aviculture au maroc

 

study of poultry projects

 

 

 

 

 

 

 


 

Introduction

 

 Mycoplasmoses are contagious infectious diseases affecting the hen, turkey and many other avian species: Palmipeds, pigeons, guinea fowl, quail, game. And even they have been found in humans, plants and insects.

  They result from a combination of other pathogens and are favored by the surrounding stress. Mycoplasmas are prokaryotes belonging to the class of Mollicutes Order of Mycoplasmatales and the family of Mycoplasmataceae.

 

The main features of mycoplasmas are:

Total absence of a cell wall => great resistance to antibiotics, especially beta-lactams.

Small size 300nm.

Reduced size of their genome 5.108 => Dependence on Complex Culture Media 

I here are three species that are most important:

 

      Mycoplasma gallisepticum,  Mycoplasma synoviae,  Mycoplasma meléagridis

 

 

  Mycoplasma gallisepticum

 

Introduction

 

Infection with Mycoplasma gallisepticum is associated with slow onset, chronic respiratory disease in chickens, turkeys, game birds, pigeons and other wild birds. Ducks and geese can become infected when held with infected chickens. In turkeys it is most associated with severe sinusitis (see separate description in the turkey section). The condition occurs worldwide, though in some countries this infection is now rare in commercial poultry. In others it is actually increasing because of more birds in extensive production systems that expose them more to wild birds.

In adult birds, though infection rates are high, morbidity may be minimal and mortality varies.

The route of infection is via the conjunctiva or upper respiratory tract with an incubation period of 6-10 days. Transmission may be transovarian, or by direct contact with birds, exudates, aerosols, airborne dust and feathers, and to a lesser extent fomites. 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. Recovered birds remain infected for life; subsequent stress may cause recurrence of disease.

The infectious agent survives for only a matter of days outwith birds although prolonged survival has been reported in egg yolk and allantoic fluid, and in lyophilised material. Survival seems to be improved on hair and feathers. Intercurrent infection with respiratory viruses (IB, ND, ART), virulent E. coliPasteurella spp. Haemophilus, and inadequate environmental conditions are predisposing factors for clinical disease

 

Signs

  • Coughing.
  • Nasal and ocular discharge.
  • Poor productivity.
  • Slow growth.
  • Leg problems.
  • Stunting.
  • Inappetance.
  • Reduced hatchability and chick viability.
  • Occasional encephalopathy and abnormal feathers.

 

Post-mortem lesions

  • Airsacculitis.
  • Pericarditis.
  • Perihepatitis (especially with secondary E. coli infection).
  • Catarrhal inflammation of nasal passages, sinuses, trachea and bronchi.
  • Occasionally arthritis, tenosynovitis and salpingitis in chickens.

Diagnosis

 

Lesions, serology, isolation and identification of organism, demonstration of specific DNA (commercial PCR kit available). Culture requires inoculation in mycoplasma-free embryos or, more commonly in Mycoplasma Broth followed by plating out on Mycoplasma Agar. Suspect colonies may be identified by immuno-flourescence.

Serology: serum agglutination is the standard screening test, suspect reactions are examined further by heat inactivation and/or dilution. Elisa is accepted as the primary screening test in some countries. HI may be used, generally as a confirmatory test. Suspect flocks should be re-sampled after 2-3 weeks. Some inactivated vaccines for other diseases induce 'false positives' in serological testing for 3-8 weeks. PCR is possible if it is urgent to determine the flock status.

Differentiate from Infectious Coryza, Aspergillosis, viral respiratory diseases, vitamin A deficiency, other Mycoplasma infections such as M. synoviae and M. meleagridis (turkeys).

 

Treatment

 

Tilmicosin, tylosin, spiramycin, tetracyclines, fluoroquinolones. Effort should be made to reduce dust and secondary infections.

 

Prevention

 

Eradication of this infection has been the central objective of official poultry health programmes in most countries, therefore M.g. infection status is important for trade in birds, hatchingeggs and chicks. These programmes are based on purchase of uninfected chicks, all-in/all-out production, biosecurity, and routine serological monitoring. In some circumstances preventative medication of known infected flocks may be of benefit.

Live attenuated or naturally mild strains are used in some countries and may be helpful in gradually displacing field strains on multi-age sites. Productivity in challenged and vaccinated birds is not as good as in M.g.-free stock.

