CHRONIC RESPIRATORY
DISEASE (CRD, AIR
SACCULITIS, MG INFECTION)
Is a slow spreading chronic upper and lower
respiratory tract infection of chickens, turkeys
(infectious sinusitis) and other birds (4-8 weeks)
 Characterized by:
• Rales (excessive mucous)
• Coughing, gasping (struggle for breath)
• Nasal discharge and rhinitis
• Conjunctivitis
• Air sacculitis

ETIOLOGY
Mycoplasma gallisepticum
Family: Enterobacteriaceae
Characteristics:
– Smallest self replicating prokaryote
– 300 – 800 nm in size
– Lacks rigid cell wall
– Highly pleomorphic
– Coccoid, coccobacillus and filamentous
– G –ve

TRANSMISSION
 Between flocks
Direct contact, carriers & droplets. Spread is
slow between houses and pens suggesting
that aerosols are not normally a major route
of transmission. Fomites appear to a
significant factor in transmission between
farms
 Within a flock
Spread from bird to bird
 Vertical transmission is present (35% of
eggs infected)

Factors influencing
susceptibility
 Infection more severe in stress conditions
even vaccination stress
 Recovered birds remain infected for life;
subsequent stress may cause recurrence of
disease
 More severe in cold weather especially
sudden change in weather
 Young birds more severely affected than
adults
 Poor ventilation, overcrowding, damp litter,
ammonia production, irritation to respiratory
mucous membrane

CLINICAL SIGNS
 Nasal discharge, coughing, gasping and
sneezing
 Thin & weak birds with razor blade breasts
 Shaking of head (encephalopathy)
 Low feed intake and low FCR
 Poor carcass quality (Stunting) and weight
gain
 Out break occurs between 4 – 8 weeks of
age
 CRD COMPLEX: Mixed infection with E. coli,
ND,IB,ILT,IC cause serious losses

PATHOGENESIS
 Organism enters through respiratory tract,
conjunctiva or via infected embryo
 Localizes in epithelium of respiratory tract
 Irritation and damage of tracheal lining,
airsacs and lungs
 Destruction of cilia
 Secondary infection (bacterial & viral
infections) CRD complex
 Septicaemia

POSTMORTEM LESIONS
 Sinus mucosa is coated with turbid
mucus
 Excessive mucus in trachea
 Cheesy material in bronchi
 Consolidated spots in lungs
 Airsacculitis, Air sacs are often cloudy
and contain large amounts of exudate
 Perihepatitis, pericarditis and salpingitis
 Muscles are pale and flabby

POSTMORTEM LESIONS
Early stage Advanced stage CRD COMPLEX
• Excess mucous
in trachea.
• Plugs or pus in trachea.
• Perihepatitis and pericarditis (especially with
secondary E. coli infection)
• Consolidated
and solid spots
on lungs.
• Muscles pale and flabby
• Formation of a creamy color (fibrinous) layer
over heart and liver. Thickness of layer will
indicate the advancement of CRD stage.
• Cheesy material
in lungs
• Catarrhal inflammation
of nasal passages,
sinuses, trachea and
bronchi.
• Air sacculitis i.e.
inflammation of
air sacs
• Occassionally arthritis
and salpingitis in
chickens.
• Beaded or
Lymph-follicular
appearance.
• Caseous
exudate in air
sacs. "Foamy or

DIAGNOSIS
 Field
Clinical signs and lesions
 Isolation and identification of organism
 Sampling site:Upper respiratory tract (trachea)
 Primary inoculation:
• Frey’s medium
• 0.1-1 mm smooth colonies with dense elevated
centers
 Serological identification
Serum plate/ Tube agglutination test
Haemagglutination inhibition test
Antigen capture ELISA
 Molecular diagnosis PCR
Commercial kits available

DIFFERENTIAL DIAGNOSIS
• Newcastle disease
• Infectious bronchitis
• Infectious laryngotracheitis
• Infectious coryza

CONTROL
1. Ideally maintain Mycoplasma-free flock
2. Medications of breeders to eliminate egg transmission.
3. Before purchasing chicks from a hatchery, it should be
confirmed that they are free from CRD
4. Blood serum testing of breeder chickens for MG
antibodies has become a routine to test flocks for a MG
infection
5. Before coming in contact with flocks, workmen should
take shower and put on special clothes
6. Strict biosecurity measures should be adopted
7. Egg dipping in antibiotic solutions e g, Tylosin
8. Antibiotic therapy to chicks
9. Disposing of dead birds by incineration, deep burial or
by means of special disposal pits.

Severe gasping in chicks
originated from infected
breeding flocks

Cheesy pus in the thoracic
air sacs

Airsacculitis

Airsacculitis

Swelling of the paranasal
sinuses in turkeys

Swelling of the paranasal
sinuses in turkeys

Acute foamy air sacculitis

Creamy colour (fibrinous) layer
formation due to MG associated
with secondary bacterial infection

Cloudy appearance of the
abdominal air sacs

MYCOPLASMA SYNOVIAE
 Chronic subclinical upper respiratory
infection
 Characterized by swollen joints (hock)
 Viscous creamy to grey exudate in synovial
membranes, tendon sheaths and joints
 Synovitis
 Bursitis
 Hepatitis
 Hepatomegaly
 Spleenomegaly