Efficacy of Feed Coated Newcastle Disease I2 Vaccine in Village Chickens in Gombe State, Nigeria

A study of response of village chickens to vaccination with ND I2 vaccine coated on maize grit as vaccine carrier was carried out in some selected LGAs of Gombe State, using haemagglutination inhibition (HI) test. Vaccination efficacy of maize grit coated with Newcastles Disease I2 vaccine has been compared between adult and young, village chickens. The study showed that 94.3% of the vaccinated village chickens (adults and chicks) seroconverted with protective levels of antibodies against ND virus. Those vaccinated with the maize grit coated vaccine exhibited antibody titres of between 1:16 to 1:8192 with GMT values of 109 to 245. There was a significant difference (P<0.05) in the response of the vaccinated adult village chickens as compared to the younger birds (chicks). It is concluded from the study that maize grit is a very suitable vaccine carrier for the delivery of ND I2 vaccine to village chickens. Efficacy of Feed Coated Newcastle Disease I2 Vaccine in Village Chickens in Gombe State, Nigeria


Introduction
Newcastle disease (ND) is an acute, contagious and highly pathogenic viral disease of both domestic and wild birds worldwide [1][2][3][4]. This disease is caused by a diverse group of viruses with the highly virulent strains endemic in Nigeria [5,6]. It is considered the most economically important avian viral disease in the world especially in developed countries due to its devastating effect on the industry [7][8][9]. It can produce mortality of up to 100% among infected populations of birds [10,11], and unfortunately the prognosis is poor [12,13]. Vaccination is currently the most effective method of controlling endemic Newcastle disease in both commercial and village chickens, but is rarely given priority in rural communities in Nigeria where majority of poultry are kept [14][15][16]. The administration of vaccines is by far the most humane and cost effective method of combating the spread of diseases [15,17]. The protection afforded by an efficacious vaccine not only removes the need for the administration of treatments, but also guards against the economically damaging consequences of disease [15,18]. Avirulent NDV 4 and ND I 2 strains of ND vaccines have been reported to give varying degrees of successes in both laboratory and field trials [19][20][21][22]. This study is therefore aimed at studying the responses of village chickens to Newcastle disease I 2 vaccine coated on maize grit as vaccine vehicle.

Study area
This study was carried out in some selected LGAs of Gombe State, Nigeria. Gombe State located between latitude 9°30 ' and 12° 3 '

Source of Newcastle disease (ND) I 2 vaccine
The Newcastle disease I 2 vaccine that was used in this study was obtained from Viral Research Department, National Veterinary Research Institute (NVRI), Vom, Plateau State, Nigeria. The vials of the vaccines were 50 dose vials meant to be reconstituted in 50 ml of chlorine free water and to be giving orally at 1 ml/ bird. The batch number of the vaccines and expiration dates were 4 / 2011 and Oct / 2012 respectively.

Selection of villages for the Newcastle disease I 2 vaccination
Five (5) out of the eleven (11) Local Government Areas (LGAs) of Gombe State were selected for the study. In each LGA, four villages were selected, and from each village four (4) households that owns moderate number of village chickens and that were willing to volunteer, cooperate and give full support for the success of the study were randomly selected. The Local Government Areas that were used for this study were Gombe, Akko, Kwami, Funakaye and Yamaltu Deba Local Government Areas.

Processing and coating of vaccine carrier with the Newcastle disease I 2 vaccine
Maize grit that was used as the vaccine carrier in this study was maize that was per boiled for 15 minutes, washed and spread immediately to dry under the sun. The dried per boiled maize was then polished ('surfe') to remove the maize husk and then crushed into a gritty mash. The maize grit was soaked in hot water and allowed to stand until the water cools, washed thoroughly and sieved to reduce the starch content and was again sun dried. Using a weighing scale, the Journal of V Journal of Veterinary Science & eterinary Science & T Technology echnology maize grit was weighed and packaged in polythene bags of 1 kg/package and stored at room temperature. Two vials of the 50 doses of ND I 2 vaccines were reconstituted in 100 ml of chlorine free water and used to mix each 1 kg of the maize grit (at a ratio of 1 ml to 10 g of the dried maize grit) using a hand sprayer. The maize grit coated ND I 2 vaccine was administering to the village chickens as previously described by Alders and Spradbrow [17].

Vaccination procedure
The village chickens from the selected households in the five LGAs were locked up in cages, raffia baskets and empty rooms when they returned to their owners' houses to roost in the evening from the scavenging of the day. They were denied access to any source of feed throughout the night before administering the ND I 2 vaccine coated feed to them the following morning. Some village chickens from a different village were used for the normal oral vaccination in water. Each of the birds used in the study were labeled using small number tags tied to their wings and were bled through the wing web vein prior to vaccination.

Blood sample collection
The vaccinated village chickens were bled twice on days zero and 28 post vaccination. Blood samples was collected from the live experimental village chickens through the brachial vein (wing vein) or jugular vein of adult and grower village chickens of both sexes using sterile 2 ml syringes and 21G needles. Each blood was carefully dispensed into plain vacutainer tubes, labeled appropriately and kept at a slanting position at room temperature to allow blood samples to clot. For chicks with tiny brachial veins through which a syringe and needle could not be used to collect blood directly, their veins were punctured using sterile 23G needles and then labeled strips of filter paper (Whatman ® filter paper 1, Cat No 1001 125) were used to tap blood samples from the punctured veins and allowed to saturate up to a distance of 1-2 cm of the length of the strip as previously described [25,26]. Samples were air dried, labeled on both sides and stored in plastic bags and stored at 4°C for onward transport to the laboratory. In the laboratory, serum samples were eluted from the strips by punching 2 disks (6 mm in diameter) using a file punch and placed in a well of a microtitre plate and 100 µl of normal saline was added and the plate incubated at 4°C overnight.