 

Mycoplasma synoviae

Introduction

 


Infection with Mycoplasma synoviae may be seen in chickens and turkeys in association with synovitis and/or airsacculitis. It occurs in most poultry-producing countries, especially in commercial layer flocks. Infection rates may be very high. Spread is generally rapid within and between houses on a farm, whilst illness is variable and mortality less than 10%.

Infection is via the conjunctiva or upper respiratory tract with a long incubation period, 11-21 days following contact exposure. Transmission may be transovarian, or lateral via respiratory aerosols and direct contact. Survival of the infectious agent outwith the bird is poor but fomite transmission between farms is important. Predisposing factors include stress and viral respiratory infections.

 

Signs

  • There may be no signs.
  • Depression.
  • Inappetance.
  • Ruffled feathers.
  • Lameness.
  • Swelling of hocks, shanks and feet (sometimes severe and bilaterally asymmetrical).
  • Faeces may be green in acute infections.
  • Effects on egg production appear to be minor under good management.

Post-mortem lesions

  • Joints and tendon sheaths have viscid grey to yellow exudate.
  • Some strains can lead to amyloidosis.
  • Swollen liver, spleen and kidney have been seen in the past but are not common now.
  • Green liver.
  • Exudate becomes caseous later.
  • Sternal bursitis.
  • Airsacculitis - usually in heavy broilers and associated with condemnations.

Diagnosis

 

Lesions, serology, isolation (difficult - requires NAD) and identification. Differentiate from viral arthritis, staphylococcal arthritis, Mycoplasma gallisepticum infections, Ornithobacterium rhinotracheale, viral respiratory disease with colibacillosis.

Serology: SAG used routinely, Elisa in some countries - PCR and/or culture used to confirm. False positives post inactivated vaccines are, if anything more common than in the case of M.g.

 

Treatment

Tilmicosin, chlortetracycline, oxytetracycline, tylosin.

 

Prevention

 

Eradication of this infection is also possible using similar techniques as described for Mycoplasma gallisepticum. These are based on purchase of uninfected chicks, all-in/all-out production, and biosecurity. Maintenance of Mycoplasma synoviae free status seems to be more difficult than for Mycoplasma gallisepticum. In some circumstances preventative medication of known infected flocks may be of benefit.

Vaccines are not widely used though they are available in some countries. Infected birds do develop some immunity to the effects of repeated inoculation.


Mycoplasma meléagridis

 

Introduction

 

A disease of turkeys characterised by respiratory and skeletal problems caused by Mycoplasma meleagridis. The organism has also been isolated from raptors, it occurs in most turkey-producing countries but is now much rarer in commercial stock. In adult birds though infection rates are high, morbidity may be minimal. Pathogenicity is quite variable. Mortality is low, though up to 25% of infected birds show lesions at slaughter.

Infection is via the conjunctiva or upper respiratory tract with an incubation period of 6-10 days. Transmission is venereal in breeders, with transovarian and then lateral spread in meat animals. Infected eggs result in widespread distribution of infection and increased risk of further vertical transmission. The infective agent does not survive well outside the bird. Predisposing factors include stress and viral respiratory infections.

 

Signs

Post-mortem lesions

Diagnosis

 

Lesions, serology, isolation and identification of organism, demonstration of specific DNA (commercial kit available). Culture requires inoculation in mycoplasma-free embryos or, more commonly in Mycoplasma Broth followed by plating out on Mycoplasma Agar. Suspect colonies may be identified by immuno-fluorescence.

Serology: SAG used routinely - culture used to confirm. Differentiate from Mycoplasma gallisepticumMycoplasma synoviae, other respiratory viruses.

 

Treatment

 

Tylosin, spiramycin, tetracyclines, fluoroquinolones. Effort should be made to reduce dust and secondary infections.

 

Prevention

 

Eradication of this infection is also possible using similar techniques as for Mycoplasma gallisepticum. These are based on purchase of uninfected poults, all-in/all-out production, and biosecurity. Infected males are particularly prone to transmit infection and may warrant special attention. In some circumstances preventative medication of known infected flocks may be of benefit.

Vaccines are not normally used. Infected birds do develop some immunity. Birds infected from their parents seem to be immuno-tolerant and particularly prone themselves to transmit.