EVALUATION OF VACCINATION DURING DISEASE OUTBREAK AS A DISEASE CONTROL OPTION: CASE STUDY ON NEWCASTLE DISEASE

ABSTRACT

This study investigated the response to Newcastle disease vaccination in previously vaccinated and unvaccinated poultry flocks experimentally infected with Newcastle disease virus. A total of

90 day old cockerel chicks procured from a local hatchery were used for the study. They were

brooded under deep litter system for 3 weeks after which they were divided into 2 groups, A and B of 45 birds per group. Members of group A were subsequently vaccinated against Newcastle disease using NDV-I2 intraocular. Members of group B received no vaccination. Five ml of blood was collected from 10 birds per group for serology. At 6weeks of age, members of group A were further divided into 3 equal groups A1, A2, and A3 while members of group B were divided into B1, B2 and B3 of 15 birds per group. All groups were housed differently but were fed and managed in similar approach. Five ml of blood were collected from 5 birds per subgroup for serology. Concurrently, 4 birds experimentally infected with kudu-113 strain of Newcastle disease virus were each introduced into pens housing groups A2, A3, B2 and B3 as source of infection, to simulate a natural infection. Groups A1 and B1 controlled their respective groups. Upon manifestation of clinical infections by the 4 exposed groups, all the group members had

5ml  of  blood  collected  for  serology.  Concurrently,  members  of  groups  A2  and  B2  were

vaccinated upon manifestation of clinical infections while A3 and B3 were not. All the groups were monitored till week 10 post hatch when observations were terminated with special attention paid to variables like incubation period, clinical signs, number and pattern of morbidity and mortality including the results of antibody titres of the groups on days 21, 42, 56, 63 and 70 post hatch. The results showed that clinical signs of patent infection were 6 days post infection in the previously unvaccinated groups B2 and B3. However, the period was extended to day 7 PI among the previously vaccinated groups A2 and A3. On day 11 PI, morbidity was 100% among members of groups B2 and 92.86% among groups B3. However, it was 42.86% and 64.29% respectively for members of groups A2 and A3. There were no morbidity nor mortality among members of groups A1 and B1. Mortality started on day 8 PI in the infected B groups and on day

14 PI, it was 100% among group B2 and 71.43% in group B3. However, mortality was first recorded among the infected group A members on day 11 PI. Total mortalities were 14.29% and

50% respectively for groups A2 and A3. The antibody titre among groups A and B members at week 3 of age was zero. On week 6 of age corresponding to 3 weeks post vaccination of group A

members, the GMT among groups A1 to A3 was 4096 while among the B groups the value remained zero. On day 56, the mean titre among A1 members dropped to 3026, A3 128 while A2

remained 4096. Among B groups, B2 rose to 115.2, B3 1024 while B1 remained zero as they never received any vaccination/virus. At day 63 post hatch, the GMT among A1 had declined to

106, A3 115.2 while A2 remained 4096. B3 had GMT of 921.6, B2 had recorded 100% mortality while B1 remained zero. At day 70 post hatch, the GMT of A1 was zero, A2 4096 and A3

1945.6.  B3  was 768  and  B1  zero.  This  study showed that  maternal immunity had  waned

completely  in  unvaccinated  birds  at  3  weeks  of  age.  Also,  vaccination  of  previously unvaccinated birds upon clinical infections showed exacerbated morbidity and mortality relative to those earlier vaccinated. Moreover, vaccination of previously vaccinated birds in the face of clinical Newcastle disease infection proved more beneficial than allowing the infection to run its course.

CHAPTER ONE INTRODUCTION

BACKGROUND OF STUDY

Livestock are  important for proper nutrition, sources of  income, employment, draught  power,   means  of  alleviating  poverty,  ensuring  food  security  and sustainable livelihoods among others (Bazeley et al., 1999; Anon 2002; Perry and Grace 2009; Okello et al., 2011; FAO 2012).

Livestock production systems occupy about 30 per cent of the planet’s ice-free terrestrial surface area (Steinfeld et al. 2006) and are a significant global asset with a value of at least $1.4 trillion. The livestock sector is increasingly organized in long market chains that employ at least 1.3 billion people globally and directly support the livelihoods of 600 million poor smallholder farmers in the developing world (Thornton, 2006). Keeping livestock is an important risk reduction strategy for vulnerable communities, and livestock are important providers of nutrients and traction for growing crops in smallholder systems. Livestock products contribute

17 per cent to kilocalorie consumption and 33 per cent to protein consumption globally,  but  there  are  large  differences  between  rich  and  poor  countries (Rosegrant, 2009). Currently, livestock is one of the fastest growing agricultural subsectors in developing countries. Its share of agricultural GDP is already 33 per

cent and is quickly increasing. This growth is driven by the rapidly increasing demand for livestock products, population growth, urbanization and improvements in incomes in developing countries (Delgado, 2005).

