LT is a viral infection in hens, pheasants and paecocks characterized by catarrhal haemorrhagic to fibrinous inflammation of the respiratory tract. It is manifested in laryngotracheal form, suffocation, rales and cough are observed. The head and the neck are strongly extended forward and upward during inspiration (Image 1).
Image 1 The head and the neck are strongly extended forward and upward during inspiration
The mucous coats of the larynx and the trachea are catarrhally haemorrhagically to fibrinously inflamed (Image 2).
Image 2 Haemorrhage and inflammation in the larynx and the trachea
Haemorrhagic laryngotracheitis (Image 3).
Image 3 Haemorrhagic laryngotracheitis
Most outbreaks are encountered between the age of 4 and 14 weeks although the disease affects fowl of any age. LT is caused by a herpesvirus that is relatively resistant.
The morbidity rate of LT reaches 50 - 70% and the death rate: 10 - 20%. Often, it goes on as a complicated infection after the involvement of E. coli, Staphylococcus aureus, Mycoplasma gallisepticum, etc.
In some cases, casts of haemorrhagic or fibrinous exudate are formed that could almost completely obturate the larynx and the trachea (Image 4).
Image 4 Fibrinous exudate almost obturate the larynx and the trachea
Source of the infection are sick and convalescent birds, the latter being prolonged carriers of the virus (up to 1 - 2 years).
In the conjunctival form of LT, wet eyes, tear secretion and oedema of infraobital sinuses are observed (Image 5), especially in a complicated infection.
Image 5 Oedema of infraobital sinuses
The typical clinical and morphological signs are sufficient to assume the presence of LT. The diagnosis is confirmed with the detection of intranuclear inclusion bodies in the trachea throughout the histological study in the early stages of the disease, serological studies (VN, ELISA) etc.
LT should be differentiated from IB, SHS (swollen head syndrome), Mycoplasma synoviae infections, etc.
Premises, contamined with the LT virus, should be freed, cleansed, disinfected and occupied again after 5 - 6 weeks. The vaccination of unaffected birds and these from other premises of the infected farm could protect and stop subsequent outbreaks.
(Source: "Diseases of poultry - A colour atlas" - Ivan Dinev & CEVA Santé Animal, 2010)