Introduction:
Mycoplasma gallisepticum causes chronic respiratory disease (CRD) of chickens and infectious sinusitis (IS) of turkeys, characterized by rales, coughing, nasal discharge, sinusitis and the development of severe lesions on the air sacs. These diseases are considered to be an important problem in broilers, breeders and commercial layers. In layers and breeders, it is usually subclinical, but causes a reduction in the number of eggs laid per hen over the production cycle. Turkeys are more susceptible to M gallisepticum, frequently resulting in swollen infraorbital sinuses and is thus called “infectious sinusitis.”
Transmission:
Transmission depends on the size of the reservoir of infection, the number of susceptible individuals and the distance between them. Transmission may be more likely during the acute phase of infection and is influenced by the ability of the strain to multiply in the respiratory tract. M gallisepticum is transmitted vertically within some eggs (transovarian) from infected breeders to progeny, and horizontally via infectious aerosols and through contamination of feed, water, and the environment, and by human activity on fomites (shoes, equipment, etc). Infection may be latent in some birds for days to months, but when birds are stressed horizontal transmission may occur rapidly via aerosols and the respiratory route, after which infection and clinical disease spread through the flock. Once individuals or flocks are infected, they remain infected for life and act as carriers or reservoir for infection. Flock-to-flock transmission occurs readily by direct or indirect contact from the movement of birds, people, or fomites from infected to susceptible flocks. Morbidity is high and mortality low in uncomplicated cases.
Clinical signs:
Under natural conditions, the incubation period may vary considerably (from three to 38 weeks). The most common clinical signs are nasal discharge, tracheal rales, coughing, sneezing and swelling of one or both infra-orbital sinuses (mostly in turkeys) and mild conjunctivitis (Figure 1 & 2). Appetite remains near normal as long as the birds can eat. Sometimes, ataxia, lameness, swelling of the hock and enlargement of the eyeballs are observed. Non-specific signs, such as a reduction in growth rate and egg production and increased feed conversion efficiency are common. Clinical symptoms are generally more severe in males than in females, and turkeys appear more diseased than chickens.
Diagnosis:
History, clinical signs, and typical gross lesions may be suggestive of M gallisepticum infection. Serology by agglutination and ELISA methods are commonly used for surveillance. Rapid plate agglutination test can also be done as confirmatory (Figure Hemagglutination-inhibition is used as a confirmatory test. M gallisepticum should be confirmed by isolation from swab samples of infraorbital sinuses, nasal turbinates, choanal cleft, trachea, air sacs, lungs, or conjunctiva. Primary isolation is made in mycoplasma medium containing 10%–15% serum. Colonies on agar medium are used for species identification by immunofluorescence with species-specific antibodies.
Treatment:
Most strains of MG are sensitive to a number of antibiotics, including tylosin & tetracyclines, but not to penicillin’s. Regulations on the use of antibiotics in food animals are rapidly evolving and should be considered before use.
Prevention & Control:
Prevention is based largely on obtaining chicks from MG free breeder flocks. These birds should be kept under good biosecurity conditions to prevent the introduction of MG, and monitored regularly with serology or PCR to continually confirm MG free status. Inactivated, oil-emulsion vaccines (MG Bac) are available and help to prevent egg production losses, but not infection. Live vaccines (F-strain, TS-11) can be used during the growing phase to provide some protection during lay. Broilers are usually not vaccinated for MG.
Dr.J.Shiva Jyothi
M.V.Sc., Ph.D
Contract Teaching Faculty
Department of Veterinary Microbiology
College of Veterinary Science
Mamnoor, Warangal (U)
Dr.S.Vamshi Krishna
M.V.Sc., Ph.D
Assistant Professor & Head
Department of Veterinary Microbiology
College of Veterinary Science
Mamnoor, Warangal (U)
P.V.Narsimha Rao Telangana Veterinary University
Mobile: 8712908696
Email Id: vkvamshi1@gmail.com