Seroprevalence of Avian Leukosis Virus Antigen Using ELISA Technique in Exotic Broilers and Nigerian Local Chickens in Zaria , Nigeria

In an attempt to determine the seroprevalence of avian leukosis virus (ALV) in exotic broiler chickens and Nigerian local chickens in Zaria, Nigeria, a total of 600 sera (300 from exotic broiler chickens and 300 from Nigerian local chickens), obtained from the live bird market in Zaria, Nigeria, were tested for ALV p27 antigen by the antigen capture enzyme linked immunosorbent assay (ac-ELISA) technique. The age range of the Nigerian local chickens sampled in this study was 6 – 24 months, while that of the exotic broiler chickens used in this study was 2-3 months. Fourteen out of the 300 sera obtained from the exotic broiler chickens tested positive to ALV p27 antigen, which represents 4.70%, while 180 of the 300 Nigerian local chicken sera were confirmed positive to the antigen, representing 60.00%. Thirteen (92.86%) of the fourteen sera from the exotic broiler chickens were lowly positive (ELISA Units range of 10-20%) to ALV p27 antigen, while only one (7.14%) serum sample was moderately positive to ALV p27 antigen with an ELISA Unit of 29.33%. Of the 180 sera from the Nigerian local chickens that tested positive to ALV p27 antigen , 79 (43.89%) were lowly positive with ELISA Units ranging from 10.67% to 21.33%, while 101 (56.11%) serum samples were moderately positive to ALV p27 antigen with ELISA Units ranging from 28.0% to 73.33%. A higher seroprevalence of ALV was detected in Nigerian local chickens than the exotic broiler chickens.


Introduction
their envelope glycoprotein, nucleotide sequence, virus-serum neutralization tests, virus interference, The poultry sector in Nigeria, if properly and host range (Payne and Fadly, 2003).Subgroups A, harnessed has the potential of improving the nation's B, C, D, and J are oncogenic and exogenous ALVs, economy and improving the health status of the while subgroup E is endogenous and regarded as majorly poor populace, by providing affordable having extremely low pathogenicity (Calnek et al., source of protein so as to meet the recommended daily 1991).Avian leukosis virus subgroups A and B are intake of 0.8g/kg of protein (Shane and Neil, 2006).most commonly associated with lymphoid leukosis Disease has been identified as one of the most and less commonly erythroid leukosis in layers, while important factors that affect poultry production in ALV subgroup J is mainly associated with myeloid Nigeria (Alabi et al., 2007).Avian leukosis is one of leukosis in broilers (Payne et al., 1991).In addition to avian oncogenic diseases ravaging the poultry causing tumours, ALV may induce immunoindustry all over the world (Payne and Venugopal, suppression and other production problems in affected 2000).Yet there is paucity of information on the flock (Arshad, 1998).disease status in the northern part of Nigeria where The clinical signs of AL are not pathognomonic local chickens constitute the majority of poultry (Davidson, 2004) and include in appetence, abnormal population (Majiyagbe and Lamorde, 1997).
feathering, paleness of comb and wattles, loss of Avian leukosis is caused by certain members of weight, decreased egg production, depression, paralysis the leukosis/sarcoma group of avian retroviruses, and death (Abdel-Latif and Khalafalla, 2005).Avian commonly referred to as avian leukosis viruses leukosis virus is transmitted vertically from hen to (ALVs).They are classified into six (6) subgroups; A, chick through the egg and horizontally from bird to B, C, D, E and J (Kahn, 2005) based on the variation in bird by direct or indirect contact (Cottral et al., 1954).
The enzyme-linked immunosorbent assay were tested using colorimetric sandwich ELISA for (ELISA) is useful for the detection of ALV group-the presence of ALV group specific antigen (p27) as specific antigen (p27) which is common to all of the described by the manufacturer (Affini-Tech LTD, subgroups.It is a sensitive, safe, rapid and easy to USA).The ELISA was carried out at the Chemical perform diagnostic tool (Smith et al., 1979).The ALV Pathology Laboratory, ABUTH.ELISA diagnostic method is reported to have a 99.2% The intensity of the colour produced from the sensitivity and 100% specificity, and can be used ELISA test was measured photometrically at 405clinically for screening purpose (Pham et al., 1999; 410nm using ELISA reader.The ELISA units (EUs) Silva et al., 2007).Although evidences have shown for all samples tested on the Affini Tech ALV Antigen that some lesions which mimic AL have been observed Detection Test Kit was calculated using the formula in birds in Zaria, the disease is yet to be confirmed by below: highly sensitive and specific diagnostic methods.Therefore this study has become necessary to ascertain the status of ALV antigen in chickens in The Positive Control value was set at 100 ELISA Zaria, Northern Nigeria.To the best of our knowledge, Unit (EU).this is the first report on the prevalence of avian The ELISA unit values obtained were leukosis virus in Zaria, Northern Nigeria.
interpreted as recommended by the manufacturer.Enzyme-linked immunosorbent assay units less than

