Prevalence of antibodies to Mycoplasma gallisepticum (Mg) in indigenous and exotic chicken in Southwestern Nigeria

¹Department of Veterinary Pathology, Faculty of Veterinary Medicine, University of Ibadan, Ibadan, Nigeria, ²Department of Pathobiology, School of Veterinary Medicine, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

^&Corresponding author
Benjamin Obukowho Emikpe, Department of Pathobiology, School of Veterinary Medicine, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

Introduction    

The Nigerian indigenous (local) chicken constitutes over 70% of the nation´s poultry population, and they are reared in most rural and peri-urban areas for their meat and eggs [1]. These birds have been known to play important roles in the epidemiology of several important poultry diseases such as Egg Drop Syndrome (EDS), infectious bursa disease, and Newcastle disease, infectious bronchitis and fowl typhoid [2]. Avian mycoplasmosis has been reported to be endemic in Nigeria, especially in exotic chickens despite integrated control measures and the use of chemotherapeutic agents [3]. There is no vaccine available locally and the recently introduced imported vaccines are mainly used for parent stock. The diagnosis of avian mycoplasmosis in the past has been based mainly on clinical signs and gross post-mortem findings with very low isolation of the causative agent. Therefore, serological evidence or diagnosis has been advocated for the determination of Mycoplasma-induced disease and epidemiological investigations [4]. There are reports on the seroprevalence of Mycoplasma infection in local chicken in other parts of Africa and the Northern part of Nigeria with fewer reports in southern Nigeria [5]. The diagnoses in most of the reports in Africa were based on the rapid plate agglutination technique test and haemagglutination-inhibition test [6] with little on ELISA. This paper describes the results of an ELISA-based serological survey to determine the relative distribution of Mycoplasma gallisepticum (Mg) activity in unvaccinated Indigenous and exotic chickens in the humid Southwestern parts of Nigeria.

Methods     

Study area: this study was carried out in the humid southwestern part of Nigeria, where most of the intensive poultry production in Nigeria is concentrated specifically in Ibadan and Lagos.

Birds sampled: a total of 226 healthy adult local chickens under a free-range management system from 48 flocks were sampled. The flock size varied from between 8-20 birds per household. All the chickens had no history of vaccination. One out of every three adult birds per household flock was randomly selected for blood collection for fear of mortality, the owner did not allow a larger number of birds to be sampled. In addition, a total of 368 clinically healthy adult laying birds between 20 and 54 weeks old and 144 pullets (0-8 weeks old) under an intensive system of management from 24 flocks were sampled the flock size varied from 3,000-100,000 birds. All the chickens had no history of vaccination against Mg infections.

Serological test: the indirect enzyme-linked immunosorbent assay (ELISA) was employed to detect antibodies against Mycoplasma gallisepticum (Mg) infection. Based on the manual of the ELISA kit, the test was validated if the normal control average optical density (OD) is less than 0.200 and the corrective positive control (CPC) is between 0.250 and 0.900.

Data analysis: data were analyzed using the SAS GLM mode statistical package (SAS, 1992) Chi-square analysis was used to determine significant differences between the seroconversion rates. Significance is reported at the p<0.0.5 level.

Results     

The overall prevalence of Mg in the local chicken was 81.4% while in the commercial flocks; a prevalence rate of 64.8% was obtained. The difference in the seroprevalence of Mg concerning the type of birds was statistically significant (p=0.025). With regards to the age of birds, the highest prevalence of Mg antibodies was recorded in adult birds between 34-51 weeks of age (81.8%) as compared to 78.1% recorded in birds less than 2 weeks of age, 46.5% recorded in birds between 20-34 weeks, and 17.5% recorded in birds which were 8 weeks old. The difference between the seroprevalence of Mg concerning the age of birds was statistically significant (p=0.000). The location of birds had a significant effect (p=0.001) on the seroprevalence of Mycoplasma gallisepticum antibodies of which a seroprevalence of 81.3% was recorded for birds sampled from Ibadan, and 39.6% for birds sampled from Lagos as shown in Table 1.

Discussion     

This study found Mycoplasma gallisepticum (Mg) antibodies in 81.4% of local chickens and 64.8% of commercial chickens. The findings of this study compared to similar Nigerian studies with similar objectives and focus from three decades ago warranted this current study. Jibril et al. [7] found a Mycoplasma gallisepticum (Mg) seroprevalence of 23% and 64.5% in commercial and local chicken in southeast Nigeria, compared to 81.4% and 64.8% in this study. Despite the lack of recent studies comparing Mg antibodies in local and commercial chicken in Nigeria, Messa et al. [8] reported a 48.8% seroprevalence for Mycoplasma gallisepticum in backyard village chicken in Mozambique, lower than this study's 81.4%. The differences in Mycoplasma gallisepticum seroprevalence in these study areas may be due to geographical location, disease endemicity, and bird exposure. The high Mg infection rate in local chickens in this study may be due to free-range management and increased pathogen exposure.

In this study, 64.8% of commercial birds tested positive for Mycoplasma gallisepticum. This commercial chicken seroprevalence is lower than the 74.3% recorded in Ibadan, Nigeria by Bakre et al. [3]. The varied study results suggest Mycoplasma gallisepticum is endemic in Nigerian commercial chicken. The commercial flock's high Mg antibody seroprevalence highlights the epidemiological implications of vertical transmission through infected breeders, as chicks from infected flocks are usually infected for life. Unfortunately, Nigeria has no preventable Mg infection strategies other than post-infection control. Most farms sampled lack biosecurity measures, which may explain the high prevalence in commercial stocks. Commercial and local chicken have wide antibody titers, suggesting they were naturally exposed at different immune response stages. Natural infection may be possible because Nigeria has no local Mg vaccine and no routine Mg vaccination, especially in chickens.

This study found that Mg infection is more common in older flocks. This finding corroborates the finding reported by El-Ashram et al. [9] but contradicts the report of Hossain et al. [10], who found MG antibody seroprevalences of 71.6% in birds at 16-23 weeks and 18-20 weeks, respectively. This current study found a high seroprevalence of Mg, highlighting the need for a national control program to reduce vertical transmission in breeder farms through strict biosecurity and routine vaccination of Indigenous chicken with the Mg vaccine.

Conclusion     

The study found significant differences in the prevalence of Mycoplasma gallisepticum (Mg) antibodies among local and commercial chicken flocks, with a higher prevalence in local birds compared to commercial birds Additionally, the age and location of the birds significantly influenced the seroprevalence of Mg, with adult birds (34-51 weeks) showing the highest prevalence and birds from Ibadan exhibiting a higher prevalence compared to those from Lagos. It is recommended that farmers and poultry producers prioritize the vaccination and management practices that target the local chicken flocks, particularly the adult birds, to reduce the risk of Mg infections. Furthermore, the location of the birds should also be considered in disease management strategies, with a focus on the Ibadan region where the prevalence of Mg is higher.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

The authors of this study contributed to the research in the following: Godspower Obokparo Ohore was responsible for conceptualizing the study, designing the methodology, data collection, analyzing the data, and drafting the original manuscript. Samson Akparorue, Stephen Owarioro Akpavie, Theophilus Aghogho Jarikre, Benjamin Obukowho Emikpe contributed to data analysis, as well as reviewing and editing the manuscript. Derrick Adu Asare reviewed and edited the final manuscript. All the authors read and approved the final version of this manuscript.

Table     

Table 1: effect of type of bird, age, and location on seroprevalence of Mycoplasma gallisepticum

References