Caprine arthritis and encephalitis virus infection in goats of Bangladesh: Serological detection and its associated risk factors.

Background and Aim: Caprine arthritis and encephalitis (CAE) is a multisystemic persistent viral disease of goat that causes significant economic losses to the farmers and livestock sector. However, no information in this country is available regarding CAE virus (CAEV) infection. Therefore, this study aimed to estimate the seroprevalence of CAEV infection among the goat population in the selected goat-prone districts in Bangladesh and to identify the associated risk factors of the disease. Materials and Methods: From July 2021 to June 2022, 446 goat serum samples were randomly collected from the study area. Goat owners were interviewed using a pretested questionnaire to determine the risk factors. A commercial indirect enzyme-linked immunosorbent assay kit was used to screen blood serum for CAEV antibodies. Logistic regression models were used to analyze risk factors and serological data to identify the potential risk factors. Results: Out of 446 serum samples, 19 samples were seropositive against CAEV. The overall seroprevalence was 4.26% (95% confidence interval [CI]: 2.58-6.57). The multivariable logistic regression model identified sex (Female; odds ratio [OR]: 3.98; 95% CI: 1.13-13.95), animal age (12-48 months; OR: 4.93, 95% CI: 0.63-38.13), and biosecurity status (Poor biosecurity; OR: 1.66, 95% CI: 0.46-5.92) as potential risk factors for CAEV seropositivity. Conclusion: This study revealed the serological detection of CAEV in Bangladeshi goats where seroprevalence is found to be relatively low. To eradicate the disease, screening and culling of infected goats from the herd might be implemented.

Prevalence and identification of caprine pasteurellosis in pneumonic goats in Bangladesh.

Objective: This research aimed to assess the prevalence of caprine pasteurellosis, isolate and identify pasteurellosis (Mannheimia haemolytica and Pasteurella multocida) in pneumonic goats, and discover the main bacterial cause of pneumonia. Materials and Methods: One hundred and five samples (94 nasal swabs and 11 lung tissues) from goats suspected of having pneumonia were taken and transferred aseptically to the laboratory. Following the processing of the collected samples, Pasteurella spp. was isolated with the aid of plate culture methods. Biochemical characteristics were used to identify all bacterial isolates, which were then verified by polymerase chain reaction (PCR). Antimicrobial susceptibility testing was also carried out to evaluate the sensitivity profiles of various antibiotics. The Pasteurella haemolytica serotype-specific antigen (PHSSA) gene was used to identify isolates of M. haemolytica, and the KMT1 gene was used to identify isolates of P. multocida. Results: From the 105 clinically suspicious samples, 51 (48.57%) were identified to be Pasteurella spp. through bacteriological testing and also by PCR targeting the 16S rRNA gene. Of these, 47.87% (45/94) were nasal swabs, and 54.55% (6/11) were lung tissues. Among confirmed samples, 70.59% (36/51) were identified as M. haemolytica, and 29.41% (15/51) were identified as P. multocida. Resistance to tetracycline, streptomycin, oxytetracycline, gentamicin, and ceftriaxone was found in 50%-83% of the isolates. In addition, PCR identified the PHSSA and KMT1 genes from isolates of P. multocida and M. haemolytica, respectively. Conclusion: The present study revealed that M. haemolytica and P. multocida primarily caused pasteurellosis in pneumonic goats in Bangladesh. However, when treating these animals, the proper choice of antimicrobials should be made to control this disease.

Antimicrobial Resistance Profile of Common Foodborne Pathogens Recovered from Livestock and Poultry in Bangladesh.

Multidrug-resistant (MDR) foodborne pathogens have created a great challenge to the supply and consumption of safe & healthy animal-source foods. The study was conducted to identify the common foodborne pathogens from animal-source foods & by-products with their antimicrobial drug susceptibility and resistance gene profile. The common foodborne pathogens Escherichia coli (E. coli), Salmonella, Streptococcus, Staphylococcus, and Campylobacter species were identified in livestock and poultry food products. The prevalence of foodborne pathogens was found higher in poultry food & by-product compared with livestock (p < 0.05). The antimicrobial drug susceptibility results revealed decreased susceptibility to penicillin, ampicillin, amoxicillin, levofloxacin, ciprofloxacin, tetracycline, neomycin, streptomycin, and sulfamethoxazole-trimethoprim whilst gentamicin was found comparatively more sensitive. Regardless of sources, the overall MDR pattern of E. coli, Salmonella, Staphylococcus, and Streptococcus were found to be 88.33%, 75%, 95%, and 100%, respectively. The genotypic resistance showed a prevalence of blaTEM, blaSHV, blaCMY, tetA, tetB, sul1, aadA1, aac(3)-IV, and ereA resistance genes. The phenotype and genotype resistance patterns of isolated pathogens from livestock and poultry had harmony and good concordance, and sul1 & tetA resistance genes had a higher prevalence. Good agricultural practices along with proper biosecurity may reduce the rampant use of antimicrobial drugs. In addition, proper handling, processing, storage, and transportation of foods may decline the spread of MDR foodborne pathogens in the food chain.

