improved feeding, housing and health-care systems, and produced along commercial lines (GRM, 2007). In the Ethiopian highlands more than 66% of rural households own chickens and the average flock size per rural family was estimated at 7-10 mature chickens (Tadelle and Ogle, 2001; Wilson, 2010). The latest available figures indicate that village poultry contributes 98.5% of the national egg production and 99.2% of the national poultry meat production (Tadelle et al., 2002). This indicates the importance of village poultry production in Ethiopia where chickens serve as a good source of protein and ready cash for villagers. School children often use income generated from selling poultry or eggs sell to buy supplies for school. It is common to see families who invested in small stock such as goats and sheep or other business enterprises from sales of chickens as reported elsewhere (Clarke, 2004; Alders and Pym, 2009). Additionally, village chickens are active in pest control, provide manure which can be used as a fertiliser, are required for special festivals and are essential for many traditional ceremonies (Alders et al., 2010). In Ethiopia honoured guests are served with “doro wot”, a traditional stew made of chicken meat and boiled eggs.

Newcastle disease

It is generally accepted that the first reported outbreaks of ND occurred in 1926, in Newcastle-Upon-Tyne, England, whence the name, and in Java, Indonesia (Lancaster, 1976). It is believed that the disease might have occurred earlier elsewhere but had gone unnoticed. In the USA it was initially recognized by mild respiratory and neurological signs which were subsequently termed pneumoencephalitis, and later found to be ND (Ishida et al., 1985). Since then, isolations of NDV have been made from all over the world from both wild and domestic species (Aldous and Alexander, 2001). Although the exact geographic distribution is difficult to determine because of the widespread use of ND vaccines in commercial poultry, the disease is believed to exist on all the continents, including Africa, and remains a major concern of the agricultural community because of economic losses that have occurred due to illness, death and reduced production or vaccination costs. Newcastle disease is believed to be endemic in the village poultry populations in Africa and is regarded as the most important constraint to the development, survival and productivity of village chicken flocks (Alexander et al., 2004; Alders, 2009). Serological and virological evidence has demonstrated the presence of the disease in village poultry in many African countries (Sharma et al., 1986; Bell et al., 1990; Bell, 1992; Echeonwu et al., 1993; Awan et al., 1994; Chrysostome et al., 1995; Orjaka et al., 1999; Abolnik et al., 2004; Zeleke et al., 2005b; Otim et al., 2007; Servan de Almeida et al., 2009; Snoeck et al., 2009; Cattoli et al., 2010). In countries where ND is endemic, outbreaks of the disease could result in mortalities of upto 100% in a susceptible population depending on the virus strains involved (Spradbrow, 1999; Alexander et al., 2004; Alexander, 2011). The virulent form of the disease, with an intracerebral pathogenicity index (ICPI) of ≥0.7 is considered a notifiable disease that must be reported to the World Organization for Animal Health (OIE). In 2004, of the 42 African countries that reported to the OIE, 24 of them reported ND outbreaks, with the incidence ranging from one outbreak (Sudan, Namibia and Niger) to 137 outbreaks (Togo), whilst in four countries the disease was reported to be present only (OIE, 2008a). Between January 2005 and December 2011, several countries reported clinical disease, on average 53 outbreaks (range 29-84) were reported from 54 countries and 3 islands, while in a few countries disease was suspected without confirmation, or information was not available on the disease status at all (WAHID, 2012) .

Aetiology and pathogenicity

Newcastle disease is caused by avian paramyxovirus serotype 1 (APMV-1) viruses, which, with viruses of the other eight APMV serotypes [APMV-2 to APMV-9], have been placed in the genus Avulavirus, belonging to the sub-family Paramyxovirinae, family Paramyxoviridae, (Mayo, 2002; OIE, 2008b). Recently a new serotype of APMV (APMV- 10), isolated from penguins, has been confirmed (Miller et al., 2010a). Newcastle disease virus (NDV) is a single-stranded RNA virus with an envelope bearing glycoprotein spikes, of which one function is to initiate haemagglutination (HA). In chickens the pathogenicity of NDV is chiefly determined by the strain of the virus, although dose, route of administration, age of the chicken, health status and environmental conditions could also play a role (Alexander and Senne, 2008). In general, the younger the chicken the more acute the disease is. Newcastle disease virus strains are grouped into five phenotypes based on their pathogenicity and clinical signs induced in infected chickens (Beard and Hanson, 1984, Alexander and Senne, 2008; OIE, 2008b): (i) viscerotropic velogenic, associated with high mortality (up to 100%), often associated with sudden death, without other clinical signs; this type of the virus may cause oedema around the eyes and head; (ii) neurotropic velogenic, marked by sudden onset of upper respiratory signs with high mortality (50-90%, depending on the age of the chicken) and associated with central-nervous signs but diarrhoea is usually absent; (iii) mesogenic with moderate mortality (up to 50%), presenting with respiratory and occasionally nervous signs and also moderate to severe egg production declines for 1-3 weeks; (iv) lentogenic (Hitchner-forms) with mild or sub-clinical respiratory infections; and (v) asymptomatic enteric with sub-clinical intestinal infection and no gross lesions.

