Chronic Respiratory Disease (CRD)



The microorganisms of the class Mollicutes (Mycoplasma) were first identified in 1898 as the etiologic agent of the bovine contagious pleuropneumonia (BCPP) and thereafter, all similar agents were named pleuropneumonia-like (PPLO-like) organisms.

Avian Mycoplasmosis is caused principally by three species of Mycoplasma organisms. Mycoplasma gallisepticum (MG), Mycoplasma synoviae (MS) occur in chickens and turkeys. Mycoplasma meleagridis (MM) occurs in turkeys. Mycoplasma meleagridis may be seen in other species such as pheasant, quail, guineas, and pigeons. Mycoplasma synoviae causes infectious synovitis where as Mycoplasma gallisepticum causes chronic respiratory disease (CRD), which is a serious problem, particularly in chicken flocks.

Since 1994, Mycoplasma. gallisepticum conjunctivitis has become an emerging disease in finches. This disease has been responsible for major declines in house finch populations in the eastern U.S., and was recently reported in western house finch populations. Mycoplasma gallisepticum can also affect other finch species, although its impact has not been as severe.


Avian mycoplasmosis can be caused by several species of Mycoplasma (class Mollicutes, order Mycoplasmatales, family Mycoplasmataceae) including Mycoplasma gallisepticum, M. synoviae, M. meleagridis and M. iowae. M. gallisepticum is the most important pathogen in poultry. It also causes disease in other avian species. M. gallisepticum infections are also known as chronic respiratory disease (CRD) of chickens, infectious sinusitis of turkeys and house finch conjunctivitis. Several strains of M. gallisepticum have been reported, including the R (poultry), P (psittacine) and house finch strains. Strains may vary greatly in their pathogenicity for different species of birds. In one study, budgerigars developed severe disease after experimental infection with the R strain of M. gallisepticum but not the house finch strain.


The disease is spread both vertically and horizontally.
Vertical Transmission
The organism can be incorporated into eggs by infected breeders and chickens hatched carrying the mycoplasma infection.
Horizontal Transmission
Disease transmission may also take place from direct contact with infected birds and will spread throughout the flock in this way. Transmission may also occur by contact of healthy birds with equipments contaminated by infected birds.

Clinical signs

In Layers / Breeders
• Nasal and ocular discharge, (watery eyes) rattling in the wind pipes, coughing, gasping (dyspnea), sneezing and shaking of the hed.
• Feed consumption drops off leading to decreased egg production and loss of weight.
• Male birds frequently have the most prominent signs.
• Reduced hatchability and chick viability.
• Occasional encephalopathy and abnormal feathers
In Broilers
• Most outbreaks occur between 3rd and 6th weeks of age .
• Poor feed conversion, sharp decline in weight gain.
• Slow growth
• Leg problems
• Morbidity rate fairly high but not great mortality.
• Poor carcass quality, high contamination rate. Thin and weak birds with razor-blade breasts.
In Turkeys
• often accompanied by swelling of the paranasal (infraorbital) sinus.
• Conjunctivitis with a frothy ocular exudate
• Production is lower in infected flocks, decreased weight gain, feed efficiency and egg production.


• Disinfect the farm and equipments with right disinfectant.
• Mycoplasmas are resistant to antibiotics that act on cell wall, such as penicillin, but are sensitive to tetracyclines (oxytetracycline, chlortetracycline and doxycycline), macrolides (erythromycin, tylosin, spiramycin, lincomycin, and kitasamycin), quinolones (imequil, norfloxacin, enrofloxacin and levofloxacin) or tiamulin. Drugs that accumulate in high concentrations in the mucosal membranes of the respiratory and genitourinary tracts, such as tiamulin and quinolones( enrofloxacin, specially levofloxacin) are recommended.


• If the mycoplasmosis is clubbed with other bacterial infections like E.coli administer mycoplasmosis drugs with gram -ve levofloxacin with colistin or Neomycin and Doxycycline through drinking water in addition to the above treatment for 3 to 5 days.

For Chicks

• Chicks arrived from known infected parent flocks should be treated with a suitable antibiotic( levofloxacin with colistin) during the first 48 hours after placement and then subsequently at 20 - 24 days for 24 to 48 hours period.
• Efforts should be made to reduce dust and secondary infections. Improve the ventilation for having good results of medicine.
• Medicate all Mycoplasma-positive broilers for the first 7-10 days in the feed or water.
• Ethereal oils based Herbal bronchodialator and anti-inflammatory agents are increasingly becoming acceptable to veterinarians, because they are free from side effects compared to allopathic contemporaries and deliver quicker symptomatic relief compared to allopathic as well as herbal (cough syrups) contemporaries.


• Establishment of Mycoplasma free breeding flocks.

Stock free of Mycoplasma infection can be produced by vaccination. Vaccinate breeders against E. coli, MG, MS, NDV, IBV, ILT and infectious bursal disease (IBD) to prevent the disease.

Vaccinate progeny against ND, IB, ILT and IBD, hatch and place Mycoplasma infected stock separate from mycoplasma negative stock to reduce the spread of the organism. Treat all Mycoplasma positive flocks with antibiotics to reduce spread into eggs.

• Treating infected hatching eggs with the antibiotic to kill the organism contained in the eggs.
• Before purchasing chicks from a hatchery, it should be confirmed that they are free from CRD.
• Chicks should be raised at the place where there is no approach of infected birds.
• Complete fencing of the breeding farms and sufficient isolation of prevent airborne infections from infected flocks.
• Disposing of dead birds by incineration, deep burial or by means of special disposal pits.
• Using vaccines that are free from contamination of Mycoplasma gallisepticum.
• Construction of the houses must be done in such a way that prohibit the entrance of any type of wild birds and wandering animals.
• Prohibition of visitors in the farm.
• Before coming in contact with flocks, workmen should take shower and put on special clothes.
• Strict bio-security measures should be adopted.
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