First Isolation and Molecular Characterization of Chicken Astrovirus and Avian Nephritis Virus in Chickens in Bangladesh.

Chicken astrovirus (CAstV) and avian nephritis virus (ANV) are enteric viruses of poultry and have infected a wide range of poultry species worldwide, causing runting-stunting syndrome (RSS), which requires virus screening and results in serious economic damage. No confirmed cases have been reported from Bangladesh. In the present study, CAstV and ANV were monitored in Bangladesh. We monitored samples for CAstV and ANV and compared their genomic sequences to other reference strains. We found 8/31 flocks (25.8%) were positive for CAstV, 6/31 flocks (19.3%) had mixed infection of CAstV and ANV, and 1 flock (3.2%) was positive for ANV. Only ANV and a combination of CAstV and ANV were found in broilers and broiler breeders, but CAstV was found in all types of chickens. We isolated two of each from CAstV and ANV through specific pathogen-free chicken embryonated eggs via the yolk sac route. Phylogenetic analysis based on the ORF1b conserved region of CAstV and ANV suggested that the locally circulating strain was closely related to the strains isolated from India and Brazil. This report is the first molecular characterization of CAstV and ANV in Bangladesh. This study highlights that CAstV and ANV are circulating in Bangladeshi poultry.

Erratum: Genetic Evolution and Transmission Dynamics of Clade 2.3.2.1a Highly Pathogenic Avian Influenza A/H5N1 Viruses in Bangladesh.

[This corrects the article DOI: 10.1093/ve/veaa046.].

Potential risk factors of avian influenza virus infection in asymptomatic commercial chicken flocks in selected areas of Bangladesh during 2019.

OBJECTIVE: Avian influenza is a zoonotic disease with a pandemic potential that can infect avian and mammalian species, including humans. Studies aimed at investigating avian influenza virus (AIV) status in asymptomatic chickens and their shedding are uncommon in Bangladesh. Therefore, the current study aimed to examine the distribution of AIV subtypes in asymptomatic commercial chicken flocks and to identify the possible risk factors associated with this infection in two selected sub-districts of Bangladesh. MATERIALS AND METHODS: A total of 582 oropharyngeal swabs were collected from 23 chicken farms during 2019 and evaluated for the presence of AIV and its subtypes by real-time reverse transcription PCR assays. Risk factors associated with AIV infection were analyzed from questionnaire data. RESULTS: Overall, AIV prevalence was 7.73% (n = 45) with 7.39% and 7.92% in Dhamrai and Gazipur Sadar sub-districts, respectively. In AIV-positive samples, the prevalence of A/H5N1, A/H5N2, A/H9N1, and A/H9N2 was 31.11%, 28.89%, 6.67%, and 8.89%, respectively. None of the samples were positive for N6 and N8. The odds ratio (OR) of AIV infection was 1.15 in broiler versus layer and 2 in Sonali versus layer chickens. The OR was 1.95 for medium versus small, 2.6 for large versus small flock size, 1.5 for moderate versus good biosecurity, and 2.92 for poor versus good biosecurity practicing farms. CONCLUSION: The results demonstrated that A/H5N1, A/H5N2, A/H9N1, and A/H9N2 are circulating in asymptomatic chickens of selected areas. Strict farm biosecurity practices and avoiding higher flock density are recommended to prevent AIV spread in the study.

First report on the seroprevalence of avian encephalomyelitis virus antibody in Sonali (cross-bred) chickens in Bogura, Bangladesh.

