عملي 1

Mycoplasma gallicepticum(CRD)

Cause
The underlying cause of CRD is Mycoplasma gallisepticum (MG). The condition is frequently triggered by respiratory viruses such as ND and IB and subsequently complicated by bacterial invasion. The main agents involved in the infection are Mycoplasma gallisepticum and E. coli.

Transmission

The main problem is that parent birds infected with Mycoplasma gallisepticum can transmit the organism through the egg to their offspring (vertical transmission). In addition, infection can occur by contact or by airborne dust or droplets (horizontal transmission). The incubation period varies from 4 days to 3 weeks.

Species affected

Chickens and Turkeys.

Clinical signs

Young chickens (broilers or layer pullets) will show respiratory distress. The birds frequently show lack of appetite, decreased weight gain and increased feed conversion ratios.
In adult birds the most common signs are sneezing and general respiratory distress. In laying birds a drop in egg production between 20-30 % can occur.
In breeders hatchability can be affected and day-old chick quality produced from hatching eggs coming from infected flocks will be reduced.
CRD does not normally cause an alarming number of deaths. The effect is more of a chronic nature causing reduced weight gain and higher feed conversion ratios in broilers and lower egg production in breeders and layers. In this way the overall economic losses can be very high.

Internal lesions

A reddish inflamed trachea and/or frothy, cheesy exudate in the airsacs, especially in complicated cases (e.g. with secondary E. coli infections) are observed. In mild MG infections the only lesion might be slight mucus in the trachea and a cloudy or light froth in the airsacs.


Diagnosis
Diagnosis of MG infection can be made based on clinical signs and post mortem lesions followed by confirmation in the laboratory using blood (serum) samples for serology or organs swabs for identification by PCR or mycoplasma isolation.

Differential diagnosis

Respiratory virus infection (Newcastle disease or infectious bronchitis) with secondary infection (E. coli, etc.) can give similar
lesions.

Treatment

Treatment of MG-infected chickens or turkeys with suitable antibiotics or chemotherapeutics has been found to be of economic value, but will not eliminate MG from the flock.

Prevention

Prevention by monitoring and vaccination has become a more effective method of combating the disease especially in layers. Economic losses in commercial layers can be reduced by proper use of MG vaccines. Eradication programs (first in breeder flocks).

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