Limited efficacy of West Nile virus vaccines in large falcons (Falco spp.)

Abstract

West Nile virus (WNV) can lead to fatal diseases in raptor species. Unfortunately, there is no vaccine which has been designed specifically for use in breeding stocks of falcons. Therefore the immunogenicity and protective capacity of two commercially available WNV vaccines, both approved for use in horses, were evaluated in large falcons. One vaccine contained adjuvanted inactivated WNV lineage 1 immunogens, while the second represented a canarypox recombinant live virus vector vaccine. The efficacy of different vaccination regimes for these two vaccines was assessed serologically and by challenging the falcons with a WNV strain of homologous lineage 1. Our studies show that the recombinant vaccine conveys a slightly better protection than the inactivated vaccine, but moderate (recombinant vaccine) or weak (inactivated vaccine) side effects were observed at the injection sites. Using the recommended 2-dose regimen, both vaccines elicited only sub-optimal antibody responses and gave only partial protection following WNV challenge. Better results were obtained for both vaccines after a third dose, i.e. alleviation of clinical signs, absence of fatalities and reduction of virus shedding and viraemia. Therefore the consequences of WNV infections in falcons can be clearly alleviated by vaccination, especially if the amended triple administration scheme is used, although side effects at the vaccination site must be accepted.

Current Progress of Avian Vaccines Against West Nile Virus

“…Reduced morbidity and pathogenicity were also observed upon experimental vaccination of wild birds. Thus, a reduced pathology was noted in sandhill cranes (Grus Canadensis) vaccinated with the Fort Dodge inactivated vaccine [103], clinical signs alleviations were also reported after administration of three doses of Duvaxyn ® or Recombitek ® Equine West Nile virus vaccines in large falcons [96], and reduced clinical scores and antigen deposition in their organs upon DNA vaccination were also documented [113]. Likewise, a less pronounced and shorter loss of weight and a lack of clinical signs were described in RSP-vaccinated magpies that survived to viral challenge [64].…”

“…Another study reported that a single intramuscular vaccination of Western scrub-jays with the pCBWN vaccine protected 100% (3/3) of the birds, and that 80% (4/5) of the corvids intramuscularly vaccinated with a single dose of the Fort Dodge West Nile-Innovator DNA equine ® vaccine or the Recombitek ® Equine West Nile virus formulation also survived to the infection compared to the 40% (2/5) of survival reached by the control group [105]. Dispensation to falcons of the Duvaxyn ® inactivated vaccine resulted in 80% (4/5) and 100% (4/4) protection when administered twice or thrice, respectively, and 100% protection with two (5/5) or three doses (4/4) was achieved with the Recombitek ® Equine West Nile virus formulation, while only 50% (4/8) survival was recorded in non-vaccinated animals [96]. Two DNA vaccines that express the ectodomain of the E protein of WNV of lineage 1 or 2 also tested in large falcons conferred protection against a WNV challenge and, based on their results with different protocols, the authors indicated that protection was dependent on the lineage, regimen, and way of administration used.…”

“…As commented above, most of the tested vaccines conferred protection when animals were challenged, but, in none of them, induction of sterilizing immunity was observed, as viral replication could be detected in vaccinated birds, although with the exception of one study performed in vaccinated Western scrub-jays in which no reduction of viral titers was reported [105], those were usually lower in vaccinated than in sham-immunized animals [64,96,98,103,[109][110][111]113]. For instance, viremia was detected in 4/22 rE vaccinated partridges 3 dpi, and antibody titers increased significantly after viral challenge to levels similar to those found in non-vaccinated animals [63].…”

“…On the other hand, in many cases [64,96,103,109,113], viremia reached levels below what is considered necessary to be a competent reservoir [7], although, for some vaccines, two [113] or three [96,103] doses were required to achieve it. In this respect, it was reported that for Culex pipiens and Culex quinquefasciatus [129], two vectors considered key to virus maintenance, these levels must be above 10 5 pfu/mL, although lower viremia levels (around 10 4 pfu/mL) also seemed to be relevant for other vectors, such as Culex univittatus or Culex perexiguus [68].…”

“…In fact, several commercial formulations are currently available for equid vaccination, and its effectiveness was demonstrated after immunization of horses, which led to a marked decrease of severe WNV disease (WND) in the following years in the US [94,95]. In many cases, experiments with birds have tested some of these commercially available vaccines approved for use in equids [18,19], such as the formalin-inactivated whole-WNV vaccine originally developed by Fort Dodge (Fort Dodge, IA, USA), which has been commercialized under different names (West Nile-Innovator, Duvaxyn ® renamed EQUIP WNV ® ) [96][97][98][99][100][101][102][103][104], and was licensed in 2003 and subsequent years (Vetera ® ), a DNA-based vaccine subsequent formulation expressing the prM and E WNV proteins also from Fort Dodge (West Nile-Innovator DNA equine ® ) [97,105], which was licensed in 2004 in the US but later removed from the market in 2010, and a recombinant live canarypox virus vaccine (ALVAC ® ) that expresses the prM/E WNV proteins (Recombitek ® Equine West Nile virus in the US, Merial, GA, USA; or Proteq WNV ® in Europe) [96,105].…”