OBJECTIVES: The study intended to detect the presence and distribution of avian encephalomyelitis virus (AEV)-specific antibodies in Sonali (cross-bred) parent chickens regarding farm location, flock size, and age in Bogura district of Bangladesh, a Sonali chicken belt. MATERIALS AND METHODS: A total of 275 Sonali parent chickens' blood samples were collected randomly from 39 flocks during laying age with a healthy and non-vaccination history against AEV. Blood samples were collected aseptically from the wing veins of chickens using 3-ml syringes and sera were separated. Then, the sera were transferred to the laboratory by maintaining a cool chain. Indirect enzyme-linked immunosorbent assay was used to detect the specific antibodies against AEV present in the sera samples. RESULTS: Overall, 70.18% of the chickens were found seropositive for AEV antibodies. Based on the location, the highest seropositivity was recorded in Bogura Sadar [91.30%, confidence intervals (CI) 79.21%-97.58%], and the lowest was in the Adomdighi sub-district (45.45%, CI 29.49%-63.08%). For flock size, AEV seropositivity was significantly (p < 0.05) higher in the large flock (82.22%, CI 72.74%-89.48%). Regarding age groups, the seropositivity of AEV was significantly (p < 0.05) increased with chickens' age. Higher seropositivity was noted in chickens aged >51 weeks (89.32%, CI 81.69%-94.55%). CONCLUSION: The results indicate that AEV is circulating in the environment, and chickens were exposed to the field strain of AEV. To the best of our knowledge, this is the first report on AEV in chickens in Bangladesh. Proper vaccination and standard farm biosecurity practice could minimize AEV infection in chickens. A detailed epidemiology study, detection, and characterization of the AEV would be essential for effective AEV infection control.

Seroprevalence of Brucellosis in goats in some selected areas of Bangladesh.

OBJECTIVE: This study aimed to explore the seroprevalence of Brucella spp. in goats in some selected areas of Bangladesh. MATERIALS AND METHODS: This study was conducted in different goat-populated regions of Bangladesh from July 2017 to June 2018. A total of 208 serum samples were randomly collected from goats in Jashore (n = 50), Jhenidah (n = 22), Tangail (n = 40), Savar (n = 46), Thakurgaon (n = 18), and Bandarban (n = 32) areas. The samples were subjected to determine the presence of antibodies against Brucella spp. by rose bengal plate test (RBPT) and competitive enzyme-linked immunosorbent assay (c-ELISA). RESULTS: Overall, the seroprevalence of Brucellosis in goats was 4.33% (n = 9/208) by RBPT and 2.40% (n = 5/208) by c-ELISA. The seroprevalence of brucellosis on the basis of RBPT was 6% (buck: 0%, doe: 6%) in Jashore, 4.5% (buck: 0%, doe: 4.5%) in Jhenidah, 2.5% (buck: 0%, doe: 2.5%) in Tangail, 4.35% (buck: 0%, doe: 4.35%) in Savar, 6.25% (buck: 0%, doe: 6.25%) in Bandarban, and 5.56% (buck: 0%, doe: 5.56%) in Thakurgaon. On the other hand, the seroprevalence of brucellosis by c-ELISA was 4% (buck: 0%, doe: 4%) in Jashore, 4.5% (buck: 0%, doe: 4.5%) in Jhenidah, 3.13% (buck: 0%, doe: 3.13%) in Bandarban, and 5.56% (buck: 0%, doe: 5.56%) in Thakurgaon. Brucellosis was more prevalent (p > 0.001) in does aging 3-4 years. CONCLUSION: Goats from different areas of Bangladesh are caring antibodies against Brucella organisms. Further bacteriological investigations are necessary.

Efficacy of two vaccines against recent emergent antigenic variants of clade 2.3.2.1a highly pathogenic avian influenza viruses in Bangladesh.

H5N1 highly pathogenic avian influenza viruses (HPAIVs) have caused outbreaks in poultry in Bangladesh since 2007. While clade 2.2.2 and 2.3.4.2 HPAIVs have not been detected since 2012, clade 2.3.2.1a viruses have caused continuous outbreaks since 2012 despite the use of vaccines. In this study, we evaluated the efficacy of two H5 vaccines licensed in Bangladesh, RE-6 inactivated vaccine, and a recombinant herpesvirus of turkeys vaccine with an H5 insert (rHVT-H5), for protection against recent field viruses in chickens. We selected three viruses for efficacy tests (A/chicken/Bangladesh/NRL-AI-3237/2017, A/crow/Bangladesh/NRL-AI-8471/2017 and A/chicken/Bangladesh/NRL-AI-8323/2017) from 36 H5 viruses isolated from Bangladesh between 2016 and 2018 by comparing the amino acid sequences at five antigenic sites (A-E) and analyzing hemagglutination inhibition (HI) titers with reference antisera. The RE-6 and rHVT-H5 vaccines both conferred 80-100% clinical protection (i.e. reduced morbidity and mortality) against the three challenge viruses with no significant differences in protection. In addition, both vaccines significantly decreased viral shedding from infected chickens as compared to challenge control chickens. Based on these metrics, the current licensed H5 vaccines protected chickens against the recent field viruses. However, the A/crow/Bangladesh/NRL-AI-8471/2017 virus exhibited antigenic divergence including: several unique amino acid changes in antigenic epitope sites A and B and was a serological outlier in cross HI tests as visualized on the antigenic map. The continuing emergence of such antigenic variants which could alter the dominant antigenicity of field viruses should be continuously monitored and vaccines should be updated if field efficacy declines.

