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Eduardo Lucio Decanini
Applied Investigation, S.A. Tehuacán, Puebla, Mexico
Newcastle disease (ND), caused by a serotype 1 avian Paramyxovirus in its velogenic presentation, continues to be a constant threat for many Latin American countries and other regions.
Even though we know that ND is capable of infecting many and diverse wild bird species – and that some of them have clearly acted as vectors for introducing the virus to countries which are free of the disease- also, we must understand that vaccinated commercial birds are a constant source of pathogen virus recycling in the environment as they release the virus in nasal secretions and droppings, as it will be understood below.
For example, one has only to leave some birds without vaccination in certain very populated poultry areas so that they end up dying with pathognomonic clinical signs of ND.
How can such an elevated viral concentration be maintained so as to establish and remain as a constant threat for poultry producers?
Broilers
In countries wherein ND is enzootic, in general at least one emulsion inactivated “dead” viral vaccine having added adjuvants and one or two applications of active “live” viral vaccines with lenthogenic strains are used in broilers.
Egg-laying
Immunization plans in egg-laying birds contemplate the use of 3 to 4 emulsion inactivated viral vaccines during production or breeding and multiple re-vaccinations with active virus during production and in the egg production cycle.
Despite these intense plans, the velogenic virus is still in the air. How can this be explained?
The main factors whereby this disease continues representing a constant challenge for our poultry industry are exposed below.
During 2004, there were losses in egg production in several companies which produced commercial egg in Mexico.
Losses were characterized in that they affected the external quality of the egg’s shell, generating mango-shaped eggs presenting around the egg-laying peak or after the birds were housed in the production barns.
The production drops could be from 8 to 30% and lasted from 6 to 9 weeks, and later, the birds recovered the production curve.
No important clinical sign was observed in birds (diarrhea, respiratory or nervous signs) and no virus could either be recovered when we processed samples for viral isolation in chicken embryo.
Figure 1. Eggs having the shape of a mango which are smaller an...
