Infectious Laryngotracheitis
The causative agent for infectious Laryngotracheitis is an alphaherpesvirus, the ILTV. It induces a contagious disease in chicken characterized by respiratory signs, decreased egg production, and high mortality. In addition, as other herpesvirus, it can establish a latent infection in the trigeminal ganglia of chickens. Vaccination is an option to fight the disease.
Strains: The SA2 ILT vaccine strain originated from an Australian field isolate and was attenuated through sequential passages in chicken embryos (Purcell & Surman, 1974). The A20 vaccine strain was developed by further passages of the SA2 strain in chicken embryonic cell culture (Blacker et al., 2011). A20 (SA2 strain further attenuated by 20 passages in cell culture and then 5 passages in embryonated eggs - (Bagust TJ, McGavin DR, 1996).
Immunity: It has been shown that immunity does not develop well in chickens vaccinated at less than 2 weeks of age (Cover et al., 1960; Gelenczei & Marty, 1964).
The colacal-brush method: Mucosal surfaces, such as those in the respiratory, gastrointestinal, and urogenital tracts, are equipped with specialized structures known as mucosa-associated lymphoid tissue (MALT). MALT consists of highly organized lymphoid tissues located at various mucosal sites and contains antibody-producing plasma cells that help protect against infections. The primary function of MALT is to produce and secrete specific immunoglobulin A (IgA) antibodies in response to antigens along the mucosal surfaces. One example of MALT, called cloaca-associated lymphoid tissue (CALT), includes antigen-presenting cells such as dendritic cells, macrophages, B cells, T cells, and MHC II molecules. CALT is also associated with blood vessels and high endothelial venules. Studies have shown that the cloaca-associated mucosal vaccination route generates more antibodies than other mucosal vaccination routes, providing enhanced protection for chickens on the farm.