ND, avian influenza in poultry and efficacy of vaccines

According to Economic Survey of Pakistan 2017-18, poultry farming is the most important section of livestock sector and is fulfilling 32.7 % of the total meat production of the country. Almost 700 billion rupees have been invested in this industry while annual growth of poultry industry is 10%.

However, different types of viral and infectious diseases are the barriers to achieve high economic benefits in poultry industry. Different Newcastle disease and Avian Influenza (H9N2) are two major loss causing diseases of poultry in the country.

Newcastle disease virus (NDV), is the virus from Paramyxoviridae family and avian influenza virus (AIV), is the member of Orthomyxoviridaegroup. These are two important pathogens which are causing serious economic losses in poultry sector. Several viral subtypes of both diseases have been identified which can cause mild sub-clinical problems to severe infections.The virulent strains of Avian Avula virus (AAvV-1s) and low pathogenic Avian Influenza (LPAI) H9N2 strains are endemic in Pakistan. The continuous co-circulation of these viruses in poultry causes huge direct and indirect economic losses and threat to global food security. Consequently, the evaluation of the degree of diversity in genetics of prevailing strains of field viruses is very essential. It is also important to estimate their genetic relationship with previously characterized viruses.

At present, limited molecular epidemiological data are available regarding the causes of ND and AI outbreaks in vaccinated commercial poultry farms. A study was conducted on the two diseases to find out different isolates of NDV and AIV (H9N2), their tissue tropism and vaccine efficacy. Five out of recently isolated viruses of ND were phylogenetically characterized by the F-gene’s complete coding region. These isolates were belonging to the already most prevalent genotypical sub-groupVIIi of NDV.The analysis of two Pakistani Avian Influenza isolates revealed that these were LPAIV H9N2 strain in poultry. These two isolates were phylogenetic analyzed on the basis of HA-gene and comparative analysis was done with already isolated specimens of H9N2 strains of Eurasian origin. The phylogenetic analysis revealed that our isolates were genetically closely related to H9N2 viruses classified into Mideast group B and clustered with other viruses belonging to India, Iran, Israel, Saudi Arabia, the United Arab Emirate and Pakistani isolates. Mideast B is divided into two sub-lineages, B1 and B2, which have virus strains isolated from 2004-2008 and 2008-2015 respectively. The two Pakistani H9N2 isolates investigated in this study were clustered into sub-lineage B2 which contains previously characterized Pakistani viruses.

The comparison of the observed data from 180 experimental broiler birds revealed that there was alteration in tissue tropism of the NDV andH9N2 viruses in mono and mixed infections of NDV and H9N2. It was observed that in mono NDV infection, the proportion (percentage) of the detection of NDV in different organs of the birds was more as compare to concurrent or sequential co-infection of NDV and H9N2 viruses, while proportion of detection of H9N2 in various organs of the birds was not affected in mono H9N2 or mixed NDV and H9N2 infection.

To evaluate the efficacy of commonly-used commercial vaccines for NDV and H9N2, a study was conducted on 100 birds. It was observed from the results that despite of reports of genetic re-assortments and emergence of new genotypes of H9N2 and NDV, vaccines are still providing effective antibody titer under experimental conditions and other environmental and infectious problems may be associated with poor vaccine efficacy and disease outbreaks in field conditions.

—Contributed by Irfan Irshad and Dr Asim Aslam