Cattle, pig, sheep, goat and poultry are the main livestock of economic importance in Nigeria. Their production systems vary according to species, product type and climate among others.   With the exception of poultry and pigs, other livestock species are constituted mainly by indigenous, unimproved stocks managed under traditional methods with low input system (Ogbeide, 2015). As the production of large animals –  cattle, pigs, sheep and  goat are  usually beyond the economic capability of most poor households (Kristjanson et al., 2004), poultry production is a more popular means of providing animal source food, alleviating poverty or addressing   the   food   insecurity   problems   endemic   in   the   tropical   region (Kristjanson et al., 2004). According to Tadelle and Ogle (2001), Alders (2004), Dolberg (2008), Alders and Pym (2009), and Anon (2014b), poultry plays important economic, nutritional and sociocultural roles in the livelihoods of poor rural households and some urban dwellers in many low-income countries.

The United Nations Millennium Development Goals (MDGs) in 2000, agreed on a set  of  eight  targets  in  response  to  the  world’s  main  development challenges. Included in the MDGs was a programme to ‘eradicate extreme poverty and hunger’ (Anon 2014a). An estimated 2.6 billion people in the developing world live on less

than $2 a day and, of these, about 1.4 billion are extremely poor – surviving on less than $1.25 a day (FAO 2012). Among this group, poultry production has been recognized as a means of saving for basic necessities, such as medication, clothes and  educational expenses  for  children (Bagnol,  2009).  For  many  households, chickens can be an entry point to the production of other livestock species, such as goats and cattle (Copland and Alders, 2009). Chickens also play a broader role in village life. They provide food for special festivals, religious offerings and traditional ceremonies (Alders, 2001). They are also important item used in strengthening social relationships as shared assets.

Apart from the economic roles of poultry to  many households in Nigeria, its nutritional significance as a protein source is laudable. Chicken meat and eggs are important sources of animal protein, which contains essential amino acids and micronutrients (Copland and  Alders,  2009).  Proteins  are  a  significant  part  of balanced  human  diet  and  in  developing  countries,  there  is  deficiency of  this important part of human nutrition. According to (Maqbool, 2002), approximately

66% of the populations in the developing world live on protein deficient diet. Moreover, there is a wide acceptance of poultry products as their consumptions are not constrained by religious and/or cultural observances. Again, it is claimed to have some health benefits over most other meat sources. Chicken meat does not

contain the trans-fats that contribute to coronary heart disease, which can be found in high amounts in beef and mutton (Farrel, 2015).

Currently, the demand for meat across countries and regions of the developing countries has been reported to be on increase with a 2030 projection of per capita consumption of 36.7 kilogram (kg) of meat per year (FAO 2003). This projection however varies across the Sub-Sahara Africa, Asia, Latin America and the Caribbean. It could be as low as 13.4 kg for Sub-Sahara Africa, 11.7 kg for South Asia and, as high as 58.5 kg for East Asia and 76.6 kg for Latin America and the Caribbean by 2030 (FAO 2003).These current increases in demand have implications for production both in quantity and the quality of livestock to be produced and the subsequent meat products to be obtained from them.

Among the most serious constraints to livestock production in general and poultry production in particular are disease conditions of various etiologies and clinical manifestations.   Diseases constitute serious constraints to both commercial and village chicken production and thus impede the hope of improved egg and meat supplies.

Of all the poultry diseases, Newcastle Disease (ND) is the single greatest constraint to poultry production (Alders and Spradbrow, 2001; Alexander, 1988, 2001; Kitalyi, 1998; Spradbrow, 1993-94). The 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, sub- family Paramyxovirinae, family Paramyxoviridae, in the current taxonomy (Lamb et al., 2000; Mayo 2002).

The disease manifest as acute and chronic viral infectious disease of both domestic and wild poultry and other species of birds regardless of sex and age (Alexander,

2003; Haque, 2010; Iram et al., 2013).