Table of contents :

• Acknowledgments
• Summary
• Table of contents
• List of figures
• List of tables
• List of abbreviations
• CHAPTER ONE: INTRODUCTION AND LITERATURE REVIEW
  • 1.1 Introduction
  • 1.2 Newcastle disease
    • 1.2.1 Aetiology and pathogenicity
    • 1.2.2 Diagnosis
      • 1.2.2.1 Clinical diagnosis
      • 1.2.2.2 Serological diagnosis
      • 1.2.2.3 Virus isolation and molecular diagnosis
      • 1.2.2.4 Nucleotide sequencing and phylogenetic studies
    • 1.2.3 Epidemiology of Newcastle disease
      • 1.2.3.1 Host range
      • 1.2.3.2 Transmission and spread
      • 1.2.3.3 Persistence of the virus
      • 1.2.3.4 Prevention and control of Newcastle disease
    • 1.2.4 Newcastle disease in public health and bioterrorism
    • 1.2.5 Newcastle disease and other poultry diseases in Ethiopia
  • 1.3. Study rationale and research questions
  • 1.4 Study setting
  • 1.5 Description of the study area
  • 1.6 Objectives of the study and outline of the thesis
• CHAPTER TWO: SEROPREVALENCE OF NEWCASTLE DISEASE AND OTHER INFECTIOUS DISEASES IN BACKYARD CHICKENS AT MARKETS IN EASTERN SHEWA ZONE, ETHIOPIA
  • 2.1 Abstract
  • 2.2 Introduction
  • 2.3 Materials and methods
    • 2.3.1 Study area, study design and sample size
    • 2.3.2 Sampling procedure and sample analysis
    • 2.3.3 Data analysis
  • 2.4 Results
  • 2.5 Discussion
• CHAPTER THREE: SEROLOGICAL AND MOLECULAR INVESTIGATION OF NEWCASTLE DISEASE IN HOUSEHOLD CHICKEN FLOCKS AND ASSOCIATED MARKETS IN EASTERN SHEWA ZONE, ETHIOPIA
  • 3.1 Abstract
  • 3.2 Introduction
  • 3.3 Materials and methods
    • 3.3.1 Study area
    • 3.3.2 Study design and sample size
    • 3.3.3 Sampling procedures
    • 3.3.4 Serological testing
    • 3.3.5 RNA extraction and RT-PCR assay
    • 3.3.6 Data analysis
  • 3.4 Results
  • 3.5 Discussion
• CHAPTER FOUR: HOUSEHOLD LEVEL RISK FACTORS FOR NEWCASTLE DISEASE SEROPOSITIVITY AND INCIDENCE OF NEWCASTLE DISEASE VIRUS EXPOSURE IN BACKYARD CHICKEN FLOCKS IN EASTERN SHEWA ZONE, ETHIOPIA
  • 4.1 Abstract
  • 4.2 Introduction
  • 4.3 Materials and methods
  • 4.3.1 Study areas
  • 4.3.2 Study design and data collection
  • 4.3.3 Serological testing
  • 4.3.4 Data analysis
  • 4.4. Results
  • 4.4.1 Descriptive statistics
  • 4.4.2 Univariable analysis
  • 4.4.3 Multilevel mixed-effects logistic regression models
  • 4.5 Discussion
• CHAPTER FIVE: MOLECULAR CHARACTERIZATION AND PHYLOGENETIC ANALYSIS OF NEWCASTLE DISEASE VIRUS ISOLATED IN THE BACK YARD CHICKEN AT VILLAGES AND MARKETS IN ETHIOPIA
  • 5.1 Abstract
  • 5.2 Introduction
  • 5.3. Materials and methods
    • 5.3.1 Study area, sample collection and virus isolation
    • 5.3.2 Haemagglutination and haemagglutination inhibition assays
    • 5.3.3 Viral RNA extraction and molecular detection
    • 5.3.4 Amplification for sequencing
    • 5.3.5 Phylogenetic analysis
  • 5.4. Results
    • 5.4.1 Virus isolation and detection by rRT-PCR
    • 5.4.2 Phylogenetic analysis of F and HN genes sequence
  • 5.5 Discussion
• CHAPTER SIX: EVALUATION OF ENZYME-LINKED IMMUNOSORBENT ASSAYS AND HAEMAGGLUTINATION INHIBITION TESTS FOR THE DIAGNOSIS OF NEWCASTLE DISEASE VIRUS INFECTION IN VILLAGE CHICKENS USING A BAYESIAN APPROACH
  • 6.1 Abstract
  • 6.2 Introduction
  • 6.3 Materials and methods
    • 6.3.1 Serum samples
    • 6.3.2 Blocking ELISA
    • 6.3.3 Indirect ELISA
    • 6.3.4 Haemagglutination inhibition test
  • 6.4 Prior information, assumptions and test evaluation
  • 6.5 Sensitivity analysis
  • 6.6 Results
    • 6.6.1 Descriptive results
    • 6.6.2 Evaluation of test performance
    • 6.6.3 Test dependence
    • 6.6.4 Sensitivity analysis
  • 6.7 Discussion
• CHAPTER SEVEN: POULTRY MARKETS CONTACT NETWORKS IN ETHIOPIA – IMPLICATIONS FOR DISEASE SPREAD AND SURVEILLANCE
  • 7.1 Abstract
  • 7.2 Introduction
  • 7.3 Materials and methods
    • 7.3.1 Study area
    • 7.3.2 Selection of poultry markets
    • 7.3.3 Questionnaire data collection
    • 7.3.4 Network characteristics
    • 7.3.5 Data analysis
  • 7.4 Results
    • 7.4.1 Trader characteristics and poultry trade movement
    • 7.4.2 Network data analysis
      • 7.4.2.1 Poultry movement
      • 7.4.2.2 Centrality measures of the networks
• 7.5 Discussion
• CHAPTER EIGHT: GENERAL DISCUSSION AND CONCLUSIONS
  • 8.1 Introduction
  • 8.2 Infectious poultry diseases in village chickens
  • 8.3 Newcastle disease in household flocks
  • 8.4 Molecular analysis and phylogenetic studies
  • 8.5 Serological diagnosis of Newcastle disease and test evaluation
  • 8.6 The role of markets in poultry disease spread and surveillance
  • 8.7 Prospects for further research
  • 9. REFERENCES
  • 10. APPENDICES

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