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