Newcastle disease (ND) is an economically important, contagious poultry viral disease reported across the globe. No recent reports on ND circulating in Malaysia. Therefore, the aim of the study is to characterize 16 Newcastle disease viruses (NDVs) isolated from chickens in Malaysia in the year of 2019. All isolates were genotypically analyzed using reverse transcription-polymerase chain reaction (RT-PCR) with primers specific to the viral fusion (F) protein gene. Analysis of the F protein cleavage site’s deduced amino acid sequences revealed that from the Newcastle disease virus (NDV) isolates, three of them were virulent with two different motifs of 112RRQKRF117 and 12RRRKRF117 while other isolates were avirulent. Phylogenetic analysis demonstrated that three isolates were grouped in genotype VII, five in genotype I while eight in genotype II. All genotype VII isolates were clustered under sub-genotype VII.2 (VIIh and VIIi) which is the same strain causing previous outbreaks in Malaysia. Therefore, findings in this study demonstrated that there is no new introduction of NDV genotypes in Malaysia. However, farms should implement biosecurity measures at strict level as well as executing continuous monitoring and surveillance of the disease as these implementations would help them to conduct proper preventive measures and control of panzootic viruses in future.

An inactivated oil-based Newcastle disease vaccine was prepared using Mukteswar vaccine strain. The virus was propagated in 10-day old embryonating eggs and inactivated by 0.12% formalin for 48 hours at 37 degree C. The vaccine was formulated with 1 part antigen (aqueous phase) and 4 parts oil base. The oil base contained Tween-80 1%, Arlacel-A 10% and Mineral oil 89%. The stability of the vaccine was found satisfactory after 6 months and its viscosity and injectability was fairly ideal. The antigenicity of the vaccine was determined in 16 week-old pullets. The seromonitoring of the vaccinated and the control pullets was carried out for three months post- vaccination by Haemagglutination inhibition (HI) test. Blood samples were taken at fortnightly intervals. The Geometric mean HI titre of the vaccinated pullets on the day of vaccination 15, 30, 45, 60, 75, 90, 105 and 120 days post- vaccination was 18.4, 4.9, 87.5, 192.3, 257.6, 111.4, 91.7, 63.9 and 30.0. However, in non-vaccinated control pullets it was found to be 18.4, 3.7, 3.7, 4.3, 3.8, 4.0, 3.5, 2.8 and 2.3 respectively. The inactivated oil-based vaccine induced a marked antibody response which continued upto three months.

A mixed viral infection of Newcastle Disease (ND), Marek’s Disease (MD) and Avian Leukosis (AL) was reported in village chickens. Analysis of the deduced amino acid sequences of the F protein cleavage site of ND virus showed that the isolate was virulent with sequence KRRKR for the C-terminus of the F2 protein and phenylanine (F) at residue 117, the N-terminus of the F1 protein. Basic Local Alignment Search Tool (BLAST) analysis showed the isolate was ND which was 96% similar identity with Indonesia Sukorejo genotype VII, MD 99% similar identity with China very virulent strain and ALV 100% similar identity with Taiwan ALV strain. Due to the free ranging type of management, causes of the diseases in the poultry were uncertain as many factors can contribute to the disease occurrence. However, good hygiene practices can help to improve the farm’s sanitary. Basic biosecurity system can be applied although the success may be limited. Vaccination is another alternative that can be considered to prevent the diseases with the help from certain parties.

The quick diagnosis of Newcastle disease requires known serum against the disease. In this study, an attempt was made to raise anti- Newcastle disease virus hyperimmune serum in rabbits. Three different inoculum were prepared to inoculate in the rabbits; (i) Fresh harvested allantoic fluid containing Newcastle disease virus (NDV) Mukteswar vaccine strain; (ii) Freshly harvested ND virus pelletted through centrifuging at 40,000 rpm for two hours and resuspended in normal saline and (iii) Pelletted virus (centrifuged and suspended as in ii) with addition of incomplete Freund's adjuvant. It was observed during the monitoring of haemagglutination inhibition (HI) titre that the serum collected after series of inoculation of 1st and 2nd inoculum provided maximum titre upto 1:256. However, the serum collected after series of injection of 3rd inoculum gave maximum HI titre 1:1024. This study suggested that antigen containing incomplete Freund's adjuvant provided better immune response against Newcastle disease virus in rabbits.

Forty-seven Newcastle disease virus (NDV) strains isolated from fecal samples of waterfowls in Alaska and Siberia from 1991 to 1996 were analyzed for their virulence. None of the viruses formed plaques on MDBK cells in the absence of trypsin. Of these, 29 strains showed virulent character by the mean death time with the minimum lethal dose in chicken embryos comparable to velogenic NDV strains. Of the 29 strains, 11 were sequenced for their fusion protein (F) gene. The results showed that 5 of them contained a pair of dibasic amino acids at the cleavage site of the F, which is of a virulent type. The present results suggest that potentially virulent strains of NDV are maintained in migratory waterfowl populations in nature, and that some of those may be transmitted to domestic poultry and acquire pathogenicity during passages in chicken population