Detection of an emerging novel sublineage Ind2001BD1 and lineage PanAsia of foot-and-mouth disease virus serotype O in cattle in Manikgonj district of Bangladesh, 2018.

Background: Foot-and-mouth disease (FMD) is an endemic disease of cloven-hoofed animals in Bangladesh and multiple outbreaks occur every year because of the FMD virus (FMDV). Aim: The aim of the present investigation was to determine the molecular characterization of the VP1 coding region of FMDV serotype O outbreak in cattle. Methods: A total of four tongue epithelial specimens were collected from clinically FMD-positive cattle during June 2018 in Manikgonj district of Bangladesh. Results: All four isolates were recorded positive for FMDV serotype O. The phylogenetic analysis showed that two isolates were clustered within an emerging novel sublineage Ind2001BD1 under lineage Ind2001 of FMDV serotype O, which was identified during 2012-2016 in Bangladesh. One isolate was clustered within the lineage PanAsia of FMDV serotype O and was closely related to an isolate identified in Nepal in 2009. The phylogenetic reconstruction revealed that all the four isolates belong to the Middle East-South Asia topotype. Conclusion: Therefore, multiple lineages of the FMDV serotype O are circulating among the cattle in the outbreak area, which make it more complex for the FMD control program in Bangladesh. A comprehensive study on the genetic characteristics of FMDV across the country is required for effective FMD prevention and control strategy.

Impact of global climate change on livestock health: Bangladesh perspective.

The global carbon emission rate, due to energy-driven consumption of fossil fuels and anthropogenic activities, is higher at any point in mankind history, disrupting the global carbon cycle and contributing to a major cause of warming of the planet with air and ocean temperatures, which is rising dangerously over the past century. Climate change presents challenges both direct and indirect for livestock production and health. With more frequent extreme weather events including increased temperatures, livestock health is greatly affected by resulting heat stress, metabolic disorder, oxidative stress, and immune suppression, resulting in an increased propensity for disease incidence and death. The indirect health effects relate to the multiplication and distribution of parasites, reproduction, virulence, and transmission of infectious pathogens and/or their vectors. Managing the growing crossbreeding livestock industry in Bangladesh is also at the coalface for the emerging impacts of climate change, with unknown consequences for the incidence of emerging and re-emerging diseases. Bangladesh is now one of the most vulnerable nations to global climate change. The livestock sector is considered as a major part of food security for Bangladesh, alongside agriculture, and with one of the world's largest growing economies, the impacts are exaggerated with this disaster. There has been no direct study conducted on the impact of climate change on livestock health and the diseases in Bangladesh. This review looks to explore the linkage between climate change and livestock health and provide some guidelines to combat the impact on livestock from the Bangladesh perspective.

Genetic evolution and transmission dynamics of clade 2.3.2.1a highly pathogenic avian influenza A/H5N1 viruses in Bangladesh.

