Abstract
Avian pox can severely impact turkey production systems. Vaccination programs in Mexico use commercially available Fowlpoxvirus vaccines, that are used across different bird species. Nonetheless, there are reports of sporadic disease outbreaks among vaccinated turkeys, which suggest that heterologous vaccines may provide limited immunity, presenting the need to develop homologous vaccines that can better protect turkeys. This study compared the protection granted to turkey chicks by a commercial Fowlpoxvirus vaccine and by a live attenuated Turkeypoxvirus vaccine after a challenge with a field isolated Turkeypoxvirus virus. Histopathology, polymerase chain reaction, and sequencing of DNA were used for viral identification. A Turkeypoxvirus strain was first isolated in chicken embryo lesions, and subsequently adapted through serial passes in chorioallantoic membrane to produce the homologous vaccine. The attenuated virus was used as a vaccine when a 104.4 embryo ID50/mL titre was reached. Three groups of three-week-old turkey chicks were used for challenge experiments. Subjects in Group 1 were immunized with the attenuated Turkeypoxvirus vaccine (homologous vaccine). Chicks in Group 2 were vaccinated with the commercially available heterologous vaccine (Fowlpoxvirus). Subjects in Group 3 were not vaccinated and received only saline solution (control group). Two weeks after vaccination, animals from Group 1 reached a 97.7 ND50 seroneutralization titre, while levels reached in Group 2 birds and in control chicks were 11.7 ND50 (Group 2) and zero, respectively. At this time, all groups were challenged with a suspension of a field-isolated Turkeypox virus. The homologous vaccine afforded 100% protection in Group 1 (10/10 individuals), while only 10% (1/10) of individuals in Group 2 were protected by the commercial heterologous Fowlpoxvirus vaccine. None of the non-immunized birds in Group 3 were protected (0/10). These results show that the homologous vaccine afforded a greater protection against a Turkeypox virus infection than that observed for the heterologous vaccine, and that a homologous vaccine can be efficiently produced by isolating and attenuating the virus from turkeypox lesions, through chorioallantoic membrane serial passes.
Highlights
Domestic turkeys (Meleagris gallopavo gallopavo) are the second most important species for Mexican poultry husbandry, after the meat and egg-laying chicken varieties (Gallus gallus), reaching an average year production of close to 15,000 tonnes of meat.[1,2,3,4]Similar to other species of birds, such as chickens, pigeons, canaries and psittacids, turkeys are susceptible to avian pox infections.[3]
Attenuation of a Turkeypoxvirus field strain. These results show that the homologous vaccine afforded a greater protection against a Turkeypox virus infection than that observed for the heterologous vaccine, and that a homologous vaccine can be efficiently produced by isolating and attenuating the virus from turkeypox lesions, through chorioallantoic membrane serial passes
polymerase chain reaction (PCR) from lesions on turkeypoxvirus-infected chicken embryo chorioallantoic membranes resulted in a 578 bp amplification fragment, consistent with what is expected for the known 4b protein of avian pox (Figure 2)
Summary
Domestic turkeys (Meleagris gallopavo gallopavo) are the second most important species for Mexican poultry husbandry, after the meat and egg-laying chicken varieties (Gallus gallus), reaching an average year production of close to 15,000 tonnes of meat.[1,2,3,4]. Similar to other species of birds, such as chickens, pigeons, canaries and psittacids, turkeys are susceptible to avian pox infections.[3] Avian pox is caused by a DNA virus of the genus Avipoxvirus, family Poxviridae, and has two main presentations: the cutaneous or dry form is the most common and is characterized by proliferative lesions and scabs on the skin that can develop into secondary bacterial infections. There is a third systemic form, that is exclusive to canaries, and causes hepatic necrosis, pulmonary nodules, and high mortality.[5] For the cutaneous and diphtheritic forms mortality is low, but the disease can heavily impact meat and egg production, causing considerable economic losses.[3]
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