Effect of West Nile virus DNA-plasmid vaccination on response to live virus challenge in red-tailed hawks (Buteo jamaicensis)

Vaccination of Zoo Birds against West Nile Virus—A Field Study

West Nile virus (WNV) is known to cause disease and death in humans and various animals worldwide. WNV has circulated in Germany since 2018. In 2020, four birds tested positive for the WNV genome at Zoopark Erfurt (Thuringia). Moreover, virus neutralization assays detected neutralizing antibodies (nAb) against WNV in 28 birds. In addition, nAb against WNV and Usutu virus (USUV) were found in 14 birds. To protect valuable animals and to reduce the risk of viral transmission from birds to humans, we performed a field study on WNV vaccination at the zoo. To conduct the study, 61 birds from the zoo were categorized into three groups and subjected to a vaccination regimen, where each bird received either 1.0 mL, 0.5 mL, or 0.3 mL of a commercial inactivated WNV vaccine three times. The vaccinations were administered at three-week intervals, or as per modified vaccination schedules. Furthermore, 52 birds served as non-vaccinated controls. Adverse vaccination reactions were absent. The greatest increase in nAb titres was observed in birds that received 1.0 mL of vaccine. However, pre-existing antibodies to WNV and USUV appeared to have a major effect on antibody development in all groups and in all bird species, whereas sex and age had no effect. After vaccination, no death was detected in vaccinated birds for more than 1 year.

Current Progress of Avian Vaccines Against West Nile Virus

Birds are the main natural host of West Nile virus (WNV), the worldwide most distributed mosquito-borne flavivirus, but humans and equids can also be sporadic hosts. Many avian species have been reported as susceptible to WNV, particularly corvids. In the case that clinical disease develops in birds, this is due to virus invasion of different organs: liver, spleen, kidney, heart, and mainly the central nervous system, which can lead to death 24–48 h later. Nowadays, vaccines have only been licensed for use in equids; thus, the availability of avian vaccines would benefit bird populations, both domestic and wild ones. Such vaccines could be used in endangered species housed in rehabilitation and wildlife reserves, and in animals located at zoos and other recreational installations, but also in farm birds, and in those that are grown for hunting and restocking activities. Even more, controlling WNV infection in birds can also be useful to prevent its spread and limit outbreaks. So far, different commercial and experimental vaccines (inactivated, attenuated, and recombinant viruses, and subunits and DNA-based candidates) have been evaluated, with various regimens, both in domestic and wild avian species. However, there are still disadvantages that must be overcome before avian vaccination can be implemented, such as its cost-effectiveness for domestic birds since in many species the pathogenicity is low or zero, or the viability of being able to achieve collective immunity in wild birds in freedom. Here, a comprehensive review of what has been done until now in the field of avian vaccines against WNV is presented and discussed.

A Recombinant Subviral Particle-Based Vaccine Protects Magpie (Pica pica) Against West Nile Virus Infection

The mosquito-borne West Nile virus (WNV) is a highly neurovirulent Flavivirus currently representing an emergent zoonotic concern. WNV cycles in nature between mosquito vectors and birds that act as amplifier hosts and play an essential role in virus ecology, being, thus, WNV a threat to many species. Availability of an efficient avian vaccine would benefit certain avian populations, both birds grown for hunting and restocking activities, as well as endangered species in captive breeding projects, wildlife reservations, and recreation installations, and would be useful to prevent and contain outbreaks. Avian vaccination would be also of interest to limit WNV spillover to humans or horses from susceptible bird species that live in urbanized landscapes, like magpies. Herein, we have addressed the efficacy of a single dose of a WNV recombinant subviral particle (RSP) vaccine in susceptible magpie (Pica pica). The protective capacity of the RSP-based vaccine was demonstrated upon challenge of magpies with 5 × 10³ plaque forming units of a neurovirulent WNV strain. A significant improvement in survival rates of immunized birds was recorded when compared to vehicle-inoculated animals (71.4 vs. 22.2%, respectively). Viremia, which is directly related to the capacity of a host to be competent for virus transmission, was reduced in vaccinated animals, as was the presence of infectious virus in feather follicles. Bird-to-bird transmission was recorded in three of six unchallenged (contact) magpies housed with non-vaccinated WNV-infected birds, but not in contact animals housed with vaccinated WNV-infected magpies. These results demonstrate the protective efficacy of the RSP-based vaccine in susceptible birds against WNV infection and its value in controlling the spread of the virus.