The first outbreaks to be recognized occurred in poultry in 1926, in Java, Indonesia (Kraneveld,   1926),   and   in   Newcastle-upon-Tyne,  England   (Doyle,   1927). However, there are earlier reports of similar disease outbreaks in Central Europe before this date (Halasz, 1912). The disease is characterized by respiratory and nervous system impairments including gastrointestinal tract and reproductive system (Nanthakumar et al., 2000; Tiwari et al., 2004). The most susceptible avian species to this disease are chickens (Rezaeianzadeh et al., 2011). Annual economic losses caused by this disease worldwide are in millions of dollars (Waheed et al.,

2013; Susta et al., 2010). Due to the severe nature of Newcastle Disease and the related consequences, NDV is included in “LISTED” agents (reportable disease) by Office International des Epizooties (OIE) (Aldous and Alexander, 2001; Boynukara et al., 2013). The disease is reported consistently from all continents of the globe (Munir et al., 2012). The first case in Nigeria was reported in 1952 (Hill

et al, 1953). It was reported to be the most prevalent disease of local and exotic birds (Saidu et al., 1994, Halle et al., 1999). A serological survey carried out in Nigeria in chicken managed under various systems showed 72% of antibodies against NDV in free range chicken and 62.9% in traditionally managed backyard flocks (Ezeokoli et al., 1984).

In several developing countries, ND is endemic and has greatest impact on villages where people’s livelihood depends upon poultry farming (Mohamed et al., 2011; Rezaeianzadeh et al., 2011).

Being of viral etiology, the disease can only be prevented by observing adequate hygienic measures and vaccination in endemic areas. Stamping out policy is also part of control measures. Vaccination programs as preventive measures are among the  most reliable  methods for controlling the disease (FAO, 2015). Currently, many inactivated and live ND vaccines are available around the world (Shim et al.,

2011; Xiao et al., 2013).

Vaccinations  have  effects  at  the  individual and  population levels.  Efficacious vaccines  reduce  or  prevent clinical signs  without  necessarily preventing virus replication. They  may also  increase  the  dose  of  virus  needed  to  establish an infection and/or reduce the level and duration of virus shedding following infection (Pasick, 2004).

Although proper vaccination protects the birds from clinical disease, it does not prevent virus replication and shedding, which results in  recovered birds acting as sources of infection (Chukwudi et al., 2012). There have been reported cases of occasional outbreaks of ND in vaccinated commercial chickens (Okoye et al.,

2007).These have called for practices such as emergency vaccination of birds post appearance of clinical signs. According to Okwor et al., (2012) post infection or emergency vaccination of chickens against some avian pathogens is commonly practiced in many developing countries of Africa and Asia. The authors have also shown that post-exposure or post-infection vaccination can be used in the management of an outbreak of fowlpox in chickens.

STATEMENT OF THE PROBLEM

The  single  greatest  constraint  on  village  chicken  production  in  developing countries  is  Newcastle disease. Newcastle disease is  a  highly virulent poultry disease that can wipe out entire flocks. It is a major constraint on production in many developing countries and impairs the capability of village chickens as a means of improving food security and alleviating poverty.

Although proper vaccination may protect poultry from clinical disease, post vaccination outbreaks  have  been  reported  creating  lacunae  regarding  possible cause of action to take in the face of such challenge. Also, there are reported cases

of vaccine failures due to poor handling and delivery methods especially in developing countries. In addition, strict biosecurity measures as a control strategy in Newcastle disease has proved highly beneficial but does not entirely rule out outbreaks of infections.

OBJECTIVES OF THE STUDY

1.  It  is  the  aim of this  study to  investigate the  effect of  post  vaccination exposure to velogenic strain of ND in a previously vaccinated chicken flock.

2.  To  investigate  the  effect  of  post  infection  vaccination  of  previously vaccinated flocks exposed to velogenic strain of ND.

3.  To investigate the effect of vaccination during an outbreak in previously unvaccinated flock.

SIGNIFICANCE OF THE STUDY

The findings of this research will impact on the resolution of yet unresolved issue of the benefits of vaccination during viral disease outbreaks as a control strategy. Moreover, the issue of recommendation in cases of outbreaks in previously unvaccinated flocks needs resolution.

The outcome may also be useful in designing control programmes and response approaches in cases of outbreaks of viral disease of livestock such as FMD in Cattle, Avian influenza in Chicken and PPR in small ruminants.

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