Serology
Serum samples were tested for Newcastle disease virus specific antibodies using a modification of the Hemagglutination Inhibition (HI) test previously described by Baba et al. [27].

Data analysis
Hemagglutination inhibition titres obtained were expressed as geometric mean titre (GMT) values according to the method described by Garner et al. [28] using the formula X geo =antilog 10 {1/n (∑f i log 10 X i )} where n=number tested, X i =the reciprocal of dilution and f i =frequency. The data generated from the study was entered to excel spreadsheet. All categorical data were entered into contingency tables and analyzed using chi square test, while the geometric means of all numeric data were compared using t-statistic or analysis of variance (ANOVA) for paired or multiple data columns respectively using Statgraphic plus Version 5.0, November 2000 (Statistical Graphics Corp.). The level of statistical significance was set a p-value less than or equal to 0.05.  (Tables 3 and 4). The direct oral drench group showed a baseline titre of 1:2 to 1:64 with GMT of 3.6 and 1:512 to 1:2048 with GMT of 861 (Table 5). There was no statistical difference (P>0.05) noted among the vaccines from the different LGAs.

Discussion
The use of maize grit as the vaccine vehicle to deliver the ND I 2

LGA
No  vaccine in this study was meant to obviate the problem of chasing, catching and vaccinating individual bird which is difficult in the natural habitat of the village chickens. The choice of maize in this study to be used as vaccine carrier is in accordance to similar research by Ibrahim et al. [29] that reported maize to be a reliable vaccine carrier. The findings of this study showed that the ND I 2 vaccine coated on maize grit has led the vaccinated village chickens to seroconvert with high antibody titres in all the study areas. This finding concurs with field records in Mozambique which indicates that ND I 2 vaccine provided approximately 80% protection in the field in the face of an outbreak when coated on suitable carrier food [17] and also confirmed the findings of Echeonwu et al. [22] who reported the efficacy of the same vaccine under laboratory trials using maize meal waste (maize offal) as the vaccine carrier. The efficacy of any vaccine is determined mainly by assessment of the level of antibody produced in the target birds and the ability of the vaccinated bird to resist exposure to the virulent infectious agent when compared to the unvaccinated birds [30]. The advantage of the feed coated ND I 2 vaccine over the use of drinking water in the village chicken is that most village chickens are used to early morning feeding in the study area and this makes it easy for the vaccine coated feeds to be consumed early before the vaccine virus gets inactivated by environmental conditions. Whereas if the vaccine was to be given in drinking water, only a small percentage of the chickens may take the water within the required time, due to the availability of surface water in the environment. The study showed that significantly larger proportion of vaccinated adult village chickens seroconverted to higher antibodies levels than the chicks. This finding may not be unconnected to the possible repeated exposure and/or well developed immune system in the adult chickens leading to an adequate response. The high NDV HI antibody titres recorded in the vaccinated chickens in this study must have resulted from anamnestic response in the birds due to previous natural expose to NDV.
Although all the village chickens vaccinated with both the feed coated and direct oral drench vaccine demonstrated high antibody titres, the later demonstrated a more uniform response and hence higher GMT values. This could be because it was not possible to ensure that all the village chickens in the mass application of the ND I 2 vaccine coated on the maize grit receive the same and exact dose of the vaccine. This difference in the feed in take also appears to have been the primary cause for the difference in titres between the adult chickens and chicks in this present study. The adult chickens consumed much of the feed while the chicks just picked tiny grains. This resulted in higher immune response in the adult chickens when compared to the chicks. Similarly, Erick et al. [31] found that a significantly large proportion of vaccinated adult chickens attaining protective immunity against NDV as compared to growers and chicks which were attributed to repeated exposure and/or well developed immune system in adult chickens leading to an adequate response to vaccination. Other factors to consider include the prevalence of other infectious diseases like IBD capable of immunosuppressing the village chickens. El-Yuguda et al. [32] have reported significant depression of primary antibody of chickens to ND vaccine when administered one week after IBD infection or vaccination. It is therefore fundamental to monitor the prevalence of other infectious diseases capable of immunosuppression and to implement specific vaccination programme for their control. Also the rearing of ducks, guinea fowls, pigeons and doves (which are natural fliers) together with village chickens further compounds the difficulty in ND control strategies among the village poultry population. But vaccination in these classes of birds may be attempted using the feed coated ND I 2 vaccine by spraying over the locations where these birds usually scavenge for food. Since guinea fowl vaccination using different feeds as vaccine vehicles have been reported by Baba et al. [21] using thermostable NDV-V 4 vaccine. It is therefore suggestive that thermostable ND I 2 vaccine coated on feed such as maize grit be used to vaccinate freeliving and scavenging birds.     Table 5: Distribution of ND HI antibody titres of village chickens pre-vaccination and post-vaccination with oral drenches of ND I 2 vaccine.