Page 6 - National Poultry Newspaper

Photo: William Moreland
Coronaviruses are di- vided into Alpha-, Beta-, Gamma- and Delta- coro- navirus groups.
Then there is the prob- lem of back passage of the vaccine in the host leading to a pathogenic virus.
Photo: Martin Sanchez
How knowledge of avian coronavirus infectious bronchitis virus in poultry relates to COVID-19 in humans
TO better understand the challenges associated with the COVID-19 dis- ease in humans, poultry health professionals can draw on many years of experience attempting to control avian coro-
navirus infectious bron- chitis virus in poultry.
virus — one that is easily killed by soap and com- mon disinfectants. Where do coronavi- ruses come from?
ders the vaccine safe but not immunogenic, where- as under attenuation will create a vaccine capable of inducing a strong im- mune response but may cause a severe vaccine reaction.
It is important to em- phasize the COVID-19 virus is not associated with poultry or poultry products.
Bats are widely accept- ed as the reservoir for mammalian (Alpha- and Beta-) coronaviruses.
Page 6 – National Poultry Newspaper, April 2020
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Coronaviruses are re- sponsible for a wide variety of existing and emerging diseases in hu- mans and other mammals including food animals, as well as in birds includ- ing poultry.
There are about 1240 different bat species har- bouring as many or more different coronavirus types.
Based on our knowledge of producing vaccines against IBV, production of a live-attenuated vac- cine against COVID-19 with acceptable safety and efficacy may prove to be very difficult. What about using killed vaccines against coronaviruses?
Diseases associated with coronavirus infec- tions cover a wide range including respiratory, en- teric, neurological, renal and hepatic.
It is likely that the COVID-19 virus origi- nated from bats.
The coronavirus IBV affects poultry, causing respiratory disease in chickens and is in the avian Gammacoronavi- rus group.
Furthermore, prelimi- nary data show some vi- ruses isolated from bats to be close relatives.
There are killed or inac- tivated vaccines against IBV for poultry, however they are difficult to de- velop.
Avian viruses in the Gammacoronavirus group do not infect or cause disease in humans.
The reservoir for avian coronaviruses, including IBV, is not clear.
The COVID-19 virus is in the Betacoronavirus group, along with SARS- CoV and MERS-CoV.
There are some closely related viruses in wild and domestic birds — pheasants, ducks, geese and pigeons, to name a few — but unequivocal evidence of a true reser- voir is lacking.
In addition, for killed vaccines to be effective, they must be given after a live-attenuated ‘prim- ing’ vaccine, which as discussed above has sig- nificant safety issues.
It was previously shown that SARS-CoV does not infect or cause disease in poultry.
Why is it difficult to produce a vaccine against coronaviruses?
Because the COVID-19 virus belongs to the same group as SARS-CoV and uses the same ACE-2 host cell receptor, it is highly unlikely that the COV- ID-19 virus will infect or cause disease in poultry, but it remains to be sci- entifically proven.
Protective immunity against a respiratory dis- ease, such as infectious bronchitis virus in poul- try or COVID-19 in hu- mans, requires a strong local immune response.
In humans, killed vac- cines against respiratory viruses are used, for ex- ample against influenza virus, but this requires growing the virus to high titers, inactivating it and using safe adjuvants.
Based on knowledge at hand, and current lack of evidence of bird infec- tions with the COVID- 19 virus, poultry and poultry products are not consid- ered to be a source of COVID-19 infection for humans.
In poultry, we achieve this by using live attenu- ated vaccines, but live coronavirus vaccines are difficult to produce be- cause attenuation often renders them unable to produce a strong local immune response.
This has proved diffi- cult to achieve for human coronaviruses.
Why don’t we have recombinant vaccines against IBV in poultry?
The COVID-19 virus is primarily spread among people via respiratory droplets that contain the virus, with infections oc- curring via the nose, eyes and mouth.
The coronavirus sur- face-spike glycoproteins are embedded in a lipid envelope and have con- formationally dependent epitopes that induce neu- tralizing antibodies in the host.
Though highly infec- tious, it is an enveloped
Over attenuation ren-
SARS-CoV and MERS- CoV came from a bat res- ervoir, infected an inter- mediate host then jumped to humans.
An intermediate host for the COVID-19 virus has not been identified yet.
Chemicals such as for- malin or beta-Propiolac- tone used to kill the virus can destroy the integrity of the spikes, thus yield- ing a vaccine that does not induce a protective immune response.
Attenuation is accom- plished by passage of the virus in a laboratory host system, for example em- bryonating chicken eggs or cell culture, but there is a fine line between at- tenuation and maintain- ing the virus’ ability to infect and induce an im- mune response.
And could a recombi- nant vaccine be devel- oped for the COVID-19 virus?