Avian Vaccination: Current Options and Strategies

Researchers have generated an array of potential avian antiviral vaccines. However, vaccine and viral complexity, small profit margins, the cost of development and manufacturing, and the small population at risk relegate most avian vaccine use to commercial species. Some vaccines designed for use in nonavian species are used to prevent or ameliorate disease in exotic and companion birds. This article highlights newly developed vaccines that may be used in exotic and pet birds. Information pertinent to vaccine choice and strategy is provided, including disease lethality, species affected, and previous knowledge regarding vaccine safety and efficacy. Other avian species of concern are also included.

A recombinant fusion protein consisting of West Nile virus envelope domain III fused in-frame with equine CD40 ligand induces antiviral immune responses in horses

West Nile Virus (WNV) is endemic in the US and causes severe neurologic disease in horses since its introduction in 1999. There is no effective pharmaceutical treatment for WNV infection rendering vaccination as the only approach to prevention and control of disease. The purpose of this study was to evaluate a recombinant vaccine containing domain III (DIII) of the WNV envelope glycoprotein with and without a natural adjuvant equine (CD40L) in producing virus neutralizing antibodies in horses. Serum IgG1 concentration in the groups of horses vaccinated with the DIII-CD40L+TiterMax and DIII-CD40L proteins were significantly increased (p<0.05) after the second booster vaccination compared to other groups. Serum IgG4 and IgG7, IgG3 and IgG5 concentrations were not significantly increased among all groups. Western blot results showed that animals immunized with the DIII-CD40L protein (with or without TiterMax) exhibited the highest specific anti-DIII antibody activities after vaccinations. Moreover, animals immunized with the DIII-CD40L protein (with or without TiterMax) exhibited significantly stronger neutralization activity (p<0.05) compared to other groups starting at week eight. The DIII-CD40L protein (with or without TiterMax) stimulated more CD8⁺T cells, but not CD4⁺T cells in equine PMBCs. The results demonstrated that vaccination with recombinant WNV E DIII-CD40L protein induced superior humoral and cellular immune response in healthy horses that may be protective against WNV-associated disease in infected animals. CD40L could be utilized as a non-toxic, alternative adjuvant to boost the immunogenicity of subunit vaccines in horses.

DNA vaccines encoding the envelope protein of West Nile virus lineages 1 or 2 administered intramuscularly, via electroporation and with recombinant virus protein induce partial protection in large falcons (Falco spp.)

As West Nile virus (WNV) can cause lethal diseases in raptors, a vaccination prophylaxis of free-living and captive populations is desirable. In the absence of vaccines approved for birds, equine vaccines have been used in falcons, but full protection against WNV infection was not achieved. Therefore, two DNA vaccines encoding the ectodomain of the envelope protein of WNV lineages 1 and 2, respectively, were evaluated in 28 large falcons. Four different vaccination protocols were used, including electroporation and booster-injections of recombinant WNV domain III protein, before challenge with the live WNV lineage 1 strain NY99. Drug safety, plasmid shedding and antibody production were monitored during the vaccination period. Serological, virological, histological, immunohistochemical and molecular biological investigations were performed during the challenge trials. Antibody response following vaccination was low overall and lasted for a maximum of three weeks. Plasmid shedding was not detected at any time. Viremia, mortality and levels, but not duration, of oral virus shedding were reduced in all of the groups during the challenge trial compared to the non-vaccinated control group. Likewise, clinical scoring, levels of cloacal virus shedding and viral load in organs were significantly reduced in three vaccination groups. Histopathological findings associated with WNV infections (meningo-encephalitis, myocarditis, and arteritis) were present in all groups, but immunohistochemical detection of the viral antigen was reduced. In conclusion, the vaccines can be used safely in falcons to reduce mortality and clinical signs and to lower the risk of virus transmission due to decreased levels of virus shedding and viremia, but full protection was not achieved in all groups.

Improvement of DNA vaccination by adjuvants and sophisticated delivery devices: vaccine-platforms for the battle against infectious diseases

Advantages of DNA vaccination against infectious diseases over more classical immunization methods include the possibilities for rapid manufacture, fast adaptation to newly emerging pathogens and high stability at ambient temperatures. In addition, upon DNA immunization the antigen is produced by the cells of the vaccinated individual, which leads to activation of both cellular and humoral immune responses due to antigen presentation via MHC I and MHC II molecules. However, so far DNA vaccines have shown most efficient immunogenicity mainly in small rodent models, whereas in larger animals including humans there is still the need to improve effectiveness. This is mostly due to inefficient delivery of the DNA plasmid into cells and nuclei. Here, we discuss technologies used to overcome this problem, including physical means such as in vivo electroporation and co-administration of adjuvants. Several of these methods have already entered clinical testing in humans.

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

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.