1994).
In this study, a total of 600 sera (three hundred Experimental birds: The Nigerian local chickens from local chickens and three hundred from broilers) vary greatly in phenotypic characteristics such as size, were tested for ALV p27 antigen by ELISA technique.conformation, and plumage color.They are generally Fourteen out of the 300 sera obtained from exotic hardy, adapted to harsh management and environbroilers tested positive to ALV p27 antigen which mental factors, with little or no veterinary inputs as represents 4.70%, while 180 of the 300 sera from compared to the exotic breeds of chickens.
Nigerian local chickens were confirmed positive to the A total of 600 sera samples were used in this antigen, representing 60.00%.Thirteen (92.86%) of study.Three hundred Nigerian local chickens (6 -24 the fourteen sera from exotic broiler chickens were months old) and 300 exotic broiler chickens (2 -3 lowly positive (EUs range of 10-20%) to ALV p27 months old), obtained from Sabon-gari live-bird antigen, while one (7.14%)serum sample was market, Zaria, were sampled, using simple random moderately positive to ALV p27 antigen, with an EU of sampling technique.
29.33%.Of the 180 sera from Nigerian local chickens Blood sampling and serology: Three milliliters of that tested positive to ALV p27 antigen , 79 (43.89%) blood was obtained from each bird, dispensed into a were lowly positive, with EUs ranging from 10.67% to separate test tube and transported on ice packs to the 21.33%, while 101 (56.11%) serum samples were Chemical Pathology Laboratory, Ahmadu Bello moderately positive to ALV p27 antigen, with EUs University Teaching Hospital (ABUTH), Shika, ranging from 28.0% to 73.33%.where the serological test (ELISA) was performed.The blood was allowed to stand for one (1) hour to Discussion allow the blood to clot.The blood was then centrifuged Avian leukosis has been reported worldwide to be a at 1,000 g for 10 minutes (WOAH, 2008) so as to major cause of serious economic losses to the poultry clearly separate the serum from the blood.The sera industry.Negative impact of the disease on chickens were dispensed into serum tubes and stored frozen ato include reduced growth, unevenness of growth rates 20 C until used.Test tubes and serum tubes were within flocks, and a greater susceptibility to labeled appropriately using indelible marking pen.
developing serious disease when challenged by immunosuppressive viruses or secondary bacterial difficult to achieve in commercial poultry.This is invaders (Bagust et al., 2004).Decreased egg production, because the Nigerian local chickens could serve as decreased egg weight and shell thickness as well as source of contamination of the environment and fertility, hatchability and liveability problems have also spread of ALV.Strict adherence to biosecurity on been observed (Gavora et al., 1980;Gavora et al., farms could be beneficial in limiting the spread of 1982).These production problems, which are these group of viruses from infected poultry farms to attributable to ALV infection, are common occurrences uninfected farms.Screening of breeder chickens for in the poultry industry in Nigeria.
ALV and removal of chickens found to be viraemic, Results of this study showed a prevalence of may also help in controlling the spread of ALV from 4.70% (14/300) in exotic broiler chickens which dam to chicks as the virus is known to be transmitted agrees with the findings of other workers who also got vertically.Also, efforts should be channeled into low prevalence rates such as 1.25% by Olabode et al. developing vaccines that will protect birds against the effect of this important group of retroviruses of chickens.( 2009), less than 5% by Owoade et al. (2006), and 3.33% by Mohammadi et al.(2008).A prevalence of negative while EUs greater than Study area: The study was carried out in Zaria, 10 were considered positive for ALV p27 antigen.Kaduna State, located in the Northern Guinea Elisa Units (EUs) 10-25 were considered weakly o Savannah Zone of Nigeria, between latitude 7 N and positive, EUs 25-75 were considered moderately o o o 11 N, and longitude 7 and 44 E. The average annual positive, while EUs greater than 75 were considered as rainfall ranges from 1000 to 1250mm with strongly positive for ALV P27 antigen.o o temperatures ranging from 17 C to 33 C (Saidu et al., Results