GENERAL INTRODUCTION: PICORNAVIRIDAE

PICORNAVIRIDAE

A General Introduction has been added to each disease chapter in an attempt to give a brief updated overview of the taxonomic, biological and other characteristics of the virus family or group of bacteria /protozoa that cause disease in livestock and, where relevant, involve wildlife. As the text of the three-volume book Infectious Diseases of Livestock is currently under revision the Editors are aware that there are inconsistencies between the updated introductions to chapters and the content of the chapters themselves. Once the chapters have been updated – a process that is currently underway – these inconsistencies will be removed.

Picornaviridae are a large family of viruses within the Order Picornavirales that infect mainly mammals and birds but also fish, amphibians and reptiles. Currently the family comprises 80 virus species grouped into 35 genera. With the remarkable exception of foot-and-mouth disease (FMD) virus and possibly viruses that cause swine vesicular disease (Enterovirus B) and Seneca Valley virus infection (Senecavirus A) – because the resulting vesicular disease may be confused with FMD – the Picornaviridae do not cause economically important diseases of mammalian livestock. Nevertheless, in addition to the genus Aphthovirus, another 8 genera (Cardiovirus, Enterovirus, Erbovirus, Hunnivirus, Kobuvirus, Pasivirus, Senecavirus and Teschovirus) contain viruses that infect and may cause disease in non-avian domestic livestock (Picornaviridae.com, 2017; Maclachlan & Dubovi, 2016; Table 1). There are also 3 additional unclassified picornaviruses which have been isolated from cattle and pigs (Picornaviridae.com, 2017; Table 1). On the other hand, viruses in this family cause important human disease such as poliomyelitis and hepatitis A, the former being the target of an on-going global eradication programme. Seneca Valley virus is interesting because it is oncolytic and therefore under investigation as potentially useful in human cancer therapy.

‘Picorna’ apparently has two derivations: (i) pico = small and rna = ribonucleic acid; and (ii) a siglum for polio, insensitivity to ether, coxsackievirus, orphan virus, rhinovirus and ribonucleic acid (the two r’s being contracted to one). However, terms such a ‘coxsackie’, ‘orphan’ and ‘rhinovirus’ are now historic in viral systematics.

Many enteroviruses have a range of immunological variants that do not induce effective cross-immunity (Table 1). Wide antigenic variation occurs between FMD viruses because, although there are only seven serotypes, there is also considerable intratypic variation, particularly pronounced within the SAT serotypes.

Virions are small (≈30nm), unenveloped with icosahedral symmetry (i.e. roughly spherical), that replicate in the cytoplasm of infected cells. The capsid comprises 60 protomers, each made up of four polypeptides derived from the cleavage of a single polyprotein. A small protein (VPg) is covalently linked to the 5’ end of the single-stranded RNA genome of positive-sense which is between 6.7 – 10.1 kb in length and polyadenylated at the 3’ end (Maclachlan & Dubovi, 2016).

Table 1 Infections of mammalian livestock caused by viruses within the Picornaviridae family

Genus

Species (former names)

Virus common name

Livestock species affected (source of infection)

No. identified
serotypes

Disease

Aphthovirus

Foot-and-mouth disease virus

Foot-and-mouth disease virus

Artiodactyla

7

Vesicular disease, acute myocarditis

Equine rhinitis A virus

Equine rhinitis A virus

Horses, dromedary camels

1

URTD, sometimes with systemic effects

Bovine rhinitis A virus

Bovine rhinitis A virus

Cattle

2

Mild URTD

Bovine rhinitis B virus

Bovine rhinitis B virus

Cattle

5

Mild URTD

Cardiovirus

Cardiovirus A
 (Encephalomyocarditis virus)

Encephalomyocarditis virus

Pigs (rodents)

1

Acute myocarditis/encephalomyelitis/reproductive failure

Enterovirus

Enterovirus B

Swine vesicular disease virus

Pigs

2

Vesicular disease

Enterovirus E
 (Bovine enterovirus)

Enterovirus E
(Bovine enterovirus group A)

Cattle, sheep

4

Subclinical or mild respiratory, enteric or reproductive disease

Enterovirus F
 (Bovine enterovirus)

Enterovirus F
(Bovine enterovirus group B)

Cattle, alpaca

6

Subclinical or mild respiratory, enteric or reproductive disease

Enterovirus G
 (Porcine enterovirus B)

Enterovirus G (porcine enterovirus)

Pigs, sheep, goats

21

Apparently subclinical

Enterovirus I

Dromedary camel enterovirus

Dromedary camels 

1

Unknown

Erbovirus

Erbovirus A
 (Equine rhinitis B virus)

Equine rhinitis B virus

Horses

3

Mild URTD

Hunnivirus

Hunnivirus A

Hunnivirus A

Cattle, sheep

3

Unknown

Kobuvirus

Aichivirus B

Bovine kobuvirus

Cattle, sheep

2

Unknown

Aichivirus C

Porcine kobuvirus

Pigs

1

Unknown

Aichivirus D

Kagovirus

Cattle

2

Unknown

Unassigned

Caprine kobuvirus

Goats

1

Unknown

Sapelovirus

Sapelovirus A
 (Porcine sapelovirus /
 Porcine enterovirus A)

Porcine sapelovirus

Pigs

1

Diarrhoea, reproductive failure

Senecavirus

Senecavirus A

Seneca Valley virus

Pigs

1

Vesicular disease

Teschovirus

Teschovirus A
 (Porcine teschovirus)

Porcine teschovirus

Pigs

13

polioencephalomyelitis (Teschen/Talfan disease), reproductive failure

Unassigned

Unassigned

Bovine picornavirus 1

Cattle

1

Unknown

Unassigned

Unassigned

Bovine picornavirus Japan

Cattle

2

Unknown

Unassigned

Unassigned

Porcine picornavirus Japan

Pigs

1

Unknown

URTD – Upper respiratory tract disease
Note: Diseases/causative agents in bold print are covered in existing chapters; new chapters will be added when justified

References

  1. International Committee on Taxonomy of Viruses https://talk.ictvonline.org/taxonomy/ (accession date: 26/05/2017)
  2. Picornaviridae.com. http://www.picornaviridae.com/ (accession date 31/05/2017)
  3. MACLACHLAN N.J. & DUBOVI, E.J. (eds.), 2016. Veterinary Virology, 5th edition, Academic Press.