Evolution of Newcastle disease virus in Egypt

Evolution of Newcastle disease virus in Egypt.

Saad A. Moussa^*, Mohammed Ahmed Mahmoud Abdullah^**, Ehab E. Nabawy^***.

^* Animal Health Research Institute, Agriculture Research Center (ARC), Egypt.

* Saadmoussa999@gmail.com.

^** Damanhur Branch, Animal Health Research Institute.

^*** Dep. Of vet. Public health, Vet. Med. Faculty, Zagazig University.

ABSTRACT

In Egypt, Newcastle disease virus (NDV) outbreaks are occurring frequently, researchers try to study epidemiology of the virulent NDV isolates from these outbreaks. Velogenic & mild NDV strains was successfully isolated in Egypt from 1950 till now. NDV  still  reported  to  cause  severe  outbreaks  with  high  losses  in  infected  flocks  during  2005,  velogenic  NDV  caused  outbreaks  among  commercial  chicken  in   Egypt   so, it is obligatory to study the protective immunity of commercially  available  vaccines  for  prevention  and  control  of   the disease. VIIb NDV genotype was previously described as the predominant sub-genotype of genotype VII circulating with severe outbreaks in Egypt in last decade.

INTRODUCTION

Newcastle disease (ND) is one of the most devastating viral diseases of poultry and has great economic impact in the poultry industry causing bird mortality reaches 100% between the infected flocks (Alexander et al. 2003). Newcastle disease, caused by Newcastle Virus, is a serious illness of birds, particularly chicken and turkey and has been one of the major causes of economic losses in the poultry industry (Alexander 1988). NDV is an enveloped, single stranded, nonsegmented RNA of negative sense virus. NDV is the only member of the genus Avulavirus, subfamily Paramyxovirinae that belonged to family Paramyxoviridae in the order Mononegavirales and is designated avian paramyxovirus-1 (APMV-1) (Murphy et al., 1995; Mayo, 2002). Ten serogroups of avian paramyxoviruses have been recognized:  APMV-1 to APMV-10 (OIE, 2012). Of these, APMV-1 remains the most important pathogen for poultry (Alexander et al. 2003). Newcastle disease virus is regarded as being endemic in many countries including Egypt (OIE, 2009: OIE 2012). Exotic Newcastle Disease Virus (ENDV) is very virulent strain causes severe losses in pet and game birds in USA and these birds are considered a good reservoir for transmitting the virus between domestic commercial flocks causing severe losses in poultry production (OIE, 2008). Infection by NDV is categorized into different pathotypes according to the strain affecting the flock and clinical signs appear; lentogenic strains which cause mild respiratory symptoms and used as secondary live vaccines, mesogenic strains which are fatal only for young chicks, viscerotropic velogenic strains which are fatal for all ages of chicken and almost characterized with enteric signs and neurotropic velogenic strains which are characterized with nervous signs (Alexander and Allan, 1974; Beard et al. 1984). 

The viral genome consists of 15,186 nucleotides (Deleeuw and Peeters et al. 1999) and contains six genes encoding six major polypeptides: nucleoprotein (NP), phosphoprotein (P), matrix protein (M), fusion (F) protein, haemagglutinin neuraminidase (HN) and large RNA dependent RNA polymerase protein (L), HN, M, F proteins which are related to viral envelope and three proteins NP, P, L are related to viral genomic RNA (Millar, 2009). Fusion protein plays very important role in NDV virulence and pathogenicity to induce and promote the fusion between virus and target cell membranes (Lamb and Kolakofsky, 1996). It is synthesized as a fusion inactive precursor (F0) and must be proteolytically cleaved into F1 and F2 polypeptides by host proteases to become fusion active protein (Morrison et al. 1993). There are 10 genotypes of Newcastle disease virus isolates based on differences on fusion protein gene (Huang et al. 2004). Recently, (NDV) separated into 15 genotypes, class I viruses comprise a single genotype, while class II contains 15 genetic groups including 10 previously established (I–IX, and XI) and five new genotypes (X, XII, XIII, XIV and XV). Sub genotypes were identified among class I and class II genotypes (Diel et al. 2012).

