Avian Mycoplasmosis Management with Macrolide Antibiotics
Avian mycoplasmosis is one of the most economically key diseases in poultry. Losses result from decreased egg production, less fertility in breeders, increased mortality, medications costs and carcass condemnation.
However, the incidence of this disease could be reduced by the application of adequate prevention and control programs. It is caused by four pathogenic mycoplasma species namely Mycoplasma gallisepticum (MG), Mycoplasma synoviae (MS), Mycoplasma meleagridis (MM) and Mycoplasma iowae (MI); although other Mycoplasma species have also been incriminated in the disease. Of all these, MG has been reported to be the most economically significant mycoplasma pathogen of gallinaceous and certain non gallinaceous avian species and causes chronic respiratory disease (CRD) in chickens and infectious sinusitis in turkeys.
MG and MS are pathogenic for chickens and turkeys; MI is pathogenic primarily for turkeys while MM infects turkeys only. MG has been reported to have been isolated from infected falcons, parrots, pheasants, geese, quails, patridges, ducks and geese.
The disease causes cough, rales, ocular and nasal discharges, decreased feed intake, decreased feed conversion, decreased egg production, fertility and hatchability. Avian mycoplasmosis can lead to a significant reduction in egg production of between 10-20% in infected layer and broiler breeder flocks. It also causes infectious sinusitis in turkeys.
Mycoplasmosis is transmitted vertically and horizontally. Infected parent birds transmit the disease to their progeny. Mycoplasmosis is also considered a highly horizontally transmissible disease that is spread among birds through exchange ocular or nasal discharge. Mycoplasma cannot survive outside of the body of a host for long periods of time and requires exchange of recently expelled fluid discharge from an infected individual. For this reason, sites where birds come into close contact, such as bird feeders and roosting sites are the primary sites of infection.
The incubation period of avian mycoplasmosis varies ranging between 6-21 days for experimentally infected poultry and is variable under natural infection. Infected birds may be asymptomatic for days or months until stressed. Presence of concurrent infection with New castle disease virus, infectious bronchitis virus, Esherichia coli or other pathogens make avian mycoplasmosis more severe. The syndromes caused by avian mycoplasmosis are chronic respiratory disease (CRD) an upper respiratory disease primarily seen in chickens and infectious sinusitis of turkeys caused by MG; infectious synovitis caused by MS and air sacculitis caused by MG, MS and MM
Application of strict biosecurity procedures is essential to prevent horizontal transmission of mycoplasma from contaminated to healthy flocks. Due to the fact that mycoplasma could be vertically transmitted, it is important to maintain breeding stocks free from the infection. Application of control programs of breeding flocks is very important to reduce the incidence of this disease.
Monitoring mycoplasma could be performed using several techniques such as: Plate Agglutination Test, ELISA and PCR. However, due to the intensification of the poultry industry, it is sometimes difficult to guarantee the effectiveness of control strategies and maintain 100% mycoplasma free flocks. Several antibiotics have been used for the treatment of mycoplasma infection such as macrolides, tetracyclines, tiamulin, spectinomycin and lincomycin.