Newcastle disease burden in Nepal and efficacy of Tablet I-2 vaccine in commercial and backyard poultry production

Abstract

Poultry (Gallus domesticus) farming plays an important role as an income generating enterprise in a developing country like Nepal, contributing more than 4% to the national GDP. It is also one of the major sources of protein for growing population. Newcastle Disease (ND) is a major poultry disease affecting both commercial and backyard poultry production worldwide. There were more than 90 reported cases of ND outbreaks in Nepal in 2018, with over 74,986 birds being affected. ND might be responsible for over 7% of total poultry mortality in the country. Recent outbreak of ND in 2021 affected many farms throughout Nepal, and caused massive poultry production loss. ND is caused by a single stranded RNA virus which presents very similar clinical symptoms as Influenza A (commonly known as Bird flu), adding much complexity to clinical disease identification and intervention.We conducted a nationwide ND and Influenza A prevalence study, collecting samples from commercial and backyard poultry farms from across the major poultry production hubs of Nepal, and conducted both serological and molecular assessments-giving us disease exposure history and identification of floating strains of ND Virus (NDV). Of 600 commercial chickens tested from various farms, both NDV (n=381, 64%) and IA (n=125, 21%) antibodies were detected in the majority of the samples. In backyard chicken (n=108, 39 farms), sero-prevalence was also relatively high for both NDV (n=38, 35%) and IA (n=17, 16%). Out of the 40 commercial farms, majority had detectable NDV (n=31, 78%) and IA (n=15, 38%) virus present. In backyard farms (n=36), we also detected NDV (n=6, 16%) and IA (n=1, 3%) virus. We Genotyped (strain) detected NDV, and found Genotype II to be present in most of the commercial farms (which might be coming from live vaccine usage) and Genotype I in some backyard poultry samples. The identified Genotype I strain is reported for the first time, and hence could be an endemic NDV strain found in Nepal. Our 2021 ND outbreak investigation identified Genotype VII c as the causative strain.Additionally, we have developed a thermostable I-2 NDV vaccine (Ranigoldunga™) in tablet formulation and tested on various (mixed) breeds of chicken (G. domesticus). This vaccine seems to be highly effective against NDV, including a virulent 2021 outbreak strain (Genotype VII c). The I-2 Tablet ND vaccine showed more than 85% efficacy when administered either ocularly or in water, and has a stability of 30 days in room temperature.

Safety and Immunogenicity of ND Vaccines Used in Nepal

“…Moreover, ND I-2 vaccine was shown to induce protective levels of antibodies up to 90 days post vaccination in village chickens [24]. A recent study showed that thermostable I-2 NDV vaccine in tablet formulation is effective against NDV, including a virulent 2021 outbreak strain with 85% efficacy [10]. These findings, together with ours, highlight the importance of continuous use of NDV vaccination in the farms.…”

“…Vaccination together with stringent biosecurity measures are practiced worldwide to prevent NDV infection in the farm [15]. Most of the commercial poultry farms in Nepal also practice regular vaccination against NDV [10]. Despite vaccination, ND outbreaks are common each year leading to a huge economic loss [1,3].…”

“…Thus, recent outbreaks of NDV in Nepal, including those in the vaccinated farms, is unlikely to be linked to the use of live-attenuated vaccines. Rather, a recent study showed that NDV genotype VIIc (GVIIc) was the probable causative agent for the widespread outbreak of ND in 2021 in Nepal [10]. NDV GVIIc represents a velogenic strain with severe clinical outcomes [16,17].…”

“…The better performance of this vaccine, in part, may be associated with its thermostability. I-2-based NDV vaccines are stable at room temperature for several days [10,20]. Though due care was given to maintain cold chain at our end, it is uncertain whether there was any breakage in the proper cold chain maintenance at any stage of the vaccine storage and transportation chain.…”

“…Vaccination against ND is commonly practiced in the commercial farms while its use is limited in the backyard poultry of Nepal [10]. ND vaccination strategy is conventional and mostly utilizes the live-attenuated F, LaSota, I-2 or R2B strains administered through intraocular route, in drinking water, or in muscles [3,11].…”