This study used serological method to estimate the level of circulating antibodies against Newcastle disease (ND) in apparently healthy guinea fowl, raised under traditional management system obtained from the major live bird market of Sokoto State, Nigeria. Competitive Enzyme Linked Immunosorbent Assay was used to analyze two hundred and twenty nine (229) sera for Newcastle disease virus antibodies from randomly selected guinea fowls presented at live bird market. Overall, seroprevalence of 40.6 % (93/229) was detected. The male specific prevalence was 41.9 % (83/198) while female specific prevalence was 32.3 % (10/31) detected. Age specific prevalence showed adults guinea fowl to had 44.4 % prevalence while younger ones had 29. 1%. The findings of this study as it’s relate to epidemiology and transmission dynamics of ND is discussed.
Newcastle disease is a major viral disease of economic importance in poultry and rated as one of the greatest constraints to the development of rural poultry production in Nigeria and in most developing countries, causing serious threats to poultry industry (Anosa and Adene, 2007; Oladele et al., 2003). The disease had been reported to be acute, rapidly spreading, contagious, nervous and respiratory disease of birds of all ages (Okeke and Lamorde, 1988). The clinical signs of ND are known to vary based on the virulence and tropism of the ND virus involved, species, age, immune status of the birds, as well as, the prevailing environmental condition (Alders and Sprabrow, 2002). ND is endemic often causing outbreak in backyard and commercial poultry in most parts of Africa and Nigeria (Ezeokoli et al., 1984; Adene, 1996). The impact of ND was said to be more in Nigeria where over 90% of the poultry were rural poultry that were left to roam freely to scavenge for food and water bringing them into close activity space with wild birds (Adene and Oguntade, 2006).
It is pathogenic for the domestic chickens, turkeys, guinea fowls and other poultry. Wild birds may not show clinical disease but do develop antibodies to the virus (Orajaka et al., 1999; Sa’idu et al., 2004). These birds act to maintain ND viruses which serve as sources of frequent outbreaks in rural and backyard poultry (Alexander, 2001; Sa’idu et al., 2004). Outbreak of ND had been caused by contamination of poultry feed with faeces of pigeon in the UK (Alexander, 2011). Wild birds and semi-domestic birds are known to be susceptible and develop antibodies to ND hence, play major roles in the spread of ND viruses especially in Nigeria as well as other African countries with poor poultry husbandry practice (Oladele et al., 1996; Sa’idu et al., 2004). The circulation of ND viruses in wild birds and maintenance in the environment were responsible for most outbreaks in backyard and commercial poultry even after vaccination (Sa’idu et al., 2008). Natural outbreak of Newcastle disease (ND) was reported in a flock of guinea-fowl in Nigeria, affecting 1,029 birds of which 250 (24.3%) died. Paralysis of the legs and wings, coughing, sneezing, white diarrhoea and complete cessation of egg production were observed (Haruna et al., 1993).
Live bird market has been identified as one of the high risk areas for disease transmission due to high concentration and interaction of a wide variety of birds brought from different sources (Jibril et al., 2014). In view of this, this study was conducted to determine the prevalence of Newcastle Disease Virus among apparently healthy guinea fowls in live bird market of Sokoto state in order to determine the seroprevalence of the disease among guinea fowl that were presented in the market.
Materials and Methods
The study was conducted in Sokoto. Sokoto is the capital of Sokoto State, located at 13°N and longitude 30°E and 90°E in the North Western part of Nigeria. It lies roughly between longitude 30°E and 15°E of Greenwich and between 4°N and 14°N of the equator. It covers approximately an area of 56,000 square kilometers (Anon, 2001). Sokoto metropolis is located in the Sudan savannah zone with grass vegetation, sandy soil and humidity, which is usually below 40% except in few wet months when it approaches 60% (Iloeje, 1971).
Sample Size Determination
Sample size was estimated using the formula of Thrusfield, 2005.
n = z2 p (1-p)/d2
Where: n = number of samples, z = standard normal deviation at 95 % confidence interval, p = expected prevalence (p = 17.0 %, Abraham et al., 2014), d = desired absolute precision and q = 1-p, n = 217.
A total of 229 samples were collected to increase the chance of antibody detection.
Data forms were used to record vital information of each bird sampled before sample collection. A total of 229 blood samples were collected from randomly selected guinea fowls at the point of slaughter. Samples were transported in an ice park at 4°C container to the City Campus Central laboratory, Usmanu Danfodiyo University Sokoto, Nigeria, where the sera were harvested. Clotted blood samples were centrifuged (BOSCH ® Digital Centrifuge USA) at 3000 revolutions per minute for 5 minutes. The clear sera were then harvested by decantation and delivered into corresponding clean plain vials that were appropriately labeled. All sera were stored at -20ºC (VT-8, Denmark) to preserve their immunological and other biochemical properties prior to serology (Brown and Torres, 2008).