Asian lineage A/H5N1 highly pathogenic avian influenza viruses (HPAIVs) have been responsible for continuous outbreaks in Bangladesh since 2007. Although clades 2.2.2 and 2.3.4.2 HPAIVs have disappeared since poultry vaccination was introduced in 2012, clade 2.3.2.1a viruses have continued to be detected in Bangladesh. In this study, we identified A/H9N2 (n = 15), A/H5N1 (n = 19), and A/H5N1-A/H9N2 (n = 18) mixed viruses from live bird markets, chicken farms, and wild house crows (Corvus splendens) in Bangladesh from 2016 to 2018. We analyzed the genetic sequences of the H5 HPAIVs, to better understand the evolutionary history of clade 2.3.2.1a viruses in Bangladesh. Although seven HA genetic subgroups (B1-B7) and six genotypes (G1, G1.1, G1.2, G2, G2.1, and G2.2) have been identified in Bangladesh, only subgroup B7 and genotypes G2, G2.1, and G2.2 were detected after 2016. The replacement of G1 genotype by G2 in Bangladesh was possibly due to vaccination and viral competition in duck populations. Initially, genetic diversity decreased after introduction of vaccination in 2012, but in 2015, genetic diversity increased and was associated with the emergence of genotype G2. Our phylodynamic analysis suggests that domestic Anseriformes, including ducks and geese, may have played a major role in persistence, spread, evolution, and genotype replacement of clade 2.3.2.1a HPAIVs in Bangladesh. Thus, improvements in biosecurity and monitoring of domestic Anseriformes are needed for more effective control of HPAI in Bangladesh.

Seroprevalence of major avian respiratory diseases in broiler and sonali chicken in selected areas of Bangladesh.

OBJECTIVE: This study was conducted to investigate different respiratory diseases in broiler and sonali birds in some selected districts of Bangladesh. MATERIALS AND METHODS: We were collected a total of 460 blood samples from 46 farms with 36 broiler farms and 10 sonali farms (cross-breed) from 2015 to 2017. All the collected serum samples were tested for determining specific antibodies of avian rhinotracheitis (ART) virus, infectious laryngotracheitis (ILT) virus, infectious bronchitis (IBV) virus, and Ornithobacterium rhinotracheale (ORT) infection using commercially available enzyme-linked immunosorbent assay kits. RESULTS: The overall seropositivity was highest in ORT (45.9%), followed by IBV (37.6%), ART (2.6%), and ILT (0.4%). Out of 360 broiler samples, highest seropositivity was recorded in ORT (43.3%) and lowest in IBV (31.4%). Surprisingly, no broiler samples were found positive for ART and ILT. In case of sonali, the seropositivity was highest in IBV (60%) and lowest in ILT (2%). With respect to types of birds and age groups, the seropositive percentage of all four pathogens was found higher in sonali than broiler. Between two age groups of sonali, the seropositive percentage of ART (12%), ORT (55%), ILT (2%), and IBV (60%) was highest at 21-60 weeks of age compared to 5-20 weeks of age. However, based on location, the seropositive of ORT and IBV was highest in Jamalpur (63.3%) and Fulbariya and Trishal (50%) and lowest in Sreepur (16.7%) and Jamalpur (3.3%). CONCLUSION: The four pathogens are ubiquitous in nature for the sonali chickens, and the prevalence of ORT and IBV was the most prevalent viruses in the study areas. This study indicates a need for improved surveillance and characterization of ORT and ART circulating in all types of poultry in Bangladesh.

Outbreak investigation, molecular detection, and characterization of foot and mouth disease virus in the Southern part of Bangladesh.

OBJECTIVE: The objective of the study was to investigate Foot and Mouth Disease virus (FMDV) outbreak in cattle in the Sarankhola Upazila under Bagerhat district of Bangladesh with isolation, identification, and molecular characterization of FMDV during April 2018. MATERIALS AND METHODS: This Upazila is located at southern border of Bangladesh and surrounded by mangrove forest Sundarban. The outbreak investigation team collected epidemiological data from outbreak location. In addition, the team collected a total of 30 (15 calves, 15 adult) tongue epithelial tissue samples from a clinically FMD-affected cattle. The confirmation of FMDV and its three serotypes (A, O, and Asia-1) was performed by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). An amplified product of the VP1 region of FMDV genome was sequenced by Sanger sequencing method after cultivation and reconfirmation of FMDV into the BHK21 cell line. Genetic variability was studied by constructing a phylogenetic tree. RESULTS: The investigation survey was carried out in overall 8,393 (8,393/15,580; 53.89%) cases including 3,050 (3,050/8,393; 36.34%) cases in calf and 5,343 (5,343/8,393; 59.77%) cases in adult cattle. The overall case fatality rate (CFR) was recorded as 2.27% (354/15,580) with significantly highest CFR in the calf (71.46%; 253/354) compared to an adult. The collected all 30 samples found with FMDV positive and mixed infection of all samples with serotype Asia-1 and serotype O were observed. In BHK 21 cell line, the eight FMDV positive samples showed a typical cytopathic effect during the third passage. Finally, DNA sequence data of two isolates found closely related with the isolates of bordering country India and Myanmar. CONCLUSION: The investigation identified the risk factors involved in an outbreak of FMDV, namely, sharing the common paddy land after harvesting, no FMD vaccination, the interaction between cattle and wildlife, and cross bordering movement.

