Risk Factors Analysis of Mycoplasma Gallisepticum Infection

Risk Factors Analysis of Mycoplasma Gallisepticum Infection Seroprevallence and risk factors analysis of Mycoplasma gallisepticum infection of chickens in Bhola district, Bangladesh. Mahfuzul Islam  and Md. Shahidur Rahman Khan ABSTRACT This study was aimed to determine the seroprevalence and risk factors (types of chickens, age groups and seasons) of Mycoplasma gallisepticum (MG) infection in chickens. The study was conducted from April 2011 to March 2012. A total of 480 blood samples were collected considering types of chicken (backyard chicken and commercial layer chicken), age groups (pullet, adult and old) and seasons (summer and winter) from different upazila of Bhola district of Bangladesh. On the basis of serum plate agglutination test, 268 chickens were found positive for MG (55.83%). According to the results, the higher (62.5%) and lower (53.61%) prevalence of MG infection was found in backyard chickens and commercial layer chicken respectively. The prevalence was recorded highest in pullets (60.63%) followed by adult (55.63%) and old chickens (51.25%), respectively. The prevalence was highest (60.42%) in winter and lowest (51.25%) in summer. It is usually recommended that MG infection is still an importan t disease problem in chickens in Bangladesh. So, preventive strategies, such as appropriate husbandry and hygiene, sanitary handling of chicks and eggs, routine health monitoring, chemoprophylaxis and vaccination should be emphasized. Keywords: chickens, Mycoplasma gallisepticum, risk factors, seroprevalence. INTRODUCTION In Bangladesh, poultry industry has made remarkable progress in the last decades from a backyard venture to a considerably sophisticated commercial industry. In spite of the rapid growth of poultry industry, it is still prone to certain infectious threats which may cause great economic losses. Inadequate measures adopted by the stakeholders for the control of diseases in addition to certain management problems have rendered the poultry farming a risky business. A number of microbial diseases are the major health hazards being faced by poultry industry, among which mycoplasmosis is the most important. Mycoplasmosis is caused by four major pathogens viz. M. gallisepticum (MG), M. synoviae (MS), M. meleagrides (MM) and M. iowae (MI) (Bradbury, 2001 and Evans et al., 2005) of which MG is the most important species that causes chronic respiratory disease (CRD) in chickens (Ley, 2008). Birds of all age groups are susceptible to this disease but young birds are more prone to infection than adults (Seifi and Shirzad, 2012). MG is readily transmitted horizontally from both clinically infected and carrier birds through direct contact. Mycoplasma organisms can survive in the host bird for approximately 24 hours and fomites can serve as an infectious route. Vertical transmission from some carrier birds occurs through trans-ovarian transmission. Poultry can carry the MG organisms with no clinical signs until a stressful event triggers clinical disease. Incubation period varies from 6-21 days and presentation of clinical signs can be highly variable (Ley, 2008). The clinical signs with MG infection in chicken include respiratory rales, nasal discharge, coughing, and occasionally conjunctivitis (Ley, 2003). MG can be diagnosed by studying their different properties such as morphological, cultural characteristics, biochemical and serological properties of the causal agent (Ley, 2008). Among serological tests the serum plate agglutination (SPA) test could be used as a tool for quick detection of MG infection (Seifi and Shirzad, 2012). Commercially available attenuated strains of Mycoplasma gallisepticum (MG) are commonly used as vaccine within the layer industry to control MG-induced mycoplasmosis (Evans et al., 2012). However, total eradication of MG infection through test and slaughter is the most effective control method (Ley, 2003). But in practical it is expensive and the emergence of multiage complexes in the commercial layer industry makes this approach impractical (Levisohn and Kleven, 2000). Due to economic importance diagnosis and prophylaxis of avian mycoplasmosis have received attention. Reports on seroprevalence of mycoplasmosis in chickens are very much limited in the Bhola district of Bangladesh. So, the aim of the present study was to determine the seroprevalence of Mycoplasma gallisepticum (MG) infection in chickens and analysis the risk factors (types of chickens, age groups and seasons) to take effective control measures such as appropr iate husbandry and hygiene, sanitary handling of chicks and eggs, routine health monitoring, chemoprophylaxis and vaccination. MATERIALS AND METHODS This study was conducted in the Laboratory of District veterinary hospital, District Livestock Office, Bhola, Bangladesh during the period from April 2011 to March 2012. Study area and selection of bird: A total of 480 blood samples were collected from the wing vein of unvaccinated and healthy chickens considering types of chicken (Backyard Chicken and Commercial layer Chicken), age groups (pullet, adult and old) and seasons (summer and winter) from different upazila of Bhola district of Bangladesh Blood collection and serum preparation: In live birds, 2 mL blood were collected from wing vein by using fresh disposable plastic syringe (5 mL) and collected blood was kept in room