Marcin Śmiałek DVSc1, Joanna Welenc DVM1, Prof. Andrzej Koncicki1
Avian metapneumoviruses (aMPV) are highly contagious disease agents causing upper respiratory tract infections predominantly in turkeys, but also in chickens. The disease caused by aMPV has different courses in turkeys and chickens and because of this is designated turkey rhinotracheitis (TRT) in flocks of turkeys, with infectious inflammation of the nares and windpipe as its symptoms, but in flocks of chickens it is termed swollen head syndrome (SHS).
Metapneumovirus infections inflict significant losses on the poultry industry mainly as consequences of poorer body weight gains, directly caused deaths, declines in laying performance, and immunosuppression making birds more vulnerable to secondary infections.
Metapneumoviruses were first identified in the late 1970s in Southern Africa but from that time onwards they have come to be distributed across the whole world apart from Australia and Canada.
One of the most serious consequences of bird infections with aMPV is the risk of immunosuppression, which arises principally because of damage to the natural defensive barrier that the mucous membranes of the respiratory tract provide. This immunosuppression renders birds more susceptible to secondary infections, which are most frequently bacterial but may also be of another nature, and such infections in turn lead to a more severe clinical disease course and heavier production losses.
The similarity of the clinical course of TRT to those of other diseases demands exhaustive laboratory diagnostic testing for definitive confirmation of this disease. For this, ELISAs and PCR techniques are extremely useful tools.
Two main courses of action can currently be distinguished for limiting losses due to TRT: (1) flock biosecurity and (2) specific immunoprophylaxis. Two types of vaccine are currently used in the immunoprophylaxis of TRT, these being attenuated live vaccines based on A or B subtypes and inactivated vaccines. Despite the widespread vaccination of poultry, cases of wild-type strains of aMPV defeating post-vaccination immunity are frequently observed.
A more detailed treatment of these issues may be found through the link to the articles which provided the basis for this very brief report.
This summarises articles published in Polski Drobiarstwo [Polish Poultry Farming], issues 3, 4, and 5, 2018. The full articles may be found at https://polskie-drobiarstwo.pl/archiwum/numery?rok=2018
1Chair of Avian Diseases, Department of Veterinary Medicine, University of Warmia and Mazury in Olsztyn, Poland