Prevalence and molecular characterization of infectious bronchitis virus isolated from chicken in Bangladesh.

AIM: The present study was aimed to determine the prevalence of infectious bronchitis virus (IBV) as well as virus isolation, identification, and molecular characterization of various strains circulating in Bangladesh. MATERIALS AND METHODS: A total of 371 swabs and organ samples were collected from four types of chicken including layer, Sonali (local), broiler, and broiler breeder under eight districts (Rangpur, Bogura, Tangail, Dhaka, Gazipur, Mymensingh, Jamalpur, and Cumilla) during 2014-2016 in Bangladesh. RESULTS: Out of 371 samples, 65 samples were positive in reverse transcriptase polymerase chain reaction (RT-PCR) for molecular identification of IBV. The overall prevalence was 17.52% recorded and among the selected types of chicken, the highest prevalence of IBV was found in layer that was 42.22% followed by 17.24% in Sonali, 14.93% in broiler breeder, and lowest prevalence was 11.94% in broiler chicken, respectively. Moreover, the prevalence of IBV was recorded highest in aged chicken at 41-60 weeks, which was 54.55% in layer, 27.27% in Sonali, and, afterward, 14.68% was found in broiler breeder, respectively. Frequency of IBV more frequently in winter (22.67%) followed by rainy (15.87%) and summer season (11.58%). The highest prevalence of IBV was found Tangail district (41.67%) followed by Mymensingh (24.42%), Gazipur (19.32%), Dhaka (15.38%), Jamalpur (16.67%), Bogura (13.68%), Cumilla (5.88%), and Rangpur (9.26%), respectively. Samples that were found high positive in IBV RT-PCR (Ct value below 30) were subjected to inoculation into chicken egg embryo to observe characteristic changes in chicken embryo. Swabs and organ samples were processed and passaged in 9-day-old embryonated chicken eggs through allantoic cavity route. IBV virus suspected samples inoculated into chicken egg embryos after 3-5 passages showed dwarfing and curling of the embryos which are characteristic lesions of IBV. Allantoic fluid was collected from all inoculated eggs and performed partial sequencing of S1 gene for three isolates. After sequencing, the phylogenetic tree was constructed from the nucleotide sequences of IBV isolates. Two of the isolates are 4/91 IBV and another one matched with QX-like IBV. CONCLUSION: The results revealed that the three isolates from different places in Bangladesh were identified for the 1st time as which will help for IBV control strategy.

Seroprevalence of Mycoplasma gallisepticum antibody by ELISA and serum plate agglutination test of laying chicken.

AIM: Mycoplasma gallisepticum (MG) is important avian pathogens responsible for chronic respiratory diseases of chicken and turkeys, which result in large economic loss for the poultry industry. The objectives of this study were determination of seroprevalence of MG antibody of commercial layer chicken at laying period in selected areas of Bangladesh. MATERIALS AND METHODS: A total of 563 blood samples were collected randomly from selected commercial layer chickens at laying period during the period from July to December, 2013. Indirect enzyme linked immunosorbent assay (iELISA) and serum plate agglutination (SPA) test were performed to detect the presence of antibodies against MG. RESULTS: Of 563 samples, 64.47% and 56.13% showed an overall prevalence of MG antibodies in iELISA and SPA test respectively. Prevalence of MG was recorded the highest (69.63%) at 50-55 weeks of age compared with lowest (53.26%) at 56-61 weeks of age (p<0.05). Significant (p<0.05) effect of breed were observed in the seroprevalence of MG infection in layer birds in the present study. The overall, 68.77%, 63.74% and 59.37% prevalence were found respectively in sonali, ISA Brown and White leg horn. The prevalence of MG antibodies was the highest (70.13%) in December followed by November (68%), October (65.67%), August (63.46%), September (58.54%) and July (51.78%) month. The seroprevalence of MG antibodies was higher (69.63%) in most of the large flocks and lower (56.82%) in small flocks. CONCLUSION: Therefore, might be suggested that the commercial layer farms should be routinely checked to monitor MG infection and the reactor birds should be culled since MG organism has the potential to transmit vertically. The correlation between MG antibody in month and flock size was not significant (p=0.359 and p=0.868, respectively).