Protection conferred by recombinant turkey herpesvirus avian influenza (rHVT-H5) vaccine in the rearing period in two commercial layer chicken breeds in Egypt

Abstract

The effectiveness of recombinant turkey herpesvirus avian influenza (A/swan/Hungary/4999/2006(H5N1)) clade 2.2 virus (rHVT-H5) vaccine was evaluated in two layer chicken breeds (White Bovans [WB] and Brown Shaver [BS]). One dose of rHVT-H5 vaccine was administered at day 1 and birds were monitored serologically (haemagglutination inhibition test) and virologically for 19 weeks. Maternally-derived antibody and post-vaccination H5 antibody titres were measured using the Chinese (A/Goose/Guangdong/1/96(H5N1)) HA and the Egyptian (A/chicken/Egypt/128s/2012(H5N1)) HA as antigens. The challenge was conducted at 19 weeks of age and on six experimental groups: Groups I (WB) and II (BS), both vaccinated and challenged; Groups III (WB) and IV (BS), both vaccinated but not challenged; Groups V and VI, unvaccinated specific pathogen free chickens, serving respectively as positive and negative controls. The challenge virus was the clade 2.2.1 highly pathogenic avian influenza H5N1 A/chicken/Egypt/128s/2012 at a dose of 10(6) median embryo infective dose. For both breeds, complete maternally-derived antibody waning occurred at the age of 4 weeks. The immune response to rHVT-H5 vaccination was detected from the sixth week. The seroconversion rates for both breeds reached 85.7 to 100% in the eighth week of age. Protection levels of 73.3%, 60% and 0% were respectively recorded in Groups I, II and V. No mortalities occurred in the unchallenged groups. Group I showed superior results for all measured post-challenge parameters. In conclusion, a single rHVT-H5 hatchery vaccination conferred a high level of protection for a relatively extended period. This vaccine could be an important tool for future A/H5N1 prevention/control in endemic countries. Further studies on persistence of immunity beyond 19 weeks, need for booster with inactivated vaccines, breed susceptibility and vaccinal response, and transmissibility are recommended.

Comparison of the effectiveness of rHVT-H5, inactivated H5 and rHVT-H5 with inactivated H5 prime/boost vaccination regimes in commercial broiler chickens carrying MDAs against HPAI H5N1 clade 2.2.1 virus

“…The broiler DOCs used in the study had high MDA titres (9.1 log 2 ), reflecting the intensive multi-vaccination regimes (injected six times using different inactivated H5 vaccines) in breeder flocks. Similar results have been obtained in previous studies conducted in Egypt published by Abdelwhab et al (2012b) and Kilany et al (2014a). In the present study, MDA regression in vaccinated groups (I, II and III) was faster than Group IV (unvaccinated controls).…”

“…These results may explain the important role of cell-mediated immunity induced by the rHVT-H5 vaccine as described by Rauw, et al (2012). It is commonly accepted that the higher the homology between the H5 gene in the commercially used inactivated AI vaccines seeds and the circulating viruses, the higher the protection (against mortalities) conferred by those vaccines Kilany et al, 2013;Kilany et al 2014a;Rauw, et al, 2012;Abdelwhab et al, 2012b). However, it is important to note that the rHVT-H5 showed protection against challenge with H5N1 strains of various clades (1, 2.2, 2.2.1, 2.3.4 and 2.1.3) (CEVA, 2012).…”

“…Recently, Kilany et al (2014a) showed that rHVT-H5 conferred a high level of protection for an extended period of time in commercial layer chicken flocks. The current study has been conducted to evaluate the protective efficacy of rHVT-H5 vaccine when administered alone or with a booster of inactivated H5N1 vaccine in commercial broiler chickens carrying MDAs.…”

“…FAO with its government partners conducted field and controlled laboratory studies on this rHVT-H5 vaccine and assessed costeffectiveness as well as feasibility of implementation in different poultry production sectors in Egypt (Peyre, 2014). Kilany et al (2014a) conducted a study on two commercial layer chicken breeds in Egypt, and showed that day-old chicken (DOC) vaccination with rHVT-H5 vaccine conferred adequate protection during the rearing period (up to 19 weeks of age) with little MDA interference during the first 8 weeks of age. The present study, simulating the prevailing AI field vaccination practices in the broiler sector, was thus carried out with the aim of assessing the comparative effectiveness of rHVT-H5 as prime/boost with a single rHVT-H5 DOC vaccine and with an inactivated vaccine alone, in commercial broiler chickens that carry high MDA levels.…”

“…Large-scale avian influenza (AI) mass vaccination against H5N1 HPAI is the most widely used control intervention in Egypt . Although AI vaccination is an important and widely implemented disease control tool, very little to no post-vaccination monitoring is taking place in the country (Peyre et al, 2009;Kilany et al, 2014a). More than 12 billion doses of different AI-H5 inactivated vaccines, mainly based on Eurasian and American H5N2, Eurasian H5N1 and, more recently, local Egyptian H5N1 subtype viruses, have been applied (unpublished data, General Organization of Veterinary Services (GOVS) 2014).…”