Infectious bronchitis virus (IBV) and Newcastle disease virus (NDV) have a worldwide distribution and are a major cause of economic losses for poultry production. The occurrence of co-infection is quite common in commercial birds in Pakistan since both are endemic in the country. The virus and its disease-causing potential have individually been investigated before, however, there is a paucity of data revealing their cumulative effect and subsequent disease-causing potential in vaccinates and non-vaccinated upon challenge with these viruses.

The current study involved biologic and molecular identification of Newcastle disease virus and infectious bronchitis virus originating from different farms located in and around the vicinity of district Lahore followed by transmission and challenge protection experiment in commercial broiler chicken. A higher percentage of farms were infected with infectious bronchitis (50.85%) followed by Newcastle disease (32.2%) and mixed infection (16.95%).

Biologic and molecular characteristics of the isolates characterized both of the select isolates as highly pathogenic. Findings revealed it has the potential to cause severe infection in commercial poultry. Following exposure of vaccinates to both viruses either alone or in combination, the challenge-protection experiment revealed an increased severity of infection in IBV and NDV infected birds as compared to those infected with the individual virus at one time.

The respiratory system-based symptoms were much evident in birds challenged with IBV while birds infected with NDV showed symptoms involving both respiratory and gut system. A variable degree of congestion and hemorrhages were evident in different organs including trachea, lungs, proventriculus, cecal tonsil and kidney.

Further, when challenged together, the distribution of viruses expressed much more tissue tropism affecting almost all the organs of the body as compared to distribution upon individual challenge. Taken together the study concludes that both IBV and NDV can cause severe infection in the commercial poultry.

Owing to similar tissue tropism, infection with one virus may facilitate the other one while enhancing cumulative disease pathogenesis in commercial chicken. Notably, the used vaccine/s against currently prevailing IBV and NDV strains provide partial protection to birds especially in the case of co-infection.

Muhammad Saeed Imran,

Lahore, April 5.