Serology and Serological Techniques
Sera samples were screened for the presence of antibodies to Newcastle Disease Virus using ID Screen® NDV competition obtained from ID-vet Innovative Diagnostics, Montpellier, France. The test is a competitive ELISA for the detection of Nucleo-Protein antibodies in serum of poultry. The principle of this technique is based on the formation of a colourless reaction following interaction of a positive test serum in a well, coated with NDV antigen after addition of a chromogenic substrate. Optical density was read using ELISA reader (Optic System IVYMEN® 2100C, USA) at 450nm.
The data obtained was analysed using GraphPad Instat ®. Chi-square was used to measure the strength of association between sex, age and prevalence of NDV. Values of P < 0.05 at 95 % confidence interval were considered significant.
The overall prevalence was found to be 40.6 % (93/229). Table 1, indicated the sex specific prevalence of Newcastle Disease virus in guinea fowl. The males showed a higher prevalence rate (41.9: 83/198). However, this difference is not statistical significant (p > 0.05). In Table 2, adult guinea fowls shows a higher prevalence rate when compared with the young birds.
Table 1: Sex specific prevalence of Newcastle Disease Virus in guinea fowl in live bird Market of Sokoto, Nigeria
|Sex||Number Sampled||Number Positive||Prevalence (%)||Relative Risk||95 % CI|
χ2 = 0.675; p value = 0.41; CI = confidence interval
Table 2: Age specific prevalence of Newcastle Disease Virus in guinea fowl in live bird Market of Sokoto, Nigeria
|Age||Number Sampled||Number Positive||Prevalence (%)||Relative Risk||95 % CI|
χ2 = 1.460; p value = 0.227; CI = confidence interval
This serological study revealed the presence of circulating antibodies of Newcastle disease (ND) among apparently healthy guinea fowls in Sokoto major live bird market, with 40.6% of guinea fowls tested positive. This shows that ND is still an endemic viral disease of domestic poultry in the study area (Saidu et al., 2004). Antibodies detected most likely would be as a result of natural infection since vaccination of the village poultry is rarely undertaken in Nigeria (Abdu et al., 1987). Guinea fowl, turkeys and peacocks are susceptible to ND and local husbandry practices, where different species of birds are raised together in the same compound, encourage cross infection by ND virus among the different species (Saidu et al., 2004). The detection of high prevalence of circulating antibodies to ND in the live bird market is a major concern in relation to other birds. These birds are exposed to birds from multiple sources having a higher tendency of circulating the virus and may serve as a source of infection to house hold chickens when introduced (Killian, 2009; Jibril et al., 2014). This study however, shows a relatively lower prevalent rate of ND virus in village chickens when compared with what has been reported earlier (41%) by Adu et al., (1986). Ezeokoli et al.(1984) reported 73% prevalence of antibodies against NDV in traditionally managed backyard flocks in Zaria while Orakaja et al. (1999) reported 63% in south eastern Nigeria. El-Yuguda et al. (2007) reported a prevalence of 46% in village chickens in Borno State; Salihu et al. (2012) reported an ND prevalence of 54.67% in Nasarawa State. This observed differences in the rates of NDV antibodies may be as a result of ecological variations in ND activity or sampling methods and may perhaps be a reflection of the impact of environment on the viability of NDV and epidemiology (Orajaka et al., 1999). However, studies conducted by Ameji et al. (2011) and Jibril et al. (2014) has showed a lower prevalence of 25.5% and 35.8 % in live bird markets of Kogi and Zamfara State respectively in Nigeria. Studies in other part of Africa have reported a similar prevalence in unvaccinated local chickens. This study shows a higher prevalence in male (41.9 %) when compared to females (32.3 %) guinea hen. This report is similar to the studies conducted by Jibril et al. (2014) that showed a higher prevalence among males’ chickens in live bird markets and housed hold in Zamfara State, Nigeria. However, recent studies conducted by Alkali et al. (2017) have showed a higher prevalence rate among females (15.32 %) than males (14.02 %).
From this study, adult guinea fowls show a higher prevalence (44.4 %) of antibodies to NDV when compared with younger ones (29.1 %). However, studies conducted by Alkali et al. (2017) has showed that, higher prevalence was recorded in young birds (Less than three months) and least in adults (13.66%).
Newcastle disease in endemic in the study area, live bird markets is an important factor to be considered in the transmission dynamics of Newcastle disease virus. The disease is presence in all sexes and ages of guinea fowl in the study area.