temperature for about 1-2 hour(s). A clean straw color serum was seen around the clotted clump and the serum was poured into a labeled screw capped vial and stored at -20 ºC until used. Serum plate agglutination (SPA) test: The SPA test was conducted with crystal violet stained M. gallisepticum commercial antigen (Nobilis ® MG) obtained from Intervet Company Ltd. (The Netherlands). Following the manufacturers instruction, 0.03 mL antigen and 0.03 mL serum was placed side by side with pipette in a glass plate and mixed well by stirring with glass rod, followed by rocking. Results were read within 2 min. In positive cases granules were formed slowly which could be seen during rocking. In the negative case, no such granules were formed. Agglutination was assigned score from +1 to +3. Only the sera samples having agglutination score +2 or greater were recorded as positive and were included for calculation of percent prevalence. RESULTS AND DISCUSSION Overall prevalence of MG infection in backyard and commercial layer chicken The overall prevalence of MG infection was 55.83% (Table 1). The present finding is in agreement with previous reports of Godoy et al. (2001), Biswas et al. (2003) and Zhang et al. (2001) who reported 59.1%, 54.9% and 53.0% seroprevalence of MG infection in chickens, respectively. Results also showed a higher prevalence of M. gallisepticum in backyard checkens (62.5%) as compared to commercial layer chicken (53.61%). Hossain et al. (2007) showed the overall seroprevalence of MG infection in different flocks of commercial layer chicken in Rajshahi district of Bangladesh was recorded as 55.13%. Similar reports were demonstrated by Sikder et al. (2005) who reported 56.9% seropositive layer chickens for MG infection in Patuakhali district and by Sarkar et al. (2005) who reported 58.9% seropositive layer chickens for MG infection in some model breeder poultry farms in Feni district of Bangladesh. On the other hand, there was no seroprevallence data available in case of backyard checkens. But in this studty the higher prevalence of M. gallisepticum in backyard checkens is may be due to more natural infection. Prevalence of MG infection in different ages Results showed the maximum prevalence in pullets (60.63%) followed by adult (55.63%) and old (51.25) chickens, respectively (Table 2). Previously, Mukhtar et al. (2012) recorded the highest prevalence (54.84 %) was found in pullets, followed by 46.34 %, and 44.44 % in adult and old laying flocks, respectively. This finding also supports the report of Hossain et al. (2007) who recorded the highest prevalence of MG infection was 72.72% in 18-25 weeks age group whereas lowest prevalence was 44.00% in 66 weeks and above age group. Similar report was also demonstrated by Sikder et al. (2005) who reported highest MG infection (71.42%) at 18 weeks of age and lowest (55.17%) at 63 weeks of age. This finding also supports the report of Sarkar et al. (2005) who recorded 73.80% MG infection at 20 weeks of age in comparison to 45.16% at 55 weeks of age. Highest infection in the young chickens is due to the vertical transmission of the organisms. Seasonal incidence of MG infection Results showed a higher prevalence of M. gallisepticum in winter (60.42%) as compared to the summer (51.25%) season (Table 3) and similar report was published earlier (Sarkar et al., 2005) that reported 62.4% prevalence of MG infection in winter in comparison to 53.1% in summer. Similar to our findings, higher prevalence of MG infection during winter season (61.48 %) than in summer (47.74 %) has been reported earlier (Heleili et al., 2011). Mukhtar et al. (2012) showed the disease was more prevalent in winter season (45.13 %) in comparison with the summer season (36.30 %). Hossain et al. (2007) showed the seropositivity in chickens was 61.49% in winter compared to 47.74% in summer. Similar report was demonstrated by Sarkar et al. (2005) who reported 62.44% prevalence in winter in comparison to 53.10% in summer. This seasonal variation in infection might be due to the sudden change in temperature and cold stress on the birds. CONCLUSIONS In consequence, M. gallisepticum is prevalent in Bhola district of Bangladesh and also it could cause severe economic losses. The prevalence of MG infection is higher in backyard chickens in comparison to commercial layer chickens. Additionally, it was proved that the occurrence of MG have a consequential relationship with age groups and seasons. Keeping in view, efforts should be made towards educating the poultry farmers for the effective control of MG in both backyard and commercial poultry farms through improving biosecurity. Moreover, detailed studied on the country wide prevalence of MG should be designed to know the current status of disease in Bangladesh. ACKNOWLEDGMENTS The author expresses his deepest sense of gratitude and sincere thanks to Dr. Pradip Kumar Karmaker, District Livestock Officer, Bhola for his constructive and informative suggestions and constant inspiration in course of the research work period. 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Table 1: Overall seroprevalence of Mycoplasma gallisepticum infection in chickens Legend: No.=Number, %=Percentage Table 2: Seroprevalence of Mycoplasma gallisepticum among various age group Legend: No.=Number, %=Percentage Table 3: Seroprevalence of Mycoplasma gallisepticum among seasons Legend: No.=Number, %=Percentage 1