History of ND in Egypt

In Egypt, NDV outbreaks are occurring frequently, some researchers try to study epidemiology of the virulent NDV isolates from these outbreaks. Newcastle disease is well documented in Egypt in year 1942 (Daubney and Mancy, 1948). Since that date the recognition of velogenic NDV was successfully carried out by El-Nassari, (1957); Eissa, (1960); Lancaster and Alexander, (1975) while Ahmed et al. (1966) record the first occurrence of mild NDV in Egypt. Severe outbreaks of NDV have occurred in Upper Egypt in 1950 with high mortalities in chicken (El-Nassari et al. 1960). The Pathogenicity of NDV in other species was reported in pigeon (Ahmed and Reda, 1967) and free flying birds (Moussa et al., 1988). NDV was isolated and identified using HI and AGPT were carried out periodically by many authors (Ahmed et al. 1965; Ismail et al. 1981, Bekhet and Abdel hamid, 1990). The  genetic  resistance  of  the  Egyptian  native  breeds  was  reported   by Hassan et al.  (2004).  Determination  of  virulence  using  gene  analysis  was  carried  out  for  local  velogenic  isolate   SR/76   by   Hussein et al. (2005). NDV  still  reported  to  cause  severe  outbreaks  with  high  losses  in  infected  flocks  during  2005,  velogenic  NDV  caused  outbreaks  among  commercial  chicken  in   Egypt   these   outbreaks raised concerns regarding the protective immunity of commercially  available  vaccines  for  prevention  and  control  of   the  virus in poultry (Abdel moneim et al. 2006; Amer et al. 2006). The phylogenetic analysis showed Egyptian NDV isolates are closely related with the genotype II of class II NDV strains. So, sequences of the F genes of 2006 Egypt isolates are closely related to that of the 2005 suggesting that these strains are probably circulating in the vaccinated bird population in Egypt until development of an outbreak (Mohamed et al. 2011).

Phylogenetic analysis showed that NDV strains isolated in Egypt are closely related with the NDV strains isolated in China after complete genome sequence (Mahmoud et al. 2009). Investigation of 9 isolates of Newcastle disease virus (NDV) recovered from 386 cloacal swabs from birds migrating to Egypt revealed differences among isolates from various or even the same species of birds. Pathogenicity tests in susceptible chicken and pigeon by different routes of application suggested the categorization of all isolates as velogenic strains of NDV, whereby 7 isolates exhibited marked viscerotropic characters for chicken may prove that the migratory birds are main source of NDV infection in Egypt (Ahmed et al. 2010). Hussein et al. (2012) they record that mixed infection with IBV and NDV circulating among broiler flocks demonstrating high mortality which reached more than 60% in some flocks, Increased mortalities might be related to the occurrence of mixed infection by both viruses. NDV genotype VII was isolated from H5N1 infected broiler flock 2012, this isolate was in close range to Chinese strains so this study reports the characterization of Newcastle Disease Virus genotype VII in broiler chicken co-infected with Avian influenza H5N1 virus (Hussein et al. 2014). Isolation  and  characterization  of  Newcastle  disease  virus  (NDV)   from recent outbreaks affecting poultry  farms  in  Egypt  between  2011  and  2012,  clinically  infected  NDV  vaccinated  broiler   farms   in Fayoum, Behira and  Giza  Provinces.  velogenic  genotype  isolate  clustered and published class  II  genotype  VII  sub  genotype  d  NDVs  and  closely  related  to  Middle  East  isolates,  and   concluded   that   spread of velogenic genotype strain to  Egypt  via  Middle  Eastern  countries  is  likely  to  be  the  source  of  infection  (Radwan   et   al. 2013).

Phylogenetic analysis of genotype VII revealed that all the virulent viruses belonged to genotype VIIb, according to the unified nomenclature and classification system of NDV proposed by Diel et al. (2012). Also, VIIb was previously described as the predominant sub-genotype of genotype VII circulating with severe outbreaks in Egypt (Saad et al. 2017& 2021; Selim et al. 2018; Zanaty et al. 2019).

CONCLUSION

The causative agent of recent ND outbreaks in vaccinated broiler flocks from Egypt was found to belong to velogenic genotype VIIb. This strain was genetically close to other Egyptian genotype VII isolates obtained during the last decade with high pathotypic features (Radwan   et   al. 2013 Saad et al. 2017 & 2021 Selim et al. 2018 Zanaty et al. 2019).

Results of the in vivo study revealed that adequate heterologous antibody levels, induced by the proposed vaccination program, sufficiently protected birds from morbidity and mortality. However, virus shedding was quantitatively affected in relation to the time of challenge after vaccination. Altogether, with an absence of vaccines able to induce homologous antibody to the presently circulating viruses, higher antibody levels, which depend on efficient and timely implementation of the vaccination program, are considered as highly important in relation to the reduction of virus shedding (Saad et al. 2017).