Managing Chronic Respiratory Disease in Poultry: Practical Diagnostic and Prevention Insights

Chronic Respiratory Disease (CRD), caused primarily by Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS), remains one of the most persistent challenges in commercial poultry systems¹,². Despite biosecurity measures and improved management, Mycoplasma infections continue to circulate in Indian flocks, contributing to respiratory distress, reduced weight gain, and higher medication costs³. 

Early diagnosis and targeted control are essential to minimize economic losses and ensure flock performance. Field evidence from northern Indian states has highlighted how MG and MS continue to affect commercial broiler flocks that have never been vaccinated against these pathogens³. This underlines the silent spread of Mycoplasma and the need for early molecular screening even in apparently well-managed farms. 

Field Epidemiology: What Vets Are Still Seeing 

Recent field investigations across poultry farms in Haryana and Rajasthan detected Mycoplasma in about 11.6% of screened samples, with MG accounting for 60% and MS for 10%³. Interestingly, non-pathogenic species like M. gallinarum and M. gallinaceum, often considered harmless, were also isolated. They occasionally act as the cofactors that worsen viral respiratory infections⁴. 

Practical Takeaway: 
When respiratory signs persist despite broad-spectrum antibiotics, consider Mycoplasma involvement, even if clinical signs appear mild or sporadic. Mixed infections, particularly with E. coli and IBV, often mask the true primary pathogen. 

Diagnosis: Beyond Culture, Toward PCR Precision 

Traditional culture on Frey’s medium remains valuable for isolation but is limited by Mycoplasma’s fastidious growth and overgrowth by commensals such as Acholeplasma laidlawii¹³. Field studies show that PCR-based detection can identify up to three times more positive samples than culture alone³. 

In one large-scale screening, PCR detected 26.7% MG and 12.8% MS infections—significantly higher than isolation-based detection³. PCR not only confirms infection rapidly but also enables strain differentiation through sequencing of regions such as the IGSR (16–23S rRNA) for MG and vlhA for MS³. 

Tip for Practitioners: 

• Use pooled tracheal or air sac swabs for PCR testing. 

• Always maintain a cold chain during transport to preserve organism viability. 

• If mortality is ongoing, collect samples from fresh carcasses (<6 hours postmortem) to avoid false negatives. 

Strain Variation and Field Relevance 

Molecular typing has shown that Indian MG isolates share high genetic similarity with strains from Thailand, Colombia, and Israel³. This points to a possible global circulation of similar MG lineages, possibly due to trade or shared vaccine ancestry. 

However, reliance on single gene regions like vlhA for MS typing may be limiting because of antigenic variability at its 3′ end³. For practical epidemiology, vets involved in surveillance should advocate the inclusion of multiple gene targets (pvpA, gapA, mgc2) for more robust typing in national monitoring programs. 

Control Strategies: Ground-Level Priorities 

While molecular diagnosis enhances detection, field control still depends on disciplined management and biosecurity. 

1. Biosecurity Reinforcement: 

• All-in–all-out rearing systems. 

• Control movement of people and vehicles. 

• Disinfect feed delivery routes and maintain proper litter composting (>60°C). 

2. Vaccination: 
Where vaccination is used, it should be planned with flock cycles—live vaccines at 3–4 weeks and killed vaccines from 12 weeks, maintaining an 8-week gap. Vaccination in high-stress conditions (summer heat, feed change) should be avoided to prevent immune suppression. 

3. Monitoring and Diagnostics: 
Regular PCR screening—especially before introducing new breeder or layer flocks—helps prevent silent carriers from entering the system. 

4. Rational Antimicrobial Use: 
Empirical use of tylosin, doxycycline, or enrofloxacin combinations is common, but periodic antibiogram testing is essential. Resistance monitoring not only guides therapy but prevents the long-term persistence of MG in flocks³.  

Practical Tips and Field Tricks 

• Suspect CRD early: Moist rales, sneezing, and stunted growth are early indicators. 

• Don’t overlook non-pathogenic Mycoplasma: They can worsen concurrent IB or ND outbreaks. 

• Target “problem sheds”: Once infection occurs, thorough disinfection and downtime (>14 days) are mandatory before restocking. 

• Environmental hygiene: Maintain humidity below 70%, ammonia <20 ppm, and ensure litter is dry to minimize recurrence. 

• Communication with farmers: Reinforce that “no visible symptoms” ≠ “no infection.” Carriers can silently transmit Mycoplasma. 

Looking Ahead 

Given the evolving genomic profiles of MG and MS, there’s a growing need to integrate molecular diagnostics into field decision-making. Broader surveillance across states, coupled with antimicrobial sensitivity profiling, will refine control strategies and improve therapeutic success. 

Ultimately, a combined approach including biosecurity, molecular monitoring, and rational medication will remain as the cornerstone for reducing CRD prevalence and sustaining poultry productivity. 

References 

1. Felice V, Lupini C, Mescolini G, Silveira F, Guerrini A, Catelli E, Di Francesco A. Molecular detection and characterization of Mycoplasma gallisepticum and Mycoplasma synoviae strains in backyard poultry in Italy. Poultry science. 2020 Feb 1;99(2):719-24. 

2. Yadav JP, Tomar P, Singh Y, Khurana SK. Insights on Mycoplasma gallisepticum and Mycoplasma synoviae infection in poultry: a systematic review. Animal Biotechnology. 2022 Dec 12;33(7):1711-20. 

3. Yadav JP, Singh Y, Batra K, Kumar R, Mahajan NK, Jindal N. Isolation, molecular characterization and phylogenetic analysis of Mycoplasma gallisepticum and Mycoplasma synoviae strains recovered from commercial broiler chicken flocks affected with respiratory tract infections. The Microbe. 2025 Jul 26:100485. 

4. Tomar P, Singh Y, Mahajan NK, Jindal N. Isolation and Phylogenetic Analysis of Avian Mycoplasmas from Poultry Affected with Respiratory Infections in India. Indian Journal of Animal Research. 2021 Feb 1;55(2).

Related Experts

Dr. Ram Moorthy D

B.V.Sc & A.H. degree from Bombay Veterinary College, Parel, Mumbai (1993), an M.Sc. in Human Nutrition from Alagappa University, Chennai (1999), and an M.B.A. from the Indian Institute